1 SPATIAL VARIATBILITY OF SELECTED SOIL PROPERTIES IN AND BETWEEN MAP UNITS by COENRAAD HENDRIK FRAENKEL Submitted in accordance with the requirements for the degree of M.Sc. in Soil Science In the faculty of Natural and Agricultural Sciences, Department of Soil, Crop and Climate Sciences, University of the Free State, Bloemfontein, South Africa Study leader: Dr. P.A.L Le Roux Co – Study leader: Prof. L.D. Van Rensburg November 2008 2 DECLARATION I hereby declare that this dissertation hereby submitted for the Magister Scientiae degree at the University of the Free State is my own work and has not been submitted to any other University. A also agree that the University of the Free State has the sole right to the publication of this dissertation. Signed: 2 3 CONTENTS…………………………………………………………………………...i ABSTRACT………………………………………………………………………….ii OPSOMMING………………………………………………………………………iii ACKNOWLEDGEMENTS………………………………………………….....iv LIST OF TABLES………………………………………………………………….v LIST OF FIGURES……………………………………………………………….vi LIST OF SYMBOLS AND ABREVIATIONS…………………………vii CHAPTER 1 ..................................................................................................................... 16 1 .1 Mot iva t i on ........................................................................................................ 16 1 .1 .1 Sp a t i a l v a r i a t i o n o f s e l e c t ed so i l p ro p e r t i e s i n and b e t w een ma p u n i t s ................................................................................................. 16 1 .1 .2 Th e r e l a t i o n sh ip b e t w ee n p hy s i ca l p ro p e r t i e s o f s e l e c t ed so i l f o r ms a nd t h e ro o t d en s i t y o f ma i z e .................................. 16 1 .1 .3 Th e hy dro lo g i c a l ch a r ac t e r o f s e l e c ted so i l f o r ms ................ 17 1 .2 H y p ot h e s i s an d Ob j e c t i v e s ....................................................................... 19 1 .2 .1 H y po th e s i s ................................................................................................ 19 1 .2 .2 O b je c t i v e s ................................................................................................ 20 2 .3 .1 Ex pe r imen t a l S i t e ................................................................................. 20 2 .2 .2 Ex pe r imen t a l ma t e r i a l s ...................................................................... 20 2 .2 .3 Ex pe r imen t a l d e s ign ............................................................................ 23 2 .2 .4 A g ron o mi c a l p r a c t i c e s ........................................................................ 25 2 .2 .4 .1 La n d p r ep a ra t io n ........................................................................... 25 CHAPTER 2 ..................................................................................................................... 27 2 .1 In t rod u c t ion ..................................................................................................... 27 2 .2 L i t e ra tu r e Rev i ew ......................................................................................... 29 2 .2 .1 V ar i ab i l i ty o f s o i l p ro p e r t i e s .......................................................... 29 2 .2 .1 .1 S ta t i s t i ca l v a r i a t i o n o f so i l p ro p er t i e s ............................... 29 2 .2 .1 .2 Sp a t i a l v a r i a t i o n o f so i l p rop e r t i e s . ..................................... 43 2 .2 .1 .3 Y ie ld v a r i a t i on i n r e l a t i on to s o i l p ro pe r t i e s .................. 45 2 .3 M e th od o lo g y ................................................................................................... 46 2 .3 .1 So i l Su rv ey .............................................................................................. 46 2 .2 .6 So i l an a ly s i s ............................................................................................ 47 2 .2 .7 S t a t i s t i c a l and sp a t i a l a n a ly s i s ....................................................... 48 2 .3 R e su l t s an d Di sc u s s io n .............................................................................. 49 2 .3 .1 F ac t o r s o f So i l Fo r ma t io n ................................................................. 49 2 .3 .1 .1 C l ima t e .............................................................................................. 49 2 .3 .1 .2 Pa r en t Ma te r i a l .............................................................................. 52 2 .3 .1 .3 To po g raph y ...................................................................................... 53 2 .3 .1 .4 B i o lo gy and t i me ........................................................................... 53 2 .3 .2 Sp a t i a l v a r i a t i o n o f so i l s ................................................................... 55 2 .3 .2 .1 Sp a t i a l d i s t r i bu t io n o f s o i l s ..................................................... 55 2 .3 .3 2 D es c r ip t i on o f t h e mo d a l p ro f i l e s ......................................... 56 2 .3 .3 S p a t i a l v a r i a t i o n o f p hy s i c a l an d ch e mi c a l p r o pe r t i e s ........ 62 2 .3 .4 Sp a t i a l V a r i a t i o n wi th in ma p u n i t s .............................................. 66 3 4 2 .3 .5 Sp a t i a l v a r i a t i o n b e t we e n ma p un i t s ............................................ 69 2 .4 Con c lu s io n ....................................................................................................... 70 CH A PTER 3 ................................................................................................................. 72 3 .1 In t rod u c t ion ..................................................................................................... 72 3 .2 L i t e ra tu r e Rev i ew ......................................................................................... 73 3 .2 .3 So i l t ex tu r e .............................................................................................. 76 3 .2 .4 So i l s t ru c tu r e .......................................................................................... 80 3 .2 .4 Bu lk d en s i t y ............................................................................................ 85 3 .2 .5 So i l w a t e r con t en t ................................................................................ 86 3 .3 M eth o do lo g y ..................................................................................................... 89 3 .3 .1 T r ea t me n t s ................................................................................................ 89 3 .3 .2 P l an t S a mp l ing ....................................................................................... 89 3 .3 .2 .1 A bo v e g ro un d d ry w e igh t .......................................................... 89 3 .3 .2 .2 Roo t s a mp l i n g ................................................................................. 89 3 .3 .3 So i l ph y s i c a l me a s u r e me n t s ............................................................. 90 3 .3 .4 S t a t i s t i c a l ana ly s i s ............................................................................... 91 3 .4 R e su l t s an d Di sc u s s io n .............................................................................. 92 3 . 4 . 1 I n t e r a c t i o n o f s o i l p h y s i c a l p r o p e r t i e s ................................ 92 3 . 4 . 1 . 1 A h o r i z o n ....................................................................................... 92 3 .4 .1 .2 B ho r i zo n ......................................................................................... 94 3 . 4 . 1 . 3 C h o r i z o n ....................................................................................... 96 3 . 4 . 2 R e l a t i o n s h i p b e t w e e n r o o t d e n s i t y a n d s o i l p h y s i c a l p r o p e r t i e s . ........................................................................................... 100 3 . 4 . 3 Ma s t e r h o r i zon s .................................................................................. 102 3 . 4 . 4 Th e P ro f i l e .............................................................................................. 103 3 .5 Con c lu s io n ..................................................................................................... 104 CH A PTER 4 ............................................................................................................... 106 4 .1 In t rod u c t ion ................................................................................................... 106 4 .2 M e th od o lo g y ................................................................................................. 107 4 .2 .1 Ex pe r imen t a l s i t e ................................................................................ 107 4 .2 .2 Ex pe r imen t a l d e s ign .......................................................................... 107 4 .2 .3 Ex pe r imen t a l me a su reme n t s ........................................................... 108 4 .2 .4 C a l cu l a t i o n o f K .................................................................................. 109 4 .2 .5 S t a t i s t i c a l P ro c ed ur es . ..................................................................... 109 4 .3 R e su l t s an d d i s cu ss io n ............................................................................. 109 4 .3 .1 V o lu me t r i c w e tn es s - t i me r e l a t i on sh ip s .................................... 112 4 .3 .2 M a t r i c s u c t i on – t i me r e l a t i o n sh i ps ........................................... 116 4 .3 .3 H y drau l i c h ea d – d ep th r e l a t i o ns h ip s ........................................ 116 4 .3 .4 H y drau l i c con d u c t iv i t y ..................................................................... 119 4 .4 Con c lu s io n ..................................................................................................... 124 CH A PTER 5 ............................................................................................................... 125 REFERENCES .............................................................................................................. 126 APPENDICES ................................................................................................................ 132 4 5 ABSTRACT So i l s va ry a t a l l l ev e l s o f obse rva t i on . Wh en d e sc r ib ing so i l phys i ca l o r chemi ca l p rope r t i e s we i n i t i a l ly t h ink i n t e rms o f ho mo g en eo u s ma te r i a l . Howev e r , f o r ch a r ac t e r i z ing th e l an d u se a b i l i ty i t i s n e ce ss a ry t o co n s id e r va r i ab i l i t y w i th in and be tween s o i l ma p u n i t s a s s o i l s v a r y s ig n i f i c a n t ly o v e r a l an d a n d w i t h i n a ho mo geneous so i l . Th e comb i n a t i on s o f knowl edge abou t so i l i n t e r r e l a t io n s h i p s an d t h e r ep re se n t a t i on o f th e so i l v a r i ab i l i t y w i l l b e u se fu l in t h e p roces s o f cha r ac t e r i z ing t he v a r i ab i l i t y o f s o i l p rope r t i e s f o r d i f f e r en t l and u se ab i l i t i e s , f o r ex ample p r ec i s i on ag r i cu l tu r e . The ob j ec t i v es o f th i s s tudy we re th e r e fo r e t o ( i ) c h a r ac t e r i z e t h e sp a t i a l v a r i a t i o n o f s e l e c t ed s o i l p r o p e r t i e s i n a n d be t w een ma p un i t s ( i i ) de sc r ib e t he r e l a t i onsh ip b e tw een phys i c a l p rop e r t i e s o f s e l ec t ed so i l f o rms a n d th e roo t d en s i t y o f ma iz e ( i i i ) c h a r ac t e r i z e th e h y d r o l o g y o f t h e Tuk u l u , S ep a n e an d B l o e md a l s o i l f o rms a t Pa r ady s . A f i e l d exp e r i me n t wa s co nd u c t ed o n a 5 5 h a c u l t i v a t ed f i e ld on th e e x p e r i me n t a l f a r m o f t h e U n i v e r s i t y o f t h e F r e e S t a t e , P a r ad y s ( S -3 2 ˚35 ’2 1 ’ ’ , E -77 ˚4 3’ 6 ’ ’ ) . The ex p e r imen t a l s i t e w a s s ub d i v id ed i n to 75 exp e r i me n t a l p l o t s . F o r o b j e c t i v e 1 a l l 75 p l o t s w er e a n a ly s ed fo r p H , C a , K , Mg , N a an d 7 t ex t u re c l a s s e s . F o r o b j e c t iv e 2 , 13 p lo t s we re s e l ec t ed f ro m t he 75 ex p e r imen t a l p lo t s t o co v e r a r an g e o f r e l a t i ve d ry b i o ma s s y i e ld p lo t s . Roo t s amp le s and so i l s a mp l e s w e r e t ak e n p e r ma s t e r h o r i zo n . Th e y w e r e an a l y s e d f o r s i l t + c l ay co n ten t , wa t e r s t ab l e ag g r ega t e s , mod u lu s o f r up tu r e , b u lk d en s i t y and o rg an i c ca rb o n c o n t en t . F o r o b je c t i v e 3 , t h r e e mo d a l p r o f i l e s we re s e l ec t ed and t h e i n s t an tan eo u s p ro f i l e me t ho d w a s u sed t o d esc r ibe t he vo lume t r i c we tnes s – t i me r e l a t i onsh ip , t he hy d rau l i c h e ad – d ep t h r e l a t i on sh i ps an d t h e h y d rau l i c co n d u c t iv i t y . I t w as c l ea r t h a t mo s t o f t h e so i l p hy s i c a l an d ch e mi c a l p rop e r t i e s h ad a s t ro ng r e l a t i o n sh i p w i t h c l ay . I t wa s f o u nd t ha t t he r e w a s a 5 6 h ighe r va r i a t i on be tw een map un i t s t han w i th i n ma p un i t s . Desp i t e a ny v a r i a t i on Inv e r se D i s t an c e W e igh t in g ( IDW ) fa i r l y a c cu ra t e ly p r ed i c t ed t h e va r i a t i on w i th in ma p un i t s va ry ing f r om 9 7 % to 99% i r r e s p e c t iv e o f ho r i zo n o r s o i l . I t a l so a ccu r a t e ly p red i c t ed th e v a r i a t i on b e t w een ma p u n i t s v a ry in g f ro m 9 1 % to 94 % . I t wa s fo u nd th a t t h e A an d C h o r i zo n h a s va r y ing i n t e r r e l a t i on s h ip du e to v a ry in g s i l t + c l ay co n t en t s . Th e B ho r i zon i s t h e ma in f a c to r t ha t d i s t in g u i sh es t h e t h r ee s o i l s . T h e s i l t + c l a y c o n t e n t o f t h e B h o r i z o n f o r T u k u l u v a r i e d b e t w e e n 3 1 % a n d 3 4 % , t h e S e p a n e b e t w e e n 4 9 % a n d 5 5 % , a n d t h e B l o e m d a l b e t w e e n 2 8 % a n d 3 4 % . T h e B l o e m d a l h a d t h e h i g h e s t r o o t l e n g t h i n d e x ( R L I ) f o l l o w e d b y t h e S e p a n e a n d T u k u l u . I t was c l e a r t h a t i n t h e ca se o f t h e B lo e md a l a n d Tuk u lu , t h e C ho r i zon con t ro l s t he hy d ro logy , wh i l e i n t h e ca se o f t he Sepan e i t i s t he B ho r i zon . I t ma y be conc lud ed t ha t t h e va r i a t i on i n so i l p rop e r t i e s i s h ighe r b e t w een th an wi th in ma p u n i t s . So i l p hy s i c a l p ro pe r t i e s h av e a c lo se i n t e r r e l a t io n s h i p a nd v a ry ing e f f e c t s o n t h e R L I . Th e h y d ro l og y o f t h e B l o emd a l a n d T u k u l u i s i n f l u en c e d b y th e C h o r i zo n , wh i l e t h e S e p an e i s i n f l u en ce d b y th e B h o r i zon . 6 7 OPSOMMING G r on d v a r i e ë r me r k w a a rd i g . G r on d i s g en e i gd o m b e sk ry f t e wo rd i n t e r me v an ‘n h o mo g en e l i gg a am. A lho ew e l , a s d aa r g ek y k w o rd n a ‘n g ro n d s e v e rmo ë v i r ‘n s ek e re g ron d geb ru ik , moe t d i t b e sk ry f wo rd i n t e r me v a n d i e v a r i a s i e i n - en t u s sen k aa r t een he d e . D ie r ed e h i e rv o o r i s d a t g ron d b e t ek en i sv o l v e r sk i l oo r ‘n l and sk ap en i n ‘n p ro f i e l . ‘ n Ko mb i n as i e oo r d i e i n t e rv e rwan t sk ap t u s sen g r on d - e i en sk ap p e en d i e v e r mo ë o m d i t t en to o n t e s t e l , i s h an d ig i n d i e p r os es o m g ro nd v a r i a s i e v i r s e ke r e l a n d e l i ke g eb ru i k e t e ka r ak t e r i s ee r . D ie doe l s t e l l i ngs v i r d i e s t ud i e was dus a s vo lg : om ( i ) d i e v a r i a s i e v an g r on d e i en sk ap pe i n en t u s s en ka a r t e en hed e t e k a r ak t e r i s e e r ( i i ) d i e i n t e rv e rw a n t sk ap t u s s en g ro nd f i s i e se e i en sk ap p e en d i e w o r t e ld ig the id v an mi e l i e s t e b e sk ry f , en l a a s t en s ( i i i ) o m d i e h id r o l o g i e se e i en sk app e v an d i e B l o e md a l , T u k u l u en S e p an e op P a rad y s t e b es k r y f . ‘ n 55 h a G e p lo eg d e l an d i s g eb ru ik i n ‘n v e l d ek sp e r i me n t o p d i e p roe fp l aa s v an d i e Un iv e r s i t e i t van d i e Vry s t aa t ( -32 ˚3 5 ’2 1 ’ ’ S , - 77 ˚4 3 ’6 ’ ’ O ) . D i e p r o e f t e r r e in w a s o nd e rv e rd e e l i n 7 5 p r o e fp e r s e l e . V i r d o e l s t e l l i n g 1 w a s d i e to t a l 7 5 p e r s e l e g ea n a l i s e e r o m p H , C a , K , M g , N a en 7 t ek s t u u r k l a s s e t e b ep a a l . V i r d o e l s t e l l i n g 2 w a s 1 3 p e r s e l e g es e l ek t e e r wa t g ev a r i ee r h e t vo lg en s r e l a t i ewe b io ma ssa . Op d i e p e r s e l e i s wo r t e l - en g ro nd mon s t e r s g en ee m. D i e g ron d mon s t e r s i s g e an a l i s e e r v i r s l i k + k l e i , w a t e r s t a b i e l e agg reg a t e , b r eek s t e rk t e , b ru tod ig th e i d en o rgan i e s e k oo l s to f i n ho ud . V i r do e l s t e l l i ng 3 w a s d i e v e l d d r e in e r i n g s me to d e g eb ru ik o m d i e vo l u me t r i e s e wa t e r i n ho ud – t y d v e rh ou d in g , d i e h id r o l i e se d ru k – d i ep t e ve rho ud ing en d ie h id ro l i e s e ge l e id i ng v e rmo ë – d i ep t e v e r ho ud ing t e k a ra k t e r i s e e r . 7 8 V an a f d ie s t u d i e w a s d i t d u id e l i k da t d i e g ron d f i s i e s e en - ch emi s e e i en sk ap p e ‘n s t e rk v e rwan t sk ap he t me t d i e s l i k + k l e i i nh ou d . D aa r w a s ‘n g r o t e r v a r i a s i e tu s se n k a a r t ee n h ed e a s b in n e k aa r t e en h ed e . No g t an s h e t “ In v e r s e D i s t an c e W ei g h t i n g ( I D W ) ” d i e v a r i a s i e b in n e (97% to t 99 %) en t u s sen k a a r t een h ed e (9 1 % t o t 94 % ) r e d e l i k a kk ur a a t v oo r s p e l on g e ag d i e ho r i so n o f g ro n d t i p e . D i e A en C ho r i so n h e t v a r i ë r en d e i n t e rv e rw an t sk app e ge too n . D ie B ho r i so n i s d i e h oo f f a k t o r w a t tu s s en d i e d r i e g ro nd t i pe s o n d e r s k e i . D i e s l ik + k l e i i n h ou d v an d i e B h o r i so n h e t t u s s en 31 % en 34 % g ev a r i e ë r , d i e S e p an e t u s s en 4 9 % en 5 5 % en d i e B l o em d a l tu s sen 28 % en 3 4 % . D i e B l o e md a l h e t d i e h oo g s t e o o re en s t emme n d e W L I g eh ad , g evo lg deu r d i e S ep an e en Tuk u l u g ron d t i p es . D i t w a s du ide l i k da t i n d i e g ev a l v an d i e B lo emd a l en Tu k u lu , d i e C ho r i so n d i e h oo f f a k to r i s wa t d i e v loe i v an w a te r b e ïnv lo ed d eu r d i e p r o f i e l , t e r wy l d i e B ho r i so n in d i e g ev a l v an d i e S ep a n e d i e ho o f f a k to r w as . D i e v a r i a s i e w a s g r o t e r t u s se n k a a r t ee n h ed e a s in k aa r t ee n h ed e . D i e g ron d f i s i e s e e i ens k ap pe h e t ‘n s t e rk i n t e rv e rwan t skap en v a r i ë r e nd e i nv lo ed e o p W L I g e t oo n . D i e v lo e i v an w a t e r i n d i e B l o e md a l en T uk u l u wo r d h oo fs aak l ik b e ï n v l oe d d eu r d i e on d e r l ig g en d e C ho r i so n , t e rwy l d i e B h o r i s o n i n d i e gev a l v an d i e S e p an e v l oe i b e ï n v l o ed h e t . 8 9 ACKNOWLE DGEMENTS I wou ld l i ke t o t h an k t he fo l l owing pe r sons and i n s t i t u t i ons : D r . P .A .L . Le Ro ux my s tud y l e ad e r fo r h i s v a lu ab l e ad v i ce , h i s r ead in e ss fo r co n su l t a t i o n and h i s mu ch -n e ed ed su pp o r t t h ro ug h o u t t h e p ro j e c t P ro f . L . D . V an R en sbu rg my co s tu dy l e ad er , w ho r ea l l y d on e mo re t h an wo u ld be exp e c t ed f ro m a co su p e rv i so r . H i s v a luab l e adv i ce , r e ad ine s s fo r con su l t a t i on an d men to r sh ip w i l l a l w ay s b e r e me mb e red . Th e Na tu ra l R e sea r ch Found a t i on fo r fu nd ing t h e r e sea rch p ro j e c t . M r. C .B . Bo th ma fo r h i s wo nd e r fu l co mp an ion sh ip , and sh a r in g o f k no wl edg e an d me mo ra b l e s tu d en t l i f e d u r ing th e p ro j e c t . T h e Dep a r t me n t o f S o i l , C r op an d C l i ma t e S c i en c es o f th e U n i v er s i t y o f t h e F r e e S t a t e , fo r o f f e r i n g me t h e r e s e a rch a s s i s t an t s h i p . T h e s t a f f me mb er s i n t h e D ep a r t me n t o f S o i l , C r o p and C l i m a t e S c i en c e s , e s p ec i a l l y Mr s . R v an He e r d en , f o r th e a d mi n i s t r a t i v e an d e mo t i o n a l a s s i s t anc e a n d M r s . Y . M . D es se l s fo r l abo ra to ry a s s i s t a n ce . M y b e lo ve d p a r en t s t ha t g av e me t h e o pp o r tun i t y t o f u r th e r my s t u d i e s , I w i l l b e fo rev e r g r a t e f u l . My b ro the r an d s i s t e r fo r t h e i r g r e a t l ov e an d k ind n es s in a y e a r when t i me s we r e r ea l l y t o u g h . M y w i fe M a d r é fo r he r mu ch n e ed ed l o v e and s up po r t t h r ou gh g oo d an d d i f f i cu l t t i me s . F i na l l y , I t hank th e A lmigh ty God who I be l i ev e i s t he u l t i ma t e gu ide o f t h i s work and my l i f e i n g ene ra l . I a lw ays r e tu rn ed to H im wh en I g o t s t u ck an d w h en t i me s w h ere d i f f i cu l t . “ In ev e ry ma n t h e r e i s s o me t h i n g wh ere i n I ma y l e a rn o f h i m, an d i n t h a t I a m h i s p u p i l . ” - R a l p h W a l d o E me r s o n 9 10 LIST OF TABLES Cha pt e r 2 S pa t ia l va r ia t io n o f s e l ec t ed s o i l pro p er t i e s in a nd b e tween map un i t s Tab le 2 .1 A Pea r son co r r e l a t i on ma t r i x ( r ) o f s o i l p r o p e r t i e s on t h e s low fo r mi ng t e r r ace s i n t h e Andes r eg ion ( n= 51 ) ( D e r co n e t a l . , 2 0 0 3 ) Ta b l e 2 .2 P e r c en tage o f so i l s a mp l e s i n each t ex tu r a l c l a s s ( So b i e r a j e t a l . , 20 03 ) T a b l e 2 .3 D es c r i p t i v e s t a t i s t i c s a n d s e mi - v a r i o g r am p a rame te r s o f s e l ec t ed so i l p rope r t i e s (Miao e t a l . , 2 00 6 ) T a b l e 2 .4 C o mp a r i so n o f t h e tw o r ep re s en t a t i ve s o i l p ro f i l e s ( S tu t t e r e t a l . , 2 0 0 2 ) T a b l e 2 .5 D es c r i p t i v e s t a t i s t i c s o f p a r a me t e r s me a s u red i n 2 00 2 ( Sh a h an deh e t a l . , 2 00 5 ) T a b l e 2 .6 D es c r i p t i v e s t a t i s t i c s o f p a r a me t e r s me a s u red i n 2 00 3 ( Sh a h an deh e t a l . , 2 00 5 ) T a b l e 2 .7 T h e c l i ma t e o f t h e a r e a ( WR C r ep o r t n o . 1 1 7 6 /1 / 0 3 , 2 00 3 ) Tab l e 2 .8 Co r re l a t i on ma t r i x o f t he so i l p rope r t i e s f o r t he A , B and C h o r i zon s T a b l e 2 .9 S t a t i s t i c a l v a r i a t i o n o f t h e so i l p r o p e r t i e s Cha pt e r 3 T he r e la t io nsh ip be twee n p hy s i ca l pr o p er t i e s o f s e l e c t e d s o i l fo r ms a nd t he r oo t d en s i ty o f ma i ze T a b l e 3 .1 P r i ma ry i n f luen c es o f s o i l p ro p e r t i e s on s o i l r equ i remen t s fo r op t i ma l roo t e lon ga t ion ( Log sd on e t a l . , 1 9 8 7 ) . 10 11 Tab l e 3 .2 Roo t dens i t y da t a i n r e l a t ion t o t h r ee so i l f o r ms w i th d i f f e r en t ph y s i c a l p rop e r t i e s ( D a t a mo d i f i ed f r o m V a n A n t w e r pe n , 19 88 a nd B en n i e , 1 99 6 ) T a b l e 3 .3 R o o t ch a r a c te r i s t i c s o f whe a t d u r i n g t i l l e r i n g i n t h r e e s o i l s o f v a r io u s t ex t u r e s s e l ec t e d f ro m C a l lo t e t a l . ( 1982 ) T a b l e 3 .4 M e an r oo t l eng t h d en s i t y an d t h e s t and a rd d ev i a t i on i n e ach so i l l aye r (Ama t o and R i t ch i e , 2 00 2 ) Tab l e 3 .5 V a r i a t i o n i n so i l ph y s i ca l p rop e r t i e s fo r t h e A ho r i zon o f t h e Tuku lu , Sep ane and B loemd a l so i l f o r ms T a b l e 3 .6 C o r re l a t i on ma t r ix fo r t h e A ho r i zon o f t h e T uk u l u , S ep an e an d B l o e md al so i l f o r ms Tab l e 3 .7 V a r i a t i on i n roo t d ens i t y fo r t he A , B and C h o r i zon o f t h e B l o e md a l , T uk u l u and S e p an e so i l s T a b l e 3 .8 C o r re l a t i on ma t r ix o f th e s o i l p h y s i c a l p r o p e r t i e s v s . r oo t d en s i ty f o r t he A , B a n d C h o r i zon i r r e sp ec t ive o f so i l f o rms . C ha pt e r 4 C hara c ter i s i ng t he hy dro lo gy o f the B loe m da l , T uk u l u and Se pa ne s o i l s a t P a ra dy s . T a b l e 4 .1 S u m ma r y o f t h e p h y s i ca l c h a r a c t e r i s t i c s fo r th e s e l e c t ed Tu ku lu , B lo e md a l a nd Sep an e so i l s T a b l e 4 .2 S u mma r y o f t h e pe d o l o g i ca l ch a r a c t e r i s t i c s fo r th e s e l e c t ed Tu ku lu , B lo e md a l a nd Sep an e so i l fo r ms Tab l e 4 .3 M od e l v a r i ab l e s f i t t ed t o t he so i l wa t e r con t en t - t i me d a t a o f th e B lo e md a l , T uk u lu and Sep an e s o i l s T a b l e 4 .4 S u m ma r y o f t h e h y d r au l i c c o n d u c t i v i t y and r e l a t ed mean vo l u me t r i c wa t e r con t en t f o r t he s o i l s 11 12 LIST OF FIGURES C ha pt e r 1 In tro duc t io n Fi gu re 1 .1 Lo ca t ion o f t h e exp e r i me n ta l f i e ld s i t e a t t h e Pa r ady s Exp e r i me n ta l Fa rm S ou th o f B lo e mfo n te in . F i gu re 1 .2 A d i ag r amm at i c l ay o u t o f t h e IR WH -sy s t e m ( H en s l ey e t a l . , 2 00 0 ) . F i gu re 1 .3 Th e IR WH sy s t em p rep a red ma n u a l ly w i th sp ad es a n d r ak es a t G len Ag r i cu l tu r a l I n s t i t u t e , n ea r B lo e mfo n t e in . F i gu re 1 .4 Th e co n to u r p lou gh p r ep a r in g th e d e ad - l e ve l c o n to u r s a t P a r ady s Ex p e r ime n t a l Fa r m. F i gu re 1 .5 Th e b as in p lou gh c r ea t i ng 1 0 cm deep x 1 m w id e b a s in s a lo ng th e con tou r r id g e s . F i gu r e 1 .6 R un o f f w a t e r co l l ec t ed i n t he b a s in s a f t e r a 3 0 mm r a in even t a t Pa r ady s Exp e r ime n ta l Fa rm. F i gu r e 1 .7 : S ch e ma t i c l ay ou t o f t he c o nv en t io n a l and I R WH t r ea t me n t s on th e 5 5 h a f i e ld a t Pa r ad y s E x p e r i m e n ta l F a r m . F i gu re 1 .8 S ch e ma t i c l ay ou t o f t h e IRW H s t ru c tu r e and i n s t ru me n t a t io n u s ed i n ea c h o f t h e 7 5 e x p e r i me n ta l p l o t s C ha pt e r 2 S pa t ia l v a r ia t io n o f s e l e c t e d so i l p r o pe r t i e s i n a nd b e tween map un i t s F i gu r e 2 .1 T o p s o i l pH ( H 2 O ) a s a fu nc t ion o f e l ev a t ion ( Zehe tne r & Mi l l e r , 2006 ) . F igu re 2 .2 K r iged con tou r map s ( a -d ) o f so i l NO 3 -N w i th d ep th i n 20 0 2 (Shah and eh e t a l . , 2 0 0 5 ) . F i gu re 2 .3 K r iged co n to u r ma p s o f ( a - b ) t o t a l N i n 20 0 2 and 2 00 3 , an d ( c ) mi n e r a l i z ed N i n 2 0 03 ( S h ah an d eh e t a l . , 2 0 0 5 ) . 12 13 F i gu re 2 .4 K r iged su r f ace r ep re sen t a t i on o f t he d i s t r i bu t i on o f t h e s and co n t en t in t he t op s o i l ( V en t e r , 2 0 03 ) . F i gu re 2 .5 K r ig ed su r f ace o f t he d i s t r i bu t i on o f p H ( H 2 O ) i n th e t o pso i l (V en t e r , 20 03 ) . F igu re 2 .6 K r iged su r f ace r ep re s en t a t i on o f t he d i s t r i bu t i on o f t h e OC (% ) i n t h e t op so i l (Ven t e r , 2003 ) . F i gu r e 2 .7 K r i g ed su r f a ce o f t h e me a s u r ed y i e ld ( V en t e r , 2 0 03 ) . F i g u r e 2 .8 S o i l c o r e s d r a w n u s i n g t h e h y d r a u l i c c o r e s a mp l e r . F i gu r e 2 .9 T h e l o w er 3 po s i t io n o f t h e e x p e r i me n t a l s i t e i n th e l an d sc ap e . F i gu r e 2 .10 C o n t o u r map o f t he 5 5 h a ex p e r i me n t a l s i t e . F i gu re 2 .11 S o i l ma p o f t h e ex p e r ime n ta l s i t e a t P a r ady s . F i gu re 2 .12 Tu ku lu so i l f o rm F i gu re 2 .13 S e p an e so i l f o rm F i gu re 2 .14 B lo e md a l s o i l f o rm F i gu re 2 .15 D i s t r i bu t io n o f t h e c l ay con t en t fo r t h e A , B a nd C h o r i zon . F i gu re 2 .16 D i s t r i bu t io n o f c l ay ov er t he so i l f o rms ( n =7 5) . F i gu re 2 .17 M a p i nd i ca t i ng t he a r ea s wh i ch was s e l e c t ed t o b e w i th in t he ma p u n i t s o f t h e Tu k u lu , Sep an e an d B lo e md a l s o i l fo rms . F i gu re 2 .18 Co e f f i c i en t o f va r i a t i on w i th in ma p un i t s and b e t w een ma p un i t s . F i gu r e 2 .19 A c cu r acy o f I D W p r ed i c t io n s w i t h i n map u n i t s and b e t w een ma p un i t s . F i gu re 2 .20 M a p ind i ca t i n g t he a r e a s t h a t h a s b e e n s e l e c t e d t o c h a ra c t e r i z e th e v a r i a t i o n b e t w e en ma p u n i t s . Cha pt e r 3 T he re la t io nsh ip be tw een phy s i ca l prop ert i e s o f s e l e c t e d s o i l fo r ms a nd t he r oo t d en s i ty o f ma i ze F i g u r e 3 .1 D i ag r a m s h o w i n g t h e t h r e e b as ic r o o t sy s t e ms ( K l epp e r , 1 99 6 ) . 13 14 F i gu r e 3 .2 R e l a t i o nsh i p b e tw e en so i l s t r en g th a nd pe r cen t o f c l ay ( B en n i e & B u r g e r , 1 9 8 8 ) . F i gu re 3 .3 R ep r e sen t a t i on o f po s s ib l e pa th s o f a r oo t ax i s t h ro ug h a b ed o f ag g r eg a t e s ( D i ag ram f r o m D e x t e r , 1 97 8 ) . F i gu re 3 .4 P o s s ib l e b eh av io r s o f s emin a l r o o t s p en e t r a t i ng t wo c lod s s ep a ra t ed w i th a c r ack . (Wh i t e ly and D ex t e r , 1 98 4 ) . F i gu re 3 .5 Ch an g e i n p en e t rome t e r p r e s su re w i th bu lk d en s i t y a t va r i ous wa t e r con t en t s ( H i l l e l , 2 00 4 ) . F i gu re 3 .6 R e l a t i onsh ip be tween t h e r e l a t iv e roo t l eng t h o f 7 0 - day -o l d ma i z e , c o t t o n , w h ea t , a nd g r ou nd nu t p l an t s and p en e t ro me t e r r e s i s t anc e (B en n i e , 1 9 9 5 ) . F i gu re 3 .7 R e l a t i on b e tw een co t t on r o o t pen e t r a t i on and p en e t ro me t e r r e s i s t an c e ( T ay l o r e t a l . , 19 96 ) . F i gu r e 3 .8 C h an g e i n p en e t r o me t e r p r e s su re w i th w a t e r c o n t en t a t d i f f e r en t bu lk d en s i t i e s (Be nn ie , 1 99 5 ) . F i gu re 3 .9 R e l a t i onsh ip be t ween t o t a l r oo t l eng th and va r iou s w a t e r ap p l i c a t i o ns a t o p t i mu m n i t r og en l ev e l s ( D a t a p r oc e s s ed f ro m V a n Re n sb ur g , 1 99 6 ) . F i gu re 3 .10 I l l u s t r a t i ng th e s amp l ing o f t h e so i l f o r bu lk d ens i t y de t e r min a t i on ( a ) Th e co r e i s in se r t ed i n to t h e so i l w i th a s l i d ing hammer and (b ) r e cov e red w i thou t d i s t u rb ing t h e so i l i n s id e t he cy l i nd e r . F i gu re 3 .11 R e l a t i onsh ip be tween t o t a l r oo t l eng th o r r oo t l en g th i nd ex ( R LI ) and t h e so i l p hy s i c a l qu a l i t y i n dex (SPQ I ) f o r t he A -h or i zon ( a ) , B -ho r i zon (b ) a n d C - ho r i zo n ( c ) o v e r t he 13 p lo t s i n v es t i g a t ed , i r r e sp ec t i ve o f so i l f o rm. F i gu re 3 .12 R e l a t i onsh ip be tween t o t a l r oo t l eng th o r r oo t l en g th i nd ex ( R LI ) and t h e so i l p hy s i c a l qu a l i t y i n dex ( SPQ I ) fo r t he p ro f i l e s , i r r e s pe c t i v e s o i l f o r ms . 14 15 Cha pter 4 C h ara c t er i s i ng t h e h y d ro l og y o f th e B l o em d a l , T uk u l u and Se pa ne s o i l s a t P a ra dy s . F i gu re 4 .1 Ex p e r imen ta l d e s ign fo r th e i n s t an t a n eo us p ro f i l e me t h od . F i gu re 4 .2 Vo lu me t r i c we tnes s - t ime r e l a t i onsh ip fo r t h e A , B a n d C h o r i zo n o f t h e B l o e md a l so i l fo r m. F i gu re 4 .3 Vo lu me t r i c we tnes s - t ime r e l a t i onsh ip fo r t h e A , B an d C ho r i zo n o f t he Tu ku lu so i l f o r m. F i gu re 4 .4 Vo lu me t r i c we tnes s - t ime r e l a t i onsh ip fo r t h e A , B a n d C ho r i zo n o f t he S ep ane so i l f o r m. F i g u r e 4 .5 H y d r au l i c h e ad p ro f i l e a t 3 0 c m, 6 0 c m a n d 9 0 m d ep th s o f t h e B l o emd a l so i l fo rm o v e r th e measu r ing p e r i od i n d ays a f t e r s a tu r a t i on (DAS) . F i g u r e 4 .6 H y d r au l i c h e ad p ro f i l e a t 3 0 c m, 6 0 c m a n d 9 0 m d ep th s o f t h e Tu ku lu so i l fo r m o v e r t h e me a su r ing p e r i o d i n d ay s a f t e r s a t u r a t i o n ( DA S ) . F i g u r e 4 .7 H y d r au l i c h e ad p ro f i l e a t 3 0 c m, 6 0 c m a n d 9 0 m d ep th s o f t h e S ep an e so i l f o r m o v e r t h e me a su r ing p e r i o d i n d ay s a f t e r s a t u r a t i o n ( DA S ) . F i gu re 4 .8 Hydrau l i c condu c t i v i ty cu r v e s fo r t h e B l o e md a l s o i l . F i gu r e 4 .9 H y d r au l i c c on d uc t i v i t y cu rv e s fo r t h e T u ku l u so i l . F i gu r e 4 .10 H y d r au l i c c on d uc t i v i t y cu rv e s fo r t h e S ep an e so i l . 15 16 CHAPTER 1 INTRODUCTION 1 .1 Mo t iv a t io n 1 .1 .1 Sp a t i a l v a r i a t i o n o f s e l e c t ed so i l p ro p e r t i e s i n and b e t w een ma p u n i t s So i l s v a ry a t a l l l eve l s o f ob se rv a t io n . Ty p ica l l y , wh en desc r ib i ng s o i l p h y s i ca l , ch e mi c a l , o r b i o l o g i c a l p rop e r t i e s w e in i t i a l l y t h in k i n t e r ms o f h o mo g en eo u s ma t e r i a l . T h i s i s a g oo d s t a r t i ng po in t , becau se i t s imp l i f i e s concep t s and l e ads t o r e su l t s w i t h t h e l ea s t nu mb er o f co mp l ica t i on s . Ho wev e r , f o r ch a r ac t e r i z in g so i l map u n i t s i t i s n e c es s a r y t o c o n s i d e r v a r i ab i l i t y w i t h i n a n d b e t w e e n s o i l ma p un i t s . Th e knowledg e abou t so i l i n t e r - r e l a t ionsh ip s and th e r ep re sen ta t i on o f t h e so i l v a r i a b i l i t y w i l l b e u se fu l f o r cha r ac t e r i z ing t he v a r i ab i l i t y o f l and su i t ab i l i t y fo r examp le i n p r e c i s io n a g r i cu l tu r e . I n ag r i cu l tu r e t he ma n ipu l a t i o n o f v a r i a b l e p r op e r t i e s i n c r ea se y i e ld , b u t i t i s un c e r t a in wh ich s o i l p r o pe r ty l i mi t s p r o d u c t i o n a t a ce r t a i n sp o t in a c e r t a in y e a r . T h e mo d e l l i n g o f s p a t i a l v a r i a t io n a s w e l l a s t h e in t e r p r e t a t io n o f t h e v i su a l i mag e , c a n e f f ec t i v e ly i mp ro v e th e u n d e r s t an d i n g o f v a r i a t i o n i n c r o p p r od u c t i o n . 1 .1 .2 Th e r e l a t i o n s h i p be t we e n p hy s i c a l p r o p e r t i e s o f s o i l fo r m a nd t he ro o t d e n s i t y o f ma i z e Ro o t s a r e an i mp o r t an t co mp o nen t i n an y c ro p p ro du c t io n sy s t e m (K lep p e r , 19 90 ; Ben n i e , 19 95 and Van An t wer pen , 1 9 88 ) . Va r iou s so i l phys i ca l p rope r t i e s , i nd iv idu a l l y o r comb ined w i th o the r so i l ph y s i c a l p ro pe r t i e s , h av e an i n f lu en c e on ro o t d eve lop me n t . Th ese s o i l ph y s i c a l p ro p e r t i e s co n s i s t o f so i l t ex tu re , s o i l s t r uc tu re , w a t e r 16 17 c on t en t , b u l k d en s i t y an d po ro s i t y (K l ep p e r , 19 9 0 ) . P as t s tu d i e s on ro o t d ev e l op me n t u nd e r So u th A f r i ca n co nd i t i o ns fo cu s sed he av i ly o n t h e e f f e c t o f i r r i g a t i o n p r a c t i c e s (B en n i e & Bu rg e r , 1 97 9 ; Van An tw e rp en , 1 98 8 a n d B enn i e e t a l . , 1 9 88 ) a n d t i l l a g e p r ac t i c e s ( B e n n i e e t a l . , 1 98 8 ; Sny ma n , 19 87 an d Va n d e r M e r we , 1 99 3 ) . T h e s e t i l l a g e p ra c t i c e s i n c lud e mi n imu m t i l l ag e , s t u bb l e mu l c h and no - t i l l , w h i ch wer e ma i n ly app l i ed on s an d y to s an dy lo a m s o i l s , w i th a ma ss i v e a p ed a l s t ru c tu r e . Re cen t adv an ce s i n t i l l ag e su gg es t ed t h a t t h e I n f i e ld Ra inw a te r Ha rv es t i ng ( I RWH) t echn iqu e i s s u i t ab l e fo r c l ay and d u p lex so i l s i n s emi a r i d zo ne s o f So u th Af r i c a (H en s l ey e t a l . , 20 00 ; Bo tha e t a l . , 2 0 04 ) . To da t e n on e o f t he b i op h y s i c a l s t u d i e s i n I R W H h a s fo cu s s ed o n ro o t d ev e lo p men t . T h i s i s s e en a s a s e r io u s c o n c e rn a s t h e sy s t e m c l a i ms t h a t i t i mpr oves t he r a in wa t e r p rodu c t i v i t y (Bo th a , 2006 ) . 