Field comparison of resource utilization and productivity of three grain legume species under water stress - Fantaye, Kindie Tesfaye (University of the Free State, 2004)
Grain legumes play a major role in low input agricultural systems by providing quality protein to the poor communities and improving the natural resource base used for the production of other rainfed cereal crops. The yield of the crops, however, is low mainly due to water shortage. This study had a major aim of comparing the resource use and productivity of beans, chickpea and cowpea under water stress and well-watered conditions in a semi-arid environment so as to facilitate crop choice and management practices in different legume producing environments. Resource utilization and productivity studies for a given crop or cropping system involve both the crop and its growing environment. In this study, therefore, resource utilization and productivity were studied through field experimentation with three grain legume species and analysis of rainfall/water supply behaviour of ten representative grain legume growing regions in Ethiopia. The field experiments were conducted at Dire Dawa, Ethiopia. The station lies in the semi-arid belt of the eastern Rift Valley escarpment with a long-term mean annual rainfall of 612 mm and a soil dominated by Eutric Regosol. The field experiments were conducted for three seasons in 200112002, 2002 and 2002/2003. The treatments were three water regimes, viz., well-watered (C), mid-season (MS) and late season (LS) water stress and three species arranged in a randomised split plot design using water regimes as main plot and the species as sub-plot. The experiments involved measurements of important variables in the soil-plant-atmosphere continuum. Analysis of the long-term rainfall of 10stations in chapter 2 indicated the existence of major regional differences in water supply. In some of the regions (e.g. Bahir Dar, Bako and Bole) excess water is a problem while in other areas (e.g. Dire Dawa and Jijiga) water shortage is a major bottleneck for crop production. Based on water supply, the regions were grouped as ample water supply, intermediate water supply and poor water supply regions. The study indicated the need to adjust crop choice and management practices based on site and seasonal conditions. The resource utilization and productivity of the three species was studied based on a micrometeorological approach involving phenology, growth and dry matter partitioning (Chapter 3), water use and water use efficiency (Chapter 4), radiation and radiation use efficiency (Chapter 5), water relations and carbon assimilation (Chapter 6) and yield and its components (Chapter 7). Analysis of phenology and growth indicated a reduction of leaf area and dry matter only in the MS treatment and a shortened growth period only in the LS treatment in all species. However, species differences were observed in that the reduction in leaf area due to MS stress was the least in cowpea compared to beans and chickpea. Both the timing of water supply and species influenced dry matter allocation among aboveground parts. The LS stress hastened dry matter allocation to the pod while the MS depressed it in all species. In the LS stress, beans allocated a higher percentage of the above ground dry matter to the seed than chickpea and cowpea during the mild temperature seasons while cowpea allocated the highest percentage during the high temperature season. Such high dry matter allocation to the pod is important to maintain high harvest index (HI) under water-limited environments. Water use varied across water regimes, the highest being in the C treatment followed by the MS and LS treatments in descending order in all species. However, the MS treatments resulted in the lowest water use efficiency (WOE) in all species due to low leaf area index (LAI) and high soil evaporation. Despite differences in water use, the C and LS treatments had similar WOE in all species indicating that some periods of water stress during the late stage of crop growth may increase WOE and improve water saving in water-limited environments. WOE was also strongly negatively correlated with specific leaf area (SLA) under well-watered conditions in all species and in both seasons suggesting that it could be used as a selection criterion for high WUE in the species. The MS treatment reduced extinction coefficient (K) and thereby reduced fractional radiation interception (F) in all species. Radiation use efficiency (RUE) was also negatively affected by the MS stress in beans and chickpea whereas it was not affected by any of the water stress treatments in cowpea. The relationship among soil water, leaf water potential, stomatal resistance, rate of photosynthesis (A) and transpiration (E), vapour pressure deficit and leaf temperature are described in Chapter 6. Cowpea, followed by beans, closes its stomata at higher level of soil water content and leaf water potential as compared to chickpea. Cowpea also has a capacity to photosynthesise and transpire at a higher rate under favourable water supply and also to maintain a slower rate of decline in A and E under low soil water status when compared with beans and chickpea. The magnitude and rate of A decline was higher and faster in the MS than in the LS stress, and among species, it was faster in chickpea than in beans and cowpea. Stepwise regressions of data indicate that, unlike transpiration, photosynthesis could be estimated from a few weather and physiological parameters with reasonable accuracy in all the three species. In contrast to cowpea, which is less and almost equally sensitive to both stress periods, the grain yield of beans and chickpea was found to be more sensitive to the MS than the LS stress during all seasons. The high sensitivity of beans and chickpea grain yield to the MS stress was associated with reductions in LAI, WUB, RUE and dry matter partitioning to the pod as a result of the stress. The lower grain yield reduction of cowpea under water stress is attributed to the crop's ability to adjust its stomata promptly and maintain its LAl, photosynthesis and RUE at a higher level than beans and chickpea. Simulation of grain yield with CROPGRO in beans and chickpea gave a satisfactory result with some limitations in simulating yield components. The model has shown a promising potential to be used as a decision support tool in the semi-arid regions after further calibration and testing. The results generally show that cowpea is more productive and resource efficient than beans and chickpea under water-limited conditions while beans is more productive and has higher resource efficiency than cowpea and chickpea under well-watered conditions. It is concluded that better productivity and optimum resource utilization can be achieved through proper crop-environment matching. Moreover, crop management and breeding practices should focus on increasing the WUB, RUE and HI of grain legumes to improve the yield of the crops in mid-season drought prone environments.

