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dc.contributor.advisorVan Rensburg, L. D.
dc.contributor.advisorBennie, A. T. P.
dc.contributor.authorBarnard, Johannes Hendrikus
dc.date.accessioned2018-01-25T09:13:31Z
dc.date.available2018-01-25T09:13:31Z
dc.date.issued2006-05
dc.identifier.urihttp://hdl.handle.net/11660/7717
dc.description.abstractEnglish: In South Africa a huge amount of energy was spend on irrigation research over the past two decades, mainly to optimise water application in order to prevent crop water stress. In the quest to conserve water for transpiration, researchers tended to neglect the importance of drainage or percolation, which eventually results in the accumulation of salts in the root zone. Salts also accumulate in the root zone where shallow water tables are present. Farmers along the Lower Vaal River expressed their concern about yield losses induced by build-up of salts in the root zone. The detrimental affect of salinity on field crops are extensively reported in the literature and the only way to address the problem is through leaching. Sustainable utilization of these saline or potential saline soils depends on adequate natural drainage or artificial drainage systems, which ensures a net downward flux of water and salts below the root zone for optimum development and functioning of roots. This dissertation focuses mainly on the management of salts in the root zone of apedal soils. The research was conducted on two soil types (Clovelly and Bainsvlei) reconstructed in 5000 litre lysimeters on the experimental farm, near Bloemfontein, of the Department of Soil, Crop and Climate Sciences (University of the Free State). A total of 30 lysimeters, 15 per soil type arranged in two parallel rows under a moveable rain shelter were used. It was assumed that the artificially prepared soil profiles are stable because more than 10 cropping cycles were completed before the commencement of this experiment. The first aim of Chapter 3 was to address the effect of irrigation water salinity on the accumulation of salt in the root zone under shallow water table conditions. A total of 612 mm was irrigated with irrigation water salinity treatments that varied between 15 and 600 mS m-1. Results showed that in the absence of drainage, salts will accumulate in the root zone at an alarming rate. In fact, salinity of the soil water almost doubled with respect to that of the irrigation water during only one growing season. These various saline profiles were used to characterise the impact of soil water salinity on the hydraulic characteristics of the two soils under investigation. After saturation of the profiles, drainage curves were in situ determined by allowing water to drain freely from the profiles for approximately a month. These drainage curves revealed that the initial soil water salinity did not significantly influence the hydraulic characteristics of both soils. It was possible to quantify the amount of salt removed during a drainage cycle. Although both soils are apedal, the two soils differed markedly in their discharge rates and amounts. Chapter 4 had focused on quantifying the pore volume of water required to leach excess salts from the profiles. It was found that piston flow can describe the leaching process, because one pore volume of drainage was sufficient to remove 100% of the excess salts, irrespective irrigation water salinity or soil water salinity. The results also showed that it is more efficient to remove 80% of excess salts in stead of 100%. On freely drained soils it is therefore possible to effectively and efficiently manage the salinity level of the root zone through controlled irrigation in excess of crop water demand, when necessary. Complex dynamic models are helpful in understanding the nature and complexity of solute movement in soils, but unfortunately they are not widely used by irrigators and managers. The final objective (Chapter 5) was to derive a simple model capable of estimating the depth of water required to remove excess salts from the root zone. The non-linear exponential association (y = a {1- exp –b x}) of the in situ determined leaching curves provided the best mathematical description of the fraction of excess salts removed in relation to the depth of leaching water required per unit depth of soil. Verification of the proposed model showed that it is possible to accurately estimate the leaching requirement for effective and efficient management of root zone salinity in apedal soils. It was recommended that the proposed model should be expanded to include more soil types.en_ZA