1 .1 .3 Th e h y d r o l o g i c a l ch a r ac t e r o f s e l e c ted so i l f o r ms So i l hyd ro logy i s o f c ru c i a l imp o r t ance i n coun t r i e s such a s So u th A f r i c a , wh e r e t he l a ck o f w a t e r l i mi t s r a in f e d c ro p p r od uc t ion ( H u t so n , 1 9 83 ) . T h e h y d ra u l i c co n du c t i v i t y i s a ch a l l en g i n g s o i l p r o p e r t y t o d es c r i b e b ec a u s e i t c a n cha n g e man y o rd e r s o f ma g n i tu d e o v e r sh o r t d i s t a n ce s . H e t e r og en e i ty o f so i l p rop e r t i e s w i th in an d b e tween so i l ho r i zon s cau ses so me r eg io n s t o b e mo re o r l e s s f avo u r ab l e t o f l o w . T h i s f lo w i s h ig h l y v a r i ab l e w i t h ex t r e me s r ep re sen te d b y t o r t uo us f l o w b e tw e en ind iv id u a l p a r t i c l e s and r a p id f l o w t h r o u g h l a rg e , c o n t i n u o u s ma c r o p o r e s . The spa t i a l va r i a t i on i n hyd rau l i c co nd u c t iv i t y i s i n f luen ced by a l o t mo r e t h an to p og rap hy an d so i l f o rms . Th e a mou n t o f wa t e r r e t a in ed a t r e l a t iv e l y l o w v a l u e s o f ma t r i c s u c t i o n ( b e t w e en 0 a n d 1 0 0 k P a ) d ep en d s p r i m ar i l y u p o n t h e c ap i l l a r y e f f e c t an d p o r e s i z e d i s t r ib u t i o n , and he n ce i s s t r o ng l y a f f e c t ed b y t h e so i l s t ru c tu r e . T o e xp l a in t h i s p h en o men o n , V an ap a l l i e t a l . ( 19 99 ) sug g e s t ed t h a t wh en inv e s t i g a t in g th e s t ru c tu r e o f pa r t i a l l y s a tu r a t ed so i l s , t he r e 17 18 a r e t w o l e v e l s t o b e c o n s i d e r ed : ma c r o s t r u c t u r e a n d mic r o s t r u c t u r e . M a c ro s t ru c t u r e g o v e rn s t h e s o i l w a te r ch a r ac t e r i s t i c be h av i ou r f o r t he so i l pa r t i cu l a r ly a t l ow suc t i on v a lu e s , wh i l e mic r os t ruc tu r e go v e r n s t h e b eh av i o u r o f so i l wa t e r ch a ra c t e r i s t i c a t r e l a t i v e ly h i gh suc t i on v a lue s . On t he o the r hand so i l t ex tu r e i n f lu ences th e d i f f e r en ce i n po re s i z e s i n t h e so i l ma t r ix . I n a c l ayey s o i l , t h e po re s i z e d i s t r i bu t io n i s mo r e un i fo r m, a n d mo r e o f t h e w a t e r i s a d so r b ed , s o t h a t i n c r e a s i n g t h e ma t r i c su c t i o n c au s es a g rad u a l d e c r e as e i n we tnes s . Thus t he g rea t e r t he c l ay con t en t i n gene r a l t he g r ea t e r t he wa t e r r e t en t i on a t any pa r t i cu l a r su c t ion , an d mo re g r ad u a l t he s l op e o f t h e cu r ve ( D ex t e r , 1 97 8 ) . B u l k d en s i t y a l s o ha s an e f f e c t o n th e s o i l w a t e r ch a ra c t e r i s t i c s a s an i n c r e as e i n b u l k d en s i t y me a n s a d e c r ease i n t o t a l po re sp ac e i n t h e so i l and a de c rea se i n wa te r mo v e me n t t h ro ug h t h e s o i l ( H i l l e l , 2 00 4 ) . T h e o r g an i c c a r b on c o n t en t a l s o i n c r e a s e s t h e w a t e r ho ld ing capac i t y and condu c t i v i t y l a rg e ly a s a r e su l t o f i t s i n f l u en c e o n so i l ag g r eg a t ion a nd a s so c i a t ed p o r e s i z e d i s t r i b u t ion . Th e o rg an i c c a rb o n con t en t i n c r ea s e s t h e a mo un t o f wa t e r r e t a in ed , e sp ec i a l l y a t l o w su c t ion s , bu t a t h ighe r suc t i ons so i l r i ch i n o rg an i c ca rbon r e l ea se w a te r r ap id ly b ecau se o f l a rg e po r e spaces ( Sax to n & Rawls , 2006 ) . An o th er p r ob l em i s t h a t o f f i e l d h e t e ro gen e i ty t h a t r e l a t e s to t h e s c a l e t h e h y d r au l i c me a s u re me n t s a re ma d e o n . So i l p ro p e r t i e s s u ch a s con du c t iv i t y , p o r os i t y a n d p o r e s i ze d i s t r i b u t i on a r e s c a l e d ep end an t and sho u ld b e t ak en i n t o con s id e r a t ion when s e l ec t i ng th e s a mp l e s i z e . Thu s a f i e ld e s t i ma t i on o f hy d r au l i c ch a r ac t e r wh e re a l a r g e r s amp l e i s t a k en mig h t b e mo r e d es i r ab le ( H i l l e l , 2 00 4 ) . F u r th e r s t u d i e s h av e t o b e do n e to i d en t i fy a l l t h e f a c t o r s a f f e c t i ng t he s p a t i a l v a r i a t io n o f t h e h y d r au l i c c on du c t i v i ty o f d i f f e r en t s o i l fo rms , b e fo r e a mo d e l t o ch a rac t e r i z e t h e v a r i a t io n ma y b e e s t ab l i she d . 18 19 1 .2 Hypothes i s and Object ives 1 .2 .1 H y po t h e s i s The re ex i s t ma ny i n t e r r e l a t i ons b e tween so i l p rope r t i e s t ha t we hav e t o un de r s t and b e fo re d e sc r ib in g t he va r i ab i l i t y o f so i l p rope r t i e s . An y p r ed i c t i on u s in g su b s t an t i a l s e co nd a ry i n fo rma t ion b a sed on t h e kn ow l ed g e o f t h e r e l a t i on sh ip b e tween so i l p rop e r t i e s p ro v id es b e t t e r r e s u l t s t h an p r ed i c t i o n me t h od s no t t a k ing co r r e l a t i o n i n t o con s ide r a t i on . Af te r t h e i n t e r r e l a t i onsh ip be tw een so i l p rop e r t i e s a r e unde r s tood , a su i t ab l e i n t e rp o l a t i o n t e ch n iq u e ma y b e u sed fo r s u r fa c e r ep r e s en t a t i o n o f t h e d i s t r i b u t i o n o f ce r t a in so i l p ro p e r t i e s . T h e co mb ina t ion s o f k n owl ed g e abo u t so i l i n t e r r e l a t i on sh ip s and t he r ep re se n t a t i on o f t h e s o i l v a r i a b i l i t y w i l l b e u se fu l i n th e p roces s o f cha r ac t e r i z ing t h e va r i ab i l i t y o f so i l s u i ab i l i t y f o r d i f f e r en t l a n d u s es f o r e x a mp le p r ec i s i o n ag r i c u l t u r e a n d e nv i ro n me n t a l s c i en c es . I n t h e m a i ze p ro d u c t io n a r e a o f S o u th - A f r i ca , c o m me r c i a l f a rme r s a r e con s t an t ly d eba t ing t h e q u es t i o n o n h ow t o r edu ce p rod u c t ion r i sk , bo th f i n an c i a l an d ag ro no mi ca l . I nd iv id u a l f a r me r s c an no t do mu c h to c h an g e th e i n t e rn a t i o n a l l y b as ed i n co me a n d co s t s t ru c t u r e s . Hen ce t h ey a r e c o n s t an t ly s ea r ch in g fo r i d ea s , c on cep t s a nd t e chno log i e s a i me d to r educe i npu t co s t s p e r un i t a r ea w i thou t s c a r i fy in g t h e ma x i mu m y ie ld exp e c t a t i o n s b a s ed o n th e l o n g t e r m po t en t i a l o f t he l and . I t i s o f u t mo s t imp o r t ance t h a t r e sea rch mu s t p r ov ide ag ronomi ca l gu id an ce an d su p p o r t t o f a r mer s , h e lp in g th em t o s t ay co mp e t i t i ve o n th e g lob a l l an d scap e f r o m a so i l an d wa te r ma n a g e men t po in t o f v i ew . 19 20 1 .2 .2 O b j e c t i v e s 1 . C h a r ac t e r i z a t i o n o f t h e sp a t i a l v a r i a t i o n o f s e l e c t ed so i l p r op e r t i e s i n an d b e t w een ma p u n i t s ( Ch ap t e r 2 ) 2 . Desc r i b ing t he r e l a t i o n sh ip b e t w een p hy s i ca l p rop e r t i e s o f s e l ec t ed so i l f o rms and t h e roo t den s i t y o f ma i z e ( Chap te r 3 ) 3 . C h a r a c t e r i z i n g t h e h y d ro l og y o f t he T u ku l u , S e p an e and B l o e md a l so i l fo rms a t Pa r ady s . (Ch ap te r 4 ) 1 .3 M e t ho d o l og y 1 .3 .1 Ex pe r i men t a l S i t e A f i e l d ex p e r i me n t w e re co n d u c t ed o n a 5 5 h a c u l t iv a t ed f i e l d o n t h e e x p e r i me n t a l f a r m o f t h e U n i v e r s i t y o f t h e F r e e S t a t e , P a r ad y s ( - 32 ˚35’21 ’ ’S , -77 ˚4 3 ’6 ’ ’E) . Th e exp e r i me n t a l f a r m i s l o c a ted + / -10 k m s o u th o f B l o emfo n t e in b e t w een t h e N 1 r oa d t o C o le s be rg and th e N6 ro ad t o R edd e r s b u rg a s in d i c a t ed i n F ig u r e 1 .1 . Paradys Experimental Farm N N1 N6 F i g u r e 1 .1 : Lo ca t i o n o f t h e e x p e r i me n ta l f i e ld s i t e a t t h e P a r ad y s Exp e r i me n ta l Fa rm S ou th o f B lo e mfo n te in 1 .3 .2 Ex pe r i men t a l ma t e r i a l s The ba s i c concep t s o f t h e IRWH was i n i t i a t ed by H en s l ey e t a l . ( 2 00 0 ) and c on s i s t o f a no t i l l ru n o f f s t r i p s l op ing t o w ar d s a 1 m w i d e b as i n a r e a ( F ig u r e 1 .2 ) . Th e n o - t i l l s t r i p i s u s ed 20 21 a s a c a t chmen t f o r i nduc ing runo f f by u s ing t he n a tu r a l t opog raphy o f t h e l an d a s w e l l a s t h e c ru s t in g ch a ra c t e r i s t i c s o f t h e s o i l . Ru no f f w a t e r i s c o l l ec t ed i n t he b as in s , a p ro c es s d e f in ed a s in - f i e ld ru no f f ( B o t h a , 20 07 ) . U nd er con d i t i on s wh e r e t h e d i s ch a r g e v o l u me f r o m t h e ru n o f f a r e a i s l o w er t h an th e s u r fa c e s t o r ag e c ap a c i t y o f t h e b a s in s , ru no f f f r o m t h e l an d ( Ex- f i e ld r un o f f ) i s a s su me d to b e z e ro . F i g u r e 1 .3 d ep i c t s t h e su r f a c e s t r u c t u r e o f t h e I RW H ma d e ma n u a l l y w i t h sp ade s a n d r ak e s . Th e c h a l l en g e w a s t o o b t a i n a s imi l a r s u r fa c e s t ru c tu r e o n l a rg e s c a l e u s i ng t r a c to r d r awn imp l e me n t s . Th i s w a s ob t a in ed t h r o ug h t h e d ev e l op me n t o f a c o n to u r p l ou g h wh i ch c r ea t e s a 20 cm h igh co n tou r r i d ge w i th a s l o pe s t r i v ing t o be ze ro ac r os s t he t o po g r aph y (F i g u r e 1 . 4 ) . T he s e con d i mp l e me n t , t h e b as i n p l o ug h , i s p r e s en t e d in F i g u r e 1 .5 . T h e ba s i n p lo ug h c r e a t e s a 10 c m d e e p a n d 1 m w id e b a s in ev e ry 1 . 5 m a l o ng th e p lou g h ed co n t o u r (F ig u r e 1 .5 ) . F igu re 1 .6 d emo n s t r a t e s t h e co l l e c t i on o f in - f i e ld ru no f f i n t he b a s in s b e fo re p lan t in g . 21 22 F i gu r e 1 .2 A d i ag r a mma t i c l ay o u t o f t h e I RWH -sy s t e m (H en s l ey e t a l . , 2000 ) . F i gu re 1 .3 Th e IRWH sy s t e m p r ep a red man u a l ly w i th sp ad e s a nd r ak e s a t G len ag r i c u l tu r a l i n s t i t u t e , n ea r B lo emfo n te in . F i gu r e 1 .4 Th e co n to u r p l o ug h p rep a r i n g t he d e a d - l ev e l co n t o u r s a t P a r a d y s E x p e r i me n t a l F a r m . 22 23 F i gu r e 1 .5 Th e b as i n p l ou gh c r e a t i ng 10 c m d ee p x 1 m w i d e b as i n s a lo n g t h e c o n to u r r i dg e s . F i gu re 1 .6 Runo f f w a t e r co l l e c t ed in t he b a s in s a f t e r a 30 mm ra i n e v en t a t Pa r ad y s Exp e r i me n ta l Fa rm. 1 .3 .3 Ex pe r imen t a l d e s ign T h e exp e r i me n ta l s i t e w as s u b d i v i d ed i n t o 7 5 ex p e r ime n t a l p lo t s (F ig u r e 1 . 7 ) . Ro w 3 , 8 an d 1 4 w a s t r e a t ed a s con v en t ion a l p l o t s wh i l e t he r e s t o f t h e rows wer e t r e a t ed a s IRW H p lo t s . Ea ch p lo t w a s 7 2 m x 7 2 m w i th ro ws c o n s i s t in g o f a 2 m r u n o f f a r e a an d a 1 m b a s i n a r e a . A n e u t r o n a cc es s t u b e w as i n s e r t ed i n t h e b a s in a r e a a nd o n th e r un o f f a r e a . A ra i n g au g e w a s i n s e r t ed in t h e mi d d l e o f t he p lo t t o c ap tu r e r a in f a l l . On th e t h i r t e en p lo t s wh e re r oo t s amp l e s w e re t ak en a p ro f i l e p i t w a s mad e in t h e no r th w e s t e rn c o rn e r o f th e p lo t . Th e p ro f i l e was mo rpho log i ca l l y de sc r ib ed i n de t a i l . Each o f t he p l o t s w a s s ep a ra t e ly an a l y z ed and t r e a t ed ( F i g u r e 1 .8 ) . 23 24 N IRWH Conventional IRWH Conventional IRWH Conventional IRWH F i gu r e 1 .7 : S ch e ma t i c l ay ou t o f t he c o nv en t i on a l an d I R W H t r e a t men t s o n t h e 5 5 h a f i e ld a t P a r ad y s Ex p e r i men t a l F a r m. 24 25 F i gu r e 1 .8 S ch e ma t i c l ay o u t o f t h e IR W H s t r uc t u r e and i n s t r u me n ta t i o n u s ed i n e ac h o f t h e 7 5 ex p er i me n t a l p l o t s . 1 .3 .4 A g r o n o mi c a l p r a c t i c e s 1 .3 .4 .1 Land p r ep a ra t i o n H i s to r i ca l l y t h e 55 ha l and was cu l t i va t ed i n a conv en t i ona l ma nne r wh i ch co mp r i s ed o f p lo ug h i n g t h e l and 2 50 mm – 30 0 mm d e e p a s a p r i mary cu l t i va t i on ac t i v i ty . I t was t h e n d i sked F a r ro w ed in mo s t o f t h e y ea r s t o b r e ak d o w n t h e c l o d s a s a s e co n d a ry cu l t i v a t i o n a c t i v i t y fo r p r ep a r ing t he se e d bed . Co n ven t io n a l : Fo r t h e f i e ld t r i a l s t he l and was p loughed (250 mm to 3 0 0 m m d e ep ) a s a p r i ma r y cu l t iv a t io n ac t i v i ty . A s a s e co n d a ry cu l t i va t i on ac t i v i t y t h e l and was d i sk h a r r ow ed t o b r e ak d ow n c l od s . Du r i n g o t h e r s t u d i e s t h a t w e r e co nd u c t ed o n t h e f i e l d p ro f i l e p i t s we re ma d e . Th ese p ro f i l e p i t s i n d i c a t ed th a t co mp a c t ion o c cu r r ed b en ea th t h e p l o ug h l ay e r a ro un d 3 00 mm d ee p . Ju s t b e fo r e p l a n t i ng t he t o t a l 55 h a l an d w as r i pp ed 4 5 0 mm d ee p o n t h e p l an t r ow to 25 26 e l i mi n a t e a n y co mp a c t i o n th a t mi g h t h av e o ccu r r ed . The ma i z e w a s p l an t ed i n t r a ml i ne s o n 9 00 mm i n t e rv a l s . IRWH: A c on tou r s u rv ey wa s c o nd uc t ed o n a 0 .5 m g r i d o v e r t h e t o t a l 5 5 h a e xp e r i me n t a l s i t e . T h e co n t o u r ma p w a s s t u d i e d t o d iv id e t h e a r e a i n to l a r g e r I R WH t o p o g r aph ica l t e r r a ce s . Co n t o u r r i d g e s (2 00 mm h ig h ) w e re mad e a l on g th e co n to u r l i n e s t o e l imi n a te any l a t e r a l f l ow o f w a te r f r o m t h e l an d . Th e b a s in p lou gh w a s t h en i mp l e me n t ed a lo n g t h e r i d g e s t o c rea t e t h e ba s in s a lo ng th e co n to u r r i d g e s . A g r ad er w as u sed t o g iv e t h e ru no f f a r ea a s l i gh t s l op e ( < 1%) t owards th e b as in a r ea so t h a t in - f i e ld runo f f w ou ld b e i nc r ea s ed . T h e t o t a l a r e a o f t h e ex p er i me n t a l s i t e w a s f e r t i l i z ed w i t h 3 : 1 :0 a t 15 0 k g .h a - 1 b e fo re p l an t in g . Th e ma i z e c u l t i va r P an 61 46 w a s p l an t ed a t a p l an t po pu la t i o n o f 1 6 0 00 p l an t s . h a - 1 . Th e ma i z e w a s p l an t ed on 10 J anu a ry 20 06 . Th e t o t a l a r ea o f 55 h a was t r ea t ed w i th Ro u nd up a nd 2 .4 D Es t e r b e fo re g e r mi n a t ion . 26 27 CHAPTER 2 Spatial variat ion of selected soil propert ies in and between map units 2 .1 In t ro du c t io n Re se a r ch i nv e s t i g a t io n s h ave sh o wn th a t t h e v a r i ab l e ch a ra c t e r i s t i c s o f so i l s have ma j o r e f f ec t s on t he f e r t i l i z e r r equ i r emen t and on th e nu t r i en t t r an spo r t ove r and w i th in a so i l p ro f i l e . Spa t i a l va r i ab i l i t y cause s uneven p a t t e rn s i n so i l f e r t i l i t y l eve l s and c rop g rowth , and d e c r ease s t he e f f i c i en cy o f f e r t i l i z e r s a p p l i ed i n t h e f i e ld s . Th e s i t e s p ec i f i c ma n a g emen t o f n u t r i en t s u se d i n p r ec i s io n ag r i cu l t u r e ( PA ) c a n on l y b e ma d e b y qu an t i t iv e a s s e s sme n t o f t h e s p a t i a l va r i ab i l i t y (Gup ta e t a l . , 1 99 7) . P r ec i s io n ag r i cu l tu re i s an i n t eg ra t e d i n fo rma t i o n and t e chn o lo gy b a sed ag r i cu l tu ra l ma n ag eme n t sy s t e m. Th e i n t en t i s t o ma n ag e sp a t i a l and t e mp o ra l v a r i a b i l i t y a s soc i a t ed w i th a l l a sp e c t s o f a g r i cu l tu r a l p rod u c t i o n fo r op t i mu m p r o f i t ab i l i t y , su s t a in ab i l i t y a nd p r o t e c t io n o f t he e n v i r on me n t . S t u d i e s h av e i n ve s t i ga t ed w i th i n - f i e ld va r i ab i l i t y o f so i l p rop e r t i e s and ev a lu a t ed t h e impac t o f s i t e s p ec i f i c ma n ag e me n t o n c ro p p ro d uc t i on an d o t h e r l an d u se pu rp o ses (Miao e t a l , 20 06 ) . Ho weve r fo r ma ny app l i ca t i on s o f wha t i t i s neces sa ry to con s ide r t h e v a r i ab i l i t y o f th e s o i l . I n a g r i cu l tu re t h e ma n i pu l a t i o n o f t h e s e v a r i ab l e p ro pe r t i e s o f wh a t w i l l i nc r e ase y ie ld , b u t i t i s u nce r t a in wh ich so i l p ro p e r ty l i mi t s p ro du c t io n a t a ce r t a in spo t i n a ce r t a in y e a r . Th ro ug h adv a n ced i n te r po l a t i o n t e ch n iq u e s t h e va r i a t i on i n s o i l p rop e r t i e s may b e v i su a l ly ch a ra c te r i zed , so t h a t t h e e f f e c t o f t h e v a r i a t i on on y i e ld ma y b e co r r e l a t ed . D i f f e r e n t s amp l ing me t h od s a nd i n t e rp o l a t i on t e chn i qu es a s we l l a s t h e un de r s t and in g o f s u r face s fo r 27 28 t he u se i n i n t e rpo l a t i on i s o f g r ea t impo r t ance , a s i t i s c l e a r t ha t s o i l p r o p e r t i e s w i l l b e c h a r ac t e r i z ed a c co r d i n g t o c i r cu ms t an c es u s i n g t h e app rop r i a t e s amp l ing me thod an d i n t e rpo l a t i on t e chn ique th a t su i t s t h e c i r cu ms t an c e s t h e b e s t ( H i l l e l , 2 0 0 4 ) . The mo de l l i ng o f spa t i a l va r i a t i on a s we l l a s t he i n t e rp re t a t i on o f t h e v i su a l i ma g e t o a f f ec t i v e l y d e t e r mi n e th e r e a so n wh y a r ea s d o e s no t g iv e t h e su sp e c t ed y ie l d , i s a to o l t h a t ma y b e u sed b y p r e c i s i on a g r i cu l tu r e . Th i s p roc e s s r e du ce s i n p u t s a n d c a u s es an i n c r e as e i n p r od u c t i o n . The p r e c i s e a mo un t o f f e r t i l i z e r a p p l i ca t i o n fo r ex a mp l e ma y b e d e t e r mi n ed fo r e ach p a r t o f t he l and , r a th e r t h an t r e a t i ng th e wh o l e l an d u n i f o r mly in t h e f e r t i l i ze r ap p l i ca t io n p ro c e s s . Thu s , th e c o r r ec t mod e l and i n t e r po l a t i on t e chn i qu e ma y a s s i s t t h e f a r me r i n i t s d ec i s ion mak ing . T h e o b j ec t i v es o f t h i s chap te r t h e re fo r e a r e to ( i ) d o a t h o ro u g h l i t e r a tu r e s t udy on s t a t i s t i c a l and spa t i a l va r i a t i on o f so i l p rope r t i e s , ( i i ) d e sc r i b e t he mo rpho logy o f t he so i l f o rms found a t t h e e x p e r i me n t a l s i t e , ( i i i ) d e sc r i b e t h e ch e mi c a l a n d p h y s i c a l c h a r ac t e r i s t i c s o f t h e s o i l fo r ms fo u n d a t t h e e x p e r i m e n t a l s i t e and ( i v ) ju s t i f y t h a t a so i l ma p i s i n f a c t a u se fu l sp a t i a l r ep r e sen t a t i on by i nd i ca t i ng t ha t t h e r e i s a h ighe r spa t i a l v a r i a t i on be tween ma p un i t s t han w i th in map un i t s and t ha t by u s ing t h e co r r ec t i n t e rp o l a t i on p ro c es s e s o ne w i l l b e ab l e t o cha r a c t e r i ze t h i s sp a t i a l a n d v a r i a t i o n e f f e c t i v e ly . 28 29 2 .2 L i t e r a tu r e R ev i ew 2 .2 .1 V ar i ab i l i ty o f s o i l p ro p e r t i e s 2 .2 .1 .1 S t a t i s t i ca l v a r i a t i on o f so i l p rop e r t i e s P h y s i c a l p r o p e r t i e s T e x t u r e : I n an exp e r i me n t do n e on t h e sp a t i a l v a r i ab i l i t y i n s o i l p r op e r t i e s on s lo w- fo rmi n g t e r r a ce s i n t h e A nd e s r eg io n o f E cu ad o r , D e r c o n e t a l . ( 20 03 ) sa mp l ed t he so i l i n b and s fo l l ow in g th e co n t o u r . T h ey w er e lo ca t ed ev ery 1 m b eg i n n in g a t t h e h i g h e s t p o i n t o f e l ev a t io n and in c lud ing t h e l ow e s t po in t on t h e t e r r ace . The so i l d e p t h fo r a l l s a mp l e s w a s 0 – 1 5 c m. T e x tu r e f r a c t i o n s o f s a n d , s i l t a nd c l ay we r e an a ly z ed . The S hap i ro -Wi lk W- t e s t wa s u sed t o t e s t f o r no r ma l i t y and t he Pea r son co r r e l a t i on was ca l cu l a t ed t o ex amin e t he r e l a t i o n sh i p b e t w e en p a i r s o f v a r i a b l e s . ( C od y & S mi t h , 1 99 7 ) . . S t a t i s t i c a l s i gn i f i ca n ce w as t e s t ed a t 0 .01 and 0 .05 l eve l . S t ep wi s e mu l t i p l e r eg re s s io n an a ly s i s w a s u sed to t e s t t h e hy po th e s i s on ea ch e x p e r i me n t a l s i t e a t a s i g n i f i c a n c e l ev e l o f 0 .0 1 . T h r ou gh t he s tu dy i t w a s f ou nd ( T ab l e 2 .1 ) , t h a t c l ay co n t en t w a s s ign i f i c an t ly ( P<0 .01 ) p o s i t i v e ly c o r r e l a t ed w i th ch a ra c t e r i s t i c s su ch a s p ho sph a t e (P ) (R 2 = 0 .8 4 ) , pH (R 2 = 0 .8 8 ) and a lu mi n i u m (A l ) (R 2 = 0 .54 ) , b u t n eg a t i v e l y co r r e l a t ed wi t h o rg an i c c a rb on ( O C) (R 2 = -0 .73 ) . So i l f e r t i l i t y i s no r ma l ly po s i t i v e ly co r r e l a t ed w i th c l ay co n t e n t ( S ch o l e s e t a l . , 19 94 ) . How eve r , i n t h e h ig h e r and hu mi d r eg i o ns o f t h e An des r eg io n i nc r ea s i n g c l ay con t en t i s o f t en a s so c i a t ed w i th t h e p r e sen c e o f o ld vo l can i c t u f f h av ing h ig h Al t ox i c i t y an d h ig h P f i x a t io n . S i l t an d c l ay w e r e s i g n i f i c an t ly r e l a t ed t o r e l a t i ve d i s t an ce i n f i v e t o s i x t e r r ace s . 29 30 T a b l e 2 .1 A P e a r son co r r e l a t i o n ma t r i x ( r ) o f so i l p ro pe r t i e s o n t h e s l o w fo r mi n g t e r r a ce s i n t h e And es r eg ion (n =5 1) (De rcon e t a l . , 2 0 03 ) pH(H2O) Corg N total C/N NO3- P K pH(NaF) Alex Pret Kex Caex Mgex BS CEC Silt Clay Sand Distance pH(H2O) - Corg -0.09 - N total -0.19 0.67 - C/N 0.14 0.26 -0.49 - NO3- -0.46 0.33 0.27 0.07 - P -0.47 0.19 0.08 0.14 0.71 - K 0.29 0.22 0.09 0.22 0.32 0.26 - pH(NaF) -0.20 -0.51 -0.63 0.30 0.26 0.44 0.02 - Alex -0.30 -0.60 -0.50 -0.11 -0.28 -0.09 -0.59 0.41 - Pret -0.26 -0.51 -0.54 0.20 0.17 0.35 0.05 0.81 0.43 - Kex 0.26 0.64 0.60 -0.10 -0.04 -0.18 0.42 -0.72 -0.61 -0.59 - Caex 0.19 0.63 0.69 -0.26 -0.20 -0.37 0.03 -0.90 -0.44 -0.75 0.86 - Mgex 0.28 0.55 0.63 -0.26 -0.31 -0.44 0.04 -0.92 -0.46 -0.78 0.84 0.97 - BS 0.21 0.55 0.63 -0.28 -0.29 0.43 0.01 -0.92 -0.44 -0.77 0.82 0.96 0.99 CEC -0.01 0.08 -0.08 0.21 0.41 0.32 0.29 0.35 0.04 0.28 -0.09 -0.25 -0.38 -0.14 - Silt 0.10 0.66 0.64 -0.10 0.26 0.05 0.29 -0.64 -0.71 -0.69 0.55 0.59 0.61 0.29 0.63 - Clay -0.19 -0.73 -0.71 0.17 0.02 0.27 0.04 0.88 0.54 0.84 -0.75 -0.91 -0.89 -0.18 -0.88 0.20 - Sand 0.20 0.63 0.62 -0.18 -0.17 -0.40 -0.11 -0.84 -0.34 -0.76 0.72 0.92 0.88 0.08 0.85 -0.16 0.50 - Distance -0.27 0.29 0.36 -0.18 0.45 0.46 0.37 -0.19 -0.35 0.05 0.34 0.17 0.13 -0.15 0.16 0.01 0.39 -0.16 31 I n a n o t h e r s t u d y c o n d u c t e d o n t h e s p a t i a l v a r i a b i l i t y o f s o i l p ro p e r t i e s a n d th e i r r e l a t i o n sh ip w i th soy b ean y i e ld , Cox e t a l . ( 2 0 0 3 ) f o u n d t h a t t h e v a r i a b i l i t y o f s an d , c l a y a n d s i l t f r a c t i o n s we re d ep end an t on t h e t opog raphy . Th e spa t i a l v a r i ab i l i t y e x p r e s s e d a s t h e c o e f f i c i en t o f v a r i a t i on (CV) o f t h e p ro p e r t i e s w a s a s f o l l o w s : s a n d 2 5 % , c l ay con t en t 28% , wh i ch i s an i n d i c a t i o n o f t h e r e l a t i v e l y s t ab i l i t y o f t h e se two p ro p e r t i e s . Th e s i l t f r a c t i o n h ad a l o w spa t i a l C V o f 1 1 %. I t i s t h u s c l e a r t h a t t ex tu r a l f r a c t i on s t en d to h av e a l o w spa t i a l v a r i a t i on o v e r t opog raph i c l andscapes t ha t t end t o b e mo r e l e v e l , w h i l e i t w i l l t e n d t o v a r y mo r e s p a t i a l l y w i t h a t o p o g r a p h i c l an d s c a p e t h a t va r i e s i n e l eva t i on , a s p e c t a n d s l o p e . Low co r r e l a t i on be tw e en r e l a t i v e d i s t an c e an d o th e r s o i l p ro p e r t i e s ma y b e exp la in ed in s e v e r a l w ay s : ( i ) t h a t so i l p ro p e r t i e s d id n o t s h o w a l og i c a l p a t t e rn o f s p a t i a l v a r i ab i l i t y o r a g r ad i en t i n t h e d i r e c t i o n o f t h e t e r r a c e s , ( i i ) t h e g r a d i e n t w a s h ig h ly s i t e d ep en d e n t a n d ( i i i ) t h e g r a d i en t was no t l i n ea r . C o r r e l a t i o n w e r e s i g n i f i c a n t w h e n c o n s i d e r i n g e a c h s l o w - f o r mi n g t e r r a c e se p a r a t e l y , i n d i ca t i ng t ha t sp a t i a l va r i ab i l i t y i s s i t e d e p e n d e n t . H y d r a u l i c p r o p e r t i e s : S a t u r a t e d h y d r a u l i c c o n d u c t i v i t y (K s ) : T h i s i s a c h a l l e n g i n g so i l hyd rau l i c p rope r ty t o d e s c r ib e b ec au se i t c an ch ang e ma n y o rd e r s o f ma g n i t u d e o v e r s h o r t d i s t a n ces . H e t e rogen e i t y o f so i l p rope r t i e s w i th in and be tween so i l h o r i z o n s c a u s e s s o me r e g i o n s t o b e mo r e o r l e s s f a vo rab l e t o f l ow . Th e f l o w o f wa t e r i s h igh ly v a r i ab l e w i th ex t r e me s r e p r e s en t ed b y to r tu o u s f l o w b e tw e en i n d i v i d u a l p a r t i c l e s a nd r a p i d f l o w t h r o u g h l a rge , con t i nuous ma c r o p o r e s . 32 Sob i e r a j e t a l . ( 2 0 0 3 ) fo u n d t h a t s p a t i a l p a t t e r n s w er e c l e a r l y e v i d e n t fo r t o p o g r a phy and so i l t ex tu r a l co mp o n e n t s , a s r e f l e c t e d i n s c a t t e r p l o t s . S ca t t e r p l o t s h o w e v e r , s h o w e d c o n s i d e r a b l e n o i se a n d l i t t l e t o n o spa t i a l s t r u c t u r e a t t h e c o a r se s t s a mp l ing sc a l e s o f 2 5 m a n d 1 0 m. T h e s e c o n t r a s t i ng r e su l t s sugges t n o l i n k b e t w e e n K s a n d t h e s e p h y s i c a l p r o p e r t i e s a t co a r se s amp l ing s ca l e s . Whi ch w a s r ema r k a b l e w a s t h a t t h e se s p a t i a l p a t t e rn s o f K s c o r r e s p o n d e d p e r f e c t l y w i th t he t ex tu r a l an d t o p o g r a p h i c d a t a o f t r a n s e c t 6 t h a t w as s t u d i e d . W h y d i d t h i s hyd rau l i c bounda ry o c c u r f o r o n e t o p o g r a p h i c / t e x t u re s t e p a n d n o t t h e o t h e r ? A co r r e l a t i on w as fo und on ly i n t he l o ca t i on s wh e re t h e c o n cen t r a t i on o f s a n d > 8 0 % a n d c l a y < 2 0 % , s u g g e s t i n g t h a t v e r y c o a r s e t e x t u r e s ( l o a my s a n d and s an d ) a r e i n f l u en t i a l i n c o n t r o l l i n g K s ( Ta b l e 2 . 7 ) . Ta b l e 2 .7 Pe r c en t ag e o f s o i l s a mp le s i n e a ch t ex t u r a l c l a s s (Sob i e r a j e t a l . , 2003 ) Sandy clay Sandy clay loam Clay loam Sandy loam Loamy sand Sand Transect Depth (cm) (%) (%) (%) (%) (%) (%) 2 0 - 12.5 4.3 53.2 0 22.6 15.5 4.3 40 -50 31.7 56.1 2.4 7.3 2.4 0 4 0 - 12.5 0 100 0 0 0 0 40 - 50 14.3 85.7 0 0 0 0 90 - 100 64.6 35.4 0 0 0 0 6 0 - 12.5 0 0 0 41.2 43.1 15.7 40 - 50 0 58.8 0 17.6 23.6 0 90 - 100 33.3 56.9 0 9.8 0 0 T h u s t h r o u g h t e r mi n o lo g y o f R i n g r o s e & V o ase (1991 ) t he spa t i a l v a r i ab i l i t y o f K s i s s i mi l a r t o t ha t o f s o i l t ex t u r e o n l y w h en t h e s a n d c o m p o n e n t i s g r e a te r t han 80%, s u g g e s t i n g t h a t t h e t e x t u r a l ma c r o p o ro s i t y i s mo r e s i g n i f i c an t t h an b iopo ros i t y fo r ex t r eme ly c o a r s e t e x t u r e s . I n ano the r s t udy on t he spa t i a l va r i a b i l i t y o f s o i l h y d r a u l i c c o n d u c t i v i t y a l o n g a t r o p i c a l r a i n fo r e s t c a t e n a ( So b i e r a j e t a l . , 2 0 0 3 ) , K s a t w a s me a s u r e d a l o n g a n t r a n se c t a t d e p th s o f 2 0 , 3 0 , 5 0 33 a n d 9 0 c m w i t h a c o mp a c t , c on s t an t - h e ad p e r me a me t e r . K s a t w as f o u n d t o n o t b e s i g n i f i c an t l y d i f f e r en t be tw een t h e s e so i l f o r ms a t a n y d ep th ex cep t fo r 9 0 c m . C a l c u l a t i o n s o f t h e me a n i n d i c a t e a r e l a t i v e l y c o n s t an t v a l u e fo r K s a t a t d e p t h s o f 2 0 , 3 0 a n d 5 0 c m. H a d t h e r e b e e n a so i l f o r m c o n t ro l l ed spa t i a l s t r u c tu r e o f K s a t t hey w o u l d h a v e e x p e c t e d a s t r o n g e r c o r r e l a t i o n b e t w e e n me a s u r e m e n t s o n t h e s a me s o i l f o r m t h a n b e t w e e n me a s u r e me n t s on two d i f f e r en t so i l f o rms . They con c lud ed th a t t h e s t ro n g t o p o g r a p h y d e p e n d e n c e o f so i l f o rms a long a t r a n s e c t i s n o t r e f l e c t e d i n a s i mi l a r d ep en d en c e o f K s a t a n d t e n t a t i v e l y a t t r i bu t ed t h i s l a ck o f d ep en d en ce to t h e o v e r r i d ing in f lu en ce o f b i o t u r b a t i o n - c o n t r o l l e d ma c r o p o r o s i t y . T h u s t h r o u g h b o t h s tu d i e s i t ma y b e con c lud ed t h a t t h e sp a t i a l v a r i a t i on o f s a tu r a t ed hyd rau l i c c o n d u c t i v i t y i s i n f l u e n c e d b y a l o t mo r e t h a n t o p o g r a p h y a n d s o i l f o r ms . B i o t u rba t i on con t ro l l ed ma c ropo ros i t y a n d so i l t e x t u r e w i t h a s a n d f r ac t i on o f mo r e t han 80 % fo r e x a mp le h av e a d e f i n i t e a f f e c t o n t h e sp a t i a l v a r i a t i o n i n K s a t a s w e l l . Fu r t h e r s t u d i e s h a v e t o b e don e t o i d en t i fy a l l t he f ac to r s a f f e c t i n g t h e spa t i a l v a r i a t i on o f t h e s a tu r a t e d h y d r a u l i c c o n d u c t i v i t y , b e f o r e a mo d e l t o c h a r a c t e r i z e t h e v a r i a t i o n ma y b e e s t ab l i sh e d C h e mi c a l p r o p e r t i e s C a l c i u m a n d M a g n e s i u m : B u r t & P a r k (1999 ) p r ev ious ly d e sc r ibed v a r i ab i l i t y i n ex ch ang eab le C a and Mg ac ro s s a g r an i t i c h i l l s l o p e i n Sou th w e s t Eng land . Th ey a t t r i bu t ed mi n i ma l v a r i a t i o n o f C a a n d M g i n su r f a c e s o i l s t o s i mi l a r i t i e s i n b e h a v i o r a s n u t r i en t c a t ions , w i th t i gh t cy c l i ng i n v eg e t a t i on and u n i fo rm a t mo s p h e r i c a n d l i t t e r f a l l i n p u t s . D a t a f r o m a s t u d y o n t h e s p a t i a l v a r i ab i l i t y i n so i l i o n exchang e ch emi s t ry i n a g ran i t i c u p l a n d c a t c h me n t s u g g e s t e d t h e c on t r a s t i n g b eh av io r o f C a an d M g , a n d a v a r i a t i o n o f Ca be tween p lo t s t h a t a r i s e d u e t o t h e 34 n a tu r e o f o rg an ic ma t e r i a l a s a r e su l t o f va ry ing l i t t e r d e co mpo s i t i o n r a t e s a n d v eg e t a t i on t yp e s ( S tu t t e r e t a l . , 2 0 0 2 ) . I n t h i s e x p e r i me n t h i g h C V v a l u e s a r e co mp ar ab l e w i th t hose r epo r t ed fo r ag r i cu l t u r a l s i t u a t i o n s w h e r e h i g h v a r i a b i l i t y i s a t t r i bu t ed t o d i f f e r e n ce s i n ma n a g e me n t p r ac t i c e s . Gup t a e t a l . ( 1997 ) mo de l l ed t he spa t i a l va r i ab i l i t y o f so i l c h e mi c a l p a r a me t e r s fo r s i t e - sp ec i f i c f a r mi n g u s i n g s t o c h a s t i c me t h o d s . T h e y f o u n d t h a t C a v a r i e d f r o m 5 7 6 t o 8 1 6 mg L - 1 a n d t he C V v a lu e w as 11 % in t h e x -d i r ec t i on and 9% in t h e y - d i r e c t i on . M g v a r i e d b e t w e e n 1 0 7 a n d 1 2 4 mg L - 1 a nd th e CV v a lu e w as 13% in t h e x -d i r ec t i on and 1 1 % in t h e y – d i r e c t i o n , w h i c h a r e b o t h s t a b l e c o e f f i c ie n t s o f v a r i a t i o n . T h e n o n - s i g n i f i c an t d i f f e r e n ce s i n t h e x - and y - d i r ec t i on in d i c a t ed t he p re sen ce o f s i mi l a r so i l f o r m, c r op r e s idu e , so i l mo i s tu r e and f i e l d t o p o g r a p h y i n b o t h d i r e c t i o n s a t t h e s t u d y s i t e . D e r c o n e t a l . ( 2 0 0 3 ) i n d i c a t e d i n Ta b l e 2 . 1 t h a t C a a n d M g i s 9 7 % co r r e l a t ed , w h i ch sh o w s th a t t h e d eg r e e o f v a r i a t i o n fo r b o th t h e s e p a ra me t e r s t e n d t o b e i d en t i ca l . I n t h e s a me e x p e r i me n t c o mp a r i so n s w h e r e ma d e b e t w een p red i c t ed and measu r ed da t a a n d i t w a s f o u n d t h a t t he d i f f e r ences be tw e e n t h e t w o w a s l e s s t han 10% fo r Ca & Mg , wh ich i s a c l ea r i n d i ca t i o n t h a t i f c e r t a in p a r a me t e r s su ch a s l i t t e r d e c o mpo s i t i on and v eg e t a t i o n t y p e s a r e k n o w n t h a t a g o o d p r e d i c t io n o f t h e v a r i a t i o n i n C a & M g may b e ma d e . Po ta s s ium : Gup t a e t a l . ( 1997 ) f ound i n t h e i r e x p er i me n t t h a t p o t a s s iu m c o n c en t r a t i on v a lu e s exh ib i t ed a g r e a t e r d eg r e e o f v a r i a t i on c o mp a red to Ca and Mg p a ra me t e r s (Ta b l e 2 .1 ) . The CV v a lu e fo r K w a s 19 % in t h e x - d i r e c t i on and 1 5 % i n t he y - d i r e c t i o n i n r e l a t i o n t o t h e C a and Mg concen t r a t i on v a lu e s t ha t v a r i e d b e t w e e n 9 % a n d 1 3 % re spec t i v e ly . I n t he s ame 35 e x p e r i me n t s mo d e l s i n d i c a t ed t ha t t he d i f f e r en c e i n me a s u r ed an d p red i c t ed v a lu es a r e b e t w een 16% a n d 2 6 % w h i c h i s a l o t h i g h e r t han t h e d i f f e r en ces fo r C a a n d Mg . T h i s i s a n i n d i c a t i o n t h a t K h a s a t en d en cy to h av e a h ig h e r d eg re e o f v a r i a t i on . Mi ao e t a l . ( 2006 ) condu c t ed a s t udy on t h e ma gn i tud e o f v a r i ab i l i t y i n so i l p r o p e r t i e s a n d f o u n d t h a t K had a l a rge va r i a t i on w i t h i n t h e f i e l d , r a n g i n g f r o m 6 5 t o 2 8 2 mg k g - 1 a t s i t e 1 an d f ro m 6 7 t o 1 9 2 mg kg - 1 a t s i t e 2 ( T a b l e 2 . 3 ) . Ta b l e 2 .3 D e s c r ip t i v e s t a t i s t i c s and se mi - v a r iog ra m p a r a me t e r s o f s e l e c t ed so i l p r o p e r t i e s ( Mi a o e t a l . , 2006 ) Soil Variables Field Mean Min Max CV (%) OM (g kg-1) 1 39 10 76 36.5 2 28 15 42 24.8 CEC (cmol kg-1) 1 16.5 9.1 25.1 23.6 2 11.1 6.9 17.2 26.9 pH 1 6.3 5.3 7.6 6.3 2 6.3 4.7 7.6 9.5 pH (mg kg-1) 1 35.5 14 81 45.3 2 31.4 16 107 56.8 K (mg kg-1) 1 147 65 282 26.6 2 124 67 192 28.1 S (mg kg-1) 1 9.2 7 12 10.7 2 9.3 7 19 25.1 Zn (mg kg-1) 1 1.9 1.4 2.5 13.6 2 4.2 2.6 12 48 S t u t t e r e t a l . ( 2 0 0 2 ) c o mpa r e d t w o p r o f i l e s n a me l y t h e Ty p i c P l a c a q u o d a n d t h e Ty p i c H u ma q u e p t ( T a b l e 2 . 4 ) . I n b o t h s o i l h o r i zon s ( o rg an ic a n d mi n e r a l ) o f t h e Hu ma q u ep t t h e o rd e r o f abundance fo r t he ba se f o r mi n g c a t i o n s w a s M g > C a > K > N a . A l t h o u g h t h e s a m e o r d e r o f ab u n d a n c e w a s o b s e r v e d f o r t h e P l a c a q u o d o r g a n i c h o r i zo n , t h e s e q u e n c e o f t h e mi n e r a l s u b s o i l d i f f e r ed a s f o l l ows : K > Mg > N a > Ca , r e spec t i v e ly . P r ev iou s a n a l y s i s o f b u l k s o i l mi n e r a l o g y f o r t h e P a c a q u o d p l o t s h o w e d a d o mi n an ce o f q u a r t z (51 %) , w i th 26 % K- fe ld sp a r , 15% Na-Ca f e l d sp a r a lb i t e , and 3 .8 % o f d io c t ah ed ra l p h y l lo s i l i c a t e s , t ha t 36 p ro b ab ly co mp r i se s k ao l i n i t e , mi c a an d i l l i t e . Su ch mi n e r a l c o mpo s i t i o n s a r e mo s t l i k e l y t o con t r i bu t e K and Na t h rough w ea the r ing , a ccoun t ing fo r t h e i n c rea sed p rev a l en ce o f K w i t h d e p t h i n t h e P l a c a q u o d . T h r o u g h t h i s s t u d y i t ma y b e a c l e a r i n d i c a t i o n t h a t t h e d i s t r i b u t ion o f c a t i o n s d o wn the p ro f i l e an d s p a t i a l l y , may b e a r e su l t o f t he ex chang e ma te r i a l . p H : So i l p H ( H 2 O & K C l ) h a s b e en r ecogn ized b y ma n y e x p e r i me n t s t o h av e a l o w spa t i a l v a r i a t i o n . M i ao e t a l . ( 2 0 0 6 ) fo u n d t h a t t h e C V fo r p H v a r i ed b e t w een 6 .3 % an d 9 .5 % , wh ich i s s i g n i f i c an t l y l o w e r t h a n t h e r e s t o f t h e p a r a me t e r s f o u n d i n T a b l e 2 . 3 . Z e h e t n e r & M i l l e r ( 2 0 0 6 ) f o u n d t h a t so i l a c id i t y dec r ea sed w i t h i n c r e a s e i n e l ev a t io n ( F igu r e 2 .1 ) . T h i s i s l i k e l y cau s ed b y h i g h e r a c i d i t y i n p u t s d u e t o h i g h e r r a i n f a l l , b y g r e a t e r l ea ch in g o f b as i c c a t i o n s , and b y g r e a t e r a c t i v i t y o f a c i d i c h u mi c s u b s t an c e s a s a r e su l t o f s l o w ed o rg an ic ma t t e r d ec o mpo s i t i on a t h ig h e r e l ev a t ion s . Cox e t a l . ( 2003 ) s t a t ed t ha t p H w a s t h e o n e s o i l p r o p e r t y t h a t d i d n o t h av e a h ig h s p a t i a l v a r i a t i on t h a t ch ang ed y ea r ly . I n b o th t h e i r y ea r s o f s t u d y ( 1 9 9 8 & 1 9 9 9 ) , p H h a d t h e l owes t va r i ab i l i t y o f 1 1 % a n d 1 2 % , r e s p e c t iv e l y . F r o m t h e f i g u r e s i t i s t h u s c l ea r t h a t p H i s a s o i l p ro p e r ty t h a t h a s t h e t en d en cy t o h a v e a l o w sp a t i a l va r i a t i on ov e r y e a r s i f t h e c u l t i v a t i o n p r a c t i c e s s t ay unchanged . 37 Ta b l e 2 .4 Co mp ar i so n o f t h e two r ep re sen t a t i v e so i l p ro f i l e s ( S t u t t e r e t a l . , 2002 ) Typic Placaquod Parent Material Coarse granitic drift Slope 3-5 degrees uniform Altitude (m) 405 Aspect E Surface form Hummocky Dominant vegetation Calluna vulgaris Horizon Depth(cm) Description Oi 0>1 Thin litter Calluna fragments Oa 1>12 Abundant roots, some quartz fragments present at base AE 12>19 5YR5/1, Loam Bh(s)1 19>60 5YR3/3, sandy clay loam, stoney layer (25cm), increased OM and root mat over thin placic horizon (approximately 58-60cm) Bs2 60+ 5YR5/8, weakly indurated, horizon Typic Humaquept Parent Material Coarse granitic drift Slope 3-5 degrees concave Altitude (m) 385 Aspect WNW Surface form Level Dominant vegetation Calluna vulgaris Horizon Depth(cm) Description Oi/Oe 0>2 Some litter, mainly partly decomposed, spong material Oa 2>20 Fewer Roots, dense, seeping at base Ah 20>25 7.5YR3/3, sandy loam, abundant stones, wet, high humic content Bw1 25>40 7.5YR4/3, sandy clay loam grading to 7.5YR5/4 silty clay loam, wet, some OM at base Bw(s)2 40+ 7.5YR5/6, gritty clay loam, some iron staining 38 Fi g u r e 2 .1 Top so i l p H ( H 2 O ) a s a f u n c t i o n o f e l e v a t i o n ( Z e h e t n e r & Mi l l e r , 2006 ) . N i t ro g en : Ni t rogen f e r t i l i z a t i on ha s h i s t o r i c a l l y been an i mp o r t a n t c r o p i n p u t f r o m p r o d u c t i o n , e c o n o mi c , a n d e n v i r o n me n t a l s t a n d p o i n t s . C u r r e n t l y i t r e c e i v e s mo r e s c r u t i n y b e c a u s e o f t h e i n c r e a se d co s t o f N f e r t i l i z e r a n d co n c e rn s ab o u t e n v i ron me n t a l d eg r ad a t ion , a n d d e ma n d s fo r ma n d a to ry n u t r i en t p l ann ing (D innes e t a l . , 2 0 0 2 ) . To i mp l e me n t v a r i a b l e - r a t e f e r t i l i z a t i o n o r s i t e - spec i f i c n u t r i e n t ma n a g eme n t p r ac t i c e s , d a t ab a se s t h a t p ro v i d e sp a t i a l d i s t r i b u t i o n s o f s o i l p r o p e r t i e s a r e n e eded . G eo s t a t i s t i c a l t e chn iques h av e b e en u s ed to exp lo r e t he s t ru c tu r e o f sp a t i a l v a r i a t i o n i n ag r i c u l t u r a l s o i l b y ma p p i n g a r e a s o f env i ron me n t a l c o n ce rn a n d d ev e l o p in g s i t e - sp ec i f i c f e r t i l i z e r a p p l i c a t i o n ma p s ( C a mb ar d e l l a & K a r l e n , 1 9 9 9 ) . Sh ah and eh e t a l . ( 2005 ) u sed t h e c o e f f i c i e n t o f v a r i a t i o n t o d e sc r ib e t h e v a r i ab i l i t y o f n i t ro g en . Th e p a r a me t e r s me a s u r ed v a r i ed spa t i a l l y and t e mpo ra r i l y . Amo n g the N p a ra me t e r s , N m i n v a lu es t end ed t o be t h e mo s t v a r i ab l e , w i th C V va l u e s o f 2 7 % a n d 4 6 % i n 2 0 0 2 a n d 2 0 0 3 , r e s p e c t i v e l y ( T a b l e 2 . 