Graanbone speel 'n belangrike rol in lae-inset landboustelsels deurdat dit kwaliteit proteïene aan die arm gemeenskappe verskaf en die natuurlike hulpbronbasis vir die produksie van ander droëland graangewasse verbeter. Die opbrengs van die gewasse is egter laag, hoofsaaklik a.g.v. watertekorte. Hierdie studie het die hoofdoel gehad om die hulpbronverbruik en produktiwiteit van bone, keker-ertjies en swartbekboontjies tydens toestande van waterstremming en geen waterstremming te vergelyk in 'n semi-ariede omgewing om sodoende gewaskeuse te vergemaklik en bestuurspraktyke in verskeie peulgewas-omgewings te bepaal. Die bestudering van hulpbronverbruik en produktiwiteit binne 'n gegewe gewasstelsel behels beide die gewas en sy groei-omgewing. In hierdie studie is hulpbronverbruik en produktiwiteit dus bestudeer deur veldeksperimentering waarin drie peulgewas-spesies gebruik is en die reënval/watertoevoer van tien verteenwoordigende peulgewas groeistreke in Ethiopië ontleed is. Die veldeksperimente is uitgevoer by Dire Dawa, Ethiopië. Die stasie is in die semi-ariede gordel van die oostelike Skeurvallei-platorand geleë. Die langtermyn gemiddelde jaarlikse reënval is 612 mm, terwyl die grond deur 'n Eutric Regosol gedomineer word. Die veldeksperimente is vir drie seisoene in 200112002,2002 en 2002/2003 uitgevoer. Die behandelings was drie waterverdelings, nl. goed-gewater (C), middel-seisoen (MS) en laat-seisoen (LS) waterstremming en drie spesies in 'n ewekansige verdeelde perseelontwerp waarin waterverdelings as hoofpersele en die spesies as sub-persele gebruik is. Die eksperimente het die meting van belangrike veranderlikes in die grondplant- atmosfeer kontinuum behels. Ontleding van die lang-termyn reënval van 10 stasies in hoofstuk 2 het groot streeksverskille in die watertoevoer uitgewys. In sommige van die streke (bv. Bahir Dar, Bako en Bole) is oortollige water 'n probleem, terwyl watertekorte 'n groot demper op gewasproduksie plaas in ander gebiede (bv. Dire Dawa en Jijiga). Die gebiede is aan die hand van watertoevoer gegroepeer as streke met genoegsame watertoevoer, intermediêre watertoevoer en swak watertoevoer. Die studie het die behoefte uitgewys om gewaskeuse en bestuurspraktyke na aanleiding van die perseel en seisoenale toestande aan te pas. Die hulpbronverbruik en produktiwiteit van die drie spesies is ondersoek deur gebruik te maak van 'n mikrometeorologiese benadering wat fenologie, groei en droëmassaskeiding (Hoofstuk 3), waterverbruik en waterverbruikseffektiwiteit (Hoofstuk 4), straling en stralingsverbruikseffektiwiteit (Hoofstuk 5), waterverhoudinge en koolstof-assimilasie (Hoofstuk 6) en opbrengs en die komponente daarvan (Hoofstuk 7) behels. Ontleding van fenologie en groei het gedui op 'n verlaging van blaaroppervlak en droëmassa in die MS behandeling alleenlik en 'n verkorte groeitydperk in slegs die LS behandeling onder alle spesies. Verskille tussen spesies is egter waargeneem aangesien die vermindering in blaaroppervlak a.g.v. MS stremming kleiner was onder swartbekboontjies in vergelyking met bone en keker-ertjies. Beide die tydsberekening van watertoevoer en die betrokke spesie het die droëmassa allokering onder bogrondse plantdele beïnvloed. Die LS stremming het droëmassa allokering na die peul versnel, terwyl MS stremming dit onder alle spesies vertraag het. Bone het meer droëmassa as keker-ertjies en swartbekboontjies na die peul geallokeer. Sodanige droëmassa allokering na die peul is belangrik om 'n hoë oesindeks (Hl) in waterbeperkte omgewings te onderhou. Waterverbruik het oor waterverdelings verskil; die hoogste verbruik het in die C behandeling voorgekom gevolg deur die MS en LS behandelinge in dalende volgorde onder alle spesies. Die MS behandelings het egter gelei tot die laagste waterverbruiksdoeltreffendheid (WUB) onder alle spesies a.g.v. die blaararea-indeks (LAl) en hoë grondverdamping. Ten