dc.description.abstractAfrikaans: In Suid Afrika is groot hoevelheid energie oor die afgelope twee dekades aan navorsing oor besproeiingskedulering spandeer, hoofsaaklik om watertoediening te optimiseer sodat waterstremming by gewasse verhoed kan word. In die strewe om meer water vir transpirasie beskikbaar te stel, het navorsers die belangrikheid van dreinering of perkolasie agterweë gelaat. Die fyn skedulering het daartoe gelei dat soute onder besproeiing in die wortelsone akkumuleer. Soutakkumulasie vind ook plaas waar vlak watertafels voorkom. Boere langs die benede Vaal Rivier het hul sorg uitgespreek oor oesverliese weens soutakkumulasie in die wortelsone. Die nadelige effek van versouting is wyd in die literatuur aangeteken en daarvolgens is die enigste wyse om die probleem op te los, loging. Die volhoubare benutting van versoute of potensieële versoute gronde, hang van die teenwoordigheid van natuurlike of kunsmatige dreinering af. Dreinering veroorsaak ‘n afwaardse beweging van water en soute verby die wortelsone wat optimale groeitoestande vir plantontwikkeling skep. Hierdie studie fokus grootliks op die bestuur van soute wat in die wortelsone van apedale gronde voorkom. Die navorsing is op twee gronde (Clovelly en Bainsvlei) gedoen. Die gronde is geherkonstrueer in 5000 liter lisimeters wat op die proefplaas van die Departement Grond, Gewas en Klimaat Wetenskappe (Universiteit van die Vrystaat) geinstalleer is. ‘n Totaal van 30 lisimeters, twee parallele rye van 15 lisimeters elk per grond tipe, is onder ‘n bewegende reënskerm uitgelê. Dit is aanvaar dat die gronde in die lisimeters stabiel is omdat meer as 10 gewasse voor die aanvang van die experiment daarin verbou is. Die eerste doelwit (Hoofstuk 3) was om die effek van sout akkamulasie in gronde afkomstig van besproeiingswater onder toestande van vlak watertafels, te ondersoek. ‘n Totaal van 612 mm besproeiing is met soutinhoude wat vanaf 15 tot 600 mS m-1 wissel toegedien. Die resultate het aangetoon dat onder toestande van onvoldoende dreinering, soute in die wortelsone teen ‘n verontrustende tempo akkumuleer. Die geleivermoë van die grondwater het oor een seisoen amper verdubbel in vergelyking met die elektriese geleivermoë van die besproeiings water wat gebruik is. Hierdie soutprofiele is gebriuk om die impak van grondwater-versouting op die hidrouliese einskappe van die genoemde gronde te bestudeer. Na versadiging van die profiele is, in situ dreineringskurwes bepaal deur die water oor ‘n periode van ‘n maand vrylik vanuit die grond te laat dreineer. Hierdie dreineringskurwes het aangetoon dat die grondwater-versouting nie die hidrouliese einskappe van die gronde beinvloed het nie. Dit was moontlik om die hoeveelheid soute wat tydens een dreineringsiklus geloog het, te kwantifiseer. Alhoewel beide gronde apedaal is, het die logingstempo- en hoeveelheid merklik van mekaar verskil. In Hoofstuk 4 is daar hoofsaaklik gekonsentreer op die kwantifisering van die porievolume water wat benodig word om oortollige soute vanuit die profiele te loog. Daar is gevind dat suiervloei die logingsproses die beste beskryf, omdat een porievolume water voldoende was om 100% van die oortollige soute te verwyder. Die resultate het ook aangetoon dat dit meer waterbesparend is om 80% van die soute, instede van 100%, te verwyder. Op goed gedreineerde gronde is dit moontlik om die soutinhoud van die wortelsone deur middel van beheerde oor-besproeiing effektief en doeltrefend te bestuur, sonder dat gewaswaterstremming voorkom. Dinamiese modelle is nuttig om die kompleksiteit van soutbeweging in gronde te verstaan. Hierdie modelle word egter nie algemeen deur besproeiingsboere- en bestuuders gebruik nie. Die finale doelwit (Hoofstuk 5) was om ‘n eenvoudige model te ontwikkel wat die hoeveelheid water wat benodig word om oortollige soute vanuit die wortelsone te loog, te bereken. So ‘n model is afgelei vanaf in situ bepaalde logingskurwes. Die nie-lineêre eksponensiale funksie (y = a {1- exp –b x}) het die beste wikundige passing tussen die fraksie oortollige soute verwyder en die hoeveelheid logingswater per eenheid gronddiepte gegee. Verifikasie van die voorgestelde model het aangetoon dat dit moontlik is om die logingshoeveelheid vir effektiewe en doeltreffende bestuur van soute in apedale gronde te voorspel.af
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectSoils -- Leachingen_ZA
dc.subjectSoils, Irrigated -- South Africa -- Bloemfonteinen_ZA
dc.subjectSoils -- Solute movementen_ZA
dc.subjectCrops -- Nutritionen_ZA
dc.subjectDissertation (M.Sc.Agric. (Soil, Crop and Climate Sciences))--University of the Free State, 2006en_ZA
dc.titleLeaching of excess salts from the root zone of apedal soilsen_ZA
dc.typeDissertationen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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