5 & 2 . 6 ) . T h e r a n g e i n N m i n f o r t h e 6 3 s a mp l e s c o l l e c t e d a c r o s s t h e f i e l d i n 2 0 0 2 w a s f r o m 6 to 3 5 mg k g - 1 , w i t h a me a n v a l u e o f 2 0 mg k g - 1 a n d f r o m 1 t o 3 3 mg k g - 1 , w i t h a me a n v a l u e o f 1 6 mg k g - 1 i n 2 0 0 3 . T h e N m i n 39 v a r i ab i l i t y o b s e rve d in t h e e x p e r im e n t w a s s i mi l a r t o C V v a l u e s o f 2 4 % and 3 6 .4 %. Th e r e su l t s i n Ta b l e 2 .5 a n d 2 .6 sh o w ed tha t s o i l N m e a su r e me n t s t en d e d t o b e c o me mo r e n o r ma l l y d i s t r i b u t e d i n y e a r s fo l l o wing N app l i c a t i on . To t a l N and N m i n i n 2 0 0 3 r e ma i n ed t h e sa me , w i th mo d er a t e and s t ro n g s p a t i a l d ep en d enc e , r e s p e c t i v e l y . N i t r a t e N b e c a me w e a k o r r a n d o m i n 2 0 0 3 , i n d i c a t i n g sp a t i a l i n d ep enden ce . O the r p a r ame te r s , su ch a s i n i t i a l s o i l N H 4 - N and N O 3 - N con c en t r a t i ons and so i l C mi n e r a l i zed , w e r e w e a k l y o r n o t spa t i a l l y co r r e l a t ed i n e i t he r 2002 o r 2 0 0 3 ( S h a h a n d e h e t a l . , 2 0 0 5 ) . T a b l e 2 . 5 D e s c r i p t i v e s t a t i s t i c s o f p a r a me t e r s me a s u r e d i n 2 0 0 2 ( S h a h a n d e h e t a l . , 2005 ) Parameter Mean Max Min CV Grain Yield (kg ha-1) 6430 8685 4528 14 Total N (mg kg-1) 966 1230 727 12 Organic N (mg kg-1) 963 1221 725 12 NH4-N (initial) (mg kg-1) 4 9 2 31 NO3-N (initial) (mg kg-1) 12 21 8 24 Inorganic N (initial) (mg kg-1) 16 26 11 22 NH4-N @ 24d (mg kg-1) 5 8 2 25 NO3-N @ 24d (mg kg-1) 31 44 17 19 Inorganic N @ 24d (mg kg-1) 36 52 19 18 N mineralised @ 24d (mg kg-1) 20 35 6 27 NO3-N 15 cm (mg kg-1) 29 50 18 22 NO3-N 30 cm(mg kg-1) 53 88 36 19 NO3-N 60 cm (mg kg-1) 93 148 62 18 NO -N 90 cm (mg kg-13 ) 120 193 84 18 CO -12-C @ 24d (mg kg ) 246 431 78 22 SOC (mg C.g-1 ) 9 13 2 18 Clay (%) 54 64 42 10 40 T a b l e 2 . 6 D e s c r i p t i v e s t a t i s t i c s o f p a r a me t e r s me a s u r e d i n 2 0 0 3 ( S h a h a n d e h e t a l . , 2005 ) Parameter Mean Max Min CV Grain Yield (kg.ha-1) 4298 5141 2554 13 Total N (mg.kg-1) 767 1085 552 16 Organic N (mg.kg-1) 760 1082 544 16 NH4-N (initial) (mg kg-1) 8 26 3 51 NO3-N (initial) (mg.kg-1) 4 7 2 18 Inorganic N (initial) (mg.kg-1) 12 31 7 34 NH4-N @ 24d (mg.kg-1) 7 10 4 18 NO3-N @ 24d (mg.kg-1) 21 35 7 32 Inorganic N @ 24d (mg.kg-1) 28 42 13 25 N mineralised @ 24d (mg.kg-1) 16 33 1 46 NO3-N 15 cm (mg.kg-1) 16 21 12 13 NO3-N 30 cm(mg.kg-1) 31 40 22 12 NO -N 60 cm (mg.kg-13 ) 58 71 41 11 NO -13-N 90 cm (mg.kg ) 84 105 62 11 CO2-C @ 24d (mg.kg-1) 271 370 202 16 SOC (mg.C g-1 ) 10 26 7 38 N i t r a t e N a n d c l a y c o n t e n t w e r e s ig n i f i c an t l y r e l a t ed t o y i e ld an d s e e me d t o b e r e sp o n s ib l e fo r v a r i a t i on i n h i g h - an d lo w-y i e ld p l o t s , r e s p e c t i v e l y . R e s i d u a l N O 3 - N w a s po s i t i v e ly r e l a t ed w i th y i e l d i n b o t h h i g h - and l ow-y i e ld env i ron me n t s , w h i l e c l ay c o n t en t exh ib i t ed a n eg a t iv e r e l a t i o n s h ip w i th g r a in y i e ld i n l ow - y i e l d i n g p l o t s . To t a l N i n l o w -y i e l d i n g p l o t s w a s p o s i t i v e l y r e l a t ed t o N O 3 - N and N m i n , w h i l e c l ay con ten t and N m i n w e r e n eg a t iv e ly r e l a t ed ( F igu r e s 2 .2 and 2 . 3 ) . 41 ( a ) 1 5 c m ( b ) 3 0 c m ( c ) 6 0 c m ( d ) 9 0 c m F i g u r e 2 . 2 K r i g e d c o n t o u r map s o f ( a -d ) so i l N O 3 - N w i t h d ep th i n 2 0 0 2 ( Sh a h a n d e h e t a l . , 2 0 0 5 ) . 42 (a) (b) ( c ) F i g u r e 2 . 3 K r i g e d c o n t o u r ma p s o f ( a - b ) t o t a l N i n 2 0 0 2 a n d 2 0 0 3 , a n d ( c ) mi n e r a l i z e d N in 2003 (S h a h a n d e h e t a l . , 2 0 0 5 ) . 43 2 .2 .1 .2 Sp a t i a l v a r i a t i on o f s o i l p ro p e r t i e s . K r ig ing i s u s ed t o g en e ra t e sp a t i a l p r e sen t a t i on s o f t he v a r i a t i on i n so i l p ro p e r t i e s . T h e sp a t i a l s t ru c tu r e o f t h e so i l p rop e r t i e s i s d e s c r i b e d b y a s e m i – v ar i o g ra m. I t i s e s t i ma t e d a s t h e a v e r a g e o f t h e s q u a r e d d i f f e r e n c e s b e t w e e n a l l o b s e rv a t ion s s ep a ra t ed b y a l a g d i s t a n c e . F r o m t h e v a r i o g r a m g e n e r a t ed fo r t he s o i l p r o p e r t i e s , K r ig ing ma y b e u s ed to g en e r a t e a s u r f a c e t h a t i l l u s t r a t e s t h e d i s t r i b u t ion o f v a r io u s so i l p ro p e r t i e s (D e C l e rq e t a l . , 2 0 0 1 ) . S u r f a c e r e p r e se n t a t i o n o f s o i l p r o p e r t y v a r i a t i o n h a s b e en mo d e l l e d t h r o u g h K r i g i n g f o r a n 1 8 h a l u c e r n e s t a n d i n t h e B r i t s d i s t r i c t i n t h e No r th Wes t P rov ince o f Sou t h A f r i ca ( V en t e r , 2 0 0 3 ) . Th r o u g h t h i s p r e s e n t a t i o n , t o ge the r w i th kno w l e d g e o f t h e i n t e r r e l a t i o n sh i p b e t w een s o i l p ro p e r t i e s a b e t t e r r e su l t ma y b e g en e r a t ed Phy s i ca l P rop e r t i e s S a n d c o n t e n t : Th e sand con t en t i nc r ea se s f r o m t h e w e s t e rn co rn e r a c r o s s t h e l a n d t o t h e e a s t e r n c o r n e r ( F i g u r e 2 . 4 ) . S a n d c o n t e n t i s a n i n h e r e n t s o i l p ro p e r t y a n d c a n n o t b e ma n ipu l a t ed by ma n a g e me n t p r a c t i c e s . Th e s a n d con ten t h a s i n v e r s e c o r r e l a t i on t o w a r d s s o i l p H a s a s andy so i l l oose s i t s b a s e fo r mi n g c a t i o n s t h r o u g h l e a c h i n g , r e s u l t i n g i n a d e c r e a s e i n p H . F r o m t h e s u r f a c e r ep r e sen t a t i on o f t h e s and con ten t i t i s c l ea r t h a t i n t he a r ea s fo r e x a mp l e t h e e a s t e r n c o rn e r wh e r e t he s and con ten t i s h igh a l ow p H w i l l r e s u l t ( F i g u re 2 .3 ) . T h e w at e r r e t en t i o n o f t h e s o i l a l so h a s a n i n v e r s e c o r r e l a t i on t o t he s and con ten t . An in c rea se i n s a n d c o n t e n t c a u s e s t h e s o i l t o b e mo r e f r e e ly d ra in ed r e s u l t i ng i n a d ec r eas e i n w a t e r r e t en t ion . Th e b a se fo r mi n g ca t i on s a l so d e c r e a s e s a s t h e sa n d c o n t e n t o f t h e so i l i n c r e a se s . T h i s d u e t o t h e f a c t t h a t a s a n d y s o i l l o o s e s i s b a s e f o r mi n g c a t i o n s t h r o u g h t h e p r o c e s s o f l e a ch i n g ( V e n t e r , 2 0 0 3 ) . 44 F i g u r e 2 .4 K r i g e d s u r f a c e r e p r e s e n t a t i o n o f t h e d i s t r i b u t i o n o f t h e s and con t en t i n t he t op so i l ( V e n t e r , 2 0 0 3 ) . C h e mi c a l P r o p e r t i e s p H : Th e pH ( H 2 O ) i s t h e l ow e s t i n t h e s o u t h - e a s t e r l y c o r n e r o f t h e l an d a n d in c rea s e s g r adu a l ly t o t h e n o r t h e r n p a r t ( F i g u r e 2 . 5 ) . F i g u r e 2 .5 K r i g e d s u r f a c e o f t h e d i s t r i b u t i o n o f p H ( H 2 O ) i n t h e t o p s o i l ( V e n t e r , 2 0 0 3 ) . O r g a n i c c a r b o n con ten t : Th e d i s t r i bu t i on o f O C in t h e so i l i s s p a t i a l l y r e l a t i v e l y u n i f o r m ( F i g u r e 2 . 6 ) . Th o u g h t h e r e s e e ms t o b e an a r ea i n t h e no r th ea s t e r ly co rn e r o f t he l an d tha t g r adu a l ly d e c r e a s e s t o t h e e a s t e rn co rne r . Th i s co r r e l a t e s w i th t h e s ame t r a n s e c t i n t h e p H s u r f a c e r e p r e s e n t a t i o n . Th e r e a so n ma y b e d u e 45 t o t h e i n c r e a se i n o rgan i c c a rbon , r e su l t i ng i n h ighe r mi n e r a l i z a t i o n a n d a d e c r e a s e i n p H . F i g u r e 2 .6 K r i g e d s u r f a c e r e p r e s e n t a t i o n o f t h e d i s t r i b u t i o n o f t h e O C ( % ) i n t h e t o p s o i l ( V e n t e r , 2 0 0 3 ) . 2 .2 .1 .3 Y i e ld v a r i a t i on i n r e l a t i on t o s o i l p ro p e r t i e s M ea su r ed Y i e ld : Th e ma p g en e ra t e d fo r t h e me a s u red y i e l d i n d i c a t e d t h a t v a l u e s w er e g en e r a l l y l a rge r i n t h e so u th - e a s t e rn c o r n e r o f t h e l a n d ( F i g u r e 2 . 7 ) . Th e r e i s a c l e a r r e s e mb l a n c e b e t w een me a s u r ed y i e ld and b e s t co r r e l a t ed so i l p rope r t i e s , so i l p H and O C . Th i s ma k e s i t c l e a r t h a t y i e ld may b e f a i r l y a c cu r a t e ly p r ed i c t e d f ro m s o i l p r o p e r t i e s s u c h a s p H ( H 2 O ) , O C ( % ) an d sa n d co n t en t ( % ) o f t h e so i l . 46 F i g u r e 2 .7 K r i g e d s u r f a c e o f t h e me a s u r e d y i e l d ( V e n t e r , 2 0 0 3 ) . 2 . 3 M e t h o d o l o g y 2 .3 .1 So i l Su rv ey A h y d rau l i c so i l aug e r w a s u s ed t o d r a w so i l c o r e s o n a 5 0 m g r i d (F igu r e 2 .8 ) a s i t i s mo re econo mi c a l t h an d ig g ing 7 5 p r o f i l e p i t s o v e r t h e 5 5 h a . U s i n g t h e c o r e s a mp l e r i s a l so mo r e e f f e c t i v e t h a n u s ing the co mmo n ly u sed Tho ms o n o r Ed e l ma n h an d au g e r s a s t h e c o r e s a mp le r p re se rv e s fo r e x a mp le s t ru cu r e , p ed s and o th e r mo r p h o l o g i c a l f e a t u r e s . Th i s i s e s s e n t i a l i n t h e c l a s s i f i c a t i o n a n d d e sc r ip t i on o f t h e s o i l f o rms . A p ro f i l e p i t w a s ma d e o n e a ch o f t h e t h i r t e e n p l o t s t h a t w e r e se l ec t ed i n Ch ap t e r 3 . A l l t h e o b s e r v a t i o n s ( c o r e s a n d p i t s ) w e r e c l a s s i f i ed acco rd ing t o t h e So i l C l a s s i f i c a t i o n W o r k i n g G r o u p , 1 9 9 1 , bu t on ly t he t h i r t e e n p r o f i l e p i t s we r e mo rp h o log ic a l ly d e sc r ibed i n de t a i l (App en d i x Q , R and S ) . T h e c o r e s a mp l e s w e r e d e s c r ib e d a c c o r d i n g t o s o i l f o r m, d ep th a n d f i e l d e s t i ma t e s o f t e x t u r e . 47 F i g u r e 2 .8 So i l co r e s d r awn u s ing t h e h y d r a u l i c c o r e s a mp l e r . 2 .2 .6 So i l a n a ly s i s Ea c h o f t h e 7 5 exp e r i me n ta l p lo t s w a s ch emi ca l l y & phy s i ca l l y an a ly z ed fo r Ca , M g , N a , K , p H ( H 2 0 ) , p H ( K C l ) & p a r t i c l e s i z e d i s t r i b u t i o n ( s even c l a s s ) a c co rd i n g t o t h e N o n -A f f i l i a t ed So i l A n a l y s i s W o r k C o m m i t t e e , 1 9 9 0 . 48 2 .2 .7 S t a t i s t i c a l and sp a t i a l a n a ly s i s M a p s w e r e d r a w n o f t h e d i f f e r e n t p h y s i c a l a n d c h e mi c a l p a r a me t e r s u s i n g W I S H ( L u k a s , 1 9 9 2 ) . A t h o r o u g h l i t e r a t u r e s t u d y w a s c o n d u c t e d o n v a r i o u s i n t e r p o la t i on t e chn iques ( A p p e n d i x U ) . I n v e r s e d i s t a n c e w e igh t ing ( IDW) w a s s e l ec t ed a s t he mo s t su i t ab l e i n t e rpo l a t i on t e c hn iqu e fo r t h e sp ec i f i c ana ly s i s . I t w a s u sed t o p r ed i c t p a r ame te r v a l u e s i n a r e a s w h e r e d a t a w a s d e l e t ed t o ca l cu l a t e t h e d eg re e o f ac c u r a t e p r ed i c t i o n i n a c e r t a i n a r e a wh ic h cou ld t h en b e a n i nd i ca to r o f t h e a mo u n t o f s p a t i a l v a r i a t i o n i n a c e r t a i n a r e a . T h e c o e f f i c i e n t o f v a r i a t i o n a n d t h e 2 5 % a n d 7 5 % q u a r t i l e w a s c a l c u l a t e d u s i n g N C S S , 2 0 0 0 ( H i n t z e , 2 0 0 0 ) a n d w a s u s e d a s a n i n d i c a t i o n o f t h e s p a t i a l v a r i a t i o n w i th in and b e t w een ma p u n i t s . 49 2 .3 R e s u l t s a n d D i s c u s s i o n 2 .3 .1 Fa c t o r s o f So i l Fo r ma t io n Th e so i l f o r ms ( Tu k u lu , Sep an e an d B lo e md a l ) o c cu r r i n g a t t he e x p e r i me n ta l s i t e d i f f e r s f ro m t h e Ca 2 2 Lan d ty p e d a t a s e en in App end ix T . A l l t h r ee so i l f o rms d o n o t ma k e p a r t o f t he l and t y p e d a t a . T u k u l u a n d Sepane so i l s we re on ly i nc luded i n t he u p d a t e d v e r s i o n o f t h e So u t h A f r i c an so i l c l a s s i f i c a t i o n s y s t e m . T h e fo l l o w i n g s o i l f o r mi n g f a c t o r s may t hough have an i n f l uence o n t h e o c c u r r e n c e o f t h e se t h r e e so i l f o r ms a t t h e e x p e r i me n t a l s i t e . 2 .3 .1 .1 C l i ma t e Ra in fa l l : Th e F ree S t a t e i s a summer r a in f a l l a r ea w i th t h e h ighes t and mo s t r e l i ab l e r a in f a l l occu r r ing i n Feb rua ry and M a r c h . D u r i n g N o v e mb e r , D e c e mb er and J anua ry t h e r a i n f a l l i s e r r a t i c w i t h mu c h o f i t i n t h e fo rm o f h igh i n t en s i t y r a in f a l l e v e n t s . Th e h i g h e v a p o r a t i o n d e mand and r e l a t i v e ly l ow r a in f a l l mak e t h i s a s emi - a r i d c l ima te . T h e l o n g t e r m mean r a in f a l l i s 542 .7 mm p e r annu m (Tab l e 2 .7 ) . Th e r a in f a l l t og e th e r w i th t he t o p o g r a p h y ma y c a u s e t h e mo v e me n t o f c l a y d o w n wards i n t he l and scape . Th i s may r e su l t i n t he occu r r en ce o f p edocu t an i c B h o r i zon s d o wn s lo p e and the o c cu r r en c e o f r ed ap ed a l B h o r i zo n h i g h e r u p i n t h e l a n d s c a p e . Te mp e ra tu r e : Low t e mp e r a t u r e s b e l o w f r eez ing po in t coup l ed w i t h v e ry l i t t l e r a i n fa l l a r e e x p er i e n c e d d u r i n g t h e w in t e r (Tab l e 2 . 7 ) . W h i l e h i g h t emp e r a t u r e s a r o u n d 3 0 ˚C coup led w i th l e s s t h an f r equ en t r a in f a l l ev en t s o c cu r d u r i n g s u m me r . D u r ing t h e su mmer mo n t h s t h e e v a p o r a t i v e d e ma n d i s v e r y h i g h d r o p p i n g d u r i n g a u t u mn . 50 A r i d i t y i n d e x : The h i g h t e mp e r a t u r e , l o w h u mi d i t y a n d l o w t o mo d e r a t e s t r o n g w i n d s d r i v e s a v e r y h ig h e v a p o t r a n s p i r a t i o n d e ma n d o f b e t w ee n 2 5 0 mm an d 3 0 0 mm p e r mo n th d u r in g t h e s u m me r mo n t h s , d r o p p i n g t o a r o u n d 1 0 0 m m p e r mo n t h d u r i n g w in t e r mon th s ( Tab le 2 .7 ) . Th e a r id i t y i ndex p e aks a t 0 . 4 5 d u r i n g M a r ch r e s u l t i n g i n ex c e s s o f w a t e r i n t h e so i l p ro f i l e d r a in ing t o t h e sub so i l . Th i s w a t e r c au s e s s ign s o f w e tnes s i n t h e und e r ly ing ma t e r i a l w h e r e i mp e r me a b l e ma t e r i a l s o c cu r . Th e d i s t r i b u t ion o f s o i l s o n t h i s a r ea b y i mp l i c a t i o n i s i n f l u en ced by an und e r ly ing i mp e r me a b le l ay e r . Th i s c a u s e s t h e h y d r o l o g y o f t he se so i l s t o be i n f lu en c ed b y a t r a n s i en t w a t e r t ab l e du e t o ex ces s w a te r i n t h e p ro f i l e and in t e r f l o w f rom h ig h e r l y ing so i l bod i e s . I n t h i s c l i ma t e t h e r e i s n o sho r t a g e o f r ad i a t i on o r t e mp e r a tu re i n t he s u mme r mo n th s . L e a c h i n g d u r i n g M a r c h c a n p l a y a r o l e t o r e mo v e f r e e s a l t s a n d mo v e c l a y i n t h e p ro f i l e . A l t h o u g h c a t i o n d i s t r i b u t i o n s i n t h e p r o f i l e s i n d i c a t e so me l e a c h i n g o f f r e e s a l t s , t h e i n c r ea se i n c l ay w i th d ep th i s r a the r d u e t o mi x in g p ro c e s s es l i k e b io t u rb a t io n , p e d o t u r b a t i o n a s w e l l a s f r o m w indb lown and co l lu v i a l d e p o s i t s ( L e R o u x , 1 9 9 6 ) . 51 T a b l e 2 . 7 T h e c l i ma t e o f t h e a r ea (WRC repo r t no . 1176 /1 /03 , 2003 ) . Long Parameter Jul Aug Sept Oct Nov Dec Jan Feb Mar Apr May Jun term total Rain (mm) 8.1 11.6 19.3 49 68.2 66.6 83.4 77.6 80.7 49.3 19.9 9 542.7 Evap (mm) 93.5 140 197 239 256 291 276 207 177 126 110 81.9 2198.2 Max Temp. 17.8 20.6 24.4 25.4 28.3 30.2 30.8 29.5 27.4 23.9 20.5 17.9 24.8 Min Temp. -1.6 0.9 5.2 9.2 12 14 15.3 14.8 12.6 7.8 2.8 -1.1 7.5 Ave Temp. 8.1 10.7 14.8 17.5 20.1 22 23 22.1 19.9 15.8 11.6 8.2 16.2 AI 0.08 0.08 0.09 0.2 0.26 0.22 0.3 0.37 0.45 0.39 0.18 0.11 0.232 52 2 .3 .1 .2 Pa r en t Ma te r i a l Th r ee ma i n t y p e s o f p a r en t ma t e r i a l s o c cu r i n t h i s a r e a , n a me ly D o l e r i t e , B e au fo r t S a n d s t o n e a n d Sha l e . Do le r i t e : T h e s e a r e e x a mp l e s o f b a s i c i g n e o u s r o c k s . I t h a s n o f r e e q u a r t z a n d w e a t h e r s t o s i l i c a t e c l ay s . I t con t a in s h igh a mo u n t s o f s w e l l i n g c l ay s a n d g ive s r i s e t o c l ay con ten t s o f b e t w een 30 % and 40 % . B e a u f o r t S a n d s t o n e : T h e s e p a r e n t ma t e r i a l s a r e e x a mp l e s o f 2 : 1 c l ay mi n e r a l s h ig h i n c l ay con ten t (40 % - 4 5 %) . Th ey we a th e r an d g i v e r i s e t o P e d o c u t an i c B h o r i zon s wh i ch i s h ig h ly a c t i v e i n t he s w e l l i n g a n d sh r in k i n g p r o c e s s . S h a l e : Th e in f lu en c e o f t h i s p a r en t ma t e r i a l t o so i l fo r m i s v e ry s im i l a r t o t h e s and s ton e bu t may r e su l t i n s l i gh t ly h igh e r c l ay c o n t en t s . Th e p a r en t ma t e r i a l s g iv e r i s e t o c l ay con t en t s o f 40 % . W in d b lo wn s an d s h av e a ma jo r i n f luen ce on so i l f o r m o c cu r r en ce . T h e i n f l u e n c e i s t h e h igh es t i n t he o c cu r r ence o f t h e B lo e md a l s o i l f o r m a n d d e c l i n e s t o t h e Tu k u l u a n d t h e Se p a n e s o i l f o r m. T h e i n f l u e n c e o f t h e se s i l i c a t e c l ay s sw e l l i n g a b i l i t y i s r ed u c ed b y t h e mi x u p o f w in d b l o w n s a n d s a s w e l l a s t h e c o l l u v i a l i n f l uence o f Muds tone and Scha l e . Th e i n c r ea se i n c l ay con t en t d o wn w ard s i n t h e p ro f i l e c a n b e exp la in ed b y a co mb ina t ion o f a d d i t i o n b y t h e d i f f e r e n t p a r e n t ma t e r i a l s a n d p e d o t u r b a t i o n . B e c a u se t h e w e a t h e r i n g o f c l a y f o r mi n g p a r e n t ma t e r i a l s g i v e s r i s e t o h i ghe r c l ay con ten t s i n t h e bo t to m o f t he p r o f i l e and w i n d b l o w n s a n d g i v e r i s e t o h igh e r s and con t en t s i n t op so i l s , i t r e su l t s i n an i nc r ea se i n c l a y d o w n w a r d s i n t h e p r o f i l e . Pedo tu rba t i on (b io tu rb a t i on and a rg i l l o -p ed o tu rb a t ion ) may b e r e spons ib l e f o r t h e mi x i n g . 53 2 . 3 . 1 . 3 Topog raphy Th e exp e r i men t a l s i t e i s s i t ua t ed on t h e l ow er 3 po s i t i on i n t he l an d s c ape ( F i g u r e 2 .9 ) and i s s l o p ed 0 .3 % in an e a s t e r ly d i r e c t i on . T h e s lo p e s h a p e i s l i n ea r c o n v e x ( F i g u r e 2 .1 0 ) . The d i s t r i b u t i o n o f s o i l f o r ms c a n n o t b e e x p l a i n e d b y t o p o g r a p h y u s i n g a v a i l a b l e t o p o g r a p h i c a l d a t a . A mo r e d e t a i l e d a n a l y s i s i s n e e d e d o f t h e mi c r o t o p o g r a p h y . T h e B lo e md a l w i t h a l a r g e r c o n t r i b u t i o n f r o m w i n d d e p o s i t s i s e x p ec t e d t o c o v e r t h e convex / convex pos i t i ons , w h i l e t h e S e p a n e c o v e r s t h e a r e a s w h e r e w a t e r w i l l a ccu mu la t e . A b s e n c e o f ma j o r t o p o g r aph i ca l l y f ea tu r e s i s e mp h a s i s e d b y t h e p re sen ce o f ma t e r i a l s w i th s i gn s o f w e tn es s i n t h e bo t t o m o f a l l t h e s e s o i l f o r ms . T h e t o p o g r a p h y a i d s i n i n t e r f l o w o f w a t e r f r o m h i g h e r l y i n g s o i l b o d i e s d o w n s l o p e . F i g u r e 2 .9 Th e low e r 3 p o s i t i o n o f t h e e x p e r imen t a l s i t e i n t he l and scape . 2 .3 .1 .4 B i o lo g y and t i me T i me a n d b io lo g i c a l f a c t o r s d o e s n o t d i s t i ngu i sh be tw een th e s o i l s i n t h e exp e r ime n t a l f i e ld . Th e se so i l s a r e v e r y o l d a n d t h e i n f l u e n c e o f t i me i s v i s i b l e i n t h e w e l l d e v e l o p ed h o r i z o n i z a t i o n . 54 N F i g u r e 2 .1 0 Con to u r ma p o f t he 55 ha expe r i men ta l s i t e . 55 2 .3 .2 Sp a t i a l v a r i a t i on o f s o i l s 2 .3 .2 .1 Sp a t i a l d i s t r i b u t ion o f so i l s A s o i l ma p wa s d r awn o f t h e 5 5 h a ( F i g u r e 2 . 1 1 ) . Th e Tu k u l u s o i l f o r m d o mi n a t e s t h e a r e a cov e r in g 75 % o f t he t o t a l a r e a ( 5 5 h a ) , f o l l o w ed b y th e Sep an e so i l f o r m 1 5 % a n d th e B lo e md a l s o i l f o rm 1 0 % o f t h e 5 5 h a e x p e r i me n t a l s i t e . T h e c i r c l e d a r e a s i n F i g u r e 2 .1 1 i n d i c a t e t h e e x p e r i me n t a l p lo t s t h a t w e r e mo r p h o l o g i c a l l y d e sc r ib ed i n d e t a i l f r o m a p r o f i l e . The s q u a r e s i n d i c a t e t h e mo d a l p ro f i l e fo r t h e Tuku lu (p ro f i l e n r 1 .1 , 1 .5 , 5 .1 , 7 .1 a n d 1 2 .2 ) S e p a n e ( p r o f i l e n r 1 2 . 1 , 1 3 . 1 , 1 4 . 2 , 1 5 . 1 a n d 1 5 . 2 ) a n d B l o e md a l ( p ro f i l e n r 8 .1 , 1 0 .5 , 1 1 . 1 a n d 1 1 . 3 ) w h i ch w er e mo r p h o l o g i c a l l y d e s c r i b e d i n d e t a i l ( F i g u r e 2 . 1 2 , 2 . 1 3 and 2 .1 4 ) . N Tuku lu (75%) B loemd a l ( 10%) Sepane (15%) F i g u r e 2 . 1 1 So i l m a p o f t h e e xp e r i me n t a l s i t e a t P a r a d y s . 56 2 .3 .2 2 De s c r ip t i on o f t h e mo d a l p ro f i l e s F r o m t h e s o i l su rv ey t h e t h r ee fo l l o w in g mod a l p ro f i l e s w er e i d e n t i f i e d a n d m o rp h o l o g i c a l l y d e s c r i b ed . T h o r o u g h p r o f i l e d e s c r i p t i o n s may b e fo u n d i n A p p e n d i x Q , R a n d S . Tu ku lu : The so i l i s o f t h e Tuku lu D iken i ( 1220 ) f a mi ly Th e t h i ckn es s o f t h e A , B and C ho r i zons ove r t h e 13 p ro f i l e s va r i ed w i th 10 mm in t he A h o r i z o n , 2 1 0 m m i n t he B h o r i z o n a n d 3 0 0 mm in t he C ho r i zon . The C V v a lues fo r ho r i zon t h i ckn es s w ere 0 % fo r t h e A h o r i z o n , 2 3 % f o r t h e B h o r i zon a n d 1 4 % fo r t h e C ho r i zon . The A ho r i zon i s a s andy c l ay l o am c o mp r i s i n g o f 1 8 % c l a y , w h i l e t h e B a n d C h o r i z o n i s a s a n d y c l a y o f 2 8 % a n d 4 8 % c l ay r e spec t i ve ly . Th e va r i a t i on i n c l ay con t en t w i th in t he s e l e c t ed r ang e v a r i ed b e tw een CV v a l u e s o f 1 % for t he A ho r i zon , 0 % f o r t h e B h o r i z o n a n d 3 % fo r t h e C ho r i zon . Th e p a ren t ma t e r i a l i s c h e mi c a l l y w e a t h e r e d c o l l u v i a l D o l e r i t e a n d M u d s t o n e o v e r t h e 5 s e l e c t e d T u k u l u p r o f i l e s . T h e s t r u c t u r e o f t h e A h o r i z o n i s ma s s i v e a ped a l , w i th t he B ho r i z o n h a v i n g a w e a k d ev e lop ed sub an g u la r b lo ck y s t ru c tu re o f me d iu m s i z e ( 1 0 mm – 2 5 mm) . Th e s t ru c t u r e o f t he C h o r i zon v a r i e s b e t w een a me d i u m a n d s t r o n g d e v e l o p e d p r i sma t i c s t ru c tu r e (5 mm – 15 mm) . An abundance o f r ed , ye l l o w , g r e y a n d b la c k mo t t l e s o c c u r i n t h e C ho r i zon . Th e t r an s i t i on be tw een t he ho r i zon s i n a l l c a se s i s c l e a r b e t w een t h e A h o r i zo n and B ho r i zon and ab rup t b e tw een th e B h o r i z o n a n d C h o r i z o n . L i me o c c u r r e d i n t h e B h o r i z o n o f o n l y t w o o f t h e Tu k u l u p r o f i l e s 57 ot A horizon: 175 mm ne B horizon: 385 mm uw C horizon: 485 mm+ F i g u r e 2 . 1 2 Tu k u l u s o i l f o r m . 58 S e p a n e : T h e s o i l i s o f t he Sepane Ka tdoo rn (1210 ) f ami ly . Th e t h i cknes s o f t he A , B and C ho r i zons ove r t he 5 s e l e c t e d p r o f i l e s v a r i ed f ro m 40 mm i n t h e A ho r i zon t o 200 mm i n t h e B h o r i z o n and 150 mm in t he C ho r i zon . Th e C V v a lu es fo r d ep t h b e ing 8 % f o r t h e A h o r i zon , 2 3 % fo r t h e B h o r i zo n a n d 4 6 % f o r t h e C h o r i z o n . T h e A h o r i z o n o f t h e mod a l p r o f i l e i s a s a n d y c l a y l o a m c o mp r i s i n g o f 1 9 % c l ay , wh i l e t h e B and C h o r i z o n i s a s a n d y c l ay o f 35 % and 45 % c l ay r e spec t i v e l y . Th e C V v a l u e s o v e r t h e 5 s e l e c t ed p ro f i l e s v a ry b e tw e en 6 % i n t h e A a n d B h o r i zon to 4 % i n t h e C h o r i zon . T h e p a re n t ma t e r i a l i s c h e mi c a l l y w e a t h e r e d Sh a l e o v e r t h e 5 s e l e c t ed Se p an e p ro f i l e s . Th e s t ru c tu r e o f t h e A ho r i zon i s mass i ve ap ed a l , w i th t h e B ho r i zon h av ing a me d iu m d ev e lop ed b lo ck y s t ru c tu r e o f me d iu m s i z e (10 mm – 2 5 mm) . T h e s t ru c tu r e o f t h e C h o r i zo n i s o f a w e l l d ev e lop ed me d i u m s i z e p r i s ma t i c s t r u c t u r e ( 1 0 m m – 2 5 m m ) . A n a b u n d a n c e o f r e d , y e l l o w , g rey an d b l a ck mo t t l e s o c cu r i n t h e C h o r i zon . T h e t r an s i t i on b e tw een t he A , B a n d C h o r i z o n s i n a l l c a se s i s a b r u p t . No l i me o c cu r r ed i n any o f t he ho r i zon s . 59 A horizon: ot 200 mm B horizon: up 480 mm uw C horizon: 640 mm F i g u r e 2 . 1 3 S e p a n e s o i l fo r m ( P r o f i l e 1 3 .1 ) . 60 Bloemda l : Th e s o i l i s o f t h e B l o e md a l R o o d e p l a a t ( 3200 ) f ami ly . T h e t h i c k n e ss o f t h e A , B a n d C h o r i z o n v a r i ed w i th 100 mm in t h e A h o r i z o n , 1 5 0 m m i n t h e B h o r i zon and 2 0 0 m m i n t h e C h o r i zon . Th e C V v a lu e s fo r d ep th o v e r t h e 4 se l ec t e d p ro f i l e s v a r i e d b e t w e e n 2 2 % i n t h e A h o r i z o n t o 2 7 % i n t h e B h o r i z o n a n d 6 7 % i n t h e C h o r i z o n . T h e A h o r i z o n i s a s a n d y c l a y l o a m c o mp r i s i n g o f 1 7 % c l ay , wh i l e t h e B and C h o r i z o n i s a s a n d y c l ay o f 29 % and 45 % c l ay r e spec t i v e l y . Th e C V v a l u e s o v e r t h e 4 s e l e c t ed p ro f i l e s v a ry b e tw ee n 0 % in t he A ho r i zon and B ho r i zon t o 8 % in t h e C h o r i zon . Th e p a r en t ma t e r i a l i s s l i gh t l y w e a the red c o l l u v i a l D o l e r i t e o v e r t h e s e l e c t ed p ro f i l e s . Th e s t ru c t u r e o f t h e A ho r i zon i s mass i ve ap eda l , w i th t h e B h o r i z o n h av ing a me d iu m d ev e lop ed b lo ck y s t ru c tu r e o f me d iu m s i z e (10 mm – 2 5 mm) . T h e s t ru c tu r e o f t h e C h o r i zo n i s o f a w e l l d ev e lop ed me d i u m s i z e p r i s ma t i c s t r u c t u r e ( 5 m m – 1 5 m m) . A n a b u n d a n c e o f r e d , y e l l o w , g rey and b l ack mo t t l e s o ccu r i n t he C ho r i zon . Th e t r an s i t i on b e t w een t h e A ho r i zon , B ho r i zon and C ho r i zon s i n a l l c a se s i s s mo o th . No l i me o c cu r r ed i n any o f t h e h o r i zon s 61 A horizon: ot 140 mm ne B horizon: 315 mm uw C horizon: 375 mm F i g u r e 2 . 1 4 B l o e md a l s o i l f o r m ( P r o f i l e 1 1 .1 ) . 62 2 .3 .3 Sp a t i a l v a r i a t i on o f p h y s i c a l and ch e mi c a l p ro p e r t i e s Sp a t i a l r ep re s en t a t i o n s o f p h y s i c a l and ch e mi c a l p ro p e r t i e s o f t h e 7 5 p lo t s a r e p r e s en t ed in App en d ix A - G . Tab le 2 .8 i nd i c a t e s t he co r r e l a t i on o f t h e s e l e c t ed ch emi c a l a n d p h y s i c a l p rop e r t i e s w i th o n e a n o t h e r . A l l t h e c h e m i c a l so i l p r o p e r t i e s e x c e p t K i n t h e A a n d B h o r i z o n h a v e a s t r o n g p o s i t i v e c o r r e l a t i o n w i t h t h e c l a y c o n t en t fo r t h e A , B and C h o r i zon s . Po t a s s iu m l i k e sod iu m i s a v e ry mob i l e e l eme n t . Po t a s s iu m i s a l so r ed i s t r i b u t ed b y b i o c i r c u l a t i o n . Th i s may e x p l a i n t h e un re l a t ed d i s t r i bu t ion p a t t e rn o f po t a s s ium. T a b l e 2 . 8 C o r r e l a t i o n ma t r i x o f t h e s o i l p ro p e r t i e s fo r t h e A , B a n d C h o r i z o n s ( n = 7 5 ) A horizon pHH2O pHKCl Ca K Mg Na Sand Silt Clay pHH2O 1 0.65 0.42 0.22 0.39 0.38 -0.29 0.17 0.61 pHKCl 0.65 1 0.48 0.27 0.43 0.39 -0.44 0.34 0.68 Ca 0.42 0.48 1 -0.13 0.56 0.61 -0.56 0.45 0.68 K 0.22 0.27 -0.13 1 0.09 -0.07 0.12 -0.30 0.18 Mg 0.39 0.43 0.56 0.09 1 0.53 -0.40 0.20 0.64 Na 0.38 0.39 0.61 -0.07 0.53 1 -0.59 0.26 0.80 Sand -0.29 -0.44 -0.56 0.12 -0.40 -0.59 1 -0.76 -0.58 Silt 0.17 0.34 0.45 -0.30 0.20 0.26 -0.76 1 0.25 Clay 0.61 0.68 0.68 0.18 0.64 0.80 -0.58 0.25 1 B horizon pHH2O pHKCl Ca K Mg Na Sand Silt Clay pHH2O 1 0.43 0.60 -0.24 0.60 0.42 -0.54 -0.00 0.76 pHKCl 0.43 1 0.46 0.33 0.59 0.68 -0.26 -0.20 0.55 Ca 0.60 0.46 1 -0.02 0.84 0.41 -0.61 -0.00 0.81 K -0.24 0.33 -0.02 1 0.05 0.41 0.20 -0.30 -0 Mg 0.60 0.59 0.84 0.05 1 0.61 -0.63 -0.10 0.85 Na 0.42 0.68 0.41 0.41 0.61 1 -0.20 -0.20 0.52 Sand -0.54 -0.26 -0.61 0.20 -0.63 -0.20 1 -0.50 -0.7 Silt -0.03 -0.24 -0.04 -0.28 -0.05 -0.24 -0.55 1 -0.1 Clay 0.76 0.55 0.81 -0.04 0.85 0.52 -0.70 -0.10 1 C horizon pHH2O pHKCl Ca K Mg Na Sand Silt Clay pHH2O 1.00 0.70 0.47 0.12 0.31 -0.09 -0.45 0.05 0.52 pHKCl 0.70 1.00 0.55 0.05 0.18 -0.26 -0.45 0.04 0.56 Ca 0.47 0.55 1.00 0.41 0.55 0.21 -0.74 0.21 0.77 K 0.12 0.05 0.41 1.00 0.80 0.52 -0.54 0.10 0.56 Mg 0.31 0.18 0.55 0.80 1.00 0.51 -0.58 0.00 0.69 Na -0.09 -0.26 0.21 0.52 0.51 1.00 -0.31 -0.04 0.37 Sand -0.45 -0.45 -0.74 -0.54 -0.58 -0.31 1.00 -0.49 -0.86 Silt 0.05 0.04 0.21 0.10 0.00 -0.04 -0.49 1.00 0.05 Clay 0.52 0.56 0.77 0.56 0.69 0.37 -0.86 0.05 1.00 T h e s t a t i s t i c a l c o e f f i c i e n t o f t he l i n e a r r eg re s s io n b e t w e en eac h o f t h e c h e mi c a l p r o p e r t i e s and c l ay con ten t (% ) o f t h e h o mo g e n e o u s a r e a a r e p r e s e n t e d i n T a b l e 2 . 9 . T h e c l ay con ten t 63 ( % ) h as a s t r o n g i n f l u en ce o n t h e che mi c a l p r o p e r t i e s , r eg a r d l e s s o f t he so i l f o r m a n d h o r i z o n . T a b l e 2 .9 S t a t i s t i ca l v a r i a t i on o f t h e s o i l p ro p e r t i e s A horizon Parameter a b R2 Mean CV pH (H20) 2.076x 5.2919 0.37 5.80 0.08 pH KCl 2.5439x 5.5323 0.46 4.64 0.09 Ca (cmol .kg-1c ) 0.1098x 13.06 0.46 38.93 0.24 K(cmolc.kg-1) 0.0674x 16.645 0.03 10.22 0.39 Mg(cmol -1c.kg ) 0.1348x 14.575 0.42 20.46 0.35 Na(cmolc.kg-1) 1.5626x 13.15 0.63 2.68 0.28 B horizon Parameter a b R2 Mean CV pH(H20) 3.298x 8.3393 0.58 5.97 0.11 pH KCl 3.273x 11.392 0.30 5.08 0.10 Ca(cmol .kg-1c ) 0.1834x 19.548 0.65 46.23 0.28 K(cmol -1c.kg ) -0.0203x 28.208 0.00 8.92 0.62 Mg(cmolc.kg-1) 0.2838x 21.3 0.72 23.71 0.37 Na(cmolc.kg-1) 2.0935x 22.864 0.27 2.47 0.30 C horizon Parameter a b R2 Mean CV pH(hH20) 3.3271x 23.949 0.27 6.66 0.08 pH KCl 2.9965x 30.456 0.31 5.23 0.13 Ca(cmol -1c.kg ) 0.1468x 36.971 0.59 62.31 0.30 K(cmolc.kg-1) 0.4472x 40.862 0.32 11.76 0.38 Mg(cmol .kg-1c ) 0.1407x 39.289 0.47 48.54 0.35 Na(cmolc.kg-1) 1.0867x 42.931 0.13 2.93 0.41 I nves t i g a t i ng t h e so i l map (F igu re 2 .11 ) , t og e th e r w i th t he c l ay d i s t r i b u t i o n ma p s ( F i g u re 2 . 1 5 ) , t h e c l a y c o n ten t o f t he B ho r i zon h a s a r e se mb l a n c e t o t h e so i l ma p o f t h e exp e r i me n ta l s i t e . Th e c l a y c o n t e n t i n c r e a s e s i n an ea s t e rn d i r ec t i o n o f t h e e x p e r i me n t a l s i t e . Th i s co r r e l a t e s w i th t h e so i l f o rms , a s t he Sepane ( p e d o c u t a n i c B h o r i z o n ) occu r i n t he l o w er l y ing a r ea s (Eas t e rn d i r e c t i o n ) . Th e Tu k u lu and B lo e md a l s o i l f o rm ( n eo cu t an i c B , an d r ed ap ed a l B ho r i zon s ) occu r h igh e r up t h e s l op e i n t he no r th e rn pa r t o f t he expe r imen t a l s i t e . 64 A horizon B horizon C horizon Clay % Clay % Clay % N F igu re 2 .15 D i s t r i bu t i on o f t he c l ay con t en t f o r t he A , B and C ho r i zon . 65 D u e t o c u l t i v a t i o n p r a c t i c e s ( p l o u g h i n g ) o v e r t h e l a s t 3 0 y e a r s o n t h i s ex p e r i me n t a l s i t e t h e d i s t r i b u t i on o f t h e c l ay con ten t i n t h e A h o r i zon ma y n o t h av e any r e s e mb l an c e w i th t he so i l f o rms . The C h o r i zon h a s a h ig h d eg r ee o f v a r i a t i on d u e to v a ry in g p a re n t ma t e r i a l s ( D o l e r i t e , M u d s t o n e a n d S c h a l e s ) , a n d d o e s n o t h a v e a n y r e s emb l a n ce w i t h sp e c i f i c so i l f o r ms o c cu r r i n g i n t h e e x p e r i me n ta l s i t e . Sc a l e s we r e g iv en to d i f f e r e n t c a t e g o r i e s o f B h o r i z o n c l a y c o n t e n t s n a me l y : 2 0 – 2 5 % , 2 5 – 2 8 % , 2 6 - 2 8 % , 2 9 - 3 2 % a n d 2 9 – 35 %. Th e r e su l t s i n F i g u r e 2 . 1 6 s h o w t h a t t h e d i f f e r e n t s c a l e s g iv en to t h e c l ay con ten t o f t h e B h o r i zo n fo r t h e 7 5 p lo t s h av e a c l o s e r e se mb l a n c e w i t h t h e s o i l fo r ms . T h e R 2 = 6 6 % , i s a n i n d i c a t i o n t h a t t h e c l a y c o n t e n t o f t h e B h o r i z o n i s a g o o d p a rame te r i d en t i fy ing t h e v a r iou s so i l fo rms o ccu r r i ng a t t h i s e x p e r i me n t a l s i t e . I n bounda ry a r ea s t he c l ay c o n t e n t s r e s e mb l e t h a t o f t he t wo so i l f o r ms i t ma k e s p a r t o f . y = 0.3362x - 6.0936 Scale vs Clay content (%) R2 = 0.6629 7 6 5 Sepane 4 Tukulu/ Sepane 3 Tukulu 2 Bloemdal / Tukulu 1 Bloemdal 0 20 25 30 35 40 Clay ontent (%) F i g u r e 2 . 1 6 D i s t r i b u t i o n o f c l ay o v e r t h e so i l f o r ms ( n = 7 5 ) . Scale 66 2 .3 .4 Sp a t i a l V ar i a t i on w i th in ma p u n i t s Du e t o t he s t r ong co r r e l a t i on b e twe e n t h e c l ay c o n t e n t a n d so m e o f t h e c h e mi c a l p r o p e r t i e s a s w e l l a s t h e s o i l fo r ms , t h e c l ay c o n t e n t w i l l s e r v e a s i n d i c a t o r t o d e s c r i b e t h e s p a t i a l v a r i a t i o n w i th in ma p u n i t s and b e t w ee n ma p u n i t s . S e l e c t e d o b s e r v a t i o n s f ro m e a ch o f t h e so i l fo r ms t o eva lu a t e w i th in map un i t va r i a t i on a r e sho wn i n F ig u r e 2 .1 7 . T u k u l u B lo em d a l Sepa ne Fi g u r e 2 .1 7 M ap ind i c a t i ng t he a r ea s w h i c h w a s s e l e c t e d t o b e w i t h i n t h e ma p u n i t s o f t he Tuku lu , Sepane a n d B l o e md a l s o i l f o rms . 67 Tu ku lu : T h e C V o f t h e c l a y c o n t e n t w a s l e s s i n t h e A ( 4 % ) a n d B ( 4 % ) h o r i z o n s t h a n i n t h e C h o r i z o n ( 1 6 %) ( F i g u r e 2 . 1 8 ) . Th e r a n g e b e t w e e n t h e 2 5 % - 7 5 % q u a r t i l e v a r i ed f ro m 0 i n t h e A h o r i zon , t o 1 i n t he B h o r i zon and 6 .2 5 in t h e C h o r i z o n . I n v e r s e D i s t a n c e W e i g h t i n g ( I D W ) a c c u r a t e ly p red i c t ed t h e c l ay con t en t i n a l l h o r i z o n s ( F i g u r e 2 . 1 9 ) ( A h o r i z o n = 9 9 . 7 8 % , B h o r i z o n = 99 .88% & C ho r i zo n = 9 9 . 4 1 % ) . Sepane : T h e C V o f t h e c l a y c o n t e n t w a s h ig h e r i n t h e C h o r i z o n (14%) t han i n t h e A ho r i zon (7 % ) a n d B h o r i zon (4% ) o f t he Se p an e so i l f o r m ( F i g u r e 2 .1 8 ) . Th e r a n g e b e t w e en t h e 2 5 % - 7 5 % q u a r t i l e w a s c o n s t a n t t h roughou t t he p ro f i l e a t 1 . 7 5 . T h e a c c u r a c y o f t h e p re d i c t ed v a lu e g en e r a t ed u s ing ID W (F i g u r e 2 .1 9 ) , h ad a s ma l l v a r i a t i on f r o m t h e A h o r i zon (97 .9 %) d o wn w ard s t o t h e B ho r i zon (96 .73 %) & C ho r i zon (97 .98 %) . B l o e m d a l : T h e C V w a s a b i t h i g h e r i n t he A ho r i zon (17 %) wh i l e t h e r e w a s a s ma l l v a r i a t i o n i n t h e B h o r i z o n ( 9 % ) a n d C h o r i z o n ( 6 % ) ( F i g u r e 2 .1 8 ) . T h e r e w a s a s ma l l r an g e b e t w een t h e 2 5 % - 75% qua r t i l e t h roughou t t h e p ro f i l e ( 1 .025 ) . Th e d e g r e e t o w h i c h t he ana lyzed va lue s we re p r ed i c t ed u s ing ID W ( F igu re 2 .1 9 ) , r e s e mb l ed t h e s t a t i s t i c a l v a r i a t i o n o f t h e h o r i zo n s (A h o r i zon = 9 9 . 9 3 % , B h o r i z o n 9 7 . 8 1 % & C h o r i z o n 9 7 . 6 4 % ) . 68 Coefficient of variation 20 15 Tukulu Sepane 10 Bloemdal 5 Boundary 0 A B C Horizons F i g u r e 2 .1 8 Coe f f i c i en t o f v a r i a t i on w i th in ma p u n i t s and b e tw ee n ma p un i t s . IDW accuracy 102 100 98 Tukulu 96 Sepane 94 92 Bloemdal 90 Between map units 88 86 A B C Horizons F i g u r e 2 .1 9 A c cu ra cy o f I D W p red i c t i on s w i th in ma p u n i t s and b e t w een ma p u n i t s . F r o m t h e s t u d y d o n e b y C o x e t a l . ( 2003 ) i t i s s t a t e d t h a t t h e s p a t i a l v a r i ab i l i t y o f t ex t u r a l f r a c t i o n s w i l l b e mo r e s t ab l e o n t opog raph i c l andscapes t ha t t end t o b e mo r e l e v e l , w h i l e i t w i l l t e n d t o v a r y mo r e s p a t i a l l y w i t h a t o p o g r a p h i c l an d s c a p e t h a t v a r i e s i n e l e v a t i o n , a sp e c t a n d s l o p e . T h e s t a t i s t i c a l v a r i a t i o n o f t h e c l a y c o n t e n t w i t h i n t h e p r o f i l e s f o r t h e T u k u l u , S e p a n e a n d B lo e md a l so i l f o rms w e re so me wh a t l ow er t h an t h e s t udy by Cox e t a l . ( 2 0 0 3 ) i n w h i c h C V v a l u e s o f 2 8 % o v e r t h e p r o f i l e w e r e Accuracy (%) CV 69 r epo r t ed . Th i s con fus ing t ha t t he t opog raphy o f t h e a r e a i s q u i t e l ev e l , r e su l t i ng i n a l ow e r sp a t i a l va r i a t i on i n c l ay con ten t s . I n t he ca se o f t he Tuku l u and S ep an e so i l f o r ms t h e s t a t i s t i c a l v a r i a t i on i n c r ea s ed d o wnw ard s i n t h e p ro f i l e , wh i l e t h e B lo e md a l s o i l fo r m h ad a h ig h e r v a r i a t i o n i n t h e A h o r i z o n d e c r e a s i n g t o t h e C h o r i z o n , w h i c h may b e d u e t i l l a g e p r a c t i c e s a n d t h e p r o c e s s o f l uv i a t i on . 