spyte van verskille in waterverbruik het die C en LS behandelinge soortgelyke WUB onder alle spesies gehad wat dui dat sommige tydperke van waterstremming gedurende die latere stadium van gewasgroei WUB mag laat toeneem en waterbesparing in waterbeperkte omgewings bevorder. Daar was ook 'n sterk negatiewe korrelasie tussen WUB en spesifieke braararea (SLA) onder goed-gewaterde toestande onder alle spesies in beide seisoene wat daarop dui dat dit gebruik kan word as 'n seleksiekriterium vir hoë WUB onder die spesies. Die MS behandeling het die uitdunningskoëffisiënt (K) verlaag en daardeur die gedeeltelike stralings-onderskepping (F) by alle spesies verlaag. Stralingsverbruikseffektiwiteit (RUE) was ook negatief geaffekteer deur die MS stremming in bone en keker-ertjies waarteen dit nie deur een van die waterstremmingsbehandelinge in swartbekboontjies geaffekteer is nie. Die verband tussen grondwater, blaar waterpotensiaal, huidmondjie-weerstand, fotosintese-(A) en transpirasietempo (E), dampdrukdepressie en blaartemperatuur word in Hoofstuk 6 beskryf. Swartbekboontjies, gevolg deur bone, sluit hul huidmondjies by hoër vlakke van grondwaterinhoud en blaar-waterpotensiaal in teenstelling met keker-ertjies. Swartbekboontjies besit ook die vermoë om teen 'n hoër tempo te fotosinteer tydens gunstige watertoevoer en om 'n stadiger tempo van afuame in A en E te onderhou ten tye van lae grondwaterstatus in vergelyking met bone en keker-ertjies. Die grootte en tempo van afuame in A was hoër en vinniger in die MS- as in die LS-stremming, en tussen die spesies was dit vinniger in keker-ertjies as in bone en swartbekboontjies. Stapsgewyse regressie van die data toon dat, anders as in die geval van transpirasie, kan fotosintese met redelike akkuraatheid geskat word aan die hand van 'n paar weeren fisiologiese parameters onder die drie spesies. In teenstelling met swartbekboontjies wat minder en amper ewe sensitief vir stremmingsperiodes is, is daar gevind dat die graanopbrengs van bone en keker-ertjies meer sensitief is vir die MS- as die LS-stremming in al die seisoene. Die hoë sensitiwiteit van boon en keker-ertjie graanopbrengs vir die MS-stremming was geassosieer met afuames in LAl, WUB, RUE en droëmassa allokering na die peul a.g.v. die stremming. Die laer afuame in graanopbrengs van swartbekboontjies onder waterstremming kan toegeskryf word aan die vermoë van die gewas om sy huidmondjies vinnig aan te pas en sy LAl, fotosintese en RUE by 'n hoër vlak as dié van bone en keker-ertjies te onderhou. Simulering van graanopbrengs met CROPGRO vir bone en keker-ertjies het bevredigende resultate gelewer met 'n paar tekortkominge in die simulering van opbrengskomponente. Die model het 'n belowende potensiaal getoon om na verdere kalibrasie en toetsing as 'n ondersteunende besluitnemingshulpmiddel in die semi-ariede streke gebruik te word. Die resultate toon oor die algemeen dat swartbekboontjies meer produktief en hulpbron-effektief is as bone en keker-ertjies onder waterbeperkte toestande, terwyl bone meer produktief en 'n hoër hulpbronverbruikseffektiwiteit as swartbekboontjies en keker-ertjies openbaar ten tye van genoegsame watertoevoer. Die gevolgtrekking kan gemaak word dat beter produktiwiteit en optimale hulpbronverbruik bereik kan word deur middel van gepaste gewas-omgewing passing. Bowenal behoort die fokus van gewasbestuur en teelpraktyke te val op die verhoging van WUB, RUE en Hl van peulgewasse om sodoende die opbrengs van die gewasse in middel-seisoen droogte-omgewings te verhoog.
Thesis (Ph.D. (Soil, Crop and Climate Sciences (Agrometeorology))--University of the Free State, 2004
Keywords: Beans; Chickpea; Cowpea; Gas exchange; Radiation use efficiency; Resource utilization; Productivity; Semi-arid environment; Water deficit; Water use efficiency; Legumes -- Water requirements -- Ethiopia; Legumes -- Ethiopia -- Growth