2 .3 .5 Sp a t i a l v a r i a t i on b e t we e n ma p u n i t s Th e a r ea s e l e c t ed b e t w een t h e Tuku lu and t h e Sep an e so i l f o r ms a r e s h o w n i n F ig u r e 2 . 2 0 . F i g u r e 2 . 2 0 M a p i n d i c a t i n g t h e a r e as t h a t h as b een se l e c t ed t o c h a r a c t e r i z e t h e v a r i a t i on b e t w e en ma p u n i t s . 70 T h e r e w a s a h i g h e r C V in c l ay con ten t be tween map un i t s t h an w i t h i n m a p u n i t s ( F i g u r e 2 . 1 8 ) . R eg a r d l e s s o f t h e f a c t , I D W s t i l l f a i r l y a cc u r a t e l y p red i c t ed t he l a b a n a l y z e d v a l u e s . T h e C V v a lu es va r i ed f ro m 7% in t he A ho r i zon , 13% in t h e B ho r i zon t o 1 7 % i n t h e C h o r i z o n , w h i c h a l t h o u g h i t w a s b e t w e e n ma p u n i t s w a s s t i l l l o w er t h an C V v a l u e s r e p o r t e d b y C o x e t a l . ( 2 0 0 3 ) ( C V o f C l a y = 2 8 % o v e r t h e p r o f i l e ) . Th e r a n g e be tween t he 25% - 7 5 % q u a r t i l e v a r i e d f ro m 1 .75 in t h e A h o r i z o n , 2 .5 i n t h e B h o r i zon to 8 .5 i n t he C h o r i z o n a n d t h e d eg r e e o f a c c u r a c y t o wh i ch the an a ly zed v a lu e s w e r e p r ed i c t ed v a r i ed f ro m 9 1 .1 9 % i n t h e A h o r i z o n , 9 7 . 4 7 % i n t h e B h o r i z o n t o 9 4 . 6 3 % i n t h e C h o r i z o n ( F i g u r e 2 . 1 9 ) . 2 .4 Con c lu s io n F r o m t h i s s t u d y i t w a s fo u n d t ha t t he d i s t r i bu t i o n o f s o i l s i s i n f luen c ed by t h e so i l f o rmi n g f ac t o r s , v i z . c l i ma t e ( r a i n fa l l , t e mp e r a tu re an d a r id i t y i nd ex ) , p a r en t ma t e r i a l (Do l e r i t e , B e a u f o r t S a n d s t o n e a n d S c h a l e ) , t o p o g r a p h y , b i o l o g y a n d t i me . T h e r e w e r e t h r e e ma j o r s o i l f o r ms f o u n d a t t h e e x p e r i me n t a l s i t e , v i z . T u k u l u , S e p a n e a nd B l o e md a l . T h e Tu k u lu c o v e r e d 7 5 % o f t h e t o t a l a r e a , t h e S e p a n e 1 5 % and t h e B loemd a l 10%. A co r r e l a t i on ma t r i x o f t he phy s i c a l a n d c h e mi c a l p ro p e r t i e s o f t he t h r ee so i l s i nd i ca t ed t h a t mo s t so i l phy s i c a l a n d c h e mi c a l p ro p e r t i e s h av e a s t ro n g co r r e l a t i on w i th t he s i l t + c l ay con t en t . Thu s t h e s i l t + c l ay con ten t w er e u s ed to d e sc r ib e t h e sp a t i a l v a r i a t i on o f s o i l p ro p e r t i e s i n and b e tw e en ma p u n i t s . The r e w as a h i g h e r d e g r e e o f s t a t i s t i ca l and sp a t i a l v a r i a t i o n b e t w een ma p un i t s t h an w i th in map un i t s . R ega rd l e s s o f t he h igh s t a t i s t i c a l and s p a t i a l v a r i a t i on ID W s t i l l a c cu r a t e ly p r ed i c t e d t h e l ab an a ly zed v a lu es . Th i s r e su l t ed i n t h e mo r e accu ra t e r ep re sen t a t i on o f b o u n d a r i e s b e t w e e n ma p u n i t s t h a n p r e v i o u s d i s t i n c t b o u n d a r i e s . Th i s con c l udes t ha t map s a r e i n f a c t a s i mp l e r e p r e se n t a t i o n o f a 71 c o mp l ex sy s t e m, b u t i s i n ev i t ab l e f o r o n e t o u n d e r s t a n d t h e e v o l u t i o n o f s o i l s a n d i t s n a t u r a l b e h a v i o u r . 72 CHAPTER 3 R e la t i o n sh ip b e tw ee n so i l p h y s i c a l p r o p e r t i e s a n d t h e r o o t d e n s i t y o f ma i z e u n d e r I n f i e l d R a i n w a t e r H a rv e s t i n g . 3 .1 In t roduct ion Roo t s i s a k ey f a c to r i n imp r o v i n g a g r o n o m i c a l p r o d u c t i v i t y o f c ro p p ro d u c t ion sy s t e ms , b ec au s e t h ey a r e r e sp o n s ib l e fo r ab so rb ing w a te r and nu t r i en t s f ro m t h e so i l a n d t h e t r a n s lo c a t i o n t he r eo f t o t he shoo t s (K lepp e r , 1 9 9 0 ; B e n n i e , 1 9 9 6 a n d V a n A n t w e r p e n , 1 9 8 8 ) . P a s t s t u d i e s o n r o o t d ev e l o p me n t u n d e r S o u t h Af r i can cond i t i ons focu s sed i n t h e f i e l d o f i r r i ga t i on (B enn ie & B u r g e r , 1 9 7 9 ; V a n A n t w e rp e n , 1 9 8 8 a n d B e n n i e e t a l . , 1 9 8 8 ) a n d d ry l an d t i l l ag e p ra c t i c e s (B enn ie e t a l . , 1 9 8 8 ; Sny ma n , 1 9 8 7 a n d V a n d e r M e r w e , 1 9 9 3 ) . The s e t i l l a g e p r a c t i ce s i n c l u d e mi n i mum t i l l a g e , s t u b b l e m u l c h a n d n o - t i l l , w h i c h w e r e ma i n l y a p p l i e d o n s a n d y t o s a n d y l o a m s o i l s , w i t h a ma s s i v e ap ed a l s t ru c tu re . R ecen t adv an ces i n t i l l ag e sugg es t ed t ha t t he In f i e ld R a inw a te r H a rv es t i ng ( I RW H) t e chn iq u e i s su i t ab l e fo r c l ay and d u p lex so i l s i n s e mi a r i d z o n e s o f Sou th Af r i c a (Hens l ey e t a l . , 2 0 0 0 a n d Bo th a e t a l . , 2 0 0 3 ) . U p t o d a t e n o n e o f t he b iophys i ca l s t ud i e s i n I R WH has fo cu s sed on ro o t d e v e l o p me n t . T h i s i s s e e n a s a s e r i o u s c o n c e r n a s t h e sy s t e m c l a i ms t h a t i t imp r oves t he r a in wa te r p roduc t i v i t y (Bo tha , 2006 ) . Th e o b j ec t iv es o f t h i s s t u d y w e r e t h e r e fo r e t o : ( i ) r ev i ew l i t e r a tu r e o n th e i n f lu en ce o f s o i l p h y s i c a l p r o p e r t i e s a n d r o o t d ev e lop me n t , ( i i ) i nv e s t i g a t e t h e i n t e r ac t i ons b e tw een so i l p h y s i c a l p ro p e r t i e s a n d ( i i i ) d e t e rmi n e h o w th e roo t d en s i ty r e l a t e s t o c e r t a i n so i l phys i ca l p rope r t i e s u n d e r t h e I R W H s y s t e m . 73 3 .2 Li tera ture Review 3 .2 .1 In t ro d u c t io n Th i s r ev i e w i s s t ru c tu r ed to p ro v ide f i r s t l y i n fo r ma t ion o n the t y p e s o f r o o t s y s t e ms a n d s e c o n d l y o n s p e c i f i c so i l phys i ca l p ro p e r t i e s s u ch a s t e x tu r e , s t ru c tu r e , b u lk d en s i ty and s o i l w a t e r c o n t en t t h a t i n f lu en ce s roo t d ev e l o p me n t . Roo t g ro w th i s i n f lu en c ed g re a t ly b y so i l f a c t o r s i n c l u d in g t h e so i l s t r u c t u r e , s t r en g th ( co mp r e ss ib i l i t y ) , w a t e r con ten t , t e mp e r a tu r e , p o ro s i t y , g a seou s d i f fu s iv i t y , p H , t o x i c i t y , a n d f e r t i l i t y . T h e m a i n r e q u i r e m e n t s t h a t h a s t o b e me t f o r o p t i mu m e l o n g a t i o n i s a s f o l l o w s : ( i ) a n a d e q u a t e d e l i v e r y r a t e o f c a r b o h y d r a t e s t o t h e r o o t t i p , ( i i ) so i l space fo r t h e roo t s t o mo v e in to , ( i i i ) adequ a t e s u p p l y o f i n o r g a n i c i on s fo r r o o t u p t a k e , ( i v ) adequa t e wa t e r con t en t du r ing t h e g rowing s ea son and (v ) a s u f f i c i en t s u p p l y o f c h e mi c a l e n e r g y ( B e n n i e e t a l . , 1 9 8 8 ) . M o s t o f t h e s o i l s p ro p e r t i e s i n f lu en c e mo r e t h an one o f t he above me n t ioned r e q u i r e m e n t s , a s s e e n i n T a b l e 3 . 1 . S o me o f t h e s o i l p r o p e r t i e s c h an g e r a p id ly wh i l e so me o f t he p r o p e r t i e s d o n o t c h a n g e o v e r t i me . F o r e x a mp l e , so i l s t r u c tu r e , p H a n d p o r o s i t y ma y n o t c h a n g e mu c h d u r i n g t h e g r o w ing s ea son o f c rops , bu t wa t e r c o n t e n t a n d t e mp e r a t u r e ma y c hange on an hou r ly ba s i s . 3 .2 .2 Ro o t sy s t e ms Un l e s s v a r io u s so i l f a c to r s h av e an i n f lu en c e , t h e p a t t e rn o f ro o t d ev e lop me n t p r i ma r i l y d ep en d s o n the p l an t sp ec i e s . Roo t sy s t e ms a r e o f t h r e e b as i c t y p e s ( F igu r e 3 .1 ) ( i ) F i b ro u s o r a d v en t ive ( i i ) t ap ro o t ed a n d ( i i i ) mo d i f i ed t ap r o o t s y s t e m s ( K l e p p e r , 1 9 9 0 ) . A d v e n t i v e s y s t e ms a r e ma i n l y r e l a t e d t o mo n o c o t y l e d o n c r o p s , w h i l e d i co ty l edon c rop s a r e a s soc i a t ed w i t h t a p r o o t a n d mo d i f i e d t a p r o o t s y s t e ms . 74 F i g u r e 3 . 1 D i a g r a m s h o w i n g t h e t h r e e b a s i c r o o t sy s t e m s (K leppe r , 1990 ) . M o n o c o t y l e d o n s : A c c o r d i n g t o K l e p p er ( 1 9 9 0 ) mo n o c o t y l e d o n c r o p s g e n e r a l l y p r o d u c e r o o t s f r om s t e m nodes . Th ese nodes c o n s i s t o f s e mi n a l r o o t s t h a t a r i s e f r o m i n t h e e mb r y o a n d c r o w n r o o t s . I n w h e a t t h e s e mi n a l r o o t s y s t e m c on s i s t o f a p r i ma r y r o o t a n d u p to f i v e roo t s a s so c i a t ed w i th t h e two nod es i n t h e s eed ( F i g u r e 3 . 1 ) . Th e f o l i a r n o d e s i n t h e c r o w n g ive r i s e t o a c rown r o o t sy s t e m. T h e e a r l y s emina l roo t ing sy s t em i s n o t p e r s i s t en t i f i t s u b j e c t e d t o p a t h o gen a t t ack o r i f i t i s d a ma g ed b y f ro s t h e av ing . Ea r ly i n t h e roo t d ev e lop me n t , t h e g ro w th r a t e s o f t h e ma i n ax es a r e s lo w ed and b ran ch roo t s b eg in t o g ro w . G en e r a l l y t h e a x e s e x t e n d a t a r a t e o f 1 c m d a y - 1 . V a n A n t w e r p e n ( 1 9 8 8 ) me a s u r ed v e r t i c a l r o o t d ep th s t ha t v a r i e d b e t w e e n 1 m a n d 2 m i n a r ange o f so i l s a t t h e Vaa lha r t s , Ramh a an d S a n d v e t I r r i g a t i o n S c h e me s . D i c o t y l e d o n s : D i co ty l edon t ap roo t sy s t e ms d e v e l o p f r o m t h e r a d i c l e a n d i t s b r a n c h e s K l e p p e r , 1 9 9 0 ( F i g u r e 3 .1 ) . A d v e n t i t i v e r o o t s ma y a l s o b e p r o d u ced f ro m t h e s t e ms . U su a l l y i t c o n s i s t s o f a s t r ong t ap roo t t ha t g r o w s v e r t i c a l l y a n d i s s u p p o r t e d b y s t r o n g l a t e r a l r o o t s . I n s o me s t u d i e s i t w a s f o u n d t h a t i n s o y b e a n t h a t t h e l a t e r a l ro o t sy s t e m g r ew h o r i zo n t a l fo r a f e w cen t i me t r e s a n d t h e n g r e w v e r t i c a l f o r a c o n s i d e r a b l e d e p t h . I t was a l so f o u n d t h a t 75 d i c o t s p r o d u c e f e w e r r o o t s t han th e mo n oco t s , f o r ex amp l e ma i z e , d o . Ta b l e 3 .1 P r i ma ry in f lu e n ce s o f s o i l p r o p e r t i e s o n s o i l r eq u i r e m e n t s fo r o p t i ma l r o o t e l o n g a t i o n ( Lo g s d o n e t a l . , 1987 ) . -= absent X = present Soil property Requirements Ions Pore Space Water Chemical energy Structure - x x - Porosity - x x - Water content - x x - Strength - x - - Gaseous diffusivity x - x x Temperature x - x x pH x - - - Fertility x - - - E v e n h o mo g e n o u s s o i l h o r i zon s a r e fu l l o f c r a c k s , w o r m h o l e s a n d o ld roo t ch ann e l s , wh i ch i n f lu en c es roo t d ev e lop me n t i m me n s e l y . R o o t s t e n d t o g r o w a l o n g a p e d s u r fa c e e v e n i f t h e p ed h as a l o w r e s i s t anc e t o p en e t r a t i on . A t t h e s a me t i me r o o t s g r o w a l o n g t h e su r f a c e o f a c r a c k a n d n o t i n t h e c r a c k s . The se f e a t u r e s c a u s e r o o t s t o g r o w a round r a the r t h an t h rough so i l h o r i z o n s c o n t a i n i n g c r acks and l a rge vo id s . When roo t s pene t r a t e t he so i l , t hey co mp res s t h e cy l i nd e r o f so i l immed i a t e ly a round t h e ms e l v e s ( H i l l e l , 2 0 0 4 ) . T h e c o mp r e s s i b i l i t y o f t h e so i l g r ea t l y i n f l u e n c e s t h i s p h e n o me non . Th e comp res s ib i l i t y o f t h e so i l i s u su a l ly me a su r ed a s s o i l r e s i s t anc e o r me c h an i c a l i mp ed an ce w i th a p en e t ro me t e r w h i ch mo n i to r s t h e f o r c e r e q u i r e d t o p r e s s a r o o t shaped p robe t h rough t h e s o i l . I t h a s b e e n fo u n d t h a t t h e p en e t ro me t e r p r e s s u r e (M Pa ) i s an a d equ a te i nd i c a t i o n o f t h e me c h a n i c a l i mp e d a n c e o f t he so i l and i s co r r e l a t ed w i th v a r i ab l e s s u c h a s f r e s h a n d d r y w e i g h t , e l o n g a t io n r a t e s ( m m d a y - 1 ) , r oo t l en g th d en s i ty ( c m c m - 3 ) a n d r o o t i n g d e p t h ( mm) . 76 3 .2 .3 So i l t ex tu r e So i l t ex tu re i s a v e ry b ro ad con c ep t and n o rma l ly r e f e r s t o t he r a t i o o f s a n d , s i l t a n d c l ay con te n t . H o w e v e r i t s e f f e c t o n r o o t g r o w t h a n d d e v e l o p me n t c a n b e f u r t h e r e x p la i n e d b y subd iv id ing t ex t u r e i n t o p a r t i c l e s i z e d i s t r i b u t i o n , spe c i f i c su r f a c e o f p a r t i c l e s a n d t e x tu r a l c l a s s e s (H i l l e l , 2 0 0 4 ) . T e x t u r a l p r o p e r t i e s i n f lu en c e t h e me c h an i c a l i mp e d an c e o f t h e so i l . M e ch an i c a l i mp e d an ce r e f e r s t o t h e r e s i s t a n c e o f f e r e d b y t h e so i l ma t r i x a g a i n s t d e f o r ma t i o n b y a g r o w in g r o o t . Thu s , p e r mi t t i n g r o o t e l o n g a t i o n o n l y i n a c c o rdan c e w i th t he ex t en t t o wh ich t h e roo t p r e s su r e e x c e e d s t h e me c h a n i c a l i mp e d a n c e o f t h e so i l . F o r roo t s t o e l o n g a t e d o w n w a r d i n t h e p r o f i l e i t h a s t o e x c e e d t h e b i n d i n g f o r c e s b e t w e e n so i l p a r t i c l e s a n d t h e f r i c t io n w h e n mo v i n g s o i l p a r t i c l e s . T h e s e fo r c e s a r e so i l - t o - w a t e r adh e s io n and w a t e r - t o - w a t e r c o h e s i o n fo r c e s and i n t e rp a r t i c l e cemen ta t i o n . T h e s e fo r c es a r e d ep end an t on t he w a t e r con ten t , con t ac t a r ea and d i s t ance a mo n g t h e i n d i v i d u a l p a r t i c l e s , w h i ch i s i n t u r n a l l d ep en d an t o n fo r exa m p l e so i l t ex t u re , s o i l s t ruc tu r e , b u l k d en s i ty an d so i l w a t e r c o n t e n t ( B e n n i e , 1 9 9 5 ) . Th e s e ab o v e me n t i o n ed p ro p e r t i e s h av e the fo l l o wing a f f e c t o n roo t e l onga t i o n ( L o g s d o n e t a l . , 1987 ) : i . C e men t ing ag en t s can i n c r ea se t h e s t r eng th o f t he po re c h a n n e l s ma k i n g i t d i f f i c u l t f o r t h e roo t s t o ov e rco me t he r eq u i r ed p re s su re t o mo v e p a r t i c l e s ou t o f t he w ay wh i l e r oo t s e l onga t e . i i . T h e h i g h c r i t i c a l s o i l s t r en g t h v a lu es a s so c i a t ed w i th t he c o a r s e s a n d y s o i l s h a s a a f f e c t o n e l o n g a t i n g r o o t s . i i i . O rg an i c ca rbon con ten t and w a t e r con ten t a l so mod i f i e s t h e c r i t i c a l s o i l s t r e n g t h d e c rea s ing roo t e l onga t i on . B e n n i e & B u r g e r ( 1 9 8 8 ) f ound t ha t t he c r i t i c a l s o i l s t r eng th , d e f i n e d a s t h e p r o b e p r e s s u r e a t w h i c h r o o t e l onga t i on s t opped , w a s a fun c t ion o f c l ay ( % ) and r ang ed i n co t ton s eed l ing s f rom 77 7 MPa in coa r se t ex tu r ed so i l s t o 2 .5 M Pa in c l ay so i l s . I t was a l so i n d i c a t e d t h a t t h e p e n e t r o me te r p r e s su r e i n c r ea se s w i th an i n c r ea s e i n t h e s i l t + c l ay con t en t up t o 20 % fo r so i l s w i th t h e s a me d e g r e e o f c o mp a c t i o n a n d w a t e r c o n t e n t ( F i g u r e 3 . 2 ) . F i g u r e 3 .2 Re l a t i o n sh ip b e tw e en so i l s t r en g th a n d p e r c en t o f c l ay ( B e n n i e & B u r g e r , 1 9 8 8 ) . T o d e mon s t r a t e t h e e f f e c t o f t ex tu r e on roo t d e v e l o p me n t u n d e r Sou th A f r i c an co n d i t i on s , t h e r e su l t s f r o m th r ee so i l s w i th ma ize a s t h e t e s t c r o p , V a n A n t w e r p en ( 1 9 8 8 ) , w e r e s e l e c t e d a n d p re s en t ed i n Tab le 3 .2 . A l l t h e so i l s a r e f r o m ty p es o cc u r r ed in t h e V a a lh a r t s I r r i g a t i o n Sch e me , w h e r e w a t e r a n d n u t r i e n t s a r e n o t i mp e d i n g f a c to r s . T h e s o i l s f o rms w e re a Hu t ton f ro m t he R i t ch i e f ami ly w i th a mean s i l t + c l ay con ten t o f 14 .2% ov e r t h e p ro f i l e , a C love l l y f ro m th e Se t l ago le Fami ly w i th a mean s i l t + c l ay co n te n t o f 1 6 .9 % and an O ak l e a f o f t he S t e l l a Fa mi ly w i th an mean s i l t + c l ay con ten t o f 31 .7 % . 78 T a b l e 3 . 2 R o o t d e n s i t y d a t a i n r e l a t i o n t o t h r e e s o i l f o r ms w i t h d i f f e r e n t p h y s i c a l p r o p e r t i e s ( D a t a m o d i f i e d f r o m V a n A n t w e r p e n , 1 9 8 8 a n d B e n n i e , 1 9 9 6 ) Soil Sand Texture Total root Author Location form Family Depth fractions Silt + Clay class Bulk density length Root density (mm) (%) (%) (kg.m-3) (mm mm-2) (cm cm-3) R. van 0-300 88.05 10.19 Loamy sand 1651 1.786 Antwerpen Vaalharts - M78 Hu 1110 - 300-600 84.99 15.32 Loamy sand 1728 8.826 0.456 (1988) (Irrigation) Ritchie 600-900 82.98 17.2 Loamy sand 1591 0.183 R. van 0-300 85.44 15.35 Loamy sand 1603 0.485 Antwerpen Vaalharts - M79 Cv 3100 - 300-600 82.8 17.19 Sand 1604 0.434 4.343 (1988) (Irrigation) Setlagole 600-900 81.75 18.22 Sand 1574 0.201 R. van 0-300 64 35.37 Sandy loam 1596 0.489 Antwerpen Vaalharts - M83 Oa 3100 - 300-600 68.28 30.34 Sandy loam 1524 0.478 6.39 (1988) (Irrigation) Stella 600-900 68.49 29.65 Sandy loam 1518 0.218 Bennie Hoopstad Cv 3100 - 0-300 94.6 5 Loamy sand - 0.226 (1996) (Dry Land) Setlagole 300-600 82.78 16 Sand - 1.776 0.105 600-900 83.98 16 Sand - 0.115 0-300 85.12 16 sandy loam - 0.225 Bennie Tweespruit We 2000- sandy loam 1.449 (1996) (Dry Land) Mareetsane 300-600 74.68 26 clay - 0.158 600-900 40.42 58 sandy clay - 0.101 79 D e sp i t e t h e l a rg e d i f f e r en ces i n c l ay con t en t ( Tab le 3 .2 ) , t he re w as n o d i s t i n c t d i f f e r e n ce i n roo t d e n s i ty b e t w e en th es e t h r ee s o i l f o r ms fo r e ach d i a g n o s t i c h o r i z o n , e x c ep t f o r t h e A h o r i z o n , w h i c h v a r i e d b e t w e e n 1 . 7 9 c m c m - 3 f o r t h e Hu t ton , 0 .4 9 c m c m - 3 f o r t h e C lov e l l y and 0 .4 9 c m c m - 3 f o r t h e O a k l e a f . V a n A n t w e r p e n ( 1 9 8 8 ) c o u l d a l s o f i n d n o r e l a t i o n s h i p b e t w een r o o t d en s i ty and th e c l ay + s i l t con te n t fo r any o f t h e c ro p s h e s t u d i e d . R o o t d e n s i t y r e s u l t s f r o m V a n A n t w e r p en ( 1 9 8 8 ) w e r e c o mp l e me n t e d b y t h e s t u d y d o n e b y C a l l o t e t a l . ( 1 9 8 2 ) o n s o y b e a n g r o wn i n l o a m y a n d c l a y so i l s . They found t ha t t h e r e w a s n o c l e a r d i f f e r e nc e i n r o o t d e n s i t y o v e r t h e p ro f i l e b e tw ee n th i s sp e c i f i c l oamy and c l ay so i l ex cep t fo r t h e A h o r i z o n ( T a b l e 3 . 3 ) . O n e f a c t o r t h a t sh o u l d b e c o n s i d e r e d i s t h e f a c t t h a t t h e roo t d ev e lop me n t o f d i f f e r e n t f i e l d c ro p s a c t s d i f f e r en t ly o n d i f f e r en t t e x t u r e c l a s s e s . Roo t d a t a f r o m C a l lo t e t a l . ( 1 9 8 2 ) d e mo n s t r a t e d t h a t c o a r s e r t e x t u r e d s o i l s i n f lu en ce t h e g ro w t h o f t e r t i a ry r o o t s mo r e t h an f i n e r t ex t u r ed s o i l s . F ine t ex tu r ed so i l s on t h e o t h e r h a n d h a d a l a r g e r i n f lu en ce o n s e mi n a l a n d s e co n d a ry roo t s . Coa r s e r t ex tu r ed so i l s h ave a l ow e r f e r t i l i t y , l ower u n s a t u r a t e d h y d r a u l i c co n d u c t i v i t y , a n d a l o w e r w at e r s t o r a g e c a p a c i t y . Roo t s o f v a r io u s p l an t s h ave th e t en d en cy to h av e a h ig h e r co n c e n t r a t i on o f roo t s i n a mod er a t e l oo s e - t ex tu r ed s o i l t h an i n a h e avy t ex t u r ed so i l . 79 80 T a b l e 3 .3 R o o t c h a r a c t e r i s t i c s o f w h e a t du r ing t i l l e r i ng i n t h r ee so i l s o f va r i ous t ex tu r e s s e l e c t ed f ro m C a l lo t e t a l . ( 1982 ) Textural fractions Root parameters Clayey Silty Sandy Seminal roots Mean length (mm) 42 127 129 Total length (mm) 340 1021 1290 Secondary roots Mean length (mm) 10.2 12.8 17 Total length (mm) 960 7200 16000 Tertiary roots Mean length (mm) 1.74 1.9 1.49 Total length (mm) 1220 2100 477 3 .2 .4 So i l s t ru c tu r e So i l s t ru c t u r e ex e r t s i mpo r t an t i n f lu en c es o n p l an t g ro wt h v i a roo t g ro w th a n d d ev e l o p me n t . So i l s t ruc tu r e i n g en e ra l r e f e r s t o t h e s i z e , s h a p e a n d a r r an g e me n t o f t he b a s i c s t ru c tu r a l u n i t s o r p ed s . The So i l Su r v ey S t a f f ( 1 9 9 3 ) p r o v i d e d g u i d e l i n e s t o d e s c r i b e so i l s t r uc tu r e ba s e d o n t h e p e d s t y p e , c l a s s a n d g r a d e . Ty p e s a r e f u r th e r d iv id ed in to sub g r a d e s a c c o r d i n g t o t h e sha p e a n d a r r an g e me n t o f p ed s a n d i n c l u d e s s u b g r o u p s such a s p l a ty , p r i s ma t i c , c o l u mn a r , b l o ck y , s u b a n g u l a r b l o c k y , g r a n u l a r and c ru mb . C l a s s r e fe r s t o t h e s i z e o f s t r u c t u ra l u n i t s o r p ed s . F o r e a c h o f t h e su b g r o u p t y p e s t h e r e a r e f i v e c l a s s s i z e s . F o r e x a mp l e , g r a n u l a r p e d s ( r e l a t i v e l y n o n p o r o u s p e d s) a r e d iv i d ed in to < 1 mm ( v e ry f i n e ) , 1 – 2 mm ( f i n e ) , 2 – 5 mm ( me d i u m) , 5 – 1 0 m m ( c o a r s e ) and > 10 mm ( v e ry c o a r s e ) . C ru mb (po ro u s p ed s ) a r e o n ly d iv ided i n to t h r ee s i z e c l a s se s , v i z . v e ry f i n e ( < 1 mm) , f i n e (1 – 2 mm) a n d me d iu m ( 2 – 5 m m) . G r ad e on t he o th e r h an d r e f e r s t o t h e n o r ms t o d e s c r i b e t h e s t r u c tu r a l s t ab i l i t y o f t he p ed s an d i s t h e r e fo r e d iv id e d i n t o f o u r s u b g r o u p s , v i z . s t r uc tu r e l e s s , w e a k , mo d e r a t e a n d s t r o n g . 80 81 T h e s e n o r ms a r e v e r y h e l p fu l i n i d en t i fy ing and d e sc r ib ing so i l s t r u c tu r e q u a l i t a t i v e l y , b u t d o n o t r e a l l y p r o v i d e i n fo r ma t i on o n t h e e f f e c t t h e r eo f o n p l a n t p r o d u c t i o n . Th e r e fo r e , s c i e n t i s t s o f t e n u s e a g g r e g a t e s i z e s a n d s t ab i l i t y a s a s imp le i nd i ca to r t o quan t i fy so i l s t r u c tu re (S ix e t a l . , 2 0 0 0 ) . Aggrega t e s a r e s econda r y p a r t i c l e s f o r me d t h ro u g h t h e c o mb i n a t i o n o f mi n e r a l p a r t i c l e s w i th o rg an ic and ino rg an i c s u b s t an ces . B ro mi c h & La l ( 2 0 0 5 ) s t a t e d t h a t a g g r e g a t e s o r i g i n a t e f r o m c o mp l e x a n d d y n a mi c p r o c e s s e s t h a t d e p e n d s o n t h e i n t e r ac t i on o f many f ac to r s i n c lud ing t h e e n v i ron me n t , so i l ma n a g e me n t , p l an t i n f lu ences and so i l p rop e r t i e s su ch a s mi n e r a l co mp o s i t i on , t ex tu re , so i l o r g a n i c c a r b o n , p ed o g e n i c p r o c e s s e s , m i c r ob i a l a c t i v i t i e s , ex ch ang e ab l e i o n s , n u t r i e n t s r e s e r v e s a n d mo i s t u r e av a i l ab i l i t y . Agg reg a t e s a r e o f t en g rouped i n to s i z e s : mi c ro agg reg a t e s ( < 2 5 0 μm ) a n d ma c r o a g g r e g a t e s ( > 2 5 0 μm) . T i s d a l e & O a d e s ( 1 9 8 2 ) a l s o s t a t e s t h a t t h e i r g roup s a r e o f t en fu r th e r d iv id e d b y s i z e . Howeve r , f avou rab l e so i l s t r uc tu re a n d h i g h a g g r e g a t e s t ab i l i t y a r e i mp o r t a n t t o i mp r o v e r o o t g r o w t h . D e x t e r ( 1 9 7 8 ) d e s c r i b e d t h e i n f l u e n c e o f ag g r ega t e s i z e o n ro o t d ev e lop me n t . A c co rd i n g l y ro o t s g r o w d o w n w a r d i n a p r o f i l e u n t i l i t r e a c h e s a n a g g r e g a t e . I t c o u l d t h e n mo ves a round t he a g g r e g a t e , t h r o u g h t h e a g g r e g a t e o r d i s p l a c e s t h e a g g r e g a t e a s s e e n i n ( F i g u r e 3 . 3 ) . N a r r o w r o o t s a r e mo r e e a s i l y d e f l ec t ed and l a rg e agg r eg a t e s a r e l e s s l i ke ly t o be d i s p l a c e d b y r o o t s . F i g u r e 3 . 3 R e p r e s e n t a t i o n o f p o s s i b l e p a t hs o f a r o o t a x i s t h r o u g h a b e d o f a g g r e g a t e s ( D e x t e r , 1 9 7 8 ) . 81 82 L o g s d o n e t a l . ( 1987 ) s t a t ed i n t h e i r s t udy t ha t l a rge agg rega t e s d id no t h av e ev en a s l i g h t p r e s su re ex e r t ed o n t h e m when roo t s we re mo v ing a r o u n d t h e m. T h e r o o t d i a me t e r i n c r e a s e d a s a g g r e g a t e s i z e i n c r e a s e d , b u t r o o t l e n g t h i n mo s t c a s e s s t a y e d t h e s a me . S ma l l e r agg reg a t e s had l i t t l e i n f l uence on roo t g rowth a s i t w as r ea d i l y d i sp l aced . Th i s s cen a r io r ead i l y o c c u r s i n p r o f i l e s w i t h v a r y i n g s t r uc tu r a l i n t e r f ace s e s p e c i a l l y i n t i l l e d l a n d s o r i n a r e a s w h e r e comp ac t i on i s a p rob l em. C o mp ac t ion i n un t i l l ed s u b s o i l l a y e r s ma y h a v e c r a c k s a n d b i o p o r e s w h i c h i n f l u e n c e s r o o t d e v e l o p m e n t . W h e r e c r a c k s a r e t o na r row fo r r oo t s t o move t h rough , t he r o o t s t e n d t o b u c k l e b eh i n d t h e r o o t t i p t o b u i l d u p s u f f i c i e n t s u p p o r t t o p u s h r o o t t i p s f o r w a r d ( B e n n i e , 1 9 9 5 ) . M o s t w o r k o n t h e p e n e t r a b i l i ty o f r o o t s i n s o i l s i s d o n e o n w e a k , ma s s i v e o r s i n g l e g ra in s t r u c tu red s o i l s . The r e i s d e f i n i t e l y l e s s w o r k d o n e o n me d i u m t o w e l l s t r u c tu red s o i l s . Pen e t ro me t ry s ee ms n o t t o b e t h e mo s t s u i t a b l e w a y o f s t udy ing t he pene t r ab i l i t y o f r o o t s t h ro u g h p e d s o r ma c r o a g g r e g a t e s i n s o i l s w i th c l ay con t en t s h i g h e r t h a n 2 0 % ( H i l l e l , 2 0 0 4 ) . L a r g e r a g g r e g a t e s ma y h av e l a r g e p o r e s o r w e a k p l a n e s t o a c c o m mo d a t e r o o t g r o w t h , w h i c h c a n n o t b e d e t e c t e d b y t h e p e n e t r o me t e r . W i t h s ma l l e r agg r eg a t e s t h e r e i s l e s s mech an i c a l imp e d an c e t han w i th l a rg e r agg reg a t e s . P r e f e r e n t i a l r o o t g r o w t h ma y a l s o b e c a u s e d b y n a t u r a l s t r u c t u r e d c r a ck s a n d b i o p o re s p e rmi t t i n g roo t d ev e l o p me n t w i t h mi n i mu m r e s t r i c t i o n s . T h u s , t h e r e i s p r e f e r e n t i a l r o o t p e n e t r a t i on i n t o zon e s o f w eak n e s s . Th e e f f e c t o f s i z e o f t h e a g g r e g a t e i s mu c h l a rg e r t h an t h e s t r en g t h o f t h e agg rega t e on roo t d e v e lop me n t . D e x t e r ( 1 9 7 8 ) f o u n d t ha t l a rge ax i a l r o o t g r o w t h p r e s s u r e mu s t b e e x e r t e d b y ro o t s t o p en e t r a t e t h e l a rg e agg reg a t e s . They c o n c lud ed th a t an i n c r e a s e i n a g g r e g a t e d i a me t e r c a u s e s a d ec r ea se i n t o t a l r oo t l eng th , bu t a n i n c r e a s e i n r o o t h a i r l en g th . Th e ma i n a x es o f s e mi n a l a n d mo d a l roo t s w e r e l ong e r i n t he co a r se r agg r ega t e sy s t e m. T h e d i a me t e r o f t h e ma i n a x e s r o o t s w a s a l so g r e a t e r i n t he l a rg e r agg reg a t e f r a c t i o n s . S i n c e t h e p e n e t r o me t e r me t h o d o n l y c a l c u l a t e s s o i l s t r e n g t h , a t h o r o u g h qua l i t a t i ve 82 83 s t u d y s h o u l d b e d o n e t o g a in a b e t t e r und e r s t an d i n g o f h o w t h e r o o t s a c t und e r me ch an i c a l imp e d an c e . A ma t o & R i t c h i e ( 2 0 0 2 ) d e t e r mi n e d t he e f f e c t o f a g g re g a t e s i z e o n t h e r o o t d ev e l o p me n t o f ma i z e ( Ta b l e 3 .4 ) . Th ey u s ed a s andy c l ay l oam so i l ( S C L ) ( c l ay con t en t = 3 7 .1 % ) an d pack ed so i l co lumn s w i th d i f f e r e n t a g g r e g a t e s i z e s . Th r e e t r e a t me n t s w e r e e mp l o y e d , v i z . a co lu mn w i th on ly t h e S C L s o i l , a co l u mn w i t h o n e l a r ge agg r eg a t e ( LA) i mb e d d e d i n t h e SC L so i l (SC L + LA ) and a t h i rd co lu mn w i th sma l l e r agg reg a t e s i ze s ( S C L + S A ) . T h e se a g g r e g a t e s w e r e p l aced w i th in t he 50 – 7 5 c m d e p t h i n t e rv a l . A l l t h e a g g r eg a t e s w e r e sa mp l e d f r o m a c l ay l o a m s o i l . O n e ma i z e p l a n t w a s p l a n t ed on each o f t he co lu mn s t o ob se rv e t h e d i s t r i b u t i o n o f t h e r o o t s unde r t he se two cond i t i ons . Ta b l e 3 .4 M e an roo t l en g th d en s i ty and the s t a n d a rd d ev ia t i on in e a ch so i l l a y e r ( A ma t o & R i t c h i e , 2 0 0 2 ) Soil layer or peds Root length (cm.cm-3 ) SCL SCL + LA SCL+ SA Mean (std) Mean (std) Mean (std) 0 - 25 cm 1.56 (0.4) 1.2 (0.96) 1.15 (0.85) 25 - 50 cm 1.28 (0.29) 1.02 (0.87) 1.1 (0.8) 50 - 75 cm 1.04 (0.28) 0.75 (0.56) 0.67 (0.43) 75 - 100 cm 0.68 (0.27) 0.39 (0.22) 0.42 (0.29) ( T r e a t m e n t S C L = S a n d y - c l a y l o a m s o i l , S C L + L A = s a n d y - c l a y l o a m s o i l + L a r g e A g g r e g a t e , S C L + S A = s a n d y - c l a y l o a m s o i l + s m a l l a g g r e g a t e s ) Th e r e su l t s sho w ed th a t t h e r e w a s a s i gn i f i c an t d ec r ea se i n t h e r oo t l eng th i n t h e 5 0 – 7 5 c m z o n e w i th an i n c r ea se i n t h e s i ze o f agg reg a t e s . A l a rg e p r o p o r t i o n o f t h e r o o t s me a su r e d w e r e i n f a c t l o c a t e d o n t h e s u r f a c e o f t h e p e d s . G r o w t h w a s l i mi t e d i n t h e t r e a t me n t s a n d t he on ly roo t s f ound b e y o n d t h e o u t e r 2 c m o f t h e p e d s w h e r e i n b io p o r e s o r i n s e c o n d a r y c r a c k s . B e n e a t h t h e 5 0 - 7 5 c m l a y e r , wh i ch con ta in ed t h e p ed s , t h e ro o t d ev e lop me n t w as a l so s ev e re ly d e c r ea s ed . Bo th t h e Hu t ton and C love l ly so i l f o r ms s e l e c t e d f r o m th e s t udy i n t he V a a l h a r t s i r r i g a t i o n s c h e me V a n A n t w e rp e n ( 1 9 8 8 ) ( T a b l e 3 .2 ) i s r e g a r d e d 83 84 a s a p e d a l d u e t o t h e l o w c l ay con t en t o f t h e B h o r i z o n s . Th e O a k l e a f s o i l f o r m a l s o p r e s e n t e d i n Tab l e 3 .2 was i den t i f i e d a s a n e o c u ta n i c B h o r i z o n , w i t h a c l a y c o n t e n t o f a b o u t 3 0 % . Th e o c c u r r e n c e o f b i o p o r e s a n d c r a c k s w i th in t he n eo cu ta n i c B h o r i zon p ro bab ly enh an ced t he roo t g row th t o comp arab l e l eve l s . I n t h e c a s e o f B e n n i e ( 1 9 9 6 ) ( Tab l e 3 . 2 ) , t he r e i s a s ma l l i n c r e a s e i n roo t d en s i t y f ro m t h e y e l lo w b ro wn ap ed a l B h o r i zo n o f t h e H o o p s t a d a r e a t o t h e s o f t p r i s m a t i c h o r i z o n o f t h e T w e e s p r u i t a r e a . Th i s may a l so b e a t t r i bu t ed t o t h e c r a ck s a n d b io p o re s r e su l t i n g f ro m agg r eg a t e s occu r r ing i n t h e so f t p r i sma t i c h o r i zon a s i l l u s t r a t ed i n F i g u re 3 .3 and F i g u r e 3 .4 . W a t e r cou ld h av e a l so i n f l u en ced t h e ro o t d en s i ty i n t h e so f t p r i s ma t i c h o r i zon a s i t i s p ro n e to f l u c t u a t ing wa t e r l ev e l s . F i g u r e 3 .4 Po s s ib l e b eh av i o r s o f s e mi n a l roo t s p en e t r a t i ng t wo c lo d s s e p a r a t e d w i t h a c r a c k ( W h i t e l e y & D e x t e r , 1 9 8 4 ) . D e sp i t e t h e c l ea r gu ide l i n e s fo r d esc r i b ing so i l s t r uc tu re i n t e rms o f t y pe , c l a s s a n d g r a d e , i t s e e ms t h a t t h i s c r i t e r i o n i s s e ldo m u sed t o s t udy t he e f f e c t o n r o o t d e v e l o p me n t . T h i s i s p robab ly due t o t h e c o mp l i c a t e d n a tu r e t o d es c r ib e roo t d ev e lop me n t f r o m s t ru c tu r ed s o i l s w i t h p en e t ro me t e r o n t h e o n e h an d , and t h e d i f f i cu l t y t o qu an t i fy su ch a p h e n o me n o n . H o w e v e r , f r o m t h e l i t e r a t u r e i t i s c l e a r t h a t a g g r e g a t e s i z e s p l ay a p ro mi n en t ro l e . Thu s , wh en comp ar ing l a rg e w i th sma l l agg reg a t e i t i s c l e a r t h a t l a r g e a g g r e g a t e s r e su l t i n l o w er roo t g row th , an i n c r ea se i n r o o t d i a m e t e r a n d a n o c c u r r e n c e o f g r e a t e r d e f l e c t i o n . 84 85 3 .2 .4 Bu lk d en s i ty Bu lk d en s i ty i s t h e ma s s o f d ry so i l p e r u n i t b u lk v o lu me and i s an i n d i c a t i o n o f t h e d e g r e e o f c o mp a c t i o n o f t h e s o i l . I n s o i l s w i t h a h i g h b u lk d en s i ty roo t s ma y h av e d i f f i cu l ty p en e t r a t i ng , wh i l e i n so i l s w i th a l o w b u lk d en s i ty t h e con ta c t b e t w een the roo t and th e so i l may be so lo w t h a t t r an s p o r t o f w a t e r and n u t r i e n t s may b e r e s t r i c t e d . F i g u r e 3 . 5 i l l u s t r a t e s t h a t so i l s t r eng th i n c r ea se s w i th an i n c r ea se i n bu lk den s i t y a t a c o n s t a n t w a t e r c o n te n t . P l a n t s r e s p o n d t o v a r i a t i o n i n b u l k d e n s i t y b y g row ing t h e f a s t e s t a t an i n t e rmed ia t e d en s i t y . F i g u r e 3 .5 Ch ang e in p en e t r o me t e r p re s su re w i th b u lk d en s i ty a t v a r io u s wa t e r con t en t s (H i l l e l , 2004 ) . S t i r zak e r e t a l . ( 1 9 9 6 ) e x a mi n e d t h e i n f l u e n c e o f b u l k d e n s i t y a n d b iopo re s on so i l s t r u c t u r e a n d p l a n t g r o w t h a n d fo u n d t h a t r o o t d ev e lop me n t w a s t h e g r ea t e s t a t t h e l o w e s t b u lk d en s i t i e s and d e c r e ased s h a r p l y a s t h e b u l k d e n s i t y i n c r e a s e d . Th e y a l s o fo u n d t h a t t he e f f ec t o f t h e b u l k d e n s i t y was mo re p ronounced when t h e y a l l o w e d t h e mi n i mu m s o i l w a t e r c o n t en t t o s lo w l y d e c r e a se a t o n e e n d . U n d e r w e t c o n d i t i o n s r o o t d e v e l o p me n t d e c r e a s e d w i t h a de c r e a s e i n w a t e r c o n t e n t a s t h e so i l 85 86 b e c a me d r i e r a n d h a r d e r . U n d e r d r y c o n d i t i o n s t h e r e w a s n o c l e a r t r e n d i n t h e r o o t i n g p a t t e r n . Th e y a l s o fo u n d t h a t a n i n c r e a s e i n b u l k d e n s i t y a l t e r e d t h e v o l u me t r ic w a t e r c o n t e n t o f t h e so i l , t h e mov e me n t o f w a t e r i n r e s p o n s e t o g r a d i e n t s i n w a t e r con ten t , t he roo t - s o i l co n t a c t and t h e me c h a n i ca l i mp ed a n ce to roo t g ro w th . An in c re as e i n b u lk d en s i ty s eve re ly dec r ea se s r o o t d e v e l o p me n t . 3 .2 .5 So i l w a t e r con ten t Roo t g row th i s d i r ec t l y a f f e c t e d b y t h e so i l w a t e r con ten t a s i t a c t s a s a l ub r i can t t o r educe f r i c t i on amo ng s t so i l p a r t i c l e s . I n d r i e r so i l t h e so i l s t r e n g t h i n c r e a s e s , c a u s i n g t h e r o o t l en g th t o d e c r e a se s t o a po in t wh e re r o o t e l o n g a t i o n i s a l mo s t z e r o . F i g u re 3 .6 i l l u s t r a t e s t h e r e l a t i o n sh i p b e tw een t h e r e l a t i ve roo t l eng th fo r 7 0 d a y o l d ma i z e , c o t t o n , w h e a t a n d g r o u n d n u t s a n d p e n e t r o me t e r r e s i s t a nc e . T h e h i g h c o e f f i c i e n t o f d e t e r mi n a t i o n ( R 2 = 0 .8 0 ) sho we d th a t t h e p en e t ro me t e r r e f l ec t s a c c u r a t e l y o n t h e me c h a n i ca l i mp e d a n c e e x p e r i enc ed b y th e c rop s fo r t he s o i l u s e d . T h e s l o p e o f t h e c u r v e i n d i c a t e d a sh a r p d e c l i n e i n roo t g ro w th w i th an i n c r ea se i n t h e p en e t r o me t e r r e s i s t a n c e f r o m 0 M P a t o 2 M P a . A t 2 M P a t h e r o o t l e n g t h w a s a f f e c t e d b y a b o u t 6 5 % ( F ig u re 3 .6 ) . Tay lo r e t a l . ( 1 9 9 6 ) a l s o fo u n d a n a l mos t l i n e a r d e c r e a s e i n r o o t p en e t r a t i o n ( % ) o f c o t t o n w i t h an i n c r e a s e i n p e n e t r o me t e r r e s i s t a n c e f r o m 0 M P a t o 2 M P a ( F i g u r e 3 . 7 ) . I t s e e ms t h a t r o o t p e n e t r a t i o n i s p o o r b e y o n d t h e 2 M p a t h r e s h o l d v a l u e . F i g u r e 3 .8 i l l u s t r a t e s t h a t t h e re i s a d e f i n i t e i n c r e a se i n s o i l s t r e n g t h w i t h a d e c r e a se i n w a t e r co n t en t , wh ich w i l l h av e a n eg a t iv e a f f e c t o n roo t d ev e lop me n t . Th e a mo u n t o f wa t e r av a i l ab l e t o t h e p l an t s d ep en d s w id e ly o n th e t ex t u r e , o rg an i c ma t t e r , so i l t e mp e r a t u r e , so i l s t r en g th ; a n d so i l a e r a t i on . Thu s t he r a t e o f mov e me n t o f w a t e r f r o m t h e s o i l t o t h e p l a n t s d e p e n d s o n t h e h y d r a u l i c c o n d u c t i v i t y o f t h e s o i l a n d t h e w a t e r p o t e n t i a l g r ad i en t . 86 87 F i g u r e 3 .6 R e la t i o n sh ip b e tw e en the r e l a t i v e roo t l en g th o f 7 0 -d ay -o ld ma i z e , c o t t o n , w h e a t , a n d g r o u n d n u t p la n t s a n d p e n e t r o me t e r r e s i s t a n c e ( B e n n i e , 1 9 9 5 ) . F i g u r e 3 .7 R e la t i o n b e t w een co t to n roo t p en e t r a t i on and p en e t ro me t e r r e s i s t an ce ( Tay lo r e t a l . , 1 9 9 6 ) . 87 88 F i g u r e 3 . 8 C h a n g e i n p e n e t r o me t e r p re s su re w i t h w a t e r c o n t en t a t d i f f e r e n t b u l k d e n s i t i e s (Benn i e , 1995 ) . T o c h a r a c t e r i z e t h e e f f e c t o f i r r i g a t io n a p p l i c a t i o n a mo un t s o n t h e r o o t d ev e lop me n t o f ma i z e , o p t imu m w a t er and n i t ro g en t r e a t me n t s f r o m t h e s ame f i e l d expe r i men t we re s e l ec t ed and d ep ic t ed i n F i g u r e 3 . 9 . A c c o r d i n g l y t h e t o t a l r oo t l e n g t h i n c r e a s e d exponen t i a l l y f r om 300 mm i r r i ga t i on t o abou t 450 mm, w h e r e i t p e a k e d a t a t o t a l r oo t l e n g t h o f 1 2 . 4 k m m - 2 . F u r t h e r i n c r e a s e i n i r r i g a t i o n l o w e r ed t h e t o t a l r oo t l en g t h g radu a l ly t o ab o u t 8 .5 k m m - 2 . 14 W4N4 12 W3N3 10 8 W2N2 W5N5 6 W1N2 4 2 y = -2E-06x 3 + 0.0019x2 - 0.6555x + 78.999 R2 = 0.9997 0 0 100 200 300 400 500 600 Water content (mm) F i g u r e 3 .9 R e la t i o n sh ip b e tw e en to t a l r oo t l en g th and v a r io u s w a t e r a p p l i c a t i o n s a t o p t i mu m n i t r o g e n l ev e l s (D a t a p roc e s s ed f r o m V a n R e n s b u r g , 1 9 9 6 ) . 88 Total root length (km.m -2) 89 3 .3Methodology T h e ex p e r i me n t a l s i t e and f i e l d t r i a l , a s d e s c r ib ed in Cha p t e r 1 , w a s u s ed f o r t h i s s t u d y 3 .3 .1 T r ea t me n t s F r o m t h e 7 5 p lo t s d i sp l ay ed i n F ig u re 2 .2 1 , o n l y 1 3 p l o t s w er e s e l e c t ed t o s t udy t he e f f ec t o f phys i ca l p ro p e r t i e s o n roo t d ev e lop me n t w i t h in t h e I R W H sy s t e m ( F i g u r e 2 .1 5 ) . Th e se p l o t s w e r e c h o s e n on t h e r e l a t i ve p e r f o r ma n c e o f a b o v e g r o u n d b i o ma s s a t t u s s l i n g a n d n o t a t f i n a l h a r v e s t w h e r e s e v e r e f r o s t a f f e c t e d t h e y i e ld . A t t u s s l i n g b o t h t h e l e a v e s a n d r o o t s h a s r e a c h e d t h e i r ma x imu m g r o w t h a n d h e n c e a b o v e g r o u n d b i o ma s s s h o u l d b e a g o o d i n d i c a t o r t o s e l e c t t h e p l o t s . B i o ma s s w e i g h t o f t h e i n d i v i d u a l p l o t s w as ex p re s s ed r e l a t i v e t o t h e h ig h e s t v a lu e o b t a in ed . F r o m t h es e r e l a t i v e y i e ld s , 1 3 p lo t s w e r e r ando mly s e l e c t ed ov e r t h e g rad i en t , r ep r e sen t i n g p lo t s f r o m v e ry h ig h to t h e l o w es t y i e ld o b t a in ed . 3 .3 .2 P l an t Sa mp l in g 3 . 3 . 2 . 1 A b o v e g r o u n d d r y w e i g h t P l a n t s w e r e h a r v e s t e d f r o m a n a r e a o f 2 0 m 2 , by cu t t i ng i t a s c lo s e t o t he g round a s pos s ib l e . P l an t s we re d r i ed a t 6 5 ° C u n t i l i t r e ached cons t an t w e i g h t t h e n w e i g h e d . Th e b i o ma s s w a s e x p r e s s e d i n k g .h a - 1 . 3 .3 .2 .2 Roo t s a mp l i n g S o i l r o o t s a mp l e s w e r e t ak en i n t r i p l i c a t e i n t h e b a s i n a r e a a s w e l l a s o n t h e r u n o f f a r e a a t d e p t h i n t e rv a l s o f 0 - 300 mm, 3 00 - 600 mm and 600 - 9 0 0 m m, u s i n g a 1ℓ co r e s amp l e r . Th e r o o t s o f e a ch sa mp l e w er e w a sh ed o v e r a 0 .5 mm me s h and the roo t l en g th wa s me a s u r ed u s ing an i n f r a r ed l i n e i n t e r s e c t i o n c o u n t e r ( R o w s e & Ph i l l i p s , 1974 ) . Ca l i b r a t i on o f t he i n f r a r e d l i n e i n t e r s ec t i on coun t e r was done u s in g 1 m t o 5 m c o t t o n t h r e a d l en g th s and ro o t d e n s i ty w as e x p r e s se d a s k m k m- 2 . 89 90 3 .3 .3 So i l c l a s s i f i ca t i o n F r o m t h e 1 3 p ro f i l e t h a t w a s mo rp h o lo g i c a l ly d es c r i b ed , 5 p lo t s w ere c l a s s i f i ed a s Tuku lu and Sepane r e sp e c t iv e ly , wh i l e 3 p lo t s we r e i d e n t i f i e d a s B l o e md a l . T u k u l u p r o f i l e s w e r e f o u n d t o b e i n t h e t o p a n d mi d d le p a r t o f t h e l a n d , wh i l e t h e Se p a n e so i l f o r m o c cu r r ed in t he b o t to m o f t he l and . B loemd a l so i l s occu r r ed i n t he mi d d l e o f t h e l a n d ( F i g u r e 2 .2 1 ) . 3 .3 .3 So i l p h y s i c a l me a s u r e m e n t s F o r t h e v a r i o u s p h y s i c a l a n a l y s i s s a mp l e s w e r e t a k e n f r o m e a c h d i agnos t i c h o r i z o n o f t h e 1 3 se l e c t ed p lo t s . 3 .3 .3 .1 Bu lk d en s i ty Sa mp le s w e re t aken i n t r i p l i c a t e f o r e ach d i agno s t i c ho r i zon u s ing a 1 l c o r e s a m p l e r a s i n d i c a t e d i n F igu re s 3 . 10 a & b . A f t e r s a mp l i n g t h e so i l w a s o v e n d r i e d a t 1 0 4 ° C f o r 2 4 h o u r s ( N o n - A f f i l i a t ed So i l An a ly s i s W o r k C o m m i t t e e , 1 9 9 0 ) , w e i g h ed ; a n d e x p r e s s e d i n k g .m - 3 . F i g u r e 3 . 1 0 I l l u s t r a t i n g t h e s a mp l i n g o f t he s o i l f o r b u lk dens i t y d e t e r mi n a t i o n ( a ) T h e co r e i s i n se r t ed i n to t he so i l w i th a s l i d ing h a mmer a n d ( b ) r e c o v e r e d w i t h o u t d i s t u rb ing t he so i l i n s i d e t h e cy l i nde r . 3 .3 .3 .2 Mo d u lus o f r u p tu r e T h e s o i l s a mp l e s w e r e f i r s t d r i ed i n t he oven a t 105 ˚C fo r tw en ty fou r h o u r s , b e f o r e t r a n s f e r r ed t o s ma l l r e c t a n g u l a r me t a l f r a me s . T h e so i l b r i qu e t t e s w er e p r ep a r ed and t h e fo rc e r e q u i r e d t o r u p tu r e t h e b r i qu e t t e s w a s me a s u r e d a s d e s c r i b e d b y t he Non -A f f i l i a t ed So i l Ana ly s i s Wo rk C o m mi t t e e ( 1 9 9 0 ) a n d ex p r e s s e d i n b a r . 90 91 3 .3 .3 .3 Agg reg a t e s t ab i l i t y So i l s amp le s w ere ca r e fu l l y t r an s fe r r ed t o a d ry in g r o o m ( 3 0 - 3 5 ° C) . Af t e r d ry ing fo r a week t h e s a mp l e s w e r e p r e p a red fo r t h e we t s i ev ing p r o c e d u r e d e s c r i b e d b y ( Ke mp e r & R o s e n a u , 1 9 8 6 ) . A s e r i e s o f f i v e s i e v e s w i th mesh s i ze s o f 4 mm, 2 mm, 1 mm, 0 .5 mm a n d 0 .2 5 mm w a s u s ed an d t h e s i mu la to r s i mu l a t ed fo r 1 0 mi n p e r s a mp le f r e q u en cy o f 36 cy c l e s mi n - 1 . Th e w a te r s t ab l e agg reg a t e s w e r e expr e s s ed in p e r c en t ag e o f t h e t o t a l w e igh t o f t h e o r i g in a l d r i e d sa mp le . 3 .3 .3 .4 Pa r t i c l e ana ly s i s S e v e n p a r t i c l e s i z e f r a c t i o n s w e r e d e t e r mi n e d w i t h t h e p i p e t t e me t h o d a s d e sc r i b e d b y t h e N o n - A f f i l i a t e d So i l A n a l y s i s W o r k C o m mi t t e e ( 1 9 9 0 ) . T h e t e x t u r a l f r a c t i o n s w ere c o a r s e s a n d (2 mm – 0 .5 mm) , me d iu m s a n d ( 0 .5 mm – 0 .2 5 mm) , f i n e s a n d (0 .25 mm – 0 .1 0 6 mm) , v e ry f i n e s an d ( 0 . 1 0 6 mm – 0 . 0 5 m m) , c o a r s e s i l t ( 0 .05 mm – 0 .0 2 mm) , f i n e s i l t ( 0 .0 2 mm – 0 .0 0 2 mm) a n d c l ay ( l e s s t h a n 0 . 0 0 2 m m ) . 3 .3 .4 S t a t i s t i c a l ana ly s i s Va r i a t i on i n so i l phys i ca l p rope r t i e s o f t h e d i a g n o s t i c h o r i zo n s w as d e s c r i b e d t h r o u g h c a l c u l a t i n g t h e me a n , mi n i mu m , ma x i mu m a n d coe f f i c i en t o f va r i a t i o n o f t h e o b s e r v e d v a l u e s . A c o r r e l a t i o n ma t r i x t oge th e r w i th a mu l t i p l e r eg re s s io n a n a ly s i s w a s d r a wn fo r t h e d a t a u s in g NCSS 2000 (H in t ze , 2000 ) . 91 92 3 .4 R e s u l t s a n d D i s c u s s i o n 3 . 4 . 1 I n t e r a c t i o n o f s o i l p h y s i c a l p r o p e r t i e s T h e f i e l d w a s c u l t i v a t e d f o r m o r e t h a n f o u r d e c a d e s w i t h c o n v e n t i o n a l t i l l a g e m e t h o d s . T h e s e m e t h o d s i n c l u d e p l o u g h i n g , d i s k i n g , h a r r o w i n g a n d w e e d i n g w i t h t i l l e r s w h i c h p u l v e r i z e t h e s o i l a n d d o i n g s o m o d e r a t e s t h e b i o l o g i c a l , c h e m i c a l a n d p h y s i c a l p r o p e r t i e s o f t h e s o i l ( H i l l e l , 2 0 0 4 ; B e a r e e t a l . , 1 9 9 4 a n d B r o n i c k & L a l , 2 0 0 4 ) . T h i s s e c t i o n a t t e m p t s t o t a k e s t o c k t h e p h y s i c a l p r o p e r t i e s o f t h e s o i l a n d i n t e r a c t i o n b e t w e e n p h y s i c a l p r o p e r t i e s s u c h a s t h e t h i c k n e s s , s i l t + c l a y ( S i + C l ) c o n t e n t , o r g a n i c c a r b o n ( O C ) , m o d u l u s o f r u p t u r e ( M O R ) , a g g r e g a t e s t a b i l i t y ( A S ) ( 4 , 2 , 1 , 0 . 5 a n d 0 . 2 5 m m ) a n d b u l k d e n s i t y ( D b ) o f t h e d i a g n o s t i c h o r i z o n o f t h e 1 3 p l o t s . V a r i a t i o n i n s o i l p h y s i c a l p r o p e r t i e s w a s e x p r e s s e d i n t e r m s o f t h e h o r i z o n t h i c k n e s s ( d e p t h , m m ) , S i + C l ( % ) , O C ( % ) , M O R ( b a r ) , A S ( 5 f r a c t i o n s , % ) a n d D b ( k g m - 3 ) . S t a t i s t i c a l p a r a m e t e r s t h a t w e r e u s e d t o d e s c r i b e v a r i a t i o n a r e t h e m e a n , m i n i m u m , m a x i m u m a n d t h e c o e f f i c i e n t o f v a r i a t i o n . T h e r e s u l t s o f t h e a n a l y s i s a r e s u m m a r i z e d i n T a b l e 3 . 5 f o r t h e A , B a n d C h o r i z o n o f t h e B l o e m d a l , T u k u l u a n d S e p a n e s o i l s , r e s p e c t i v e l y . R e s u l t s o n t h e i n d i v i d u a l p l o t s a r e t a b u l a t e d i n A p p e n d i x V . T h e c o r r e l a t i o n m a t r i x b e t w e e n s o i l p h y s i c a l p r o p e r t i e s f o r t h e A , B a n d C h o r i z o n o f t h e B l o e m d a l , T u k u l u a n d S e p a n e s o i l s i s p r e s e n t e d i n T a b l e 3 . 6 . 3 . 4 . 1 . 1 A h o r i z o n T h e A h o r i zo n i s s i mi l a r t o a l l t h e so i l f o r ms i d en t i f i ed i n t h e f i e l d a n d o r ig ina t e s f r o m eo l i an s an d s wh i ch h av e mi x ed n a tu ra l l y w i th t h e c l ays o r ig ina t ed f ro m t h e s ands ton e , mu ds ton e an d d o l e r i t e p a ren t ma t e r i a l o f t h e a r e a . S o i l p h y s i c a l p rope r t i e s d ev e lop ed w i th in t he con t ex t o f na tu r a l p e d o g e n i c p r o c e s s e s a n d m od i f i ed by an th r o p o g e n i c a c t i v i t i e s . C o mp a r i n g t h e me a n s o f t h e d i f f e r e n t so i l r e v e a l e d t ha t t he ho r i zon d ep th , s i l t + c l ay c o n t e n t ( S i + C l ) , o r g a n ic c a rbon con t en t (OC) , mo d u lu s o f rup tu re ( MOR) , p e r c en t age w a te r s t ab l e agg r eg a t e s (A S) o f t h e l a rg e r f r a c t i o n s ( 4 a n d 2 92 93 m m ) i n c r e a s e f r o m t h e B l o e md a l v i a t he Tuku lu t o t h e Sepane . Seve ra l s t u d i e s h a v e s h o w n a p o s i t i v e r e l a t i o n sh i p b e t ween c l ay con ten t and o rgan i c ca rbon con t en t (Soane , 1990 ; D ine l e t a l . , 1 9 9 7 ; D i mo y i a n n i s e t a l . , 1 9 9 8 ; S c h u l t e r a n d L e i nw e b e r , 2 0 0 0 ; C h e r n i e e t a l . , 2 0 0 0 ) , w h i c h e mp h a s i ze wh i ch ind i c a t ed t ha t S+C and OC i s t h e p r ima r y me c h an i s m o f a g g r eg a t ion o f so i l p a r t i c l e s i n i t s na t i ve s t a t e s . T h e r e su l t s s h o w c o n s i d e rab l e va r i a t i on i n t h e so i l p h y s i c a l p a r a me t e r s su ch a s A S and O C , i r r e sp ec t ive t h e so i l fo rm . V a r i a t i on (CV ) i n t he mo d u lu s o f rup tu re w a s g re a t e r i n t he Sep an e and Tuku lu t han i n t he B lo e md a l . Th e r e s t o f t h e p a r a me t e r s d id n o t v a r y mu c h w i t h in so i l f o rms . I n o r d e r t o s t u d y t h e i n t e r ac t i on o f t h e so i l p h y s i c a l p r o p e r t i e s a c o r r e l a t i o n ma t r i x a n a ly s i s w a s ma d e a n d t h e r e s u l t s a r e su m m a r i z e d i n T a b l e 3 . 7 . T h e s e r e s u l t s c l e a r l y s h o w th a t so i l d ep th , O C , M OR a n d Db h av e a mod er a t e ly s t ro n g po s i t i ve co r r e l a t i on w i th an i nc r ea se i n s i l t + c l a y o f t h e A h o r i z o n . Th i s w a s e x p e c t e d b e c a u s e t h e se so i l s con t a in s h igh ac t i v i t y c l ay s su ch a s mo n tmo r r i l on i t e a n d i l l i t e w i t h g r e a t su r f a c e a r e a , C EC , ch a r ge d en s i ty , d i spe r s iv i t y an d exp en d ab i l i t y t h a t c an s t i mu l a t e i n t e r a c t i o n b e t w een so i l p h y s i c a l p ro p e r t i e s . S i l t + c l ay co n t en t , O C and D b sh o w a s t ro n g p o s i t i v e co r r e l a t i o n w i t h so i l s t r eng th a s i nd i ca t ed by t h e MOR co r r e l a t i on s t a t i s t i c s . The p r e sen ce o f w a t e r c an mo d i fy so i l s t r eng th d i r ec t l y a s d e mon s t r a t ed by B enn i e ( 1 9 9 6 ) . H e s h o w e d t h a t s o i l s t r e n g t h l o w e r s e x p o n e n t i a l l y w i t h a n i n c r ea s e i n so i l w a t e r con t e n t . Thu s , r a in ac tua l l y h e lp s t o r edu ce t he ene rgy r equ i r ed fo r mo u l d b o a r d p l o u g h i n g a n d o t h e r t i l l a g e o p e r a t i o n s . I t i s o f t e n a r g u e d t h a t t h e mo u l d b o a r d p l o u g h i s a n e x c e l l e n t i mp l e me n t t o c r ea t e “ t emp o r a l ” s t ru c tu re i n so i l s w i th a mass i v e s t ru c tu r e ( Fe r t i l i z e r , 2 0 0 7 ) a s i n t h e c a s e o f t h e B d , T u and Se so i l s . L o n g t e r m e f f e c t s o f c o n v e n t i o n a l t i l l a g e o n t h e s o i l p h y s i c a l p r o p e r t i e s o f t h e s e c l a y s o i l s i n s e mi - a r i d a r e a s a r e u n k n o w n . Wa te r s t ab l e agg rega t e t e s t s a r e o f t en u s ed a s an i nd i c a to r t o d e mon s t r a t e t h e e f f e c t o f t i l l ag e o n 93 94 s o i l s t ru c t u r e ( S i x e t a l . , 2 0 0 0 ) . T h e c o r r e l a t i o n ma t r i x r e s u l t s o n t h e w a t e r s t ab l e agg r eg a t e s show a s t r o n g n e g a t i v e r e l a t i o n s h i p b e t w e e n A S 0 .2 5 an d e sp e c i a l l y S+ C ( - 0 .4 5 ) and to a l e s s e r ex t en t OC ( -0 .2 3 ) . The r e su l t s su g g e s t t h a t t h e r e i s a g r e a t e r t en d ency fo r t h e s o i l s t o d i spe r se w i th an i n c rea se i n S i + C l and O C , p ro b ab ly d u e t o t he p r e s en ce o f N a in t h e s o i l s . A c co rd i n g t o S i n g e r e t a l . ( 1 9 9 2 ) a s c l a y p a r t i c l e s s w e l l w i t h t h e i n t ak e o f w a t e r , t h ey sep a r a t e f ro m o th e r p a r t i c l e s a n d h en ce l o we r in g a g g r e g a t e s t a b i l i t y . U n d e r t h e se c o n d i t i o n s ma c r o – agg reg a t e (> 0 .2 5 mm) d i s i n t eg ra t e i n t o s ma l l e r o r mi c ro – a g g r e g a t e s ( < 0 . 2 5 m m) o r c a n d i sp e r se c o mp l e t e ly . So me o f t h e agg reg a t e s mi g h t d i sp e r s e , and r e a r r an g e t o b e f l o c c u l a t e d a n d c eme n t e d a g a i n . C a r b o n a t ed C , w h i c h e x i s t s a s p r i ma ry a n d se co n d a ry mi n e r a l s i n s emi – a r i d so i l s , i s an ex ce l l en t f l o c cu l en t a n d the r e fo re agg reg a to r i f p r e se n t i n s o l u t i o n , e sp e c i a l l y a t l o w so i l o rg an i c ma t t e r c o ncen t r a t i on s (Bo ix – Fay o s e t a l . , 2 0 0 1 ) . Howeve r , t he 10% HCl so lu t i o n t e s t c o n f i r me d t h a t c a rbona t e s a r e ab sen t i n b o th t h e t op so i l - and sub so i l , wh ich ex c lu d e ino rg an i c C t o b e an agg r eg a to r i n t h e se so i l s . Agg reg a t i on can a l so b e med i a t ed by t h e Fe and A l ox id e s and se squ ioxc id es a s i n t h e ca se o f ox i so l s (O ad es and Wate r s , 1 9 9 1 ; D a l a l a n d B r i d g e , 1 9 9 6 ) . U n f o r tu n a t e l y t h e c o n t r ib u t i o n o f t h e s e mi n e r a l s c a n n o t b e t e s t e d a s t h i s w a s n o t p a r t o f t h e s t u d y , b u t fu t u r e a n a l y s i s o f t h e w a t e r s t a b l e a g g r e g a t e s s h o u l d g i v e a b e t t e r e x p l a n a t i o n o f t he s t ab i l i t y o f t h e agg r eg a t e s . 3 .4 .1 .2 B h o r i zo n T h e B h o r i z o n i s o n e o f t h e ma i n f a c t o r s t h a t d i s t i ngu i sh t h e t h r ee so i l f o rms , v i z . a r e d a p e d a l ( B l o e md a l ) , n e o cu t a n i c ( Tu k u l u ) , p e d o c u t a n i c ( S e p a n e ) f r o m e a c h o t h e r . The s t r uc tu r a l change f ro m t h e B d v i a t h e T u t o t h e S e i s s u p p o r t e d b y a n i n c r e a s e i n t h e me a n S +C c o n t e n t , O C , M O R a n d Db ov e r t h e so i l s . Th e re i s a c l e a r d i f f e r e n c e i n B h o r i z o n d e p th s be tween t he t h r e e s o i l f o rms w i t h t h e T u h a v i n g t h e d e e p e s t a n d l e s s v a r i a b l e h o r i z o n ( C V = 2 7 % ) . T h e S + C o f t h e T u s o i l f o r m v a r i e d b e t w e e n 3 1 % a n d 3 4 % ( C V = 4 % ) a n d t h a t o f t h e S e s o i l f o r m v a r i e d b e t w e e n 4 9 % a n d 5 5 % ( C V = 4 % ) , w h i l e t h e B l o e m d a l v a r i e d b e t w e e n 2 8 % 94 95 a n d 3 4 % ( C V = 8 % ) . T h e s t a t i s t i c a l r e s u l t s s h o w h i g h v a r i a b i l i t y i n a l l a g g r e g a t e s i z e s w i t h i n s o i l f o r m s . T h e c o r r e l a t i o n s t a t i s t i c a l r e s u l t s s h o w t h a t t e x t u r e p l a y s a d o m i n a n t r o l e i n t h e p h y s i c a l p r o p e r t i e s o f t h e B h o r i z o n s . S i + C l c o r r e l a t e s s t r o n g l y i n a p o s i t i v e m a n n e r w i t h O C , M O R , A S ( 0 . 5 m m ) a n d D b . T h e s t r o n g r e l a t i o n s h i p c a n b e e x p l a i n e d b y t h e p h y s i c a l a n d c h e m i c a l n a t u r e o f t h e t y p e o f c l a y m i n e r a l s a s d e s c r i b e d i n t h e A h o r i z o n . S i + C l a l s o s h o w e d a s t r o n g n e g a t i v e r e l a t i o n s h i p w i t h t h e l a r g e r a g g r e g a t e s i z e s , w h i c h s u g g e s t t h a t t h e c l a y - b o n d s b e t w e e n m a c r o - a g g r e g a t e s a r e n o t s t r o n g a n d a r e e a s i l y b r o k e n i n t h e p r e s e n c e o f r a i n w a t e r . T h e s e s o i l s a r e k n o w n f o r i t s d i s p e r s i v i t y p r o p e r t i e s d u e t o t h e p r e s e n c e o f s o d i u m . M O R o f t h e B h o r i z o n s i s p o s i t i v e l y l i n k e d t o S i + C l , O C a n d D b a n d s h o w s n o s t r o n g a s s o c i a t i o n w i t h a g g r e g a t e s i z e f r a c t i o n s . V e r y i n t e r e s t i n g t o n o t e i s t h e s t r o n g p o s i t i v e r e l a t i o n s h i p b e t w e e n t h e A S 0 . 5 m m , O C a n d D b . A l l t h e o t h e r A S f r a c t i o n s s h o w a m o d e r a t e t o s t r o n g n e g a t i v e c o r r e l a t i o n w i t h S i + C l , a g a i n e x p o s e t h e d i s p e r s i v i t y o f t h e s e s o i l s . B e c a u s e s o i l e r o d i b i l i t y i s l i n k e d t o s o i l a g g r e g a t e s t a b i l i t y ( L e B i s s o n n a i s , 1 9 9 6 ; Z o t a r e l l i e t a l . , 2 0 0 5 ) , t h e l o w p e r c e n t a g e o f a g g r e g a t e s i n t h e l a r g e r f r a c t i o n s ( 4 a n d 2 m m ) o f t h e S e p a n e a n d T u k u l u s o i l c o n f i r m s t h e s u s c e p t i b i l i t y o f t h e s e s o i l s t o w a t e r e r o s i o n . T h e a g g r e g a t e s i z e d i s t r i b u t i o n i s d o m i n a t e d b y t h e s m a l l e r s i z e s ( 0 . 5 – 0 . 2 5 m m ) i n a l l s o i l s . B o t h t h e s e s o i l s h a v e l a r g e r s t r u c t u r a l u n i t s ( m e d i u m d e v e l o p e d s u b a n g u l a r b l o c k y a n d s t r o n g d e v e l o p e d a n g u l a r b l o c k y , r e s p e c t i v e l y ) i n i t s n a t i v e s t a t e . O n c e t h e B h o r i z o n o f t h e s e s o i l s a r e e x p o s e d t o t h e i m p a c t o f r a i n t h e p e d s w i l l e a s i l y b r e a k d o w n w h i c h l e a d s t o d e t a c h m e n t o f p a r t i c l e s a n d s m a l l a g g r e g a t e s t h a t f a v o u r s c r u s t i n g t h e n r u n o f f a n d t r a n s p o r t ( M i l l e r a n d B a h a r u d d i n , 1 9 8 6 ; S u m m e r , 1 9 9 2 ; B a r t h e s e t a l . , 1 9 9 9 ) . Unde r 95 96 r a i n f e d c o n d i t i o n s , w e t – d r y c y c l e s a r e mo s t c o m mo n w h i c h c a n b e d i s rup t agg reg a t ion i n sw e l l i ng c l ay s ( P i c co lo r e t a l . , 1 9 9 7 ) . 3 . 4 . 1 . 3 C h o r i z o n A l l t h e s o i l s h a v e a p r i s m a t i c s t r u c t u r e i n t h e C h o r i z o n a n d t h e r e f o r e c o n f i r m s t h e l o w C V i n a l m o s t a l l t h e s o i l p h y s i c a l p a r a m e t e r s , e x c e p t s o m e o f t h e A S f r a c t i o n s . T h e S e h a s t h e t h i c k e s t h o r i z o n ( m e a n = 3 9 0 m m ) , t h e l o w e s t s i l t + c l a y c o n t e n t ( 3 5 % ) a n d t h e h i g h e s t D b ( 1 7 3 0 k g m - 3 ) o f a l l t h e s o i l s . T h e C h o r i z o n o f t h e B d s e e m s t o b e t h e t h i n n e s t ( 1 5 0 m m ) w i t h t h e h i g h e s t O C c o n t e n t ( 0 . 3 4 % ) a n d M O R ( 0 . 5 7 b a r ) . T h e v a r i a t i o n w a s g e n e r a l l y l o w i n a l l t h e s o i l p h y s i c a l p r o p e r t i e s , e x c e p t f o r t h e A S f r a c t i o n s . D e s p i t e t h e l a r g e s t r u c t u r a l u n i t s p r e s e n t i n t h e n a t i v e s t a t e s o f t h e s o i l s , t h e r e i s a c l e a r a b s e n c e o f w a t e r s t a b l e a g g r e g a t e s f r a c t i o n s i n t h e 4 a n d 2 m m c l a s s e s . T h u s , o n c e a g a i n t h e r e s u l t s g i v e p r o o f t o t h e d i s p e r s i v e p o t e n t i a l o f t h e s e s o i l s a n d e m p h a s i z e t h e v u l n e r a b i l i t y o f i t t o w a t e r e r o s i o n . I n t e r e s t i n g t o n o t e t h a t a l l t h e A S f r a c t i o n s e x c e p t 0 . 5 m m , s h o w a m o d e r a t e l y s t r o n g p o s i t i v e r e l a t i o n s h i p w i t h s i l t + c l a y . T h e s i l t + c l a y c o n t e n t h a d n o r e l a t i o n s h i p w i t h t h e O C c o n t e n t a s i t i s v e r y l o w i n t h e s e s o i l s . T h e M O R s h o w s n o p a r t i c u l a r a s s o c i a t i o n w i t h t h e o t h e r s o i l p h y s i c a l p a r a m e t e r s m e a s u r e d . T h e r e w a s a n i n d i c a t i o n t h a t b u l k d e n s i t y i s i n f l u e n c e d b y t h e p r e s e n c e o r a b s e n c e o f s i l t + c l a y , O C , M O R a n d m o s t l y t h e l a r g e r a g g r e g a t e s i z e f r a c t i o n s . 96 97 T a b l e 3 . 5 V a r i a t i o n i n s o i l p h y s i c a l p r o p e r t i e s f o r t h e B l o e m d a l , T u k u l u a n d S e p a n e s o i l f o r m s Organic carbon Modulus Horizon content of Bulk Statistical depth Silt + (%) rupture AS AS AS AS AS density Horizon Soil form Parameter (mm) clay (%) (bar) 4 (%) 2 (%) 1 (%) 0.5 (%) 0.25 (%) (kg m-3) Mean 150 20 0.13 0.09 1.28 9.06 24.01 10.19 12.86 1290 Min 250 25 0.35 0.12 3.23 30.73 32.43 18.33 20.39 1360 Max 213 21 0.24 0.1 2.13 15.67 28.92 15.41 17.75 1328 Bd CV 0.22 0.11 0.42 0.13 0.4 0.65 0.12 0.24 0.19 0.02 Mean 207 22 0.18 0.15 6.18 12.81 35.14 14.98 16.81 1471 A Min 200 19 0.26 0.06 4.44 4.85 20.34 2.7 6.07 1376 Max 210 26 0.2 0.25 7.4 25.12 45.32 20.86 30.02 1520 Tu CV 0.02 0.13 0.19 0.55 0.2 0.67 0.3 0.54 0.66 0.04 Mean 218 25 0.14 0.23 16.3 14.87 14.71 14.04 7.23 1468 Min 210 22 0.19 0.1 3.93 8.3 2.43 1.76 2.6 1399 Max 250 27 0.16 0.37 33.33 22.62 22.1 27 15.44 1532 Se CV 0.08 0.08 0.15 0.48 0.81 0.37 0.55 0.76 0.75 0.04 Mean 260 31 0.19 0.17 3.33 13.47 26.06 19.47 23.63 1440 Min 200 28 0.29 0.15 2.38 12.56 11.77 13.9 6.62 1365 Max 350 34 0.23 0.2 4.22 14.43 33.23 33.76 30.23 1501 Bd CV 0.25 0.08 0.19 0.12 0.23 0.06 0.36 0.47 0.46 0.04 Mean 425 32 0.16 0.64 4.44 10.53 13.14 14.89 15.72 1665 B Min 250 31 0.22 0.44 1.19 2.83 2.02 4.13 5.45 1605 Max 500 34 0.2 0.76 8.07 20 21.38 35.88 36.13 1729 Tu CV 0.27 0.04 0.15 0.22 0.66 0.76 0.61 0.95 0.87 0.04 Mean 150 51 0.17 0.57 4.42 6.2 19.29 24.53 31.52 1779 Min 100 49 0.22 0.38 2.62 2.13 10.6 10.9 13.43 1670 Max 250 55 0.2 0.89 10.4 14 26.19 35.65 50.94 1810 Se CV 0.42 0.04 0.12 0.39 0.77 0.84 0.34 0.42 0.46 0.03 97 98 T a b l e 3 . 5 ( c o n t i n u e ) Organic Modulus Horizon carbon of Bulk Statistical depth Silt + content rupture AS AS AS AS AS density Horizon Soil form Parameter (mm) clay (%) (%) (bar) 4 (%) 2 (%) 1 (%) 0.5 (%) 0.25 (%) (kg m-3) Mean 150 44 0.09 0.57 2.03 4.07 17.45 28.09 30.48 1606 Min 50 42 0.17 0.45 1.04 1.45 14.35 11.67 21.11 1580 Max 250 49 0.13 0.64 2.67 8.32 20.33 34.65 36.54 1643 Bd CV 0.54 0.07 0.25 0.14 0.34 0.71 0.14 0.37 0.22 0.02 Mean 275 47 0.11 0.37 8.19 14.84 17.77 16.36 16.16 1586 C Min 210 43 0.16 0.27 6.2 5.49 11.13 13.25 8.72 1503 Max 310 54 0.13 0.54 10.57 24.26 27.62 18.46 22.53 1642 Tu CV 0.16 0.1 0.19 0.33 0.22 0.56 0.39 0.14 0.36 0.04 Mean 390 35 0.11 0.38 3.16 11.03 22.61 25.88 15.81 1730 Min 300 30 0.13 0.19 1.45 7.51 10.19 12.85 8.54 1656 Max 500 41 0.12 0.56 6.45 15.54 39.93 36.05 29.15 1783 Se CV 0.22 0.13 0.08 0.39 0.65 0.34 0.57 0.37 0.52 0.03 98 99 Ta b l e 3 .6 Co r re l a t i on ma t r ix fo r t h e Tu k u lu , Sep an e and B lo e md a l s o i l f roms Horizon Parameter Depth Si + Cl OC MOR AS 4 AS 2 AS 1 AS 0.5 AS 0.25 Db Depth (mm) 1 Silt +Clay (Si + Cl, %) 0.33 1 Organic carbon content (OC %) 0.18 0.42 1 Modulus of rupture (MOR, bar) 0.09 0.57 0.93 1 A Aggregate Stability 4 mm (AS 4, %) -0.07 0.05 0.03 0.13 1 Aggregate Stability 2 mm (AS 2, %) -0.11 0.02 0.08 0.11 0.18 1 Aggregate Stability 1 mm (AS 1, %) -0.06 -0.08 -0.2 -0.39 -0.45 -0.15 1 Aggregate Stability 0.5 mm (AS 0.5, %) 0.17 0.15 -0.17 -0.08 -0.34 -0.33 -0.01 1 Aggregate Stability 0.25 mm (AS 0.25, %) 0.05 -0.45 -0.23 -0.33 -0.43 -0.52 0.18 0.4 1 Bulk density(Db, kg m-3) -0.23 0.61 0.18 0.29 0.31 -0.07 0.05 -0.11 -0.46 1 Depth (mm) 1 Silt +Clay (Si + Cl, %) 0.16 1 Organic carbon content (OC %) 0.08 0.23 1 Modulus of rupture (MOR, bar) 0.4 0.62 0.34 1 B Aggregate Stability 4 mm (AS 4, %) -0.43 -0.21 0.03 0.12 1 Aggregate Stability 2 mm (AS 2, %) 0.1 -0.2 -0.23 -0.15 0.2 1 Aggregate Stability 1 mm (AS 1, %) -0.07 -0.68 0.19 -0.29 -0.1 -0.1 1 Aggregate Stability 0.5 mm (AS 0.5, %) 0.4 0.64 0.16 0.13 -0.47 0 -0.67 1 Aggregate Stability 0.25 mm (AS 0.25, %) -0.37 -0.03 -0.19 -0.18 -0.17 -0.36 0.15 -0.2 1 Bulk density(Db, kg m-3) 0.43 0.5 0.38 0.49 0.03 -0.15 -0.19 0.38 -0.45 1 Depth (mm) 1 Silt +Clay (Si + Cl, %) -0.09 1 Organic carbon content (OC %) 0.13 -0.08 1 Modulus of rupture (MOR, bar) 0.11 0.1 0.19 1 C Aggregate Stability 4 mm (AS 4, %) 0.38 0.47 -0.18 -0.05 1 Aggregate Stability 2 mm (AS 2, %) 0.47 0.32 -0.34 0.07 0.72 1 Aggregate Stability 1 mm (AS 1, %) -0.13 0.33 -0.25 -0.24 0.47 0.24 1 Aggregate Stability 0.5 mm (AS 0.5, %) -0.14 -0.18 0.24 -0.45 -0.33 -0.67 0.2 1 Aggregate Stability 0.25 mm (AS 0.25, %) -0.4 0.18 0.36 -0.01 -0.16 -0.43 0.11 0.52 1 Bulk density(Db, kg m-3) -0.23 0.44 0.2 0.18 0.25 0.11 -0.01 -0.28 0.16 1 99 100 3 . 4 . 2 R e l a t i o n s h i p b e t w e e n r o o t d e v e l o p m e n t a n d s o i l p h y s i c a l p r o p e r t i e s B a sed on t h e co r r e l a t i on ma t r i x r e su l t s su mmar i zed i n T a b l e 3 . 7 , o n l y t h e s o i l p h y s i c a l p r o p e r t i e s t h a t h a v e a c o l l e c t i v e i n f l uence on roo t d ev e lop me n t exp r es s a s t he t o t a l r oo t l e n g t h (k m m - 2 ) o r r o o t l en g t h i n d e x ( R L I ) , a s i n d i c a t ed b y an a s t e r i sk , w e r e s e l e c t e d t o fo rm a so i l phy s i ca l q u a l i t y i n d ex ( S PQI ) . T h e S P Q I w a s d ev e lop ed b y a s s e s s in g th e i n f lu en ce o f a s o i l p h y s i c a l p a r a me t e r o n ro o t d ev e lop me n t fo r eac h ma s t e r h o r i zon . A r e l a t i v e p e r fo r ma n c e v a l u e a c c o r d i n g t o t he i n f l uence on roo t d ev e lop me n t ; t h a t v a r i e s b e t w een 0 an d 1 0 , w as t h en a s s ig n ed to i nd iv idua l p lo t s . Th e co l l e c t i v e p e r fo r ma n ce o f e a ch p l o t w a s o b t a i n e d b y a d d i n g t h e d i f f e r e n t p o i n t s s c o r ed fo r a l l t h e s o i l p h y s i c a l p ro p e r t i e s . T h e t o t a l s co re o f e ach p l o t r ep r e s en t s co l l ec t i v e ly t h e SPQ I . Th e SPQ I w as t hen r eg re s sed w i th t h e R LI and t h e r e su l t s a r e p re s en t ed in F ig u re 3 .1 1 f o r t h e A - h o r i z o n ( a ) , B - h o r i z o n ( b ) a n d C - h o r i z o n ( c ) . T a b l e 3 . 7 E x t r a c t i o n o f c o r r e l a t i o n m a t r i x r e s u l t s f o r r o o t l e n g t h i n d e x ( k m m - 2 ) a s i n f l u e n c e d b y t h e d i f f e r e n t s o i l p h y s i c a l p r o p e r t i e s o f t h e A , B a n d C h o r i z o n i n t h e B l o e m d a l , T u k u l u a n d S e p a n e s o i l s Horizon Parameter A B C Depth (mm) -0.2* 0.39* -0.41* Silt +Clay (Si + Cl,%) 0.13 -0.21 -0.01 Organic carbon content (OC %) -0.01 -0.2 -0.36* Modulus of rupture (MOR, bar) 0.19* -0.45* -0.42* Aggregate Stability 4 mm (AS 4) 0.14 -0.83* -0.26* Aggregate Stability 2 mm (AS 2) -0.02 -0.06 -0.42* Aggregate Stability 1 mm (AS 1) -0.53* 0.28* 0.44* Aggregate Stability 0.5 mm (AS 0.5) 0.1 0.19 0.54* Aggregate Stability 0.25 mm (AS 0.25) -0.26* 0.18 -0.09 Bulk density(Db, kg m-3) -0.17 -0.32* -0.19 100 101 (a ) y = 0.0226x - 0.3819 R2 = 0.4297 0.600 0.500 0.400 Tukulu 0.300 0.200 Bloemdal 0.100 Sepane 0.000 0 10 20 30 40 Soil physical quality index (b) y = 0.0142x - 0.2451 R2 = 0.6759 0.500 0.400 Tukulu 0.300 0.200 Bloemdal 0.100 0.000 Sepane -0.100 0 20 40 60 -0.200 Soil physical quality index (c) y = 0.0058x - 0.1867 R2 = 0.5909 0.350 0.300 0.250 Tukulu 0.200 0.150 Bloemdal 0.100 0.050 Sepane 0.000 -0.050 0 10 20 30 40 50 60 70 -0.100 Soil physical quality index F igu re 3 .11 R e l a t i on sh ip b e tw een t o t a l r o o t l e n g t h o r r o o t l e n g t h i n d e x ( R L I ) a n d t h e s o i l p h y s i c a l qu a l i t y i nd ex (SPQI ) f o r t h e A -ho r i zon ( a ) , B - h o r i z o n ( b ) a n d C - h o r i z o n ( c ) o v e r t h e 1 3 p lo t s i nv e s t i g a t ed , r eg a rd l e s s o f so i l fo r m. 101 Root density (km.m -2) -2 Root density (km m -2) Root density (km.m ) 102 3 . 4 . 3 M as t e r ho r i zon s A h o r i z o n : A s i n d i c a t e d i n T a b l e 3 . 7 ( a ) , h o r i z o n d e p t h o r t h i c k n e s s , M O R a n d th e 1 and 0 .2 5 mm w a t e r s t ab l e agg r eg a t e f r ac t i on s w ere u s ed t o c a l c u l a t e t h e S P Q I f o r t h e d i f f e r e n t p l o t s . I t s h o u ld b e e mp h a s i z e t h a t a l l t h e s e p a ra me t e r s c o r r e l a t ed n eg a t ive ly w i th r o o t d en s i ty i nd i ca t i n g th a t t h e p r e s e n c e o r i n t e n s i t y o f t h e s e so i l p r o p e r t i e s a c tu a l ly d e c r e a s e t he t o t a l r oo t l e n g th o r r o o t l en g th i nd ex . The p o s i t i v e r e l a t i on sh ip b e tw een S P Q I an d t h e R L I r e f l e c t s o n t h e w ay t h e p lo t s h av e b e en a s se s s ed in t he i r p e r f o r ma n c e . I t i s o b v i o u s t h e p l o t t h a t h a s t h e t h i c k e s t h o r i z o n , l o w e s t M O R an d th e h ig h e s t p e r c en tag e o f 1 an d 0 . 2 5 m m w a t e r s t ab l e agg r eg a t e s w i l l have t he h ighes t SPQ I va lue and t hose w i th t h e o p p o s i t e t r e n d s w i l l h av e t h e l o w e s t v a l u e . Th e r e g r e s s io n s t a t i s t i c s sho ws t h a t SPQ I r e l a t ed l i n e a r ly t o t he R LI , b u t cou ld o n ly exp la in s 3 6 % o f t h e v a r i a t i on . B h o r i z o n : Th e w a te r s t ab l e agg r eg a t e s i z e s o f 4 mm ( 3 3 % ) h ad a n eg a t iv e c o r r e l a t i on o n ro o t d ev e lop me n t a s i nd i ca t ed b y th e R LI ( Ta b l e 3 .7 ) . A ma t o a n d R i t c h i e ( 2 0 0 2 ) a l s o f o u n d t h a t t h e l a r g e s i z e a g g r e g a t e s h a d a n eg a t iv e i n f lu en c e o n ro o t d en s i ty . Th e agg re g a t e s i ze s o f 1 mm ( 4 6 %) , 0 .5 mm ( 3 9 % ) and 0 .2 5 mm ( 3 6 %) h ad p o s i t i v e co r r e l a t i on s w i th ro o t d en s i ty o n c e aga in c o mp l eme n t ing th e s t u d y d o n e b y A ma t o a n d R i t c h i e ( 2 0 0 2 ) . F r o m t h e c o r r e l a t i o n ma t r i x t he c o mb i n a t i o n o f ma i n p a r a me t e r s wh i ch co r r e l a t ed t h e b es t w i th roo t d en s i ty a n d u sed a s p a r t o f t h e SPQ I a r e mo d u l u s o f r u p t u r e , s o i l d e p t h o r h o r i zon t h i cknes s , b u l k d e n s i t y a n d t h e w a t e r s t a b l e a g g r e g a t e f r a c t i o n s o f 4 mm, 2 mm a n d 0 .2 5 mm. A s s e e n i n F ig u r e 3 . 1 1 ( b ) t h e R 2 b e t w een t h e ma i n so i l p h y s i c a l p a r ame t e r s a n d RLI i s 68%, wh ich i nd i ca t ed t h a t t he SPQ I r e l a t e s r e a son ab ly accu r a t e t o R L I . C h o r i z o n : F ro m T a b l e 3 .7 i t i s c l ea r t h a t t h e d e p t h o f t he C h o r i z o n h a d a l a rg e n eg a t iv e co r r e l a t i on w i th R LI (41 % ) . Th e mo d u lus o f rup tu r e h ad a l a rg e n eg a t iv e co r r e l a t i on w i th ro o t d e n s i ty (42 %) and g en e r a l l y fo l l o w ed t h e t r e n d o b s e r v ed b y T a y l o r e t a l . ( 1996 ) , a sha rp dec l i ne i n r oo t g rowth w i th an i n c r ea se i n so i l s t r eng th . T h e a g g r eg a t e s i z e s o f 4 m m ( 26 % ) a n d 2 mm ( 4 2 %) h ad a l a rg e n eg a t i v e e f f e c t o n roo t d en s i ty wh i ch co r r e sponded we l l w i th t h e s t u d y d o n e b y A ma t o a n d R i t c h i e ( 2 0 0 2 ) , 102 103 whe re t hey found t ha t t h e l a r g e a g g r e g a t e s i z e s h a d a l a r g e nega t i ve i n f lu en c e o n roo t d ev e lop me n t . Th e agg rega t e s i z e s o f 1 mm ( 43%) and 0 .5 mm ( 5 4 % ) h ad p o s i t i ve co r r e l a t i on s w i th roo t d e n s i ty o nc e ag a in c o mp l e me n t i n g t h e s t u d y d o n e b y A ma t o a n d R i t c h i e ( 2 0 0 2 ) . F r o m t h e co r r e l a t i on ma t r i x t h e co mb ina t ion o f ma i n p a r a me t e r s wh i ch co r r e l a t e d t h e b e s t w i th roo t d en s i ty wh en d rawn in to a mu l t i p l e r eg r e s s io n eq u a t ion , w a s s e l ec t ed and i n t h e C ho r i zon i t w a s t h e co mb in a t ion o f t he t h i cknes s o f t h e l ay e r , MO R a n d the AS f r a c t i on s o f 4 mm, 2 mm, 1 mm a n d 0 .2 5 mm c o r r e s p o n d e d t h e b e s t w i t h r o o t d e n s i ty . A s s e e n i n F ig u r e 3 . 1 1 ( c ) t h e R 2 o f t h e l i n e a r r e l a t i o n sh i p b e t w e en SPQ I and RLI i s 4 8 %, 3 . 4 . 4 Th e P r o f i l e T h e S P Q I f o r e a c h p l o t ’ s p ro f i l e w e re ob t a in ed by add ing t h e SPQ I v a lue fo r t h e d i f f e r en t ho r i zon s . Th e SPQI ’ s fo r t h e 1 3 p l o t s w e r e t h en r eg r e s s ed w i t h t h e t o t a l r o o t l en g t h o f t h e p ro f i l e (R LI ) exp r es se d in k m. m - 2 . The g raph and t h e s t a t i s t i c a l r e s u l t s o f t he l i n e a r r e g r e s s io n a r e p r e s en t e d i n F i g u r e 3 . 1 2 . A c c o r d i n g t o t h e R 2 t he SPQ I i s ab l e t o exp l a in 79 % o f t he v a r i a t i on i n t h e R LI . Fu r th e r i n sp ec t i on o f t he da t a i n F ig u r e 3 . 1 2 r e v e a l s t h a t t h e s o i l f o r ms h av e a p ro mi n en t r o l e i n t h e SPQ I v s R LI r e l a t i on sh ip . The Tuku lu so i l f o r m w i t h a N e o c u t a n i c B h o r i z o n h a d t h e l o w es t c o r r e s p o n d i n g R L I o v e r t h e p ro f i l e . T h i s i s d u e t o t h e f a c t t h a t t h e s t r eng th o f t h e N eocu t an i c B h o r i z o n i s s o h i g h t h a t i t h a s a n e g a t i v e i n f l u e n ce o n r o o t e l o n g a t i o n . O n t h e o t h e r h a n d , t h e c l a y con ten t o f t h e n eo cu ta n i c B h o r i zo n i s t oo l o w to c r e a t e p l a n e s o f w e a k n ess t h a t s t i mu l a t e s p r e f e r en t i a l r oo t p a th s . The Se p an e so i l f o r m h ad the s e c o n d h ig h e s t R LI o v e r t h e p ro f i l e , wh i ch i s t h e r e su l t o f h ig h e r c l ay c o n t e n t s i n t h e p e d o c u t a n i c B h o r i z o n , c a u s i n g p l an es o f w e aknes s t h a t s e rve s a s p r e f e r en t i a l r oo t p a t h s d o w n w ard i n t h e p r o f i l e . T h e B l o e md a l s o i l f o r m h a d t h e h i g h e s t c o r r e s p o n d i n g R LI o v e r t he p ro f i l e , wh ich i s t h e r e su l t o f t he r ed aped a l B h o r i zo n , wh i ch i s o f l ow er so i l s t r eng th t h an t he p r ev ious two me n t ion ed , Th i s co mp lemen t s r o o t d en s i t i e s i n t h e A h o r i z o n a n d B h o r i z o n a s n o r e s t r i c t i o n b y s o i l s t r e n g t h i s a c t i n g o n r o o t s d o w n w a r d i n t h e p r o f i l e . 103 104 y = 0.0049x - 0.36 R2 = 0.7754 0.400 0.350 Tukulu 0.300 0.250 0.200 Bloemdal 0.150 0.100 Sepane 0.050 0.000 -0.050 0 50 100 150 Soil physical quality index F i g u r e 3 . 1 2 R e l a t i o n s h i p b e t w een t o t a l r oo t l en g t h o r r oo t l eng th i ndex (R LI ) and t h e so i l phy s i ca l qua l i t y i ndex (SPQ I ) fo r t h e p ro f i l e s , i r r e sp e c t i v e so i l fo r ms . 3 .5 Con c lu s io n F r o m t h e r ev i ew i t i s c l e a r t h a t so i l p h y s i c a l p ro p e r t i e s h av e a c lo s e i n t e r r e l a t i o n s h i p . P a s t s t u d i e s o n ro o t d ev e lop me n t w e r e ma i n l y a p p l i e d o n s a n d y t o s a n d y l o a m s o i l s , w i th a mass i v e ap ed a l s t ru c tu r e . Up to d a t e n o n e o f t h e b i o p h y s i c a l s t u d i e s i n I R W H h as f o c u s s e d o n r o o t d ev e lop me n t . S tudy ing t he i n t e r r e l a t i on sh ip b e twee n so i l p h y s i c a l p r o p e r t i e s i t i s c l e a r t h a t t h e A h o r i z o n i s g e n e r i c t o a l l t h e so i l f o r ms i d en t i f i ed i n t h e f i e ld and o r ig in a t e s f rom eo l i an s a n d s wh i ch i s mi x ed n a tu ra l l y w i th t h e c l ays o r ig ina t ed f ro m th e s and s to n e , s ch a l e a n d d o l e r i t e p a re n t ma t e r i a l o f t he a r e a . So i l p h y s i c a l p r o p e r t i e s d eve lop ed w i th in t h e con t ex t o f n a tu ra l p e d o g e n i c p r o c e s s e s a n d o n t h r o p o g e n i c a c t i v i t i e s . C o n c l u s i v e e v i d e n c e w e re ob t a in ed on t h e cons id e r ab l e va r i a t i on i n t h e p h y s i c a l p a r a me t e r s s u c h a s A S a n d O C , i r r e spe c t i v e t h e s o i l fo rm. T h e B h o r i zon i s t h e ma i n f a c t o r t h a t d i s t i n g u i s h e s t h e t h r e e s o i l f o r ms , v i z . a r ed ap ed a l (B lo emd a l ) , neocu t an i c (Tuku lu ) , pedocu t an i c (Sepane ) f r om each o the r . T h e c o r r e l a t i o n s t a t i s t i c a l r e s u l t s s h o w t h a t t e x t u r e p l a y s a d o m i n a n t r o l e i n t h e p h y s i c a l p r o p e r t i e s o f t h e B h o r i z o n s . T h e s t r o n g i n t e r r e l a t i o n s h i p c a n b e e x p l a i n e d b y t h e p h y s i c a l a n d c h e m i c a l n a t u r e o f t h e t y p e o f c l a y m i n e r a l s a s d e s c r i b e d i n t h e A h o r i z o n . A l l t h e s o i l s 104 Root density (km.m -2) 105 h a v e a p r i s m a t i c s t r u c t u r e i n t h e C h o r i z o n w h i c h i n m o s t c a s e s g a v e a v e r y l o w d e g r e e o f i n t e r r e l a t i o n s h i p s . D e t e r m i n i n g h o w t h e R L I r e l a t e s t o s o i l p h y s i c a l p r o p e r t i e s , i n d i c a t e d t h a t t h e A h o r i z o n h a d a v a r i a b i l i t y d u e t o c u l t i v a t i o n a n d t h e p r o c e s s e s o f o r g a n i c b r e a k d o w n . I n t h e B h o r i z o n t h e B l o e m d a l h a d t h e h i g h e s t R L I a n d l e a s t i n f l u e n c e b y s o i l p h y s i c a l p r o p e r t i e s o n r o o t e l o n g a t i o n . T h i s m a y b e d u e t o i t s l o w e r c l a y c o n t e n t a n d m a s s i v e a p e d a l s t r u c t u r e . T h e S e p a n e h a d t h e s e c o n d h i g h e s t r o o t d e n s i t y i n t h e B h o r i z o n , a l t h o u g h i t h a d a h i g h S i + C l , s t r o n g a n g u l a r b l o c k y s t r u c t u r e e t c . T h e h i g h S I + C l c a u s e d s u f f i c i e n t s w e l l a n d s h r i n k a c t i o n s t o c a u s e r o o t s t o m o v e d o w n c r a c k s a n d i n c r e a s e t h e r o o t d e n s i t y d o w n w a r d s i n t h e p r o f i l e . T h e T u k u l u h a d t h e l o w e s t B h o r i z o n R L I , w h i c h m a y b e d u e t o a S i + C l t h a t i s h i g h e n o u g h t o h a v e a r e s t r i c t i n g e f f e c t o n e l o n g a t i n g r o o t s a n d l o w e n o u g h s o t h a t t h e s w e l l i n g a n d s h r i n k i n g i s n o t s u f f i c i e n t t o f o r m c r a c k s . I n t h e C h o r i z o n t h e m o s t l i m i t i n g f a c t o r s w e r e t h e s o i l s t r e n g t h d u e t o t h e u n i f o r m p r i s m a t i c h o r i z o n t h r o u g h o u t t h e a r e a , t o g e t h e r w i t h a h i g h M O R . T h e s e t w o f a c t o r s c a u s e d a l o w R L I i n t h e C h o r i z o n r e g a r d l e s s o f s o i l f o r m . 105 106 CHAPTER 4 C h a r a c t e r i z i n g t h e h y d r o l o g y o f t h e B l o e md a l , Tu k u lu a n d Sep an e so i l s a t Pa r ady s . 4 . 1 I n t r o d u c t i o n So i l h y d ro lo g y i s o f c ru c i a l i mp o r t ance i n coun t r i e s su ch a s Sou th A f r i ca , w h e r e t h e l a c k o f w a t e r l i mi t s r a i n f e d c r o p p r o d u c t i o n ( H u t s o n , 1 9 8 3 ) . T h e h y d r a u l i c c o n d u c t i v i ty i s a c h a l l e n g i n g s o i l p ro p e r t y t o d e s c r i b e b e cau s e i t c an cha n g e ma n y o rd e r s o f ma g n i tud e o v e r sho r t d i s t an c es . H e t e ro g en e i ty o f s o i l p ro p e r t i e s w i th in and b e t w een s o i l h o r i zo n s c au ses s o me r e g i o n s t o b e mo r e o r l e s s f av o u r a b l e t o f l o w . T h e f l o w i s h i g h l y v a r i ab l e w i th ex t r e me s r e p r e s en t ed b y to r tu o u s f l o w b e t w een i n d iv id u a l p a r t i c l e s a n d r ap i d f l o w t h r o u g h l a r g e , c o n t i n u o u s ma c r o p o r e s . T h e s p a t i a l v a r i a t i o n o f t he hyd rau l i c conduc t i v i t y i s i n f l uenced b y mu c h mo r e t h a n t o p o g r a p h y a n d s o i l f o r m a n d i s a l s o s t r o n g l y a f f ec t ed by t he s o i l s t r u c t u r e . To e x p l a i n t h i s p he n o me n o n , V a n a p a l l i e t a l . ( 1 9 9 9 ) sugg es t ed t h a t wh en i nv e s t i g a t i ng t he s t ruc tu re o f p a r t i a l l y s a tu ra t ed so i l s , t h e r e a r e t w o l ev e l s t o b e con s i d e r ed n a me ly : ma c r o s t ru c tu r e and mi c r o s t r u c t u r e . M a c r o s t ru c t u r e g o v e r n s t h e s o i l w a t e r c h a r a c t e r i s t i c b e h a v i o u r f o r t h e s o i l p a r t i cu l a r l y a t l o w su c t i on va lu es , wh i l e mi c r o s t ru c tu r e g o v e rn s t he b eh av io u r o f s o i l w a t e r c h a r a c t e r i s t i c a t r e l a t i v e l y h i g h su c t i o n v a l u e s . O n t h e o t h e r h a n d so i l t ex tu r e i n f lu en ce s t h e d i f f e r e n c e i n p o r e s i z e s i n t h e s o i l . I n a c l ay ey so i l , t h e po re s i z e d i s t r i bu t i on i s mo re un i fo rm, and mo re o f t he w a t e r i s ad so rb ed , so t ha t i n c r e a s i n g t h e ma t r i c su c t i o n c a u s e s a mo r e g r adu a l d ec r e a se i n w e tn es s . T h u s t h e g r e a t e r t h e S i + C l i n g ene ra l t h e g rea t e r t h e w a t e r r e t en t i on a t a n y p a r t i c u l a r suc t ion , an d mo r e g ra du a l t h e s l ope o f t he cu rve ( D ex t e r , 1 9 7 8 ) . D b a l s o h a s a n e f f e c t o n t h e s o i l w a t e r c h a r a c t e r i s t i c s a s a n i n c r e a s e i n D b m e a n s a dec rea se i n t o t a l po re space i n t h e so i l and a d e c r e a s e i n w a t e r mo v e me n t t h r o u g h t h e s o i l ( H i l l e l , 2 0 0 4 ) . Th e O C a l s o i n c r e a s e s t h e w a t e r h o l d in g c a p a c i t y a n d c o n d u c t i v i ty l a r g e l y a s a r e s u l t 106 107 o f i t s i n f lu en ce o n so i l agg rega t i o n a n d a s so c i a t e d p o r e s i z e d i s t r i bu t i on . Th e O C in c rea se s t h e amo u n t o f w a t e r r e t a i n e d , e s p e c i a l l y a t l o w s u c t i o n s , b u t a t h i g h e r s u c t i o n s s o i l r i c h i n o r g a n i c c a rbon r e l ea se s w a t e r r a p i d l y be c a u s e o f l a r g e p o r e s p a c e s ( Sa x t o n & R a w l s , 2 0 0 6 ) . So i l p r o p e r t i e s s u c h a s c o n d u c t i v i t y , p o r o s i t y a n d p o r e s i z e d i s t r i b u t i o n a r e s c a l e d e p e n d a n t a n d s h o u l d b e t ak en i n t o co n s i d e ra t i on wh en se l ec t i ng t he s a mp l e s i z e . T h u s a f i e ld e s t i ma t i o n o f h y d rau l i c cha r ac t e r w h ere a l a rg e r s a mp l e i s t a k e n mi g h t b e m o re de s i r ab l e (H i l l e l , 2004 ) . Fu r th e r s t u d i e s h av e to b e d o n e to i d en t i fy a l l t h e f ac to r s a f f ec t i ng t he s p a t i a l v a r i a t i o n o f t h e h y d r a u l i c c o n d u c t i v i t y o f d i f f e r e n t s o i l f o r ms , b e fo r e a mo d e l t o ch a ra c t e r i ze t he v a r i a t i on may b e e s t ab l i s h ed . The ob j ec t i v e o f t h i s s t udy w ere t h e r e fo r e t o ( i ) cha r ac t e r i ze t h e hy d r au l i c p r o p e r t i e s o f t h e B l o e md a l , Tu k u l u a n d Se p a n e s o i l s , v i z . vo lu me t r i c w e tn es s - t ime r e l a t i onsh ip s , ma t r i c su c t i o n – t i me r e l a t i o n sh i p s , h y d rau l i c h e a d – d e p t h r e l a t i o n s h ip s and t he hyd rau l i c condu c t i v i t y – s o i l w a t e r c o n t e n t r e l a t i o n s h i p fo r e ac h s o i l d i a g n o s t i c ho r i zon w i th in t he p ro f i l e . 4 . 2 M e t h o d o l o g y 4 .2 .1 Ex p e r i me n t a l s i t e T h e exp e r i me n t a l s i t e and f i e l d t r i a l a s d e s c r ib ed in Ch ap te r 1 wa s u se d f o r t h i s s t u d y . F r o m t h e 7 5 p lo t s , p lo t s n r 1 .1 ( Tu k u lu ) , 8 .3 (B lo e md a l ) a n d 1 4 .2 ( S e p a n e ) w e r e s e l e c t e d . 4 .2 .2 Ex p e r i me n t a l d e s ig n T h e i n s t a n t a n e o u s p r o f i l e m e t h o d a s d e s c r i b e d b y H i l l e l , 2004 was u sed . Sp ad es we r e u sed t o d ig a t r en ch o f 4 m l o n g , 4 m w i d e a n d + / - 1 .2 m d e ep a round t h e mo d a l p ro f i l e (F igu re 4 .1 ) .Th e t r ench was dug t o r each t he s ap ro l i t e a t t he bo t t o m o f t he p ro f i l e . Th e p ro f i l e w a s l i n ed w i th p l a s t i c , w h i l e s l u r r y wa s p l a c ed b e t w een t h e p ro f i l e a n d t h e p l a s t i c s u r r o u n d i n g t h e p r o f i l e . T h e t r e n c h w a s f i l l e d u p w i t h s o i l a n d a r i d g e w a s ma de + / - 600 mm h igh a round t h e p r o f i l e , t o p re v e n t w a t e r f r o m r u n n i n g o f f wh en w e t t i ng t h e p ro f i l e . F iv e neu t ron wa t e r me t e r a cce s s t ubes we re i n s e r t ed 5 0 0 mm a p a r t ( F igu re 4 .1 ) i n t h e mi d d le o f t h e p ro f i l e u s ing a 107 108 h a n d a u g e r . T h r e e w a t e r ma r k s w i t h a u t o ma t i c l o g g e r s w e r e i n s t a l l e d 5 0 0 m m a w a y f r o m t h e a c c e s s t u b e s a t d e p t h i n t e r v a l s o f 3 0 0 m m , 6 0 0 m m a n d 9 0 0 m m ( F i g u r e 4 . 1 ) . W a t e r w as add ed t o t h e p ro f i l e un t i l t he d ra ined u p p e r l i mi t w a s o b t a i n e d . Th e p r o f i l e w as cov e r ed w i th 5 c m t h i ck i so l a t i o n ma t e r i a l t o co n t r o l t e mpe r a t u r e a n d p l a s t i c t o p r ev en t any e v ap o r a t ion and wa s l e f t t o f r e e ly d r a i n fo r a p e r io d o f 3 0 d ay s . 4 .2 .3 Ex p e r i me n t a l me a s u reme n t s Wa t e r con ten t r ead ings w er e t ak en f r equ en t ly w i th a C a mp b e l l P a c i f i c N e u c l e a r 5 0 3 D R h y d r o p r o b e d u r i n g t h e f i r s t t h r e e d ay s a f t e r w h i ch i t w a s t ak en l e s s o f t en u n t i l i t w as o n l y r ea d o n c e a w e ak a t t h e end o f t h e t r i a l . Th e w a t e r con ten t w a s exp r e s sed a s vo lu me t r i c wa t e r con t en t i n mm mm - 1 con s i s t en t en t ov e r t i me i n mo s t o f t he ho r i zons and t h e r e s ee ms t o b e s o me d o u b t o n t h e a c c u racy o f t he i n s t rume n t s . As an a l t e r n a t i v e t he l oca l r e t e n t i o n mo d e l d e v e l o p e d i n t h e D ep a r t me n t o f So i l , C ro p and C l i ma t e S c i e n c e s ( U F S ) ( V a n R en s b u r g , 1 9 8 8 ) w a s u s e d t o e s t i ma t e t h e ma t r i c s u c t i o n h e a d o v e r t i me f r o m m e a s u r e d so i l w a t e r con t e n t . Th e mo d e l u se s s i l t + c l ay co n t en t ( % ) a s i n p u t t o ma k e t h e p re d i c t i o n o f w a t e r r e t en t i o n . 0.5 m Neutron water meter access tubes 6 m Water marks Profile Trench 6 m Fi g u r e 4 .1 Exp e r ime n t a l d es ig n fo r t h e i n s t an t a n eo u s p ro f i l e me t h o d . 108 109 4 . 2 . 4 C a l c u l a t i o n o f hyd rau l i c conduc t i v i t y F i r s t l y t he d r a in age cu rv e s w e r e e s t a b l i sh ed u s i ng t h e s o i l w a t e r co n t en t c a p t u r e d b y t h e C P N . T h i s w a s e x p r e s s ed a s s o i l w a t e r co n t en t m m. m m - 1 v s . d ay s a f t e r s a tu r a t i on (DA S) . Se cond ly t h e l o ca l l y d ev e lop ed r e t en t i on mo d e l w as u s ed to p r ed i c t ma t r i c s u c t i o n f r o m w a te r con t en t u s ing s i l t + c l ay a s a i npu t . F r o m t hese t wo p a r a me t e r s t h e so i l mo i s t u r e f l u x w a s c a l cu l a t ed a s fo l l o w s : ( i ) F o r e ach D A S i n c r eme n t t h e f l u x f o r t h e sp e c i f i c h o r i z o n w a s e s t i ma t e d u s i n g t h e e q u a t i o n : d z (∆W C /∆ t ( c m d ay - 1 ) , whe re dz i s t h e d i f f e r e n c e i n d e p t h , ∆W C i s t h e d i f f e r e n c e i n w a t e r c o n t e n t b e t w e e n 1 and 2 D A S fo r e x a mp le a n d ∆ t i s t h e d i f f e r e n c e i n D A S . F lu x (q ) w a s c a l c u l a t e d b y a d d i n g t h e A , B a n d C h o r i z o n f l u x , t h u s A h o r i z o n f l u x w a s e q u a l t o A h o r i zon f l u x , B ho r i zon f l ux was equa l t o A + B ho r i zon f l ux a n d C h o r i zon f l u x w a s equ a l t o A + B + C h o r i zon f l ux . Th e Hy dr au l i c h ea d w a s ca l cu l a t ed u s ing the equ a t ion : H = Hp + Hg , w h e r e H p i s t h e ma t r i c s u c t i o n f r o m t h e r e t e n t i o n c u r v e a n d H g i s t h e t h i c k n e s s o f t h e h o r i z o n . The h y d r a u l i c h e a d w a s e x p r e s s e d i n c m . ∆H w a s c a l cu l a t ed u s ing th e equ a t ion : ∆H = ( H B h o r i z o n – H A h o r i z o n ) / z ( t h i c k n e s s o f h o r i z o n ) . F r o m th i s K w a s c a l cu l a t ed u s ing th e equ a t io n K = q /∆H . K w a s e x p r e s s e d a s c m d a y - 1 . Th e d a t a t h a t w a s u s e d t o c a l c u l a t e K c a n b e fo u n d i n A p p en d i x X . 4 .2 .5 S t a t i s t i c a l P ro c ed u r e s . C u r v e Exp e r t 1 . 3 ( 1 9 9 6 ) w a s u sed t o f i t t h e be s t mode l t o t he d r a i nage d a t a , w h i l e M i c ro s o f t Ex ce l w as u s e d t o f i t t h e b e s t t r end l i ne t o t he hyd rau l i c head – d e p t h r e l a t i o n s h i p da t a and t he hyd rau l i c c o n d u c t i v i t y – s o i l w a t e r con t en t r e l a t i o n sh i p d a t a 4 .3 R e su l t s and d i sc u ss io n A su m m a ry o f s e l e c t ed s o i l p h y s i c a l p ro p e r t i e s t o g e t h e r w i t h a s u mma r i z e d p ro f i l e d e s c r ip t i o n o f t he t h r ee s e l e c t ed p r o f i l e s i s p r e sen t ed i n Tab l e 4 .1 and Ta b l e 4 .2 . 109 110 Tab l e 4 . 1 Summar y o f t he phys i ca l cha r ac t e r i s t i c s f o r t he s e l ec t ed B loemda l , Tuku lu and Sepane so i l s Organic carbon Bulk Plot Soil Horizon Silt + content Modulus of A.S A. S A.S A.S A.S density Total Horizon nr type depth (mm) Clay (%) (%) rupture (bar) 4 (%) 2 (%) 1 (%) 0.5 (%) 0.25 (%) (kg m-3) porosity A 8.1 Bd 250 17 0.24 0.11 1.67 11.23 30.43 15.46 18.43 1342.56 0.49 A 1.1 Tu 210 16 0.33 0.14 6.36 8.77 20.34 20.86 24.37 1376.19 0.48 A 14.2 Se 210 18 0.61 0.37 9.98 14.39 20.09 1.76 2.6 1507.18 0.43 B 8.1 Bd 150 30 0.33 0.61 2.32 3.09 20.33 34.65 34.23 1589.23 0.40 B 1.1 Tu 250 25 0.39 0.76 1.19 2.83 2.02 4.13 5.45 1728.9 0.35 B 14.2 Se 100 32 0.33 0.89 2.62 2.85 18.76 19.82 50.94 1807.65 0.32 C 8.1 Bd 350 39 0.19 0.18 4.22 13.55 33.23 15.67 30.23 1405.12 0.47 C 1.1 Tu 310 41 0.22 0.54 7.64 9.54 16.53 18.46 19.09 1502.58 0.43 C 14.2 Se 500 48 0.23 0.56 1.52 15.34 11.09 28.15 12.16 1701.1 0.36 110 111 T a b l e 4 . 2 S u m ma r y o f t h e p e d o l o g i c a l c ha r a c t e r i s t i c s f o r t h e s e l e c t e d T u ku l u , B l o e m d a l a n d S e p a n e so i l f o r ms Plot nr Horizon Soil form Soil family Horizons name Depth Mottles Cutans Structure Consistency Parent material Transition Smooth, 8.1 Bd Roodeplaat 3200 A Ot 250 None none Apedal massive Loose flat 1.1 Tu Dikeni 1220 A Ot 210 None none Apedal massive Loose Clear, flat 14.2 Se Katdoorn 1210 A Ot 210 None none Apedal massive Loose Abrupt, flat Smooth, 8.1 Bd Roodeplaat 3200 B Yr 350 None none Apedal massive Loose flat Weakly developed medium 1.1 Tu Dikeni 1220 B Ne 310 None yes 10-25 mm) Sub block Slightly hard Abrupt, flat Well developed medium size 14.2 Se Katdoorn 1210 B Pd 500 None yes (10-25 mm) blocky Hard Abrupt, flat Red, black, yellow, Well developed medium size Smooth, 8.1 Bd Roodeplaat 3200 C Uw 150 grey yes (5-15mm) prismatic Hard Schale flat Red, black, yellow, Medium developed medium 1.1 Tu Dikeni 1220 C Uw 250 grey yes size (5-15 mm) prismatic Hard Dolerite/Mudstone Abrupt, flat Red, black, yellow, Medium developed medium 14.2 Se Katdoorn 1210 C Uw 100 grey yes size (5-15 mm) prismatic Hard Dolerite Abrupt, flat 111 112 4 .3 .1 V o l u me t r i c w e t n es s - t i me r e l a t i o n sh i p s T h e d r a i n a g e c u r v e s a r e p r e s en t ed i n F ig u res 4 .2 - 4 . 4 fo r t he d i f f e r en t h o r i zon s o f t h e B lo e md a l , T u k u l u a n d S e p a n e s o i l s , r e spec t i v e ly . V a r iou s mo d e l s a s i n d i ca t ed i n T ab l e 4 .3 w e re f i t t ed t o t h e d a t a s e t t o ch a r a c t e r i z e t h e d r a i n a g e p r o f i l e f o r t h e A , B a nd C h o r i zon s . Fo r t h e d i s cus s ion t he i n t e r n a l d r a i n a g e p r o c e s s i s d iv id ed in t o fou r p e r io d s , v i z . r ap id d r a in ag e p e r i o d ( i ) , mo d e r a t e d r a i n ag e p e r io d ( i i ) , s l o w d ra in a g e p e r io d ( i i i ) an d t h e n ea r c o n s t an t d r a in ag e p e r io d ( iv ) . A c c o r d i n g l y p e r io d ( i ) s t r e t ch e s f r o m 0 to 2 d ay s a f t e r s a tu ra t i o n ( DA S) , p e r i o d ( i i ) 2 - 5 D A S , p e r i o d ( i i i ) 5 – 1 8 D A S , f o l l o w e d b y p e r io d ( i v ) f r o m 1 8 DA S t o t h e e n d o f t h e d ra in ag e p e r io d . T a b l e 4 .3 M o d e l t y p e s an d t h e i r s t a t i s t i c a l co e f f i c i en t s f i t t ed t o t h e so i l w a t e r co n t en t - t i me d a t a o f t h e B lo emd a l , Tu k u lu and Se p an e so i l s Soil Statistical Horizon parameters A B C Model type MMF Model Exponential Association (3): Quadratic Fit: Equation y=(a*b+c*x^d)/(b+x^d) y=a(b-exp(-cx)) y=a+bx+cx^2 a a = 0.2904573 a = -0.026604003 a = 0.29110621 Bloemdal b b = 3.0470824 b = -9.3429491 b = -0.0010260621 c c = 0.13549045 c = 0.44820115 c = 1.0452981e-005 d d = 0.35557311 r2 r2 = 0.98 r2 = 0.94 r2 = 0.94 A B C Model type Harris Model: Logistic Model: Logistic Model: Equation y=1/(a+bx^c) y=a/(1+b*exp(-cx)) y=a/(1+b*exp(-cx)) Tukulu a a = 3.7203276 a = 0.25759274 a = 0.28965797 b b = 0.5054181 b = -0.094410141 b = -0.06794273 c c = 0.21111037 c = 0.17303465 c = 0.21924716 r2 r2 = 0.97 r2 = 0.93 r2 = 0.95 A B C Model type Rational Function: Rational Function: Rational Function: Equation y=(a+bx)/(1+cx+dx^2) y=(a+bx)/(1+cx+dx^2) y=(a+bx)/(1+cx+dx^2) a a = 0.27882798 a = 0.28129822 a = 0.28956249 Sepane b b = 1.017952 b = 0.039460831 b = 2.7038277 c c = 4.2759882 c = 0.153095 c = 10.278194 d d = -0.0011019731 d = 3.6489891e-005 d = 0.0060851941 r2 r2 = 0.97 r2 = 0.93 r2 = 0.95 112 113 B l o e m d a l : T h e d r a i n a g e r e f l e c t s o n t h e p e d o l o g i c a l c h a r a c t e r i s t i c s o f t he ho r i zon s . The A and t h e B h o r i zon b o th h av e a ma s s i v e ap ed a l s t ru c tu r e , b u t h av e d i f f e r en t t ex tu r a l p ro p e r t i e s . Th e s i l t + c l ay con ten t o f t h e A h o r i z o n ( 1 7 % ) i s c o n s i d e r a b l y l ower t han t he B ho r i zon (25%) , wh i ch exp la in s why the r e l a t i v e p o s i t i on o f t he A – cu rv e f a l l s be lo w th a t o f t h e B . A s exp e c t ed t h e C – c u rv e s h o w s the s l o w e s t d r a in ag e w h i ch c an b e a t t r i bu t ed t o t h e s l o w p e rmeab le n a tu r e o f t h e p r i s ma t i c s t ru c tu r e o f t he C ho r i zon , w i th a s i l t + c l ay con t en t o f 39%. Ph ase ( i v ) i s o f p a r t i cu l a r i n t e r e s t b e cau s e d ra in ag e i s a cc ep te d to b e n eg l ec t iv e ly s lo w a n d r e p r e s e n t s t h e d ra in ed u p p e r l i mi t o f p l an t ava i l ab l e w a t e r , v i z . 0 .21 mm mm - 1 f o r t h e A h o r i zon , 0 . 25 mm mm - 1 f o r t h e B h o r i z o n a n d 0 .27 mm mm - 1 f o r t he C ho r i zon (F igu re 4 . 2 ) . Th e vo lume t r i c w a t e r c o n t en t a t f i e l d s a t u r a t i o n (F S ) fo r t h e A , B a n d C h o r i zo n s i s 0 . 2 6 m m mm - 1 , 0 . 2 8 m m m m - 1 a n d 0 . 3 2 m m m m - 1 , r e s p ec t i ve ly . Th i s w as g en e r a l l y l ow er t h an t h e t o t a l po ro s i t y ( f t ) c a l c u l a t ed f r o m t h e b u lk d en s i ty v a lues l i s t ed i n Ta b l e 4 .1 . Th i s exp la in s t he f a c t h o w d i f f i cu l t i t i s t o co mp l e t e l y s a t u r a t e a p ro f i l e i n t h e f i e ld , d esp i t e t h e c a r e t ak en t o f i l l u p t h e p ro f i l e . T h e d i f f e r e n c e b e t w e e n F S a n d f t i s a s c r i b e d t o en t r apped a i r i n t he p ro f i l e . Phase 0 .3 2 ( i ) ( i i ) ( i i i ) ( i v ) 0.3 0.28 A horizon 0.26 B horizon C horizon 0.24 0.22 0.2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 Days after saturation (Days) F igu re 4 .2 Vo lume t r i c w e tn es s - t ime r e l a t i o n s h i p f o r t h e A , B a n d C h o r i z o n o f t h e B l o emd a l s o i l f o r m. 113 Volumetric water content (mm.mm -1) 114 Tu ku lu : Th e d ra in a g e p e r io d i s a l so d iv id ed in to fou r p h a se s exp la in ed e a r l i e r , v i z . 0 -2 DA S (ph a se i ) , 2 – 6 DA S (p h a se i i ) , 6 – 1 6 DA S (ph a se i i i ) and 1 6 – 3 0 DA S (ph a se i v ) . The r e l a t i v e p o s i t i o n s o f t h e c u r v e s a l so r e f l e c t o n t h e p e d o l o g i c a l f e a t u r e s o f t h e p r o f i l e , v i z . t h e A a t t h e t op , f o l l o w e d b y t h e B a n d C ho r i zons . Th i s was ex p ec t ed , b e ca u se o f a s t r u c t u r a l a n d t e x t u r a l d i f f e r e n c e b e t w een t he t h r ee h o r i z o n s . T h e A ho r i zon h a s a mass iv e ap ed a l s t r u c tu r e ; t h e B ho r i zon h as a w eak ly d ev e lop ed sub an g u la r b lo c k y s t ru c t u r e , wh i l e t h e C h o r i zon h a s a w e l l d ev e l o p ed p r i s ma t i c s t ru c tu r e . T h e s i l t + c l ay c o n t en t o f t h e A h o r i zon i s 16 % wh i l e t h e s i l t + c l ay con ten t o f t h e B a n d C h o r i z o n i s 3 0 % a n d 4 1 % , r e sp e c t iv e ly ( Tab le 4 .1 ) . I n p e r io d ( i v ) t h e d r a in ed u p p e r l imi t fo r t he ho r i zons a r e 0 .21 mm mm - 1 fo r t h e A ho r i zon , 0 .26 mm mm - 1 fo r t h e B h o r i zon and 0 .2 9 mm mm - 1 fo r t h e C ho r i zon , w h i l e t h e F S a t t h e s t a r t o f p h a s e ( i ) a mo u n t s t o 0 .25 , 0 . 29 a nd 0 .318 mm mm - 1 , r e s p e c t i v e l y . F S i s con s id e rab ly l o wer t han t h a t o f t h e t h eo re t i c a l po ro s i t y (Tab l e 4 .1 ) a s i n t h e c a se o f t h e B l o e md a l . Phase 0.32 ( i ) ( i i ) ( i i i ) ( i v ) 0.3 0.28 A horizon 0.26 B horizon C horizon 0.24 0.22 0.2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 Days after saturation (Days) F i g u r e 4 .3 Vo lu me t r i c w e tnes s - t ime r e l a t i on sh ip fo r t he A , B and C h o r i z o n o f t h e Tu k u l u s o i l . 114 Volumetric water content (mm.mm -1) 115 Sepane : D r a in ag e c u rv es o f t h e Se p an e ’ s ho r i zon s r ev e a l ed t ha t t he w e t t e s t r e g i me i s a s s o c i a t e d w i t h t he B h o r i z o n , w h i c h i s u n e x p e c t e d w h e n t h e t e x t u r a l p r o p e r t i e s ( s i l t + c l a y = 3 2 % ) i s c o n s i d e r ed . Th e s i l t + c l a y c o n t e n t o f t h e C h o r i zon (48 %) i s con s id e r ab ly h i g h e r t h a n t h e B h o r i z o n . Thu s , t he d i f f e r ence i n t he w a te r r eg ime s c an b e a t t r i bu t ed t ow a rd s t h e p ed o cu t an i c s t ru c tu re o f t he B h o r i zo n v e r su s t h e p r i sma c u t a n i c s t r u c t u r e o f t h e C ho r i zon . Th e sh ape o f t h e cu rve s r ev e a l fu r t h e r t h a t t h e B h o r i z o n d ra in s g ra d u a l ly s l o w er o v e r p h a s e ( i ) a n d ( i i ) , w h i l e t h e C h o r i z o n s h o w s a s h a r p d r o p i n p h a s e ( i ) . Th e A ho r i zon r e l ea sed w a t e r r a p i d l y i n p h a s e ( i ) , whe re a f t e r i t d r a ined v e r y s l o w l y . I n p e r i o d ( i v ) t h e d r a i n e d u p p e r l i mi t f o r t h e h o r i z o n s a r e 0 . 2 3 m m m m - 1 f o r t h e A h o r i zon , 0 . 26 mm mm - 1 fo r t he B ho r i zon and 0 .25 mm mm - 1 fo r t he C h o r i zon . Ag a in t h e FS o f t he ho r i zon s a r e cons id e r ab ly l o wer t h an t h e t heo re t i c a l l y ca l cu l a t ed t o t a l po ros i t y l i s t ed i n Ta b l e 4 .1 . 0.29 Phase 0 . 2 8 ( i ) ( i i ) ( i i i ) ( i v ) 0.27 0.26 A horizon 0.25 B horizon 0.24 C horizon 0.23 0.22 0.21 0.2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 Days after saturation (days) F i g u r e 4 .4 Vo lu me t r i c w e tnes s - t ime r e l a t i on sh ip fo r t he A , B and C h o r i z o n o f t h e Sepane so i l . 115 Volumetric water content (mm.mm-1) 116 4 .3 .2 M a t r i c su c t ion – t i me r e l a t i on sh i p s A c co rd ing t o t h e r e su l t s on ly t h e r e s p o n s e c u r v e s o f a f e w ma t r i c s u c t i o n r e s p o n s e c u r v e s w e r e r e l i ab l e . T h e r e s t o f t h e me a s u r e m e n t s w e r e f o u n d t o b e i n a c c u r a t e a s t h e w a t e r ma r k s u sed i s s en s i t i v e fo r t emp e ra tu r e d i f f e r en ce s , con t ac t w i th t h e so i l and o n l y g i v e s a c c u r a t e r ead ing s i n t he r eg io n b e t w e en 1 0 k Pa and 1 5 0 kPa (V ienna , 2008 ) . I n t h i s r eg a rd t h e d e c i s io n w a s ma d e r a t h e r t o p r ed i c t t h e ma t r i c s u c t i o n r e sp o n s e f r o m a l o c a l r e t en t i o n mod a l u s ing th e so i l wa t e r co n te n t f r o m t h e d r a in a g e cu rv es d i s cu s se d in s e c t i on 4 .2 .4 . Th e r e s u l t s a r e p re s en t ed i n Ap p en d ix W fo r t h e B lo emd a l , Tu k u lu and Se p an e so i l s and th e i r v a lue s w e r e u sed t o ca l cu l a t e t h e hy d rau l i c h e ad in t h e n ex t s e c t i o n . 4 .3 .3 Hy dr au l i c h ea d – d ep th r e l a t i o n s h ip s T h e h y d ra u l i c h e a d p r o f i l e cu rv es o f t h e 30 cm, 6 0 cm a n d 9 0 c m d ep th i n t e r v a l s f o r t h e B l o e md a l , T u k u l u a n d S e p a n e s o i l s a r e p r e s e n t e d i n F i g u r e s 4 . 5 – 4 . 7 . B l o e m d a l : Inv e s t i g a t ing the h y d rau l i c h e ad p r o f i l e o f t h e B lo emd a l s o i l r ev e a l ed w a t e r mov e me n t o r d r a in age f ro m th e A to t h e C . Th e on ly ex cep t ion w a s a t 30 D A S wh e r e t h e r e w a s a n e g a t i v e g r a d i e n t o v e r 30 t o 6 0 c m d ep th p ro f i l e s . I n t h i s c a s e i t s e e ms i f t h e t o p so i l d r i ed o u t t o su ch an ex t en t t ha t wa t e r s t a r t e d t o mov e u p w a r d s f r o m t h e w e t t e r B t o t h e A . 116 117 400 350 0.86 DAS 300 2.18 DAS 250 2.84 DAS 3.16 DAS 200 3.83 DAS 5.96 DAS 150 17.14 DAS 100 26.01 DAS 30 DAS 50 0 30 60 90 Depth (cm) F i g u r e 4 .5 Hy d r au l i c h e ad p ro f i l e a t 3 0 c m, 6 0 c m a n d 9 0 m d e p t h s o f t h e B lo e md a l o v e r t h e me a s u r ing p e r io d in d ay s a f t e r s a tu ra t i o n (D AS) . Tu ku lu : T h e h y d r a u l i c h e a d p r o f i l e s o f t he Tuku lu shows a pos i t i ve g rad i en t a n d h en ce d o wn wa rd f l o w f ro m t h e A ho r i zon t o t h e B ho r i zon f o r t h e 3 0 d a y d r a i n a g e p e r i o d . Ho we v er , t h e g raph a l so sho w s a n eg a t iv e s l o p e ( u p w a r d mo v e me n t f r o m t h e C t o t h e B ) , w h i c h d o n o t r e f l ec t o n t h e c o n t i n u o u s l o s s o f w a t e r o b s e r v e d i n t h e d r a i n a g e c u r v e s o f t h e B a n d C h o r i zon o f F i g u r e 4 .3 . F ro m th i s i t was d edu c t ed t h a t t h e r e t en t i on mod e l w a s n o t a b l e t o p red i c t t h e ma t r i x po t en t i a l h ead accu r a t e ly i n t h e C h o r i zon . T h i s i s p r o b ab l y b e c au s e t h e mo d e l o n l y u se s s i l t + c l ay co n t en t a s i n p u t a n d d o e s n o t c o n c e r n s o i l s t r u c t u r e w h i c h s ee ms t o b e v e r y i mp o r t an t i n l ay e r s o r p s eu d o d u p l ex s o i l s s u c h a s t h e T u k u l u a n d S e p a n e s o i l s . 117 Hydraulic head (cm) 118 300 250 0.86 DAS 2.18 DAS 200 2.84 DAS 3.16 DAS 150 3.83 DAS 5.96 DAS 100 17.14 DAS 26.01 DAS 50 30 DAS 0 30 60 90 Depth (cm) F i g u r e 4 .6 Hy d r au l i c h e ad p ro f i l e a t 3 0 c m, 6 0 c m a n d 9 0 m d e p t h s o f t h e T u k u l u o v e r t h e me a su r ing p e r io d in d ay s a f t e r s a tu r a t i on (DA S) . S e p a n e : A s i n t h e c a s e o f t h e Tu k u l u , t h e h y d r a u l i c h e a d p r o f i l e s h o w s t h a t t h e r e i s a p o s i t i v e s lo p e f r o m t he A to t he B ho r i zon , f o l l o w e d b y a n eg a t iv e s lo p e f rom t h e B to t he C . Up w ard mo v e me n t f r o m t h e C to t he B c o u l d p r o b a b l y h a p p e n s n e a r D U L , b u t i s h i g h l y u n l i k e l y , b e c a u s e b o t h t h e h o r i z o n s s h o w s a l o s s ( a l t h o u g h s ma l l ) o f w a t e r i n a l l t h e p h a s e s i n F i g u r e 4 .4 . Aga in t h e app a re n t u p w ar d f l u x i n F i g u r e 4 .7 i s p r o b a b l y t h e r e su l t o f t o l o w ma t r i x po t en t i a l su c t i o n a t t h e C h o r i zon . I n v e s t i g a t ing the h y d rau l i c h e ad p ro f i l e o f t h e Se p an e i t i s c l e a r t h a t t h e r e i s a pos i t i ve g r ad i en t f r om the 30 cm d e p th i n c remen t t o t h e 60 cm d ep th i n c r e me n t f o r t h e 3 0 d a y d ra i n a g e p e r i o d . Thu s t h e r e i s p o s i t i v e g r ad i en t o f w a t e r f l o w f rom t h e A ho r i zon t o t h e B h o r i z o n . T h e r e i s a n e g a t i v e g rad i en t f r o m t h e 6 0 c m d e p th i n c re me n t t o t h e 9 0 c m d e p t h i n c r e me n t i n d i c a t i n g t h a t t h e P e d o c u t a n i c B ho r i zon and t he p r i s ma t i c u n d e r l y i ng h o r i z o n w i t h i t s s t r o n g s t r u c tu re and h ig h c l ay con t en t c ause wa t e r t o b u i l d u p o n t o p o f t h e h o r i z o n s . Th e w a t e r w i l l t h en mov e b a ck t o a l ay e r ( A h o r i zon ) w i t h a l o w er r e t e n t i o n c a u s i n g a n e g a t i ve g r ad i en t . 118 Hydraulic head (cm) 119 350 300 0.86 DAS 250 2.18 DAS 2.84 DAS 200 3.16 DAS 3.83 DAS 150 5.96 DAS 17.14 DAS 100 26.01 DAS 30 DAS 50 0 30 60 90 Depth (cm) F i g u r e 4 .7 Hy d r au l i c h e ad p ro f i l e a t 3 0 c m, 6 0 c m a n d 9 0 m d e p t h s o f t h e Se p an e o v e r t h e me a su r ing p e r io d in d ay s a f t e r s a tu r a t i on (DA S) . 4 . 3 . 4 H y d r a u l i c conduc t i v i t y T h e h y d ra u l i c c o n d u c t i v i t y – s o i l w a t e r c o n t e n t r e l a t i onsh ip cu rves fo r t he B l o e md a l , T u k u l u an d S e p a n e s o i l s a r e p r e s e n t e d i n F ig u r e s 4 . 8 – 4 . 1 0 , r e spec t i ve ly . A summary o f t h e h y d r a u l i c c o n d u c t i v i t y a n d r e l a t e d me a n v o l u me t r i c w a t e r c o n t en t fo r t h e A , B and C h o r i zon o f t h e s o i l s a r e p re s en t ed i n Tab l e 4 .4 . 119 Hydraulic head (cm) 120 T a b l e 4 . 4 S u m ma r y o f t h e h y d r a u l i c c o n d u c t i v i t y a n d r e l a t e d me a n v o l u me t r i c w a t e r c o n t e n t fo r t h e s o i l s Horizon A B C Soil form DAS K (cm day-1) Mean WC DAS K (cm.day-1) Mean WC DAS K (cm.day-1) Mean WC 0.86 0.26 0.27 0.86 0.39 0.27 0.86 0.31 0.29 2.18 0.09 0.25 2.18 0.22 0.26 2.18 0.14 0.29 2.84 0.03 0.24 2.84 0.08 0.26 2.84 0.16 0.29 3.16 0.04 0.24 3.16 0.09 0.26 3.16 0.14 0.29 Bloemdal 3.83 0.03 0.24 3.83 0.08 0.25 3.83 0.12 0.29 5.96 0.02 0.23 5.96 0.05 0.25 5.96 0.33 0.29 17.14 0.01 0.22 17.14 0.01 0.25 17.14 0.02 0.28 26.01 0.03 0.21 26.01 0.03 0.25 26.01 0.01 0.27 30.00 0.01 0.21 30.00 0.01 0.25 30.00 0.01 0.27 DAS K (cm day-1) Mean WC DAS K (cm.day-1) Mean WC DAS K (cm.day-1) Mean WC 0.86 0.68 0.25 0.86 0.90 0.28 0.86 0.731 0.31 2.18 0.10 0.23 2.18 0.27 0.28 2.18 0.283 0.30 2.84 0.00 0.23 2.84 0.00 0.27 2.84 0.215 0.30 3.16 0.03 0.23 3.16 0.09 0.27 3.16 0.192 0.30 Tukulu 3.83 0.02 0.23 3.83 0.08 0.27 3.83 0.172 0.30 5.96 0.02 0.23 5.96 0.06 0.27 5.96 0.130 0.30 17.14 0.04 0.22 17.14 0.10 0.26 17.14 0.046 0.29 26.01 0.02 0.21 26.01 0.01 0.26 26.01 0.011 0.29 30.00 0.01 0.21 30.00 0.02 0.26 30.00 0.001 0.29 DAS K (cm day-1) Mean WC DAS K (cm.day-1) Mean WC DAS K (cm day-1) Mean WC 0.86 0.145 0.26 0.86 0.22 0.28 0.86 1.488 0.28 2.18 0.009 0.25 2.18 0.08 0.28 2.18 0.166 0.26 2.84 0.003 0.25 2.84 0.08 0.27 2.84 0.092 0.26 3.16 0.005 0.24 3.16 0.03 0.27 3.16 0.077 0.26 Sepane 3.83 0.004 0.24 3.83 0.02 0.27 3.83 0.067 0.26 5.96 0.002 0.24 5.96 0.02 0.27 5.96 0.050 0.26 17.14 0.003 0.24 17.14 0.001 0.27 17.14 0.023 0.26 26.01 0.003 0.24 26.01 0.001 0.26 26.01 0.012 0.26 30.00 0.001 0.24 30.00 0.001 0.26 30.00 0.010 0.26 120 121 B l o e m d a l : Fro m the r e l a t i v e shap e and po s i t i o n o f t h e cu rves i t i s c l ea r t h a t e a c h h o r i z o n h as i t s o w n u n i q u e K - Ө r e1 a t i onsh ip w i th in t he b o u n d a r i e s o f t h e d r a i n e d u p p e r l i mi t ( D U L ) a n d f i e l d s a t u r a t i o n ( F S ) . T h e C h o r i z o n t a k e s u p t he fu r th e s t r i gh t p o s i t i o n o n t h e g r aph wh i ch i s e x p e c t e d d u e t o t h e h ig h c l ay con ten t a n d p r i sma t i c s t r u c tu r e o f C h o r i zo n ( 39% ) . Th i s ho r i zon con t a in s smec t i c c l ay s t h a t c an be p r e su med to sw e l l a n d s h r i n k . Th i s r e s t r i c t s t h e s o i l w a t e r c o n d u c t i v i ty a s i n d i c a t e d i n t h e e x p o n e n t i a l d e c r e a s e i n K f r o m F S 0 . 3 1 c m d a y - 1 a t FS t o 0 . 01 c m .day - 1 a t D U L . T h e w e t w a t e r r e g ime be tween FS (0 .29 mm mm - 1 ) a n d D U L ( 0 . 2 7 mm mm - 1 ) r e f l e c t o n t h e s i g n s o f w e t n e s s a s i n d i c a t e d b y t h e a b u n d a n c e o f r ed , b l ack , y e l l o w a n d g r ey mo t t l e s i n t h i s h o r i zon ( Tab l e 4 .2 ) . Co mp ar ing th e K - Ө v a lu es o f t he r ed ap ed a l B ho r i zon w i th t ha t o f t he C s h o w s t h a t t h e C h o r i z o n p r o b a b l y s l o w s d o w n t h e h y d r a u l i c conduc t i v i t y o f t h e B ho r i zon , du e i t s l o w er c l ay con ten t ( 25 %) and mass i v e ap eda l s t ru c tu r e . Ano th e r f a c t o r t h a t con t r i b u t ed t o t h e l ow K v a lues o f t h e B h o r i z o n i s i t s b u l k d e n s i t y o f 1 7 2 8 k g m - 3 . T h e K v a l u e s f o r t h e B h o r i z o n r ang ed f ro m 0 . 3 9 c m d a y - 1 a t F S t o 0 .0 3 c m d a y - 1 a t D U L , w h i l e t h e w a t e r r eg i me r a n g ed f rom 0 .27 mm mm - 1 a t F S t o 0 . 2 5 m m m m - 1 a t D U L . T h e h y d ra u l i c c o n d u c t i v i t y o f t h e A h o r i z o n i s u n ex p e c t e d l y l o w w h e n t h e t e x t u r e ( s i l t + c l a y = 1 7 % ) , b u l k d e n s i t y ( 1 3 4 2 k g m - 3 ) a n d ma s s iv e aped a l s t r u c t u r e i s c o n s i d e r e d . T h i s c an b e a t t r i bu t ed t ow a r d s t h e i n f l u e n c e o f t h e l o w h y d r a u l i c c o n d u c t i v i t y o f t h e u n d e r l y i n g l a y e r s . T h e K v a l u e s f o r t h e A h o r i zon r an g ed f r o m 0 .2 6 c m d ay - 1 a t FS to 0 .0 1 c m d ay - 1 a t D U L , w h i l e t h e w a t e r r e g i me r ang ed f rom 0 .27 mm mm - 1 a t FS t o 0 .21 mm mm - 1 a t D U L . 121 122 0.600 y (0-30 cm) = 4E-07e47.953x R20.500 = 0.7468 y (30 -60 cm) = 1E-16e132.91x 2 0.400 R = 0.879 y (60-90 cm)= 8E-26e194.36x 0-30 cm 2 0.300 R = 0.9007 30-60 cm 60-90 cm 0.200 0.100 0.000 0.2 0.22 0.24 0.26 0.28 0.3 Soil water content (mm.mm-1) F i g u r e 4 . 8 H y d r a u l i c c o n d u c t i v i t y c u r v e s f o r t h e B loemda l so i l . Tu ku lu : B e c a u se o f t h e u n r e l i ab l e ma t r i c po t en t i a l h ead i t w a s no t p o s s i b l e t o c a l cu l a t e K ( K = q / (∆H/∆z ) ) . The w a t e r p o t en t i a l mo d e l u se d w a s no t ab l e t o a ccu ra t e ly p r ed i c t ma t r i c p o t en t i a l f r o m t h e me a s u red w a t e r co n t en t , and i t w a s a s su me d t h a t K = f l u x ( q ) f o r t h e C h o r i z o n . Th e r e l a t i ve sh ap e and po s i t i o n o f t h e c u r v e s s h o w s t h a t e a c h h o r i z o n h a s i t o w n u n i q u e K - Ө r e l a t i on sh ip wh ich r e f l e c t s o n t h e d i f f e r e n t t e x t u r a l a n d s t r u c t u r a l p r o p e r t i e s . T h e C h o r i z o n t a k e s u p t h e f u r t h e s t r i g h t p o s i t i o n o n t h e w e t n e s s s c a l e . Th i s i s e x p e c t ed due t o t h e h igh c l ay c o n t en t (30 %) o f t h e p r i sma t i c s t ru c t u r e . I t i s c l e a r t h a t t h e K - Ө r e l a t i o n sh ip o f t h e n eo cu t an i c B h o r i z on i s a l so p a r t i a l l y con t ro l l ed by t he s l o w p e rmeab i l i t y o f t h e und e r ly ing C ho r i zon a s i n t he ca se o f t he B l o e md a l . T h e C h o r i z o n c o n t a i n s s me c t i c c l a y s t h a t s w e l l u n d e r w e t cy c l e s and sh r in k s u n d e r d ry cy c l e s . Th e w eak ly d ev e lop ed me d i u m s u b a n g u l a r b l o c k y s t r u c t u r e o f t h e B h o r i z o n d ra i n e d a t a r a t e o f 0 . 9 c m d a y - 1 a t F S . A s t h e p o r e s e mp t y K d e c r e as e s e x p o n e n t i a l l y an d r e a c h e s a v a l u e o f 0 .0 2 cm d ay - 1 a t DU L. T h e h y d r a u l i c c o n d u c t i v i ty o f t h e A h o r i z o n i s o n c e a g a i n u n e x p e c t e d l y l o w w h e n t h e t e x t u r e ( s i l t + c l a y = 1 6 % ) , b u l k d e n s i t y (1 3 7 6 k g m - 3 ) a n d 122 Hydraulic conductivity (cm.day-1) 123 ma s s i v e a p e d a l s t r u c t u r e i s c o n s i d e r e d . T h i s c a n b e a t t r i b u t e d t o w a r d s t h e i n f l u e n c e o f t h e l o w h y d r a u l i c c o n d u c t i v i t y o f t h e u n d e r l y ing l a y e r s . T h e K v a l u e s fo r t h e A h o r i z o n r a n g e d f r o m 0 . 6 8 c m d a y - 1 a t F S t o 0 .0 1 c m d a y - 1 a t DUL, wh i l e t he wa t e r r eg i me r ang ed f ro m 0 .25 mm mm - 1 a t F S t o 0 . 2 1 mm m m - 1 a t D U L . 1.000 0.900 y (0 - 30 cm ) = 8E-13e 107.68x R2 = 0.8029 0.800 y (30 - 60 cm)= 7E-20e154.65x0.700 R2 = 0.8209 0.600 0-30 cm y (60 -90 cm) = 4E-45e335.02x 0.500 R2 = 0.9112 30-60 cm 0.400 60 -90 cm 0.300 0.200 0.100 0.000 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 Soil water content (mm.mm-1) F i g u r e 4 . 9 H y d r a u l i c c o n d u c t i v i t y c u r v e s f o r t h e Tu k u l u s o i l . S epane : Th e h e t e r o g en e i ty o f t h e h o r i zon s i s r e f l e c t ed i n t h e r e l a t i v e s h ape and p o s i t i on o f t he K - Ө cu rv es . On th e fu r th e s t r i gh t o f t he w e t n e s s s c a l e i s t h e P e d o c u t a n i c B h o r i zo n w i th a w e l l d ev e lop ed me d iu m s i z e b lo ck y s t ru c tu re , f o l l o w ed b y th e w e l l d ev e lop ed , me d i u m s i z e p r i s ma t i c s t ru c tu re o f t h e C h o r i zon and the a p ed a l s t ru c tu re o f t h e A h o r i z o n o n t h e l e f t . Th e i n t e rn a l d r a inag e r a t e i s p r o b a b l y c o n t r o l l e d b y t h e C h o r i z o n s a t F S , w h e r e a f t e r i t sh i f t s t o t h e B h o r i z o n . T h e w a t e r r eg i me o f t h e B h o r i zon v a r i ed b e t w e en FS (0 .28 mm mm - 1 ) and DUL ( 0 .2 6 mm m m - 1 ) r e f l e c t s o n t h e g o v e rn in g o f t h e B ho r i zon hyd rau l i c c o n d u c t i v i t y b y t h e C h o r i z o n . Ex a mi n i n g t h e s h a p e o f t h e c u r v e s i t c a n b e d ed u c t ed th a t t h e C h o r i zo n h a s l a rg e r p o re s i n t h e h igh e r w e tn es s r a n g e b e t w e e n F S a n d D U L . C o mp a r i n g t h e sha p e o f t h e A a n d B h o r i z o n i t s h o w s t h a t t h e s l o w h y d rau l i c conduc t i v i t y o f t he B ho r i zon i n f l uenced t h e r e l e a s e o f w a t e r f r o m t h e A h o r i z o n t o t he B h o r i z o n . T h e K v a l u e s f o r t h e A h o r i z o n r a n g e d f r o m 0 . 1 5 c m d a y - 1 a t FS t o 0 .001 c m d ay - 1 a t D U L , 123 Hydraulic conductivity (cm.day-1) 124 wh i l e t he w a te r r eg i me r ang ed f ro m 0 .26 mm mm - 1 a t FS t o 0 .24 mm mm - 1 a t D U L . 1.400 y (0 - 30 cm) = 7.8848x - 1.8941 1.200 R2 = 0.928 1.000 y (30 - 60 cm)= 24.911x - 6.7661 R2 = 0.9367 0.800 0-30 cm y (60 -90 cm)= 2E-35e289.66x 0.600 R2 = 0.8111 30-60 cm 0.400 60 - 90 cm 0.200 0.000 0.23 0.24 0.25 0.26 0.27 0.28 0.29 Soil water content (mm.mm-1) F i g u r e 4 . 1 0 H y d r a u l i c conduc t i v i t y cu rve s f o r t h e S e p a n e s o i l . 4 .4 Con c lu s io n T h e g e n e r a l o b j e c t ive o f t h i s s t udy was t o c h a r a c t e r i z e t h e hyd rau l i c p r o p e r t i e s o f t h e B l o e md a l , T u k u l u a n d S e p a n e so i l s u s ing t h e i n t e rna l d r a in ag e me t h o d . T h e v o l u me t r i c w e t n e s s – t i me r e l a t ionsh ip s o f t he B l o e md a l a n d Tu k u l u so i l f o rms w e re ma in ly i n f l u en ced by t h e comp a c t e d a n d s t r o n g p r i s ma t i c s t ru c tu r e o f t he C ho r i zon . Th e Sep a n e o n t h e o t h e r h an d wa s ma i n ly i n f l u e n c e d b y t h e P e d o c u t a n i c B h o r i z o n w i t h a mod e r a t e c l ay con ten t , sub a n g u l a r b l o c k y s t r uc t u r e a n d h i g h b u l k d e n s i t y . I t w a s fo u n d t h a t t h e s t ru c tu r e o f t h e B ho r i zon w a s t h e ma in con s t i t uen t i n f l uen c ing t he h y d rau l i c h e ad – d ep th r e l a t i o n sh ip o f t h e Se p an e so i l . F ro m t h e K -Ө r e l a t i onsh ip s t he s ame t r end was f o u n d a n d w a s c o n c luded t ha t t he hyd rau l i c conduc t i v i t y o f t h e B loemda l and Tuku lu p r o f i l e s a r e ma i n l y i n f l u e n c e d b y t h e n o n d i a g n o s t i c C h o r i z o n , w h i l e t h e h y d r a u l i c c o n d u c t i v i t y o f t h e S e p an e p r o f i l e i s ma i n l y i n f l uenced by t he Pedocu t an i c B ho r i zon . 124 Hydraulic conductivity (cm.day-1) 125 CHAPTER 5 Con c lu s io n s and R e co mme n d a t io n s Th e so i l p ro p e r t i e s o f Pa r a d y s a r e p e r c e iv ed t o v a ry mod er a t e ly c o mp a red t o o t h e r a r e a s o f S o u th A f r i c a . A g r e a t e r v a r i a t i o n i n so i l p ro p e r t i e s b e t w een t h e se so i l f o r ms t h an w i t h i n s o i l ma p u n i t s i mp l i e s t h a t s o i l ma p s can be u sed w i th con f id en ce t o p r ed i c t t he b ehav iou r o f t he l and fo r spec i f i c l and u se s . The s o i l s o f t h e B l o e md a l , T u k u l u a n d S e p a n e f o r ms r e s p o n d e d d i f f e r e n t l y t o b i o l o g i c a l ( r o o t d e v e l o p me n t ) a n d h y d r o l o g i c a l ( d r a i n ag e ) t r e a t me n t s . T h e i n t e r r e l a t ion sh ips b e tw een so i l p rope r t i e s a i d i n t h e s i mp l i fy in g , c o mp i l a t i o n a n d i n t e r p r e t a t i o n o f s o i l ma p s . Th e sy s t ema t i c v a r i a t i on i n S i + C l be tw een t he s o i l fo rms i mp l i e s t h a t i t i s t h e ma i n f a c to r c o n t ro l l i n g t h e b e h a v i o u r o f t h e s e so i l f o rms . 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J . 6 9 : 4 8 2 – 4 9 1 . 131 132 APPENDICES Appendix A Dis t r ibut ion of the c lay content for the A hor izon, B hor izon and C hor izon. 132 133 Appendix B Dis t r ibut ion of the pH w a t e r for the A hor izon, B hor izon and C hor izon. 133 134 Appendix C Dis t r ibut ion of the pH K C l for the A hor izon, B hor izon and C hor izon. 134 135 Appendix D Dis t r ibut ion of the Ca (cmol - 1c kg ) for the A hor izon, B hor izon and C hor izon 135 136 Appendix E Dis t r ibut ion of the K (cmol c kg - 1 ) for the A hor izon, B hor izon and C hor izon 136 137 Appendix F Dis t r ibut ion of the Mg (cmol c kg - 1 ) for the A hor izon, B hor izon and C hor izon 137 138 Appendix G D i s t r i b u t i o n o f t h e N a ( c mo l c kg - 1 ) f o r t h e A h o r i z o n , B h o r i z o n a n d C h o r i z o n 138 139 Appendix H C h e mi c a l a n d p h y s i c a l p r o p e r t i e s o f t h e A h o r i z o n o f t h e T u k u l u s o i l f o r m Ca K Mg Na Plot no pHH2O pHKCl (cmolc.kg-1) (cmolc.kg-1) (cmolc.kg-1) (cmolc kg-1) Total Cations Sand (%) Silt (%) Clay (%) 3.5 5.9 4.35 36.00 13.21 26.79 2.91 78.90 74.82 5 18 4.5 6.15 4.65 35.00 12.05 12.30 2.93 62.29 73.34 6 17 5.5 6.8 4.55 45.00 16.79 25.40 3.04 90.24 75.82 3 19 7.5 6.1 4.75 25.78 15.00 13.10 1.52 55.39 77.66 4 17 8.5 5.95 4.65 26.25 14.74 13.49 1.98 56.46 76.34 4 17 9.5 5.63 4.43 40.50 15.33 23.65 2.70 82.18 78.04 2 18 10.5 5.5 4.65 36.73 14.51 12.06 2.00 65.30 77.58 3 17 11.5 5.1 4.53 32.50 13.08 12.54 1.65 59.77 76.00 4 16 13.5 6.1 4.97 37.50 13.69 20.16 1.65 73.00 78.72 4 17 14.5 6.1 4.92 46.10 13.18 23.81 1.83 84.92 76.89 4 17 14.4 5.81 4.67 34.00 14.41 28.57 1.83 78.81 74.50 8 17 B 5.4 4.57 34.80 11.44 13.33 1.57 61.13 77.74 3 16 12.4 6.12 4.73 35.70 14.05 28.57 3.48 81.80 71.52 5 18 7.4 5.74 4.65 32.50 15.26 25.79 2.39 75.94 75.64 4 17 5.4 5.61 4.35 45.00 15.90 27.38 2.93 91.21 76.10 3 18 4.4 6.1 5.25 32.25 12.95 24.01 2.61 71.82 76.51 5 17 3.4 5.85 4.3 23.25 13.59 23.61 2.72 63.17 74.86 3 17 2.4 6.05 4.75 39.88 17.50 25.20 2.61 85.18 76.24 5 17 1.3 5.3 4.2 32.75 17.31 23.81 2.72 76.58 76.24 4 17 2.3 5.9 5.1 31.75 13.46 16.67 2.11 63.99 80.34 2 16 3.3 5.95 5.2 32.75 16.67 22.42 2.39 74.23 75.80 3 17 4.3 6 4.15 21.25 8.97 7.54 1.54 39.31 79.24 4 15 Continue 139 140 5.3 5.8 4.65 29.50 14.94 19.25 2.37 66.05 78.56 2 17 7.3 5.75 4.7 35.63 16.35 16.47 3.15 71.59 74.26 4 18 10.3 5.82 4.72 40.63 15.96 25.79 3.04 85.42 73.82 7 18 11.3 5.29 4.36 29.50 7.05 21.23 2.39 60.17 75.84 3 17 12.3 6.02 4.65 34.13 6.47 19.84 2.39 62.83 78.22 3 17 C 6.05 5.25 42.40 11.28 23.81 2.87 80.36 74.30 5 19 15.2 5.98 4.83 32.25 7.59 22.22 2.35 64.41 74.14 7 17 12.2 6.25 5.56 41.00 17.13 26.98 2.96 88.07 72.94 6 20 11.2 5.68 4.41 31.53 13.09 13.89 2.39 60.89 77.46 2 17 10.2 5.69 4.19 41.25 6.15 19.09 1.98 68.47 70.44 6 16 5.2 5.25 4.2 41.00 8.01 9.72 1.96 60.69 74.66 6 16 4.2 5.89 4.89 41.00 13.46 10.36 3.28 68.10 73.28 6 18 3.2 5.7 4.5 39.88 13.01 9.72 2.39 65.00 78.42 4 17 2.2 5.45 4.05 35.50 9.04 9.13 1.85 55.51 78.80 5 16 1.2 5.18 4.65 34.53 11.55 18.25 2.85 67.18 71.64 4 17 2.1 6.7 4.85 31.25 13.08 9.92 2.61 56.86 76.48 4 17 3.1 5.2 4.6 44.38 15.26 11.51 2.07 73.20 72.77 8 16 4.1 5.15 4.25 34.13 7.44 13.49 1.74 56.79 78.62 6 15 11.1 5.32 4.75 31.88 8.27 19.84 2.39 62.38 75.32 4 17 15.1 5.83 4.7 32.50 7.76 18.65 2.28 61.19 75.06 5 17 Min 5.10 4.05 21.25 6.15 7.54 1.52 36.47 70.44 2.00 15.00 Max 6.80 5.56 46.10 17.50 28.57 3.48 95.65 80.34 8.00 20.00 Mean 5.79 4.65 35.26 12.76 18.79 2.39 69.21 75.83 4.40 17.07 Std Dev 0.39 0.33 5.79 3.29 6.31 0.52 15.90 2.27 1.55 0.97 140 141 Appendix I Che mica l and phys i ca l p rope r t i e s o f t he B ho r i zon fo r t he Tuku lu so i l f o rm Ca K Mg Na Total Plot no pH pH (cmolc.kg-1H2O KCl ) (cmolc.kg-1) (cmolc.kg-1) (cmolc kg-1) Cations Sand (%) Silt (%) Clay (%) 3.5 5.53 5.41 30.53 6.15 15.87 1.74 54.29 69.02 5 26 4.5 5.8 4.55 37.88 5.59 20.63 2.83 66.93 69.76 3 27 5.5 6.38 5.4 49.30 8.46 29.37 3.65 90.78 65.42 4 29 7.5 6.1 5.35 41.38 6.35 23.81 2.65 74.18 66.26 3 28 8.5 6.05 5.45 35.38 6.54 18.06 2.83 62.80 67.84 4 27 9.5 7.05 6.44 55.10 12.05 33.17 4.17 104.50 63.66 2 32 10.5 6.56 5.62 48.10 4.72 24.60 2.78 80.20 65.76 4 28 11.5 6.28 5.31 42.50 6.82 22.22 2.96 74.50 62.92 7 27 13.5 6.91 5.74 57.00 10.82 31.75 3.74 103.31 59.18 9 31 14.5 6.43 5.58 51.10 7.95 29.37 2.96 91.37 61.3 7 29 14.4 5.49 5.49 41.00 5.59 23.81 2.61 73.01 61.94 9 27 B 5.08 4.18 29.40 3.18 12.70 1.39 46.67 63.6 10 25 12.4 5.59 4.27 35.20 5.95 12.70 1.96 55.80 62.76 9 26 7.4 5.32 4.63 32.50 6.35 11.90 1.52 52.27 67.12 4 26 5.4 5.9 5.73 39.13 5.96 19.84 3.15 68.08 67.97 5 27 4.4 6.4 5.5 39.25 6.42 30.16 2.63 78.46 59.2 10 28 3.4 6.16 5.07 39.88 6.47 19.84 2.83 69.02 65.68 4 27 2.4 6.25 5.25 44.63 6.21 22.62 2.83 76.28 63.92 5 28 1.3 5.14 4.61 28.63 5.71 14.48 2.07 50.88 67.12 2 26 2.3 5.43 4.63 28.13 5.45 12.70 1.74 48.01 66.76 5 26 Continue 3.3 6 5.1 44.50 6.47 21.83 2.61 75.41 61.76 10 27 4.3 6.45 5.08 46.13 6.54 21.23 3.41 77.31 63.58 5 28 141 142 5.3 6.55 5.18 50.38 9.87 22.42 3.59 86.25 67.46 3 29 7.3 5.19 5.14 42.88 6.41 23.02 2.50 74.80 66.73 3 28 10.3 6.55 5.32 55.25 8.08 27.78 2.93 94.04 63.4 7 29 11.3 6.07 4.13 25.88 4.87 9.92 1.30 41.97 64.1 8 25 12.3 6.3 5.19 40.13 5.83 19.84 2.48 68.28 68.16 4 27 C 5.88 4.68 31.40 7.03 12.70 1.52 52.65 68.01 4 26 15.2 6.29 5.11 52.30 6.87 20.63 2.17 81.98 63.48 5 28 12.2 6.13 5.17 47.00 6.77 22.70 2.43 78.90 65.61 4 28 11.2 6.15 4.14 33.40 5.54 11.59 1.48 52.00 63.54 7 26 10.2 6.06 4.08 33.00 5.49 13.81 1.30 53.60 68.82 5 26 5.2 6.16 4.2 36.63 5.77 21.63 2.50 66.52 65.84 4 27 4.2 6.1 4.7 42.25 6.41 25.40 2.35 76.40 67.62 4 28 3.2 6.6 5.4 50.50 9.49 31.15 3.30 94.44 64.84 4 29 2.2 5.52 4.8 30.70 5.59 11.43 1.48 49.20 60.6 9 26 1.2 6.05 5.15 39.90 5.74 18.10 2.09 65.83 68.82 4 27 2.1 5.9 5.16 42.50 6.41 24.01 2.39 75.31 65.5 4 28 3.1 6 4.8 38.75 6.22 20.24 2.07 67.27 65 4 27 4.1 5.7 4.35 25.25 5.77 11.11 1.09 43.22 61.88 8 26 11.1 6.37 5.18 47.75 9.94 27.78 2.93 88.40 62.94 5 29 15.1 6.59 5.24 53.13 10.06 27.78 2.93 93.90 62.36 4 29 Min 5.08 4.08 25.25 3.18 9.92 1.09 39.44 59.18 2.00 25.00 Max 7.05 6.44 57.00 12.05 33.17 4.17 106.40 69.76 10.00 32.00 Mean 6.06 5.04 40.85 6.76 20.85 2.47 70.93 64.93 5.38 27.45 Std Dev 0.46 0.52 8.58 1.76 6.44 0.74 17.51 2.71 2.29 1.47 142 143 Appendix J C h e mi c a l a n d p h y s i c a l p r o p e r t i e s o f t he C ho r i zon fo r t he Tuku lu so i l f o rm Ca K Mg Na Plot no pHH2O pHKCl (cmolc.kg-1) (cmolc.kg-1) (cmolc.kg-1) (cmolc kg-1) Total cations Sand (%) Silt (%) Clay (%) 3.5 5.85 4.14 35.20 9.38 41.27 4.26 90.12 52.92 6 40 4.5 6.57 5.11 52.40 8.67 46.03 2.17 109.27 51.7 3 45 5.5 6.17 4.42 45.70 8.10 38.10 1.83 93.72 48.36 5 44 7.5 6.59 5.33 69.40 14.10 61.90 3.83 149.23 47.86 4 48 8.5 6.56 5.13 67.10 8.82 60.32 3.83 140.06 49.58 2 48 9.5 5.87 4.11 34.80 7.54 44.44 3.74 90.52 53.2 5 40 10.5 5.77 4.96 59.00 4.82 25.40 1.91 91.13 57.76 3 39 11.5 6.23 4.69 57.30 16.51 50.79 2.87 127.48 43.8 8 46 13.5 6.74 4.53 53.50 10.41 38.10 2.26 104.27 45 9 45 14.5 6.54 4.53 57.15 10.28 34.13 2.39 103.95 45.38 9 45 14.4 6.58 5.18 150.50 12.46 55.56 3.83 222.34 38.86 11 48 B 7.05 5.62 54.80 6.62 23.49 1.65 86.56 41.16 12 45 12.4 7.27 5.96 68.30 4.51 56.35 3.83 132.99 44.34 6 48 7.4 6.48 4.79 61.75 12.69 50.20 3.59 128.23 46.86 5 47 5.4 6.64 5.27 71.88 15.90 70.63 4.02 162.43 47.9 6 49 4.4 6.53 5.13 67.25 14.87 59.52 3.85 145.49 45.54 5 48 3.4 6.85 5.46 82.50 20.77 79.37 4.35 186.98 41.84 5 51 2.4 6.48 4.74 60.75 13.27 51.59 3.26 128.87 46.62 4 47 1.3 6.56 4.25 74.75 17.44 65.48 4.24 161.90 44.11 5 49 2.3 6.47 4.49 46.50 13.27 55.56 2.07 117.39 51.36 4 44 3.3 6.88 5.48 84.00 21.54 81.35 4.67 191.56 38.35 7 51 4.3 6.84 5.49 81.75 21.67 83.65 4.67 191.74 41.48 4 51 5.3 6.83 5.46 84.88 21.41 85.32 4.57 196.17 43.31 2 51 7.3 6.64 5.22 72.63 16.35 69.44 4.02 162.44 41.56 6 49 10.3 7.09 4.57 53.50 10.83 65.48 2.39 132.20 48.7 4 45 Continue 11.3 5.95 4.2 38.88 7.82 39.68 1.52 87.90 52.16 4 41 12.3 6.45 4.72 39.60 10.10 53.97 3.13 106.80 44.76 5 47 C 7.9 4.57 51.60 12.00 66.67 6.70 136.96 51.36 3 45 15.2 6.47 4.75 61.40 12.62 52.38 3.39 129.79 47.06 4 47 143 144 12.2 6.78 5.39 76.90 19.44 77.78 4.52 178.64 43.36 4 50 11.2 6.53 5.18 67.90 14.21 58.73 3.83 144.66 46.37 5 48 10.2 6.27 4.88 74.50 15.95 52.38 2.61 145.44 48.2 4 46 5.2 6.08 5.14 40.80 10.97 41.27 1.30 94.35 53.1 3 43 4.2 6.59 4.42 48.60 6.97 25.71 1.91 83.20 49.82 4 44 3.2 6.22 4.58 53.80 9.33 41.75 2.17 107.05 49.28 3 45 2.2 4.43 4.75 61.40 11.18 50.79 3.39 126.76 46.85 5 47 1.2 6.05 4.34 42.90 20.51 68.25 4.09 135.75 50.5 5 43 2.1 7.18 4.71 61.63 13.59 53.57 4.02 132.81 47.42 3 47 3.1 6.94 5.24 74.00 17.44 63.49 4.02 158.95 44.68 4 49 4.1 6.45 4.77 64.88 12.05 47.62 3.15 127.70 49.32 2 47 11.1 6.24 4.53 54.00 10.19 43.65 2.83 110.67 48.3 4 45 15.1 6.67 5.29 71.63 17.88 65.48 4.24 159.22 46.54 3 49 Min 4.43 4.11 34.80 4.51 23.49 1.30 64.11 38.35 67.66 39.00 Max 7.90 5.96 150.50 21.67 85.32 6.70 264.18 57.76 171.44 51.00 Mean 6.51 4.89 62.66 12.96 54.68 3.36 133.66 47.06 118.06 46.33 Std Dev 0.52 0.45 19.37 4.66 15.46 1.11 40.61 4.12 25.35 3.01 144 145 Appendix K C h e mi c a l a n d p h y s i c a l p r o p e r t i e s o f t h e A h o r i z o n f o r t h e S e p a n e s o i l f o r m Plot no pH -1 -1H2O pHKCl Ca (cmolc.kg ) K (cmolc.kg ) Mg (cmolc.kg-1) Na (cmolc kg-1) Total Cations Sand (%) Silt (%) Clay (%) 12.5 5.53 4.55 36.90 5.95 12.70 3.22 58.76 78.84 3 18 15.5 6.15 5.06 54.60 6.21 31.75 3.30 95.86 72.53 7 18 15.4 6.24 4.95 54.80 9.13 34.92 3.57 102.41 70.06 8 19 13.4 6.33 5.11 51.90 6.56 23.81 2.96 85.23 71.45 9 18 11.4 5.9 4.58 30.53 4.63 13.89 1.96 51.00 79.82 5 15 13.3 6.79 5.18 47.70 6.72 23.97 3.04 81.43 71.43 8 20 14.3 6.25 5.1 57.00 6.77 28.57 3.83 96.17 70.3 10 20 15.3 6.25 5.25 54.40 7.28 23.65 2.70 88.03 70.56 8 19 14.2 5.43 4.95 44.10 6.67 26.98 2.78 80.53 71.44 8 18 13.2 6.42 5.55 59.03 6.93 27.02 4.37 97.35 65.44 10 21 D 5.41 4.31 40.70 6.00 22.22 3.57 72.49 75.56 3 18 7.2 5.1 4.4 44.13 7.45 26.98 3.70 82.25 74.52 5 19 5.1 5.65 4.25 37.25 5.06 11.11 3.26 56.69 74.1 4 17 7.1 6.55 5.35 51.38 11.86 33.13 4.13 100.50 74.12 4 20 10.1 6.17 4.72 46.00 8.21 21.87 3.80 79.87 75.82 2 19 12.1 5.7 4.43 47.38 6.99 21.83 3.80 79.99 70.72 7 19 E 6.54 5.25 78.75 11.79 35.71 4.02 130.28 74.38 5 20 13.1 6.25 4.85 42.50 8.97 29.40 3.72 84.60 70.5 8 19 14.1 6.27 4.95 50.00 7.05 29.76 3.91 90.73 70.83 7 19 Min 5.10 4.25 30.53 4.63 11.11 1.96 48.22 65.44 2.00 15.00 Max 6.79 5.55 78.75 11.86 35.71 4.37 130.69 79.82 10.00 21.00 Mean 6.05 4.88 48.90 7.38 25.23 3.45 84.96 72.76 6.37 18.74 Std Dev 0.46 0.38 10.43 1.92 7.03 0.59 19.97 3.36 2.43 1.33 145 146 Appendix L Che mica l and phys i ca l p rope r t i e s f o r t h e B h o r i z o n o f t h e S e p a n e s o i l f o r m Plot no pHH2O pH Ca (cmolc.kg-1KCl ) K (cmolc.kg-1) Mg c(molc.kg-1) Na (cmolc kg-1) Total Cations Sand (%) Silt (%) Clay (%) 12.5 5.17 4.61 47.40 4.05 31.75 2.00 85.20 62.56 10 26 15.5 6.13 4.72 74.00 4.41 26.98 1.96 107.35 62.26 9 28 15.4 7.09 5.6 73.70 8.10 41.27 3.26 126.33 59.61 5 35 13.4 6.33 5.11 61.90 6.23 23.81 2.09 94.03 58.45 9 29 11.4 6.53 5.1 64.30 5.95 26.98 2.00 99.23 64.7 4 29 13.3 6.32 5.11 67.90 6.36 36.51 2.09 112.85 64.1 4 32 14.3 6.22 4.91 77.50 8.82 40.00 3.13 129.45 55.72 7 35 15.3 7.15 5.9 76.70 10.15 61.90 4.43 153.19 54.6 6 36 14.2 6.6 5.77 69.40 6.92 39.68 2.35 118.35 60.52 5 32 13.2 6.6 5.26 67.60 6.92 41.90 2.26 118.69 59.42 4 32 D 5.95 4.85 52.10 5.23 18.57 1.09 76.99 61.94 8 27 7.2 5.6 4.75 47.63 2.56 16.87 1.20 68.25 61.93 8 26 5.1 5.9 4.6 30.63 4.10 24.21 1.63 60.56 62.44 8 28 10.1 6.78 5.26 51.25 5.83 29.76 2.07 88.91 57.82 7 31 12.1 6.5 5.05 66.88 4.87 23.81 1.52 97.08 66.4 2 28 E 6.27 5.57 62.88 7.05 34.13 2.26 106.31 62.7 2 34 13.1 6.84 5.31 67.13 8.14 33.73 2.83 111.82 57.57 6 35 14.1 6.85 5.34 71.75 7.82 35.71 3.04 118.33 58.05 5 35 Min 5.17 4.60 30.63 2.56 16.87 1.09 60.56 54.60 2.00 26.00 Max 7.15 5.90 77.50 10.15 61.90 4.43 153.19 66.40 10.00 36.00 Mean 6.38 5.16 62.81 6.31 32.64 2.29 104.05 60.60 6.06 31.00 Std Dev 0.51 0.38 12.40 1.92 10.56 0.81 23.00 3.17 2.36 3.45 146 147 Appendix M Che mica l and phys i ca l p rope r t i e s f o r t h e C h o r i z o n o f t h e S e p a n e s o i l f o r m Plot no pHH2O pHKCl Ca (cmolc.kg-1) K (cmolc.kg-1) Mg c(molc.kg-1) Na (cmolc kg-1) Total Cations Sand (%) Silt (%) Clay (%) 12.5 7.03 5.96 57.60 11.69 44.44 1.48 115.22 45.78 7 45 15.5 7.18 6.05 62.80 11.23 40.63 1.57 116.23 46.63 7 46 15.4 7.33 6.27 72.40 11.59 57.14 1.83 142.96 42.64 8 48 13.4 7.08 5.96 59.70 18.05 46.03 1.43 125.22 46.22 8 45 11.4 6.83 5.16 36.63 5.38 21.03 0.76 63.80 57.32 3 39 13.3 7.66 6.66 91.80 13.49 65.08 1.83 172.19 42.75 4 53 14.3 7.76 6.72 98.80 8.67 52.38 2.09 161.93 40.65 4 55 15.3 7.58 6.45 81.80 8.21 57.14 1.91 149.06 43.58 5 50 14.2 7.06 6.28 71.60 13.33 63.49 4.52 152.95 45.92 5 48 13.2 7.29 6.19 67.70 11.08 58.73 1.65 139.16 46.86 4 47 D 6.88 5.35 43.10 7.28 34.92 0.61 85.91 55.44 4 39 7.2 7.36 6.17 70.30 13.49 53.97 1.87 139.62 47.94 4 48 5.1 6.55 5.29 42.00 6.92 23.81 1.09 73.82 55.78 3 40 7.1 6.93 5.35 60.25 10.00 51.59 1.33 123.16 51.66 3 44 10.1 7.38 6.23 74.75 13.53 57.54 1.76 147.58 45.14 4 48 12.1 7.45 6.37 79.00 8.85 39.68 1.85 129.38 46.68 2 49 E 7.09 5.88 91.00 8.33 51.59 1.41 152.33 48.12 5 45 13.1 7.09 6.16 59.25 4.94 17.86 1.20 83.24 49.02 4 45 14.1 7.65 6.56 85.50 8.59 39.68 2.02 135.79 42.42 3 52 Min 6.55 5.16 36.63 4.94 17.86 0.61 60.03 40.65 2.00 39.00 Max 7.76 6.72 98.80 18.05 65.08 4.52 186.45 57.32 8.00 55.00 Mean 7.22 6.06 68.74 10.24 46.14 1.69 126.82 47.40 4.58 46.63 Std Dev 0.32 0.48 17.53 3.36 14.39 0.82 36.10 4.81 1.69 4.47 147 148 Appendix N Che mica l and phys i ca l p rope r t i e s f o r t he A h o r i z o n o f t h e B l o e m d a l s o i l f o r m Plot no pHH2O pHKCl Ca (cmolc.kg-1) K (cmolc.kg-1) Mg c(molc.kg-1) Na (cmolc kg-1) Total Cations Sand (%) Silt (%) Clay (%) 1.5 5 4.85 35.25 5.38 9.33 2.39 52.35 70.64 11 15 2.5 5.45 3.55 39.63 4.62 9.92 1.96 56.12 77.26 4 14 A 5.77 4.18 35.40 5.51 13.97 1.57 56.45 78.76 5 15 10.4 5.8 4.66 41.03 8.33 29.40 2.61 81.37 78.36 4 18 9.4 6.1 4.87 44.88 8.85 18.29 2.98 74.99 75.66 4 19 8.4 5.89 4.16 29.88 5.13 17.86 1.85 54.71 77.48 4 15 1.4 5.59 4.51 30.38 6.28 19.25 3.04 58.95 78.32 4 17 8.3 5.04 3.95 28.88 4.74 15.08 0.98 49.68 79.78 5 14 9.3 5.05 4.01 36.88 5.38 26.39 1.20 69.84 76.66 5 15 9.2 5.65 4.49 40.53 8.99 27.02 2.83 79.36 75.42 3 18 8.2 5.17 4.14 31.13 6.28 15.87 2.83 56.11 77.66 3 16 1.1 5.05 3.9 34.03 6.03 24.64 3.48 68.17 79.88 3 16 8.1 5.6 4.25 39.25 6.41 11.31 3.80 60.77 70.84 8 17 9.1 5.78 4.48 42.50 8.08 27.78 3.26 81.62 69.72 8 18 Min 5 3.55 28.88 4.62 9.33 0.98 49.68 69.72 3 14 Max 6.1 4.87 44.88 8.99 29.40 3.80 81.62 79.88 11 19 Mean 5.50 4.29 36.40 6.43 19.01 2.48 64.32 76.17 5.07 16.21 Std Dev 0.37 0.38 5.10 1.51 6.93 0.86 11.31 3.39 2.34 1.63 148 149 Appendix O Che mica l and phys i ca l p rope r t i e s f o r t he B h o r i z o n o f t h e B l o e m d a l s o i l f o r m Plot no pHH2O pHKCl Ca (cmolc.kg-1) K (cmolc.kg-1) Mg c(molc.kg-1) Na (cmolc kg-1) Total Cations Sand (%) Silt (%) Clay (%) 1.5 5.16 5.7 41.40 20.67 23.81 2.96 88.83 65.12 5 28 2.5 4.6 4.45 38.38 20.71 13.29 2.07 74.44 69.24 4 24 A 4.22 4.33 37.40 4.87 19.05 1.65 62.97 69.68 4 23 10.4 4.44 5.03 38.75 19.74 16.67 1.96 77.12 66 5 24 9.4 4.05 4.1 36.38 6.67 15.87 2.39 61.31 70.22 6 21 8.4 6.57 5.3 40.25 20.13 20.24 2.50 83.12 69.28 3 26 1.4 5.88 5.98 43.50 21.47 26.19 3.26 94.43 64.09 5 29 8.3 6.47 5.03 51.38 22.69 27.78 3.70 105.54 63.86 5 31 9.3 4.62 5.15 39.25 20.90 17.46 2.83 80.43 68.11 6 24 9.2 5.26 4.95 37.50 19.54 18.41 2.52 77.97 67.9 5 23 8.2 5.08 5.72 41.30 20.56 23.49 3.22 88.57 63.5 5 28 1.1 6.24 5 48.75 21.67 27.38 3.37 101.17 64.5 4 30 8.1 4.8 5.5 39.88 22.50 19.64 2.39 84.41 69.32 3 25 9.1 5.07 5.53 40.88 20.32 21.83 2.61 85.63 68.72 2 27 Min 4.05 4.1 36.38 4.87 13.29 1.65 61.31 63.5 2 21 Max 6.57 5.98 51.38 22.69 27.78 3.70 105.54 70.22 6 31 Mean 5.18 5.13 41.07 18.75 20.79 2.67 83.28 67.11 4.43 25.93 Std Dev 0.82 0.55 4.28 5.59 4.45 0.58 12.57 2.47 1.16 2.97 149 150 Appendix P C h e mi c a l a n d p h y s i c a l p r o p e r t i e s f o r t he C ho r i zon o f t he B loemda l so i l f o rm Plot no pHH2O pHKCl Ca (cmolc.kg-1) K (cmolc.kg-1) Mg c(molc.kg-1) Na (cmolc kg-1) Total Cations Sand (%) Silt (%) Clay (%) 1.5 6.98 5.53 70.30 10.31 44.44 4.26 129.31 43.6 4 50 2.5 6.72 5.48 69.40 10.15 36.51 4.17 120.24 44.08 4 49 A 6.14 5.04 45.70 8.97 30.16 3.30 88.14 53.96 2 43 10.4 6.15 5.03 48.38 9.49 27.58 3.26 88.70 49.76 6 43 9.4 6.41 5.23 58.50 9.68 32.94 3.70 104.81 50.18 3 46 8.4 6.07 4.99 42.63 8.33 22.82 2.83 76.60 54.84 3 42 1.4 6.67 5.37 61.13 17.50 35.32 3.91 117.86 43.72 7 48 8.3 6.19 5.06 45.50 9.23 23.81 2.96 81.50 51.75 4 43 9.3 6.95 5.59 73.63 20.96 83.33 3.15 181.07 44.74 3 50 9.2 5.94 4.96 35.00 6.46 19.05 2.52 63.03 50.38 6 41 8.2 6.65 5.38 63.00 9.90 46.03 3.91 122.84 45.17 5 48 1.1 5.92 4.42 36.13 6.15 21.83 2.61 66.71 54.76 2 41 8.1 6.32 4.29 34.63 6.03 15.87 2.93 59.46 54.16 4 39 9.1 6.21 5.1 51.75 9.55 27.78 3.48 92.56 52.16 2 44 Min 5.92 4.29 34.63 6.03 15.87 2.52 59.46 43.6 2 39 Max 6.98 5.59 73.63 20.96 83.33 4.26 181.07 54.84 7 50 Mean 6.38 5.11 52.55 10.19 33.39 3.36 99.49 49.52 3.93 44.79 Std Dev 0.36 0.38 13.51 4.15 16.91 0.57 32.86 4.39 1.59 3.66 150 151 Appendix Q Pe d o l o g i c a l c h a r a c t e r i s t i c s o f t he Tuku lu so i l f o rm Soil Clay Number family Horizons Name Depth Mottles Cutans Structure (%) Consistency Lime Transition 7.1 Tu 1220 (Modal) Dikeni A Ot 210 None none Apedal massive 18 Loose None Clear, flat Weakly developed medium B Ne 210 None yes 10-25 mm) Sub block 28 Slightly hard None Abrupt, flat well developed medium size C Uw 450 Red, black, yellow, grey yes (5-15 mm) prismatic 49 Hard None Abrupt, flat 1220 Clear, flat 12.2 Tu Dikeni A Ot 200 None none Apedal massive 20 Loose None Weakly developed medium B Ne 300 None yes 10-25 mm) Sub block 28 Slightly hard Occurrence Abrupt, flat Medium developed medium size C Uw 500 Red, black, yellow, grey yes (5-15 mm) prismatic 50 Hard None Abrupt, flat 1220 Clear, flat 5.1 Tu Dikeni A Ot 210 None none Apedal massive 17 Loose None Weakly developed medium B Ne 280 None yes 10-25 mm) Sub block 28 Slightly hard None Abrupt, flat Well developed medium size C Uw 500 Red, black, yellow, grey yes (5-15 mm) prismatic 40 Hard None Abrupt, flat 1220 Clear, flat 1.1 Tu Dikeni A Ot 210 None none Apedal massive 16 Loose None Weakly developed medium B Ne 310 None yes 10-25 mm) Sub block 30 Slightly hard Occurrence Abrupt, flat Medium developed medium size C Uw 250 Red, black, yellow, grey yes (5-15 mm) prismatic 41 Hard Occurrence Abrupt, flat 1220 Clear, flat 1.5 Tu Dikeni A Ot 210 None none Apedal massive 15 Loose None Weakly developed medium B Ne 410 None yes 10-25 mm) Sub block 28 Slightly hard None Abrupt, flat Medium developed medium C Uw 200 Red, black, yellow, grey yes size (5-15 mm) prismatic 50 Hard None Abrupt, flat Summary Min 18 Min A 200 Max A 210 Modal A 210 A 15 Max A 20 Modal A Min 28 Min B 200 Max B 410 Modal B 210 B 28 Max B 30 Modal B Min 48 Depth (mm) Min C 200 MaxC 500 Modal C 450 Clay Content (%) C 40 MaxC 50 Modal C 151 152 Appendix R Pe d o l o g i c a l c h a r a c t e r i s t i c s o f t he Sepane so i l f o rm Soil Horizon Number family Horizons Name Depth Mottles Cutans Structure Clay (%) Consistency Lime Transition 13.1Se 1210 (Modal) Katdoorn A Ot 250 None none Apedal massive 19.00 Loose None Abrupt, flat Well developed medium size (10-25 mm) B Pd 300 None yes blocky 35.00 Hard None Abrupt, flat Well developed medium size C Uw 250 Red, black, yellow, grey yes (5-15 mm) prismatic 45.00 Hard None Abrupt, flat 1210 15.1Se Katdoorn A Ot 210 None none Apedal massive 17.00 Loose None Abrupt, flat Medium developed medium size (10-25 mm) B Pd 300 None yes blocky 29.00 Hard None Abrupt, flat Medium developed medium size C Uw 150 Red, black, yellow, grey yes (5-15 mm) prismatic 49.00 Hard None Abrupt, flat 1210 15.2Se Katdoorn A Ot 210 None none Apedal massive 17.00 Loose None Abrupt, flat Medium developed medium size (10-25 mm) B Pd 400 None yes blocky 28.00 Hard None Abrupt, flat Well developed medium size C Uw 100 Red, black, yellow, grey yes (5-15 mm) prismatic 47.00 Hard None Abrupt, flat 1210 14.2Se Katdoorn A Ot 210 None none Apedal massive 18.00 Loose None Abrupt, flat Well developed medium size (10-25 mm) blocky B Pd 500 None yes 32.00 Hard None Abrupt, flat Medium developed medium size C Uw 100 Red, black, yellow, grey yes (5-15 mm) prismatic 48.00 Hard None Abrupt, flat 1210 12.1Se Katdoorn A Ot 210 None none Apedal massive 19.00 Loose None Abrupt, flat Well developed medium size (10-25 mm) B Pd 450 None yes blocky 28.00 Hard None Abrupt, flat Medium developed medium size C Uw 150 Red, black, yellow, grey yes (5-15 mm) prismatic 49.00 Hard None Abrupt, flat Summary Modal A Min A 17.00 Max A 19.00 Min A 210 Max A 250 250 Modal A 19.00 Clay Depth (mm) Modal A Content Min B 28.00 Max B 35.00 35.00 Min B 300 Max B 500 300 (%) Modal A 45.00 Modal A Min C 45.00 MaxC 49.00 Modal A Min C 100 MaxC 250 250 152 153 Appendix S P e d o l o g i c a l c h a r a c t e r i s t i c s o f t he B loemda l so i l f o r m Horizon Clay Number Soil family Horizons Name Depth Mottles Cutans Structure (%) Consistency Transition 11.1Bd (modal) 3200 Roodeplaat A Ot 210 None none Apedal massive 17.00 Loose Smooth, flat B Yr 280 None none Apedal massive 29.00 Loose Smooth, flat Red, black, yellow, Well developed medium size C Uw 50 grey yes (5-15mm) prismatic 45.00 Hard Smooth, flat 10.5Bd 3200 Roodeplaat A Ot 245 None none Apedal massive 17.00 Loose Smooth, flat B Yr 210 None none Apedal massive 28.00 Loose Smooth, flat Red, black, yellow, Medium developed medium size C Uw 250 grey yes (5-15mm) prismatic 39.00 Hard Smooth, flat 8.1Bd 3200 Roodeplaat A Ot 250 None none Apedal massive 17.00 Loose Smooth, flat B Yr 350 None none Apedal massive 25.00 Loose Smooth, flat Red, black, yellow, Well developed medium size C Uw 150 grey yes (5-15mm) prismatic 39.00 Hard Smooth, flat 11.3Bd 3200 Roodeplaat A Ot 150 None none Apedal massive 17.00 Loose Smooth, flat Apedal massive B Yr 200 None none 25.00 Loose Smooth, flat Red, black, yellow, Medium developed medium size C Uw 150 grey yes (5-15mm) prismatic 41.00 Hard Smooth, flat Summary Min Min A 150 Max A 250 Modal A 150 A 17.00 Max A 17.00 Modal A 17.00 Depth (mm) Clay Content (%) Min Modal B 25.00 Min B 200 Max B 350 Modal B 200 B 25.00 Max B 29.00 Min Min C 50 MaxC 250 Modal C 150 C 39.00 MaxC 45.00 Modal C 41.00 153 154 Appendix T La nd type Ca22 da t a 154 155 Continue 155 156 Appendix U I n t e rpo l a t i on t e chn iqu es 1 T IN A t r i a n g u l a t e d i r r e g u l a r n e t w o r k ( TI N ) w h i c h i s d e f in e d a s a v e c t o r d a t a s t r u c t u r e i s o n e m e t h o d u s ed to s to re a n d d i sp l ay su r f a c e mo d e l s . A T IN c h a r a c t e r i z e s g e o g r a p h i c s p ac e u s i n g a s e t o f i r r eg u la r ly sp a ced d a t a p o in t s , e a c h o f wh ich h as x , y and z v a l u e s ( F i g u r e 1 ) . T h e s e p o i n t s a r e c o n n e c t e d b y e d g e s t o f o r m n o n o v e r l a p p i n g t r i ang l e s and c r ea t e a c o n t i n u o u s s u r f a c e t h a t r e p r e s e n t s t h e t e r r a i n (A R C G IS 9 .1 , 2005 ) F i g u r e 1 I ma g e i l l u s t r a t in g a t r i a n g u l a t ed i r r e g u l a r n e t wo r k ( T I N ) s u r f a c e r e p r e s e n t a t i o n (C la rk , 2001 ) 2 G r id A g r i d i s a sp a t i a l d a t a s t r u c t u r e t h a t d e f i n e s sp a c e a s an a r r ay o f c e l l s o f equ a l s i ze t h a t a r e a r r ang ed in row s and co lumn s (F igu re 2 ) . I n t h e ca se o f a g r i d t h a t r e p r e se n t s a su r f a c e , e a c h c e l l c o n t a i n s a n a t t r i bu t e va lue t ha t r ep r e sen t s a ch ang e i n Z v a lu e . Th e l o ca t i on o f t he ce l l i n geog raph i c sp ace i s ob t a in ed f ro m th i s po s i t i on r e l a t i v e t o t h e g r i d s o r i g in . (A R C G IS 9 .1 , 2 0 0 5 ) F i g u r e 2 I ma g e i l l u s t r a t in g a g r i d s u r f a c e r e p r e sen t a t i on (C la rk , 2001 ) 156 157 F r o m t h i s s u r f a c e s t h a t h a s b e en e s t ab l i sh e d o n e ma y t h e n u s e a n i n t e r p o l a t i o n t e c h n i q u e t h a t w i l l su i t e t h e s i t u a t i o n t h e b e s t . Fo r e x a mp l e : I n v e r s e d i s t a n c e w e i g h i n g ( I n t e r p o l a t i o n me t h o d t h a t u s e s p o in t d a t a t h a t i s c l o s e e n o u g h t o t h e me a s u r e d v a l u e s t h r o u g h i t s i n v e r s e d i s t a n c e . ) ; fo r w h i c h a g r i d r e p re sen t a t i on w i l l be mo re a f f ec t i v e fo r t h e sp ec i f i c i n t e rpo l a t i o n t echn i q u e a s t h e d i s t a n ce b e tw een measu r ed po in t s s t ay c o n s t a n t . U n d e r s t a n d i n g t he d i f f e r en t su r f ace r ep re sen t a t i o n w i l l a s s i s t i n t h e s a mp l in g me t h o d and d en s i ty so t h a t i t mi g h t b e ad equ a t e fo r t h e p a r t i cu l a r i n t e rpo l a t i on t e chn iq u e u s ed (A R C Us e r , 2004 ) . 3 . I nve r se d i s t ance we igh ing ( IDW) I n v e r s e d i s t a n c e w e i g h i n g i s t h e w o r k h o r se o f s p a t i a l i n t e rpo l a t i o n and i s t h u s t h e me t h o d t h a t i s mo s t o f t e n u sed b y G I S a n a ly s t s . I t e mp lo y s T o b l e r ’ s l a w b y e s t i ma t i n g u n k n o w n me a s u r e me n t s a s w e i g h t e d a v e r a g e s o v e r t h e k n o w n m e a s u r e me n t s a t n e a r b y p o i n t s , g iv i n g t h e g r e a t e s t w e i g h t t o t h e n e a r e s t p o i n t s ( F ig u r e 3 ) . T h e r e a r e v a r i o u s way s o f d e f i n in g the w e i g h t s , b u t t h e o p t i o n mos t o f t e n e mp l oy ed i s t o comp u t e t hem as t he i n v e r s e squ a r e s o f d i s t a n c e ( E q u a t i o n 1 ) . W i = 1 / d 2 i ( 1 ) W i = W e i g h t o f i n f l u en c e o f s a mp l ed p o in t o n u n s a mp l e d p o i n t d = d i s t a n c e f r o m s a mp l e d p o in t t o un samp led po in t i = con s t an t r e f e r r i n g to o th e r f a c t o r s i n f lu en c ing w e igh t g iv en to s a mp l ed d a t a p o in t ; f o r ex amp l e f i x ed r ad iu s . F i g u r e 3 I ma g e i l l u s t r a t in g s u r f a c e r e p r e s e n t a t i o n b y I n v e r s e d i s t a n c e w e i g h i n g ( A R C G I S 9 . 1 , 2 0 0 5 ) 157 158 Th i s mea n s t h a t t he w e igh t g iven t o a p o i n t d r o p s b y a f a c t o r o f 4 wh en t h e d i s t a n c e t o t h e p o i n t d o u b l e s . I n a d d i t i o n , mo s t s o f t w a r e g i v e s o n e t h e o p t i o n o f i g n o r i n g a l t o g e th e r po in t s t h a t i s f u r t h e r t h an a sp ec i f i ed d i s t anc e a w ay , o r o f l i mi t i n g t h e av e r age t o a s p ec i f i ed n u mb e r o f n e a r e s t p o i n t s , o r b y a v e r a g i n g o v e r t h e c l o s e s t p o i n t s i n e a c h o f a n u mb e r o f d i r e c t i o n s e c t o r s . T h e i n v e r s e d i s t a n c e w e i g h i n g me t h o d a c h i e v e s t h e d e s i r ed o b j e c t iv e o f c r e a t i n g a s mo o t h su r f a c e w h o se v a l u e a t a n y p o i n t i s mo re l i ke t h e v a lu es a t n ea rby po in t s t han t he v a lu e s a t d i s t an t po in t s . I D W i s d e s c r i b e d a s a n e x a c t me t h o d o f i n t e r p o l a t i o n b e c a u s e i t s i n t e rpo l a t ed r e su l t s h o n o u r t h e d a t a p o i n t s e x a c t l y ( F i g u r e 7 ) . Bu t b ecau se IDW i s an ave r age i t su f f e r s f r o m c e r t a i n spe c i f i c ch a r ac t e r i s t i c s t h a t a r e g en e r a l l y und es i r ab l e . A w e igh ted ave r ag e t h a t u s es w e igh t s t ha t a r e n ev e r n eg a t iv e mu s t a lw ay s r e tu rn a va lu e t h a t i s b e t w e e n t h e l i mi t s o f t h e m e a su r e s v a lu e s – no po in t on t h e i n t e rpo l a t ed su r f ace can have an i n t e rpo l a t ed va lu e t h a t i s mo r e t han t he l a rge s t me a s u r e d v a l u e o r l e s s t h a n t h e s ma l l e s t v a l u e me a s u r e d . T h u s I D W ma y p r o d u c e c o u n t e r - i n t u i t i v e r e s u l t s i n a r e a s o f p e a k s a n d p i t s , a n d o u t s i d e t h e a r e a c o v e r e d b y t h e d a t a p o i n t s . T h e r e a r e ma n y b e t t e r me thod s o f sp a t i a l i n t e rpo l a t i on t h a t add re s s t h e p ro b l e m s t h a t w er e j u s t i d e n t i f i ed , b u t t h e ea s e o f p ro g ra mmi n g o f ID W a n d i t s con c ep tu a l s i mp l i c i t y ma k e i t a mo n g t h e mo s t p o p u l a r . O n e s h o u l d j u s t b e w a r e , a n d t a k e c a r e t o e x a mi n e t h e r e s u l t s o f i n t e r p o l a t i o n t o e n s u r e t h a t t h e y ma k e good s ense (Long ley , G o o d c h i l d , & M ag u i r e , 2 0 0 4 ) . 4 . Sp l i n e I n t e r p o l a t i o n Sp l i n e In t e rpo l a t i on e s t ima te s v a lu e s u s i n g a ma t h e ma t i c a l f u n c t i o n t h a t mi n i mi z e o v e r a l l s u r f a c e c u r v a t u r e ( F i g u r e 4 ) . T h i s r e s u l t s i n a s mo o t h s u r f a c e t h a t p a s s e s e x a c t ly t h r o u g h t h e i n p u t p o i n t s . Concep tua l l y , i t i s l i k e b e n d i n g a s h e e t o f ru b b e r s o t h a t i t p a s s e s t h r o u g h t h e p o in t s wh i l e mi n i mi z i ng th e to t a l cu rv a t u r e o f t h e su r f a c e ( F i gu r e 7 ) . I t c a n p r e d i c t r i d g e s and v a l l ey s i n t he d a t a a n d i s t h e b e s t me thod fo r r ep r e se n t i n g t h e s mo o t h l y v a r y i n g s u r f a c e s o f p h e n o me n a s u c h a s t e m p er a t u r e o r r a i n f a l l . Th e re a r e v a r i a t i on s o f sp l in e – r e g u l a r i z ed and t en s ion . A r eg u la r i z e d 158 159 s p l i n e i n c o r p o r a t e s t h e f i r s t d e r i v a t i v e ( s l o p e ) a n d t h e s e c o n d d e r iv a t iv e ( r a t e o f c h ang e i n s lo p e ) i n to i t s mi n i mi z a t ion ca l c u l a t i on s . A l t h o u g h a t e n s i o n s p l i n e u s e s o n l y a f i r s t a n d s e c o n d d e r i v a t i v e , i t i nc lud es mo re po in t s i n t he sp l i n e c a l cu l a t i on s , wh ic h u su a l ly c r ea t e s s mo o t h e r s u r f a c e s b u t i n c r e a s e s c o m p u t a t i o n t i me ( A R C U s e r , 2 0 0 4 ) . F i g u r e 4 I ma g e i l l u s t r a t i n g s u r f a c e r e p r e s e n t a t i o n b y Sp l i n e i n t e r p o l a t i o n ( A R C G I S 9 . 1 , 2 0 0 5 ) 5 . K r ig ing " K r i g i n g " i s s y n o n y mo u s w i th "op t i ma l p r ed i c t i on ” ( J o u r n e l & H u i j b r e g t s , 1 9 8 1 ) . I t i s a m e t h o d o f i n t e r p o l a t i o n w h i c h p r e d i c t s u n k n o w n v a l u e s f r o m d a t a o b s e r v e d a t k n o w n l o c a t i o n s . Th i s me t h o d u s e s v a r i o g r a ms ( A t w o - p o i n t s t a t i s t i c a l fun c t ion tha t d es c r ib es t h e i n c r eas ing d i f f e r en c e o r d e c r e a s ing c o n t in u i ty , b e t we en sa mp l e v a lu e s a s s ep a ra t i on b e t wee n th e m i n c r e a se s ) t o exp r e s s t h e sp a t i a l v a r i a t i on ; an d i t mi n i mi z e s t h e e r ro r o f p r ed i c t ed v a l u e s w h i c h a r e e s t i ma t e d b y spa t i a l d i s t r i b u t ion o f t h e p red i c t ed v a lu es ( F i g u r e 5 ) . F i g u r e 5 V a r i o g r a ms u s e d i n Kr ig ing ( Jo u r n e l & Hu i jb r eg t s , 1981 ) . Th e b a s i c i d ea i s t o d i s co v e r s o me t h i n g a b o u t t h e g en e r a l p r o p e r t i e s o f t h e s u r f a c e , a s r e v e a l e d b y t h e me a s u r e d v a l u e s , a n d t h e n t o a p p l y t h e s e p r o p e r t i e s i n e s t i ma t i n g t h e mi s s i n g p a r t s o f t h e su r f a c e . I t i s a p o w e r f u l s t a t i s t i c a l i n t e rpo l a t i o n me t h o d u s ed fo r d i v e r s e a p p l i c a t i o n s s u c h a s so i l s c i e n c e , g e o l o g y a n d p o l l u t i on mo de l l i ng . Kr ig ing a s su mes t ha t d i s t ance 159 160 o r d i r e c t i on b e t wee n s a mp le p o in t s r e f l e c t s a s p a t i a l c o r r e l a t i on t h a t c a n b e u s e d t o e x p l a i n v ar i a t i o n i n t h e su r f a c e . I t f i t s a f u n c t i o n t o a s p e c i f i e d n u mb e r o f p o i n t s o r a l l p o i n t s w i t h i n a s p e c i f i ed r ad i u s t o d e t e rmine t h e ou tpu t v a lu e fo r e ach l o ca t i on (F igu re 6 ) . Kr ig ing i s mos t app rop r i a t e wh en a sp a t i a l l y co r r e l a t ed d i s t an ce o r d i r ec t i on a l b i a s i n t h e d a t a i s k n o w n a n d i s o f t e n u s e d fo r a p p l i c a t i on s i n s o i l s c i e n c e a n d g eo lo g y . Th e p r ed i c t ed v a lu e s a r e d e r iv ed f ro m t h e me a s u re o f r e l a t i o n s h i p i n s a mp l e s u s i n g s o p h i s t i c a t e d w e i g h t e d a v e r a g e t e c h n i q u e . I t u s e s a s e a r c h r a d i u s t h a t c a n b e f i x ed o r v a r i ab l e . Th e g en e r a t ed ce l l v a l u e s c a n e x c e e d v a l u e r a n g e o f s a mp l e s , a n d t h e su r f a c e d o e s n o t p a s s t h r o u g h s a mp l e s ( F i g u r e 7 ) . F i g u r e 6 I ma g e i l l u s t r a t i n g s u r f a c e r e p r e s e n t a t io n b y K r i g i n g ( A R C G I S 9 . 1 , 2 0 0 5 ) F i g u r e 7 G r a p h i n d i c a t i n g i n t e r p o l a t i on o f v a lu e s fo r I n v e r s e d i s t an c e w e igh ing , K r ig ing and Sp l in e i n t e r po l a t i on t e chn iques ( Jou rne l & Hu i jb r eg t s , 1981 ) . 160 161 6 . Po in t i n t e rpo l a t i on S i mi l a r t o ID W , b u t t h e p o i n t i n t e rpo la t i on fun c t io n a l l o ws mo r e con t ro l o v e r t h e s a mp l i n g n e i g h b o u r h o o d . The i n f l u e n c e o f a p a r t i c u l a r s a mp l e o n t h e i n t e rpo l a t ed g r i d c e l l v a l u e d e p e n d s o n w h e t h e r t h e s a mp l e p o i n t i s i n t h e c e l l ’ s n e i g h b o u r h o o d a n d h o w f a r f r o m t h e c e l l b e i n g i n t e r p o l a t e d i t i s l oca t ed . Po in t s ou t s i de t h e n e i g h b o u r h o o d h a v e n o i n f l u e n c e . T h e w e i g h t e d v a l u e o f p o i n t s i n s i d e t h e n e i g h b o u r h o o d i s c a l cu l a t e d u s i n g a n i n v e r s e d i s t a n c e w e i g h t e d i n t e r p o l a t i o n o r i n v e r s e e x p o n e n t i a l d i s t a n c e i n t e rpo l a t i o n . T h i s me t h o d i n t e rpo l a te s a r a s t e r u s i n g p o i n t f e a t u r e s b u t a l l o w s f o r d i f f e r e n t t y p e s o f n e i g h b o u r h o o d s . N e i g h b o u r h o o d s c a n h a v e s h a p e s s u c h a s c i r c l e s , r e c t a n g l e s , i r r e g u l a r p o l y g o n s , a n n u l u s e s , o r w e d g e s ( F i g u r e 8 ) ( A R C G I S , 2 0 0 5 ) . F i g u r e 8 I ma g e i l l u s t r a t in g s u r f a c e r e p r e se n t a t i o n b y p o i n t i n t e r p o l a t i o n ( A R C G I S 9 . 1 , 2 0 0 5 ) 7 . N a t u r a l n e i g h b o u r h o o d N a t u r a l n e i g h b o u r h o o d i n t e r p o l a t i o n h a s ma n y p o s i t i v e f e a t u r e s ; i t c a n b e u s e d fo r b o t h i n t e r p o l a t i o n a n d e x t r a p o l a t i o n . Gene ra l l y works we l l w i th c l u s t e r e d s c a t t e r p o i n t s . A n o t h e r w e i g h t e d - a v e r a g e me t h o d , t h e b a s i c e q u a t i o n u s e d i n n a t u r a l n e i g h b o u r h o o d i n t e r p o l a t io n i s i d e n t i c a l t o t h e o n e u s ed i n ID W i n t e rpo l a t i o n . T h e me t h o d c a n e f f i c i e n t l y h a n d l e l a r g e i n p u t p o i n t d a t a s e t s . W he n u s i n g t h e N a t u r a l N e i g h b o u r h o o d me t hod , l oca l c o o rd in a t e s d e f in e t h e a mo u n t o f i n f l u en ce any sc a t t e r p o in t w i l l h av e o n o u t p u t c e l l s ( F i g u r e 9 ) ( A R C U s e r , 2 0 0 4 ) . 161 162 F i g u r e 9 I ma g e i l l u s t r a t i ng s u r f a c e r e p r e s e n t a t i o n b y n a t u r a l n e i g h b o r h o o d i n t e r p o l a t i o n ( A R C G I S 9 . 1 , 2 0 0 5 ) 8 . T r e n d I n t e r p o l a t i o n A t r e n d s u r f a c e d e s c r i b e s t he g e n e r a l p a t t e r n o f v ar i a t i o n o f v a l u e s f o r p o i n t d a t a a c r o s s a n a r e a . T r e n d i n t e r p o l a t i o n i s e a sy t o unde r s t and by c o n s i d e r i n g a p l a i n w h i c h i s l a y e r ed t h rough t he c loud o f p o i n t - v a l u e s i n a w ay t ha t r ep r e sen t s t h e a r ea t h e be s t . Th i s i n t e rpo l a t i o n t e chn i q u e i s u su a l ly u s e d fo r ex a mp l e i n c a s e s wh e r e a c r o p i s p H s e n s i t i v e . A r e as a b o v e o r b e lo w th e p l a in i s a r e a s n o t s u i t e d fo r t h e c rop a s pH i s e i t h e r t o a c i d i c o r t o a l k a l i n e . T h e s u r f a c e g e n e r a t e d w i l l r a r e ly pa s s t h rough t he o r ig ina l d a t a p o in t s s i n ce i t p e r fo rms a b e s t f i t f o r t h e e n t i r e su r f a c e ( F i g u r e 1 0 ) . Th e i n t e r p o l a t o r may g en e r a t e a s u r f a c e w h i c h h a s a mi n i mum a nd ma x imu m v a lu e th a t mi gh t ex c ee d th e mi n i mu m a nd ma x imu m o f th e i n p u t p o i n t s . A s t h e a r e a b e i n g i n t e r p o l a t e d b ec o me s mo r e d a t a r i c h t h e s u r f a c e b e i n g f i t t e d b e c o me s p r o g r e s s i v e l y mo r e c o mpl ex . A su r f a c e r i c h i n d a t a w i l l n o t a l w ay s g en e r a t e t h e mo s t a c cu r a t e su r f a c e . A s su ch h i g h e r i n t e n s i t y s u r f a c e s t en d t o o v e r sh o o t i n a r e a s w i t h l e s s d a t a ( a s c o mp a r e d t o t h e r e s t o f t h e s t u d y a r e a ) ; t h e se a r e a s a r e mo s t e n d a n g e r e d o f b a d r ep r e sen t a t i o n . I f t h e r e i s a t r end p re sen t i n t h e d a t a , i t c an b e u s e fu l t o e l i mi n a t e i t b y su b t r a c t i n g t h e t r e n d s u r f a c e f r o m t he da t a va lue s , pe r fo rm an i n t e rpo la t i on on t h e r ema in ing r es i d u a l s , a n d f i n a l ly , ad d th e t r end a g a i n t o t h e r e su l t i n g su r f a c e 162 163 F i g u r e 1 0 I ma g e i l l u s t r a t i n g s u r f a c e r e p r e s e n t a t i o n b y Tr end i n t e r p o l a t i o n ( A R C G I S 9 . 1 , 2 0 0 5 ) 163 164 Appendix V Va r i a t i on i n so i l phy s i c a l p r o p e r t i e s 1 . V a r i a t i o n i n s o i l p h y s i c a l p r o p e r t i e s . A d e s c r i p t i o n o f t h e v a r i a t i o n i n s o i l p h y s i c a l c h a r a c t e r i s t i c s o f t h e T u k u l u s o i l f o r m i s s e e n i n T a b l e 1 1 . 1 T u k u l u A hor i zon : T h e d e p t h o f t h e A h o r i z o n v a r i e d b e t w e e n 2 0 0 mm and 210 mm wi th a me a n o f 2 0 7 m m a n d a s t and a rd d ev i a t i on o f + / - 5 . T h e s i l t + c l ay co n t en t v a r i e d b e t w e e n 1 9 % a n d 2 6 % w i th a me a n o f 2 3 % and a s t and a rd d ev i a t i on o f + / - 3 . Th e o rg an ic c a rb o n co n t en t v a r i ed be t w een 30 % and 45 % w i th a me a n o f 3 5 % and a s t and a rd d ev i a t i on o f + / - 7 % . Th e mo d u lu s o f rup tu r e v a r i ed b e t w e en 0 .0 6 b a r and 0 .2 5 b a r w i th a me a n o f 0 .1 5 b a r an d a s t and a rd d ev i a t i o n o f + / - 0 b a r . The a g g r ega t e s t ab i l i t y (4 mm) v a r i ed b e t w een 4 % and 7 % wi th a me a n o f 6 % and a s t and a rd d ev i a t i on o f + / - 1 % . Th e agg reg a t e s t ab i l i t y (2 mm) v a r i ed b e tw ee n 5 % and 2 5 % w i t h a me a n o f 1 3 % and a s t and a rd d ev ia t i on o f + / - 9% . Th e agg r ega t e s t ab i l i t y (1 mm) v a r i e d b e t w e e n 2 0 % a n d 4 5 % w i th a me a n o f 3 5 % and a s t and a rd d ev i a t i on o f + / - 1 1 % . T h e a g g r e g a t e s t ab i l i t y ( 0 .5 mm) v a r i ed be t w een 2% and 21% w i th a mean o f 15 % and a s t and a rd d ev ia t i on o f + / - 8 % . Th e a g g r eg a t e s t ab i l i t y (0 .25 mm) v a r i ed b e t w een 6 % and 3 0 % w i th a me a n o f 1 7 % a n d a s t a n d a r d d e v i a t i o n o f + / - 1 1 % . T h e b u lk d e n s i t y v a r i e d b e t w e e n 1 3 7 6 k g . m - 3 a nd 1 5 2 0 k g m - 3 w i t h a me a n o f 1 4 7 1 k g m - 3 a n d a s t an d a rd d e v i a t i o n o f + / - 6 3 k g m - 3 . B hor i zon : Th e d ep th o f t h e B h o r i zon v a r i ed b e t w een 250 mm and 500 mm wi th a me a n o f 4 2 5 m m a n d a s t a n d a r d d e v i a t i o n o f + / - 113 mm. Th e s i l t + c l ay c o n t e n t v a r i e d b e t w e e n 3 1 % a n d 3 4 % w i t h a me a n o f 3 3 % a n d a s t a n d a r d d e v i a t i o n o f + / - 1 % . T he o r g a n i c c a r b o n c o n t e n t v a r i e d b e t w e e n 2 8 % a n d 3 9 % w i t h a me a n o f 3 5 % and a s t an d a rd d ev i a t i on o f + / - 5 % . The mo d u lus o f ru p tu re v a r i ed b e t w een 0 .4 4 b a r an d 0 . 7 6 b a r w i t h a me a n o f 0 . 6 4 b a r a n d a s t and a rd d ev ia t i on o f 0 b a r . The agg reg a t e s t ab i l i t y (4 mm) v a r i ed b e t w een 1 % and 8 % wi th a me a n o f 4 % and a s t and a rd d ev i a t i on o f + / - 3 % . 164 165 Th e agg reg a t e s t ab i l i t y (2 mm) v a r i ed b e tw e en 3 % and 2 0 % wi th a me a n o f 1 1 % and a s t and a rd d ev ia t i on o f + / - 8 % . The a g g r ega t e s t ab i l i t y ( 1 m m) v a r i ed b e t w e en 2 % a n d 2 1 % w i t h a me a n o f 1 3 % and a s t and a rd d e v i a t i o n o f + / - 8 % . T h e agg reg a t e s t ab i l i t y ( 0 .5 mm) v a r i ed be t w een 4% a n d 3 6 % w i t h a m e a n o f 1 5 % and a s t a n d a rd d ev i a t i on o f + / - 1 4 % . Th e agg r eg a t e s t ab i l i t y (0 .25 mm) v a r i ed be tween 5% and 36% w i t h a me a n o f 1 6 % and a s t and a rd d ev i a t i on o f + / - 1 4% . Th e b u l k d e n s i t y v a r i ed b e tw e en 1 6 0 5 k g m - 3 a n d 1 7 2 9 k g m - 3 w i t h a me a n o f 1 6 6 5 k g m - 3 a n d a s t a n d a rd d e v i a t i o n o f 5 9 k g m - 3 . C h o r i z o n : Th e d ep th o f t h e C h o r i zon v a r i ed b e t w een 210 mm and 310 mm wi th a me a n o f 2 7 5 m m a n d a s t and a rd d ev ia t i o n o f + / - 4 4 m m . T h e s i l t + c l ay c o n t e n t v a r i e d b e t w e e n 4 3 % a n d 5 4 % w i t h a me a n o f 4 8 % a n d a s t a n d a r d d e v i a t i o n o f + / - 5 % . T he o r g a n i c c a r b o n c o n t e n t v a r i e d b e t w e e n 1 8 % a n d 2 8 % w i t h a me a n o f 2 2 % and a s t an d a rd d ev i a t i on o f + / - 4 % . The mo d u lus o f ru p tu re v a r i ed b e t w een 0 .2 7 b a r an d 0 . 5 4 b a r w i t h a me a n o f 0 . 3 6 b a r a n d a s t a n d a rd d e v i a t i on o f + / - 0 b a r . The a g g r e g a t e s t a b i l i t y ( 4 m m) v a r i ed b e t w e en 6 % a n d 1 1 % w i th a me a n o f 8 % and a s t and a rd d ev ia t i o n o f 2 % . T h e a g g r e g a t e s t a b i l i t y (2 mm) v a r i ed b e tween 5 % and 24 % w i th a me a n o f 1 5 % and a s t and a rd d ev ia t i on o f + / - 8 % . The a g g r ega t e s t ab i l i t y ( 1 m m) v a r i e d b e t w e e n 1 1 % and 28% w i th a mean o f 18% and a s t anda rd d e v i a t i o n o f + / - 7 % . Th e agg reg a t e s t ab i l i t y ( 0 .5 mm) v a r i ed be t w een 13 % a n d 1 8 % w i t h a me a n o f 1 6 % a n d a s t a n d a r d d ev i a t i o n o f + / - 2 % . The agg r eg a t e s t ab i l i t y (0 .25 mm) v a r i ed be tween 8% and 22% w i t h a me a n o f 1 6 % and a s t and a rd d ev i a t i on o f + / - 6 % . The b u lk d en s i ty v a r i ed b e t we en 1 5 0 2 k g m - 3 a n d 1 6 4 1 k g m - 3 w i t h a me a n o f 1 5 8 5 k g m - 3 and a s t anda rd d e v i a t i o n o f 6 1 k g m - 3 . 165 166 T a b l e 1 Phy s i c a l c h a r a c t e r i s t i c s o f t h e Tu k u l u s o i l f o r m Organic Modulus Horizon Silt + carbon of A.S Bulk Plot Soil Depth Clay Content Rupture A.S A. S A.S A.S 0.25 density Rootdensity Dry weight nr type (mm) (%) (%) (bar) 4 (%) 2 (%) 1 (%) 0.5 (%) (%) (kg m-3) (km m-2) (kg.ha-1) 7.1A Tu 210 24 32 0.13 4.44 4.85 33.43 16.63 30.02 1520.12 0.0078479 8567 12.2A Tu 200 26 45 0.25 6.5 25.12 41.46 19.72 6.78 1510.62 0.0153246 4283 5.1A Tu 210 22 30 0.06 7.4 12.48 45.32 2.7 6.07 1478.22 0.0029695 7025 1.1A Tu 210 19 33 0.14 6.36 8.77 20.34 20.86 24.37 1376.19 0.0116658 7110 Mean 207.5 22.75 35 0.145 6.175 12.805 35.1375 14.9775 16.81 1471.288 0.009452 6746.25 Min 200 19 30 0.06 4.44 4.85 20.34 2.7 6.07 1376.19 0.002969 4283 Max 210 26 45 0.25 7.4 25.12 45.32 20.86 30.02 1520.12 0.015325 8567 StdDev 4.72 2.93 6.58 0.08 1.23 8.60 10.69 8.06 11.08 63.44 0.005171 1775.60 7.1B Tu 450 34 28 0.44 2.98 3.2 14.05 35.88 36.13 1605.34 0.0022271 8567 12.2B Tu 500 32 38 0.69 8.07 16.07 15.11 15.07 15 1610.96 0.0012726 4283 5.1B Tu 500 31 33 0.67 5.53 20 21.38 4.46 6.31 1714.32 0.0001061 7025 1.1B Tu 250 34 39 0.76 1.19 2.83 2.02 4.13 5.45 1728.9 0.0047724 7110 Mean 425 32.75 34.5 0.64 4.4425 10.525 13.14 14.885 15.7225 1664.88 0.0045603 6746.25 Min 250 31 28 0.44 1.19 2.83 2.02 4.13 5.45 1605.34 0.000106 4283 Max 500 34 39 0.76 8.07 20 21.38 35.88 36.13 1728.9 0.004772 8567 StdDev 113.52 1.37 4.81 0.14 2.91 7.98 8.03 14.18 13.65 58.65 0.002145 1775.60 7.1C Tu 210 47 28 0.27 8.36 5.49 11.13 16.15 22.53 1630.44 0.0008484 8567 12.2C Tu 300 54 18 0.29 10.57 24.26 15.78 17.59 8.72 1641.86 0.0001061 4283 5.1C Tu 280 46 20 0.37 6.2 20.08 27.62 13.25 14.29 1568.4 0.0000530 7025 1.1C Tu 310 43 22 0.54 7.64 9.54 16.53 18.46 19.09 1502.58 0.0011666 7110 Mean 275 47.5 22 0.3675 8.1925 14.8425 17.765 16.3625 16.1575 1585.82 0.0046663 6746.25 Min 210 43 18 0.27 6.2 5.49 11.13 13.25 8.72 1502.58 0.000053 4283 Max 310 54 28 0.54 10.57 24.26 27.62 18.46 22.53 1641.86 0.004666 8567 StdDev 43.63 4.60 4.23 0.12 1.81 8.24 6.91 2.22 5.83 61.00 0.002104 1775.60 166 167 1 . 2 Sep an e A d e sc r ip t i on o f t h e v a r i a t i on i n p h y s i c a l c h a r a c t e r i s t i c s o f t h e Sep an e s o i l f o r m i s s e e n i n T a b l e 2 . A hor i zon : T h e d e p t h o f t h e A h o r i z o n v a r i e d b e t w e e n 2 1 0 mm and 250 mm wi th a me a n o f 2 1 8 m m a n d a s t and a rd d ev ia t i o n o f + / - 1 8 m m . T h e s i l t + c l ay c o n t e n t v a r i e d b e t w e e n 2 2 % a n d 2 7 % w i t h a me a n o f 2 5 % a n d a s t a n d a r d d e v i a t i o n o f + / - 2 % . T he o r g a n i c c a r b o n c o n t e n t v a r i e d b e t w e e n 2 2 % a n d 6 1 % wi th a me a n o f 4 1 % and a s t and a rd d ev i a t i on o f + / - 1 7 % . Th e mo d u lu s o f r u p tu re v a r i ed b e t w een 0 .1 b a r and 0 .4 b a r w i th a me a n o f 0 .2 3 b a r and a s t and a rd d ev i a t i on o f + / - 0 . 1 b a r . Th e agg r ega t e s t ab i l i t y (4 mm) v a r i ed b e t w e en 4 % and 3 3 % w i th a me a n o f 1 6 % and a s t and a rd d ev i a t i o n o f + / - 1 3 % . Th e agg reg a t e s t ab i l i t y ( 2 mm) v a r i ed b e tw e en 8 % a n d 1 5 % w i th a mean o f 15 % and a s t and a rd d ev ia t i on o f + / - 6 % . Th e a g g r eg a t e s t ab i l i t y (1 mm) v a r i ed b e tw een 2 % a n d 2 2 % w i t h a me a n o f 1 5 % a n d a s t and a rd d ev i a t i o n o f + / - 8 % . Th e a g g reg a t e s t ab i l i t y (0 .5 mm) v a r i ed b e t w een 2 % and 2 7 % w i th a me a n o f 1 4 % and a s t an d a rd d ev i a t i on o f + / - 11 % . Th e agg r eg a t e s t ab i l i t y (0 .25 mm) v a r i e d b e tw ee n 3 % and 1 5 % w i t h a me a n o f 7 % a n d a s t an d a r d d e v i a t i o n o f + / - 5 %. Th e b u l k d e n s i t y v a r i e d b e t w e e n 1 3 9 9 k g m - 3 a n d 1 5 3 2 k g m - 3 w i t h a me a n o f 1 4 6 9 k g m - 3 a n d a s t and a rd d ev i a t io n o f + / - 6 0 k g m - 3 . B hor i zon : Th e d ep th o f t h e B h o r i zon v a r i ed b e t w een 100 mm and 250 mm wi th a me a n o f 1 5 0 m m a n d a s t and a rd d ev ia t i o n o f + / - 6 2 m m . T h e s i l t + c l ay c o n t e n t v a r i e d b e t w e e n 4 9 % a n d 5 5 % w i t h a me a n o f 5 2 % a n d a s t a n d a r d d e v i a t i o n o f + / - 2 % . T he o r g a n i c c a r b o n c o n t e n t v a r i e d b e t w e e n 3 3 % a n d 5 0 % w i t h a me a n o f 4 0 % and a s t an d a rd d ev i a t i on o f + / - 7 % . The mo d u lus o f ru p tu re v a r i ed b e t w een 0 .3 8 b a r an d 0 . 8 9 b a r w i t h a me a n o f 0 . 5 7 b a r a n d a s t and a rd d ev ia t i on o f + / - 0 .2 b a r . Th e agg r eg a t e s t ab i l i t y (4 mm) v a r i ed b e t w e en 3 % a n d 1 0 % w i th a me a n o f 4 % and a s t and a rd d ev ia t i o n o f + / - 3 % . T h e a g g r e g a te s t ab i l i t y ( 2 mm) v a r i e d b e t w e e n 2 % a n d 1 4 % w i th a mean o f 6% and a s t and a rd d ev i a t i on o f + / - 5 % . The a g g r eg a t e s t ab i l i t y ( 1 mm) va r i ed be tween 10% and 26% wi th a me a n o f 1 9 % a n d a 167 168 s t and a rd d ev i a t i o n o f + / - 7 % . Th e agg reg a t e s t ab i l i t y ( 0 .5 mm) v a r i ed b e t w een 10 % and 36 % w i th a me a n o f 2 5 % a n d a s t an d a rd d ev i a t i on o f + / - 1 0 % . Th e a g g r e g a t e s t a b i l i t y ( 0 .25 m m) v a r i ed b e tw e en 1 3 % and 5 1 % w i th a mean o f 32 % and a s t and a rd d ev ia t i on o f + / - 1 4 % . Th e b u lk d en s i ty v a r i e d b e t w e e n 1 6 7 0 k g m - 3 a n d 1 8 1 0 k g m - 3 w i t h a me a n o f 1 7 7 8 k g m - 3 a n d a s t and a rd d ev i a t i on o f + / - 6 2 k g m - 3 . C h o r i z o n : Th e d ep th o f t h e C h o r i zon v a r i ed b e t w een 300 mm and 500 mm wi th a me a n o f 3 9 0 m m a n d a s t and a rd d ev ia t i o n o f + / - 8 6 m m . T h e s i l t + c l ay c o n t e n t v a r i e d b e t w e e n 3 0 % a n d 4 1 % w i t h a me a n o f 3 5 % a n d a s t a n d a r d d e v i a t i o n o f + / - 5 % . T he o r g a n i c c a r b o n c o n t e n t v a r i e d b e t w e e n 1 6 % a n d 3 0 % w i t h a me a n o f 2 2 % and a s t an d a rd d ev i a t i on o f + / - 6 % . The mo d u lus o f ru p tu re v a r i ed b e t w een 0 .1 9 b a r an d 0 . 5 6 b a r w i t h a me a n o f 0 . 3 8 b a r a n d a s t and a rd d ev ia t i on o f + / - 0 .2 b a r . Th e agg r eg a t e s t ab i l i t y (4 mm) v a r i e d b e t w e e n 1 % a n d 6 % w i t h a m e a n o f 3 % and a s t and a rd d e v i a t i o n o f + / - 2 % . T h e a g g r e g a t e s t a b i l i t y (2 mm) va r i ed be tw een 8% and 16% w i th a me a n o f 1 1 % and a s t and a rd d ev ia t i on o f + / - 4 % . The a g g r ega t e s t ab i l i t y ( 1 m m) v a r i e d b e t w e e n 1 0 % and 40% w i th a mean o f 23% and a s t anda rd d e v i a t i o n o f + / - 1 3 % . Th e agg r eg a t e s t ab i l i t y ( 0 .5 mm) v a r i ed b e t w een 13% and 36% wi th a mean o f 26% and a s t anda rd d e v i a t i o n o f + / - 1 0 % . Th e agg re g a t e s t ab i l i t y (0 .25 mm) v a r i ed b e t w e en 9 % a n d 2 9 % w i th a me a n o f 1 6 % and a s t and a rd d ev i a t i on o f + / - 8 % . Th e b u lk d en s i ty v a r i ed b e t w e e n 1 6 5 6 k g m - 3 a n d 1 7 8 3 k g m - 3 w i t h a me a n o f 1 7 2 9 k g m - 3 a n d a s t and a rd d ev i a t io n o f + / - 5 2 k g m - 3 . 168 169 T a b l e 2 Phy s i c a l ch a r a c t e r i s t i c s o f t h e S ep an e s o i l fo rm Modulus Organic of A.S Bulk Root Plot Soil Horizon Silt + Carbon rupture A.S A. S A.S A.S 0.25 density density Dry weight nr type depth(mm) Clay(%) (%) (bar) 4 (%) 2 (%) 1 (%) 0.5 (%) (%) (kg m-3) (km.m 2) (kg.ha-1) 13.1A Se 250.00 27.00 54.18 0.30 3.93 8.30 17.63 27.00 15.44 1399.34 0.36 5054.00 15.1A Se 210.00 22.00 43.86 0.25 29.04 22.62 2.43 4.00 9.66 1401.22 0.28 5226.00 15.2A Se 210.00 24.00 22.19 0.10 33.33 12.50 22.10 16.00 5.37 1504.33 0.36 5483.00 14.2A Se 210.00 26.00 60.54 0.37 9.98 14.39 20.09 1.76 2.60 1507.18 0.34 2913.00 12.1A Tu/Se 210.00 26.00 25.11 0.15 5.23 16.54 11.32 21.43 3.05 1532.09 0.40 5568.00 Mean 218.00 25.00 41.18 0.23 16.30 14.87 14.71 14.04 7.23 1468.83 0.35 4848.80 Min 210.00 22.00 22.19 0.10 3.93 8.30 2.43 1.76 2.60 1399.34 0.28 2913.00 Max 250.00 27.00 60.54 0.37 33.33 22.62 22.10 27.00 15.44 1532.09 0.40 5568.00 StdDev 18.11 2.03 16.50 0.11 13.14 5.54 8.08 10.67 5.39 59.71 0.05 1129.52 13.1B Se 250.00 49.00 45.84 0.69 3.12 2.13 15.48 34.86 29.48 1798.32 0.10 5054.00 15.1B Se 150.00 52.00 49.62 0.52 10.40 14.00 26.19 10.90 28.15 1807.77 0.02 5226.00 15.2B Se 100.00 51.00 33.37 0.38 2.85 9.56 10.60 21.42 35.62 1810.44 0.04 5483.00 14.2B Se 100.00 55.00 33.02 0.89 2.62 2.85 18.76 19.82 50.94 1807.65 0.02 2913.00 12.1B Tu/Se 150.00 51.00 37.32 0.38 3.11 2.45 25.43 35.65 13.43 1670.43 0.33 5568.00 Mean 150.00 51.60 39.84 0.57 4.42 6.20 19.29 24.53 31.52 1778.92 0.10 4848.80 Min 100.00 49.00 33.02 0.38 2.62 2.13 10.60 10.90 13.43 1670.43 0.02 2913.00 Max 250.00 55.00 49.62 0.89 10.40 14.00 26.19 35.65 50.94 1810.44 0.33 5568.00 StdDev 62.32 2.31 7.24 0.22 3.42 5.20 6.53 10.40 14.35 61.90 0.13 1129.52 13.1C Se 300.00 41.00 30.01 0.47 3.19 8.32 10.19 36.05 29.15 1763.24 0.07 5054.00 15.1C Se 300.00 33.00 21.16 0.39 6.45 7.51 39.93 12.85 8.54 1783.24 0.06 5226.00 15.2C Se 400.00 33.00 19.09 0.19 3.21 15.54 18.85 33.29 12.68 1743.56 0.24 5483.00 14.2C Se 500.00 40.00 22.70 0.56 1.52 15.34 11.09 28.15 12.16 1701.10 0.28 2913.00 12.1C Tu/Se 450.00 30.00 15.53 0.30 1.45 8.45 32.99 19.04 16.54 1656.09 0.41 5568.00 Mean 390.00 35.40 21.70 0.38 3.16 11.03 22.61 25.88 15.81 1729.45 0.21 4848.80 Min 300.00 30.00 15.53 0.19 1.45 7.51 10.19 12.85 8.54 1656.09 0.06 2913.00 Max 500.00 41.00 30.01 0.56 6.45 15.54 39.93 36.05 29.15 1783.24 0.41 5568.00 StdDev 86.31 4.69 5.63 0.15 2.06 3.74 12.87 9.65 8.29 51.61 0.15 1129.52 169 170 1 . 3 B lo emd a l A d es c r ip t i on o f t he p h y s i c a l c h a r a c t e r i s t i c s o f t h e B l o e md a l s o i l f o r m i s s e e n i n Ta b l e 3 . A hor i zon : T h e d e p t h o f t h e A h o r i z o n v a r i e d b e t w e e n 1 5 0 mm and 260 mm wi th a me a n o f 2 6 0 m m a n d a s t and a rd d ev ia t i o n o f + / - 5 0 m m . T h e s i l t + c l ay c o n t e n t v a r i e d b e t w e e n 2 0 % a n d 3 2 % w i t h a me a n o f 3 2 % a n d a s t a n d a r d d e v i a t i o n o f + / - 5 % . T he o r g a n i c c a r b o n c o n t e n t v a r i e d b e t w e e n 2 1 % a n d 3 3 % w i t h a me a n o f 2 1 % and a s t an d a rd d ev i a t i on o f + / - 5 % . The mo d u lus o f ru p tu re v a r i ed b e t w een 0 .0 9 b a r an d 0 . 1 7 b a r w i t h a me a n o f 0 . 1 7 b a r a n d a s t and a rd d ev ia t i on o f + / - 0 .1 b a r . Th e agg r eg a t e s t ab i l i t y (4 mm) v a r i e d b e t w e e n 1 % a n d 3 % w i t h a m e a n o f 3 % and a s t and a rd d e v i a t i o n o f + / - 1 % . T h e a g g r e g a t e s t a b i l i t y (2 mm) va r i ed be tw een 9% and 31% w i th a mean o f 13 % and a s t and a rd d ev i a t i on o f + / - 10 %. The agg reg a t e s t ab i l i t y ( 1 m m) v a r i e d b e t w e e n 2 4 % and 32% w i th a mean o f 26% and a s t anda rd d e v i a t i o n o f + / - 4 % . Th e agg reg a t e s t ab i l i t y ( 0 .5 mm) v a r i ed be t w een 10 % a n d 1 9 % w i t h a me a n o f 1 9 % a n d a s t a n d a r d d ev i a t i o n o f + / - 4 % . The agg r eg a t e s t ab i l i t y ( 0 .25 mm) va r i ed b e t w e e n 1 3 % a n d 2 4 % w i th a mean o f 2 4 % and a s t and a rd d ev i a t i on o f + / - 4 % . The b u lk d en s i ty v a r i ed b e t we en 1 2 9 0 k g m - 3 a n d 1 4 4 0 k g m - 3 w i t h a me a n o f 1 4 4 0 k g m - 3 a n d a s t a n d a rd d e v i a t i o n o f + / - 6 3 k g m - 3 . B hor i zon : T h e d e p t h o f t h e B h o r i z o n v a r i e d b e t w e e n 5 0 m m and 250 mm wi th a me a n o f 1 5 0 m m a n d a s t and a rd d ev ia t i o n o f + / - 8 2 m m . T h e s i l t + c l ay c o n t e n t v a r i e d b e t w e e n 4 2 % a n d 4 9 % w i t h a me a n o f 4 5 % a n d a s t a n d a r d d e v i a t i o n o f + / - 3 % . T he o r g a n i c c a r b o n c o n t e n t v a r i e d b e t w e e n 2 9 % a n d 3 8 % w i t h a me a n o f 3 4 % and a s t an d a rd d ev i a t i on o f + / - 4 % . The mo d u lus o f ru p tu re v a r i ed b e t w een 0 .4 5 b a r an d 0 . 6 4 b a r w i t h a me a n o f 0 . 5 7 b a r a n d a s t and a rd d ev ia t i on o f + / - 0 .1 b a r . Th e agg r eg a t e s t ab i l i t y (4 mm) v a r i e d b e t w e e n 1 % a n d 3 % w i t h a m e a n o f 2 % and a s t and a rd d e v i a t i o n o f + / - 1% . Th e agg reg a t e s t ab i l i t y (2 mm) v a r i e d b e tw ee n 1 % and 8 % w i th a me a n o f 4 % and a s t and a rd d ev i a t i on o f + / - 3 % . T h e a g g reg a t e s t ab i l i t y (1 mm) v a r i ed be tw een 14% a n d 2 0 % w i t h a me a n o f 17% and a s t anda rd 170 171 d e v i a t i o n o f + / - 3 % . T he agg reg a t e s t ab i l i t y ( 0 .5 mm) v a r i ed be t w een 12% and 35% wi th a mean o f 28% and a s t anda rd d e v i a t i o n o f + / - 1 1 % . Th e agg reg a t e s t ab i l i t y (0 .25 mm) v ar i e d b e t w e e n 2 1 % and 37 % w i th a me a n o f 3 0 % and a s t and a rd d ev i a t i on o f + / - 7 % . Th e b u lk d en s i ty v a r i ed b e t w e e n 1 5 8 0 k g m - 3 a n d 1 6 4 3 k g m - 3 w i t h a me a n o f 1 6 0 5 k g m - 3 a n d a s t and a rd d ev i a t io n o f + / - 2 7 k g m - 3 . C h o r i z o n : Th e d ep th o f t h e C h o r i zon v a r i ed b e t w een 200 mm and 350 mm wi th a me a n o f 2 6 0 m m a n d a s t and a rd d ev ia t i o n o f + / - 6 6 m m . T h e s i l t + c l ay c o n t e n t v a r i e d b e t w e e n 2 8 % a n d 3 4 % w i t h a me a n o f 3 2 % a n d a s t a n d a r d d e v i a t i o n o f + / - 3 % . T he o r g a n i c c a r b o n c o n t e n t v a r i e d b e t w e e n 1 9 % a n d 2 3 % w i t h a me a n o f 2 1 % and a s t an d a rd d ev i a t i on o f + / - 2 % . The mo d u lus o f ru p tu re v a r i ed b e t w een 0 .1 5 b a r an d 0 . 2 0 b a r w i t h a me a n o f 0 . 1 7 b a r a n d a s t and a rd d ev ia t i on o f + / - 0 .1 b a r . Th e agg r eg a t e s t ab i l i t y (4 mm) v a r i e d b e t w e e n 2 % a n d 4 % w i t h a m e a n o f 3 % and a s t and a rd d e v i a t i o n o f + / - 1 b a r . Th e agg reg a t e s t ab i l i t y (2 mm) v a r i ed b e tw e en 1 3 % and 1 4 % w i th a mean o f 13 % and a s t and a rd d ev ia t i on o f + / - 1 % . Th e a g g r eg a t e s t ab i l i t y ( 1 mm) va r i ed be tween 12% and 33% wi th a me a n o f 2 6 % a n d a s t and a rd d ev i a t i o n o f + / - 10 % . Th e agg r eg a t e s t ab i l i t y (0 .5 mm) v a r i ed b e t w een 14 % and 34 % w i th a me a n o f 1 9 % a n d a s t an d a rd d ev i a t i on o f + / - 9 % . Th e agg r eg a t e s t ab i l i t y ( 0 .25 mm) v a r i ed b e tw een 7 % and 30 % w i th a me a n o f 2 4 % an d a s t and a rd d ev i a t i on o f + / - 11%. Th e bu l k d e n s i t y v a r i e d b e t w e e n 1 3 6 5 k g m - 3 a n d 1 5 0 1 k g m - 3 w i t h a me a n o f 1 4 4 0 k g m - 3 a n d a s t and a rd d ev i a t io n o f + / - 6 1 k g m - 3 . 171 172 Tab l e 3 Phy s i c a l ch a r ac t e r i s t i c s o f t h e B loemd a l so i l f o r m Modulus Organic of Bulk Root Plot Soil Horizon Silt + matter rupture A.S A. S A.S A.S A.S density density Dry weight nr type depth(mm) Clay(%) (%) (bar) 4 (%) 2 (%) 1 (%) 0.5 (%) 0.25 (%) (kg m-3) (km m2) (kg.ha-1) 11.10 Bd 210.00 21.00 27.69 0.09 3.24 30.73 24.01 10.19 12.86 1321.43 0.24 4283.00 10.50 Bd 245.00 20.00 33.37 0.10 2.34 11.65 32.43 18.33 19.32 1290.34 0.23 5997.00 8.10 Bd/Tu 250.00 25.00 23.74 0.11 1.67 11.23 30.43 15.46 18.43 1342.56 0.24 5997.00 11.30 Bd 150.00 20.00 26.14 0.12 1.28 9.06 28.80 17.67 20.39 1360.43 0.54 3427.00 Mean 260.00 31.75 20.90 0.17 3.33 13.47 26.06 19.47 23.63 1440.15 0.30 4926.00 Min 150.00 20.00 20.90 0.09 1.28 9.06 24.01 10.19 12.86 1290.34 0.23 3427.00 Max 260.00 31.75 33.37 0.17 3.33 30.73 32.43 19.47 23.63 1440.15 0.54 5997.00 StdDev 49.32 5.44 5.26 0.04 0.95 9.80 3.67 4.08 4.47 63.47 0.14 1177.74 11.10 Bd 50.00 49.00 37.15 0.64 1.04 8.32 16.68 11.67 21.11 1580.14 0.09 4283.00 10.50 Bd 250.00 42.00 37.67 0.58 2.67 3.43 14.35 34.54 36.54 1610.45 0.10 5997.00 8.10 Bd/Tu 150.00 43.00 33.37 0.61 2.32 3.09 20.33 34.65 34.23 1589.23 0.11 5997.00 11.30 Bd 150.00 45.00 28.90 0.45 2.10 1.45 18.43 31.51 30.03 1643.12 0.08 3427.00 Mean 150.00 44.75 34.27 0.57 2.03 4.07 17.45 28.09 30.48 1605.74 0.10 4926.00 Min 50.00 42.00 28.90 0.45 1.04 1.45 14.35 11.67 21.11 1580.14 0.08 3427.00 Max 250.00 49.00 37.67 0.64 2.67 8.32 20.33 34.65 36.54 1643.12 0.11 5997.00 StdDev 81.65 3.00 3.86 0.08 0.69 2.91 2.50 10.52 6.61 27.02 0.01 1177.74 11.10 Bd 280.00 34.00 21.50 0.16 2.38 14.43 11.77 33.76 6.62 1489.12 0.31 4283.00 10.50 Bd 210.00 32.00 20.47 0.15 3.56 12.56 28.43 14.55 30.11 1365.04 0.29 5997.00 8.10 Bd/Tu 350.00 28.00 18.92 0.18 4.22 13.55 33.23 15.67 30.23 1405.12 0.34 5997.00 11.30 Bd 200.00 33.00 22.70 0.20 3.16 13.34 30.83 13.90 27.55 1501.32 0.28 3427.00 Mean 260.00 31.75 20.90 0.17 3.33 13.47 26.06 19.47 23.63 1440.15 0.30 4926.00 Min 200.00 28.00 18.92 0.15 2.38 12.56 11.77 13.90 6.62 1365.04 0.28 3427.00 Max 350.00 34.00 22.70 0.20 4.22 14.43 33.23 33.76 30.23 1501.32 0.34 5997.00 StdDev 66.04 2.57 1.58 0.02 0.76 0.77 9.42 9.11 10.86 61.05 0.03 1177.74 172 173 Appendix W M a t r i c s u c t i o n r e s p o n s e c u r v e s (a) (b) (c) Bloemdal A horizon y = -2E-06x2 + 0.0014x + 0.2067 y = 0.0111x + 1.2649 Bloemdal B horizon Bloemdal C horizon R2 = 0.9863 R2 = 0.9933 0.5 7 1600 y = 3E-08x4 - 5E-05x3 + 0.0227x2 - 1.9908x + 426.45 0.45 6 1400 R2 = 0.9398 0.4 1200 5 0.35 1000 0.3 4 0.25 800 3 0.2 600 0.15 2 400 0.1 1 200 0.05 0 0 0 0 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 20 21 22 23 24 25 26 27 28 29 1 38 75 112 149 186 223 260 297 334 371 408 445 482 519 556 593 630 667 704 741 0 0.05 0.19 0.86 2.02 2.18 2.84 3.16 3.83 5.96 7.91 7.91 13.2 17.1 26 30 30 30 Drainage period (Days) Drainage period (days) Drainage period (Days) (d) (e) (f Tuklu A horizon Tukulu B horizon ) y = 2.6967Ln(x) - 5.0393 Tukulu C Horizon y = -6E-06x2 + 0.0007x + 3.6393 50 R2 = 0.8917 R2 = 0.5367 y = 0.7811Ln(x) - 2.3714 12 4.5 R2 = 0.0162 40 4 10 3.5 30 8 3 2.5 20 6 2 1.5 10 4 1 0 2 0.5 0 0.05 0.19 0.86 2.02 2.18 2.18 2.84 3.16 3.83 5.96 7.91 13.2 17.1 17.1 26 30 30 0 -10 0 0 0.05 0.19 0.86 2.02 2.18 2.18 2.84 3.16 3.83 5.96 7.91 13.2 17.1 17.1 26 30 30 Drainage Period (Days) 0.05 0.19 0.86 2.02 2.84 3.16 5.96 7.91 13.2 17.1 26 30 30 Drainage Period (Days) Drainage period (Days) (g) (h) (i) Sepane A Sepane B Sepane C 30 4 16 25 y = 2E-08x 4 - 3E-05x3 + 0.0105x2 + 0.6692x + 253.13 3.5 14 R2 = 0.9555 3 12 20 2.5 10 15 8 y = 0.089Ln(x) + 0.1358 2 10 R2 6 = 0.8148 1.5 4 1 5 0.5 y = -2E-05x 4 + 0.0118x3 - 2.2404x2 + 184.03x - 5259.3 2 R2 = 0.797 0 0 0 0 0 0.05 0.19 0.86 2.02 2.18 2.18 2.84 3.16 3.83 5.96 7.91 7.91 13.2 17.1 26 30 0 0.05 0.05 0.19 0.86 2.02 2.18 2.18 2.84 3.16 3.83 5.96 7.91 7.91 13.2 17.1 26 30 30 30 0 0 0.05 0.19 0.86 2.02 2.18 2.84 2.84 3.16 3.83 5.96 7.91 13.2 17.1 17.1 26 Drainage Period (days) Drainage period (Days) Drainage period (Days) F i g u r e 1 ( a – i ) M a t r i c s u c t i o n r e s p o n s e c u r v e s o v e r t h e d r a i n a g e p e r i o d fo r t h e B l o e mda l , Tuku lu and Sepane so i l s . 173 C a p p i l a r y p r e s s u r e h e a d ( - k P a ) C a p p i l a r y P r e s s u r e h e a d ( - k P a ) C a p p i l a r y P r e s s u r e h e a d ( - k P a ) C a p p i l a r y P r e s s u r e H e a d ( - k P a ) C a p p i l a r y P r e s s u r e h e a d ( - k P a ) C a p p i l a r y P r e s s u r e ( - k P a ) C a p p i l a r y P r e s s u r e H e a d ( - k P a ) C a p p i l a r y P r e s s u r e ( - k P a ) C a p p i l a r y P r e s s u r e H e a d ( - k P a ) 174 Appendix X D a t a u s e d i n t h e p r o c e s s f o r c a l c u l a t i n g t he hyd rau l i c conduc t i v i t y o f t h e B l o e mda l , T u k u l u a n d S e p a n e s o i l s T a b l e 1 D a t a u s e d f o r t h e c a l c u l a t i o n o f s o i l m o i s t u r e f l u x ( q ) o f t h e B l o e mda l DAS z (cm) Volumetric WC ∆WC/∆t (cm day-1) dz X (∆WC/∆t (cm day-1) q (flux) 0.00 0-15 0.289 15-45 0.275 45-75 0.291 0.86 0-15 0.254 0.041 0.608 0.608 15-45 0.267 0.010 0.297 0.905 45-75 0.290 0.001 0.031 0.936 2.18 0-15 0.244 0.008 0.114 0.114 15-45 0.259 0.006 0.184 0.298 45-75 0.289 0.001 0.030 0.328 2.84 0-15 0.241 0.005 0.071 0.071 15-45 0.256 0.004 0.117 0.188 45-75 0.288 0.001 0.029 0.217 3.16 0-15 0.239 0.004 0.061 0.061 15-45 0.255 0.003 0.093 0.154 45-75 0.288 0.001 0.029 0.183 3.83 0-15 0.237 0.004 0.053 0.053 15-45 0.253 0.002 0.075 0.128 45-75 0.287 0.001 0.029 0.157 5.96 0-15 0.231 0.003 0.040 0.040 15-45 0.250 0.001 0.041 0.081 45-75 0.285 0.001 0.028 0.109 0-15 0.217 0.001 0.019 0.019 17.14 15-45 0.249 0.000 0.005 0.024 45-75 0.277 0.001 0.024 0.048 26.01 0-15 0.211 0.001 0.010 0.010 15-45 0.249 0.000 0.000 0.010 45-75 0.271 0.001 0.017 0.027 30.00 0-15 0.209 0.000 0.007 0.007 15-45 0.249 0.000 0.000 0.007 45-75 0.270 0.000 0.013 0.021 174 175 T a b l e 2 D a t a u s e d f o r t h e c a l cu l a t i on o f K fo r t he B loemda l z (cm) DAS q (cm day-1) Vol WC Hp (cm) Hg H ∆H/ K (cm day-1) Mean WC 0.00 0.289 0.86 0.608 0.254 70 30 100 2.333333 0.261 0.271124 2.18 0.114 0.244 120 30 150 1.333333 0.086 0.248663 2.84 0.071 0.241 120 30 150 2.333333 0.030 0.24207 0-15 3.16 0.061 0.239 140 30 170 1.666667 0.036 0.239858 3.83 0.053 0.237 140 30 170 1.666667 0.032 0.238026 5.96 0.040 0.231 170 30 200 1.666667 0.024 0.23402 17.14 0.019 0.217 170 30 200 1.666667 0.011 0.224097 26.01 0.010 0.211 210 30 240 0.333333 0.029 0.214123 30.00 0.007 0.209 250 30 280 -1 -0.007 0.210271 0.00 0.275 0.86 0.905 0.267 110 60 170 2.333333 0.388 0.270909 2.18 0.298 0.259 130 60 190 1.333333 0.223 0.262614 2.84 0.188 0.256 160 60 220 2.333333 0.080 0.257292 0-45 3.16 0.154 0.255 160 60 220 1.666667 0.092 0.255512 3.83 0.128 0.253 160 60 220 1.666667 0.077 0.254177 5.96 0.081 0.250 190 60 250 1.666667 0.049 0.25187 17.14 0.024 0.249 190 60 250 1.666667 0.014 0.249486 26.01 0.010 0.249 190 60 250 0.333333 0.029 0.248566 30.00 0.007 0.249 190 60 250 -1 -0.007 0.24856 0.00 0.291 0.86 0.936 0.290 170 90 260 3 0.312 0.290669 2.18 0.328 0.289 170 90 260 2.333333 0.140 0.289575 2.84 0.217 0.288 170 90 260 1.333333 0.163 0.288598 0-75 3.16 0.183 0.288 170 90 260 1.333333 0.137 0.288122 3.83 0.157 0.287 170 90 260 1.333333 0.117 0.287649 5.96 0.109 0.285 170 90 260 0.333333 0.326 0.286346 17.14 0.048 0.277 220 90 310 2 0.024 0.280976 26.01 0.027 0.271 220 90 310 2 0.014 0.27404 30.00 0.021 0.270 290 90 380 4.333333 0.005 0.270611 175 176 T a b l e 3 D a t a u s e d f o r t h e c a l c u l a t i o n o f s o i l m o i s t u r e f l u x ( q ) o f t h e T u k u l u ∆WC/∆t DAS z(cm) Volumetric WC (cm day-1) dz(∆WC/∆t (cm day-1) q (flux) 0.00 0-15 0.264 15-45 0.284 45-75 0.311 0.86 0-15 0.238 0.030 0.456 0.456 15-45 0.280 0.005 0.141 0.597 45-75 0.307 0.004 0.134 0.731 2.18 0-15 0.232 0.004 0.066 0.066 15-45 0.275 0.004 0.113 0.180 45-75 0.302 0.003 0.103 0.283 2.84 0-15 0.230 0.003 0.041 0.041 15-45 0.273 0.003 0.093 0.134 45-75 0.301 0.003 0.081 0.215 3.16 0-15 0.229 0.002 0.035 0.035 15-45 0.272 0.003 0.084 0.120 45-75 0.300 0.002 0.072 0.192 3.83 0-15 0.228 0.002 0.031 0.031 15-45 0.271 0.003 0.077 0.108 45-75 0.298 0.002 0.064 0.172 5.96 0-15 0.224 0.002 0.024 0.024 15-45 0.267 0.002 0.059 0.083 45-75 0.295 0.002 0.047 0.130 17.14 0-15 0.215 0.001 0.012 0.012 15-45 0.259 0.001 0.021 0.033 45-75 0.290 0.000 0.013 0.046 26.01 0-15 0.212 0.000 0.007 0.007 15-45 0.258 0.000 0.003 0.010 45-75 0.290 0.000 0.001 0.011 30.00 0-15 0.210 0.000 0.005 0.005 15-45 0.258 0.000 0.001 0.006 45-75 0.290 0.000 0.000 0.006 176 177 T a b l e 4 D a t a u s e d f o r t h e c a l cu l a t i on o f K fo r t he Tuku lu z (cm) DAS q (cm day-1) Vol WC Hp (cm) Hg H ∆H/ mean WC K (cm day-1) 0.00 0.264 0-15 0.86 0.456 0.238 120 30 150 0.666667 0.250602 0.684 2.18 0.066 0.232 140 30 170 0.666667 0.234612 0.100 2.84 0.041 0.230 160 30 190 4.74E-15 0.230778 3.16 0.035 0.229 160 30 190 1.333333 0.229489 0.027 3.83 0.031 0.228 160 30 190 1.333333 0.228414 0.023 5.96 0.024 0.224 160 30 190 1.333333 0.22604 0.018 17.14 0.012 0.215 190 30 220 0.333333 0.219914 0.036 26.01 0.007 0.212 190 30 220 1.666667 0.213533 0.004 30.00 0.005 0.210 230 30 260 0.333333 0.210917 0.015 0.00 0.284 0-45 0.86 0.597 0.280 110 60 170 0.666667 0.282426 0.895 2.18 0.180 0.275 130 60 190 0.666667 0.277915 0.269 2.84 0.134 0.273 130 60 190 4.74E-15 0.274403 3.16 0.120 0.272 170 60 230 1.333333 0.272932 0.090 3.83 0.108 0.271 170 60 230 1.333333 0.271626 0.081 5.96 0.083 0.267 170 60 230 1.333333 0.268668 0.062 17.14 0.033 0.259 170 60 230 0.333333 0.262709 0.098 26.01 0.010 0.258 210 60 270 1.666667 0.258357 0.006 30.00 0.006 0.258 210 60 270 0.333333 0.257796 0.018 0.00 0.311 0-75 0.86 0.731 0.307 80 90 170 0 0.30885 2.18 0.283 0.302 80 90 170 -0.66667 0.304663 -0.424 2.84 0.215 0.301 90 90 180 -0.33333 0.301507 -0.646 3.16 0.192 0.300 90 90 180 -1.66667 0.300232 -0.115 3.83 0.172 0.298 90 90 180 -1.66667 0.29913 -0.103 5.96 0.130 0.295 90 90 180 -1.66667 0.296749 -0.078 17.14 0.046 0.290 90 90 180 -1.66667 0.292602 -0.028 26.01 0.011 0.290 110 90 200 -2.33333 0.289921 -0.005 30.00 0.006 0.290 110 90 200 -2.33333 0.289705 -0.003 177 178 T a b l e 5 D a t a u s e d f o r t h e c a l c u l a t i o n o f s o i l m o i s t u r e f l u x ( q ) o f t h e S e p a n e dz(∆WC/∆t DAS z(cm) Volumetric WC ∆WC/∆t (cm day-1) (cm day-1) q (flux) 0.00 0-15 0.279 15-45 0.281 45-75 0.290 0.86 0-15 0.247 0.037 0.558 0.558 15-45 0.279 0.003 0.096 0.654 45-75 0.266 0.028 0.834 1.488 2.18 0-15 0.242 0.004 0.053 0.053 15-45 0.275 0.002 0.072 0.126 45-75 0.264 0.001 0.040 0.166 2.84 0-15 0.241 0.001 0.018 0.018 15-45 0.274 0.002 0.057 0.076 45-75 0.264 0.001 0.016 0.092 3.16 0-15 0.241 0.001 0.013 0.013 15-45 0.274 0.002 0.052 0.065 45-75 0.263 0.000 0.013 0.077 3.83 0-15 0.241 0.001 0.009 0.009 15-45 0.273 0.002 0.047 0.056 45-75 0.263 0.000 0.011 0.067 5.96 0-15 0.240 0.000 0.005 0.005 15-45 0.270 0.001 0.037 0.042 45-75 0.263 0.000 0.008 0.050 17.14 0-15 0.240 0.000 0.000 0.000 15-45 0.263 0.001 0.017 0.018 45-75 0.261 0.000 0.005 0.023 26.01 0-15 0.240 0.000 -0.001 -0.001 15-45 0.261 0.000 0.008 0.007 45-75 0.259 0.000 0.005 0.012 30.00 0-15 0.240 0.000 -0.001 -0.001 15-45 0.260 0.000 0.006 0.005 45-75 0.259 0.000 0.005 0.010 178 179 T a b l e 6 D a t a u s e d f o r t h e c a l cu l a t i on o f K fo r t he Sepane z (cm) DAS q (cm day-1) Vol WC Hp (cm) Hg H ∆H/ mean WC K (cm day-1) 0.00 0.279 0-15 0.86 0.558 0.247 90 30 120 3 0.262816 0.186 2.18 0.053 0.242 130 30 160 1.666667 0.244478 0.000 2.84 0.018 0.241 150 30 180 1 0.241731 0.000 3.16 0.013 0.241 150 30 180 2.333333 0.241191 0.005 3.83 0.009 0.241 150 30 180 2.333333 0.240843 0.004 5.96 0.005 0.240 150 30 180 2.333333 0.240294 0.002 17.14 0.042 0.240 150 30 180 4 0.239806 0.010 26.01 0.050 0.240 150 30 180 2.333333 0.239838 0.021 30.00 0.000 0.240 150 30 180 4 0.24012 0.000 0.00 0.281 0-45 0.86 0.654 0.279 150 60 210 3 0.279925 0.218 2.18 0.126 0.275 150 60 210 1.666667 0.276962 0.075 2.84 0.076 0.274 150 60 210 1 0.274739 0.076 3.16 0.065 0.274 190 60 250 2.333333 0.273831 0.028 3.83 0.056 0.273 190 60 250 2.333333 0.273029 0.024 5.96 0.042 0.270 190 60 250 2.333333 0.271193 0.018 17.14 0.018 0.263 240 60 300 4 0.266677 0.004 26.01 0.007 0.261 190 60 250 2.333333 0.262328 0.003 30.00 0.005 0.260 240 60 300 4 0.26081 0.001 0.00 0.290 0-75 0.86 1.488 0.266 70 90 160 -1.66667 0.277586 -0.893 2.18 0.166 0.264 90 90 180 -1 0.264753 -0.166 2.84 0.092 0.264 110 90 200 -0.33333 0.263692 -0.276 3.16 0.077 0.263 110 90 200 -1.66667 0.263446 -0.046 3.83 0.067 0.263 110 90 200 -1.66667 0.263258 -0.040 5.96 0.050 0.263 110 90 200 -1.66667 0.262859 -0.030 17.14 0.023 0.261 110 90 200 -3.33333 0.261582 -0.007 26.01 0.012 0.259 110 90 200 -1.66667 0.259886 -0.007 30.00 0.010 0.259 110 90 200 -3.33333 0.25888 -0.003 179