Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: This study was done during 2010 and 2011 as a component study within a long-term crop rotation/soil tillage trial that was started in 2007 at the Langgewens Research Farm near Moorreesburg in the Western Cape Province of South Africa. The aim of this study was to determine the effect of crop rotation and soil tillage on the soil moisture content, mineral-N levels of the soil, leaf area index, chlorophyll content of the flag leaf, biomass production, grain yield and grain quality of spring wheat (Triticum aestivum L). The experimental layout was a randomised complete block design with a split-plot treatment design replicated four times. Wheat monoculture (WWWW), lupin-wheatcanola- wheat (LWCW) and wheat-medic (McWMcW) crop rotation systems were included in this study and allocated to main plots. This study was confined to wheat after medic/clover, wheat after canola and wheat monoculture. Each main plot was subdivided into four sub-plots allocated to four tillage treatments namely: Zero-till (ZT) – soil left undisturbed until planting with a star-wheel planter No-till (NT) – soil left undisturbed until planting and then planted with a no-till planter Minimum-till (MT) – soil scarified March/April and then planted with a no-till planter Conventional-till (CT) – soil scarified March/April, then ploughed and planted with a no-till planter. Soil samples were collected every two weeks from just before planting until before harvest, from which gravimetric soil moisture and total mineral-N (NO3--N and NH4+-N) were determined. Plant samples were collected every four weeks until anthesis, starting four weeks after emergence. From these leaf area index and dry-matter production were determined. Chlorophyll content and light interception were measured at anthesis. At the end of the growing season the total biomass, grain yield and grain quality was determined. Crop rotations which included medics (McWMcW) or canola/lupins (LWCW) led to higher mineral-N content of the soil at the start of the 2011 growing season when compared to wheat monoculture, but did not have an effect on soil moisture. Conservation tillage (minimum- and no-till) practices resulted in higher soil moisture whilst conventional-till resulted in the highest mineral-N content for 2010. There was however no differences in mineral-N content between tillage methods for 2011, whilst soil moisture content was affected in the same way as the previous year. Both crop rotation and tillage influenced crop development and biomass production. In general, increased soil disturbance together with wheat after medics and wheat after canola resulted in better development of the wheat crop with regards to dry matter production and leaf area index. The positive effect of medic and canola rotations was also evident on chlorophyll content and light interception. Grain yield was positively influenced by wheat after medics and wheat after canola, with both systems out-yielding wheat monoculture in 2010 and 2011. Minimum- and no-till resulted in the highest grain yield in both years. Crop rotation and tillage practice showed no clear trends with regards to grain quality. This illustrated the important effect of environmental conditions during grain-filling. Environmental factors such as rainfall and temperature had significant effects in both years of the study, but the importance and advantages of crop rotation, especially with a legume crop such as medics included, was evident even though this component study was done early in terms of the long-term study. The positive effect of implementing conservation tillage practices such as minimum- and no-till were also clearly shown in results obtained throughout this experiment. / AFRIKAANSE OPSOMMING: Die studie is gedurende 2010 en 2011 uitgevoer as ‘n deelstudie van ‘n langtermyn grondbewerking- en wisselbouproef op die Langgewens proefplaas naby Moorreesburg in die Wes-Kaap Provinsie van Suid-Afrika. Die doel van hierdie studie was om die effek van grondbewerking en wisselbou op grondvog, minerale stikstof in die grond, blaaroppervlakindeks, chlorofilinhoud van die blare, graanopbrengs en -kwaliteit van lente koring (Triticum aestivum L) te kwantifiseer. Die eksperiment is uitgelê as ‘n volledig lukrake blokontwerp met ‘n verdeelde perseel ontwerp met vier herhalings. Wisselboustelsels wat aan hoofpersele toegeken is sluit koring monokultuur (WWWW), lupien-koring-kanola-koring (LWCW) en medic-koring (McWMcW) in. Grondbewerking is toegeken aan subpersele. Die grondbewerkingsbehandelings het ingeslui: Zero-bewerking (ZT) – die grond is onversteurd gelaat en koring is met ‘n sterwielplanter geplant, Geen-bewerking (NT) – die grond is onversteur gelaat tot en met planttyd waar koring met ‘n geenbewerking (no-till) planter geplant is, Minimum-bewerking (MT) – die grond is in Maart/April met ‘n tandimplement bewerk en met ‘n geen-bewerking planter geplant, Konvensionele-bewerking (CT) – die grond is in Maart/April met ‘n tandimplement bewerk die grond is in Maar/April geploeg met ‘n skaarploeg en met ‘n geenbewerking planter geplant. Grondmonsters is elke twee weke versamel van net voor plant tot net voor oes. Vanaf die versamelde monsters is die grondwaterinhoud grawimetries bepaal en ook die totale minerale stikstofinhoud (NO3--N en NH4+-N). Plantmonsters is vierweekliks versamel beginnende vier weke na opkoms tot en met antese. Blaaroppervlakindeks en biomassaproduksie is bepaal. Die chlorofilinhoud en ligonderskepping is tydens antese bepaal. Aan die einde van die groeiseisoen is totale biomassa, graan opbrengs asook graankwaliteit bepaal. Wisselboustelsels, wat medics (McWMcW) of kanola/lupine (LWCW) ingesluit het, het ‘n hoër minerale stikstofinhoud aan die begin van die 2011 groeiseisoen getoon. Wisselbou het egter geen effek op grondvog gehad nie. Minimum- en geenbewerking het ‘n hoër grondvoginhoud tot gevolg gehad, terwyl die persele onder konvensionele bewerking ‘n hoër minerale stikstof inhoud gehad het in 2010. In 2011 was daar geen verskille in die minerale stikstofinhoud tussen verskillende die bewerkingsmetodes nie en grondvog gedurende 2011 is op dieselfde wyse as in 2010 beïnvloed. Beide wisselbou en bewerkingsmetode het ‘n invloed gehad op gewasontwikkeling en biomassaproduksie. Die algemene tendens was dat, soos grondversteuring toegeneem het in die koring na medics en koring na kanola, het beter gewasontwikkeling plaasgeving met betrekking tot droëmassaproduksie en blaaroppervlakindeks. Die positiewe effek van wisselbou is ook waargeneem in die chlorofilinhoud van die blare en die ligonderskeppingspotensiaal van die blaredak. Graanopbrengs is positief beïnvloed deur die wisselboustelsel, met beide koring na medics en koring na kanola wat hoër graanopbrengste as koring monokultuur vir beide jare gelewer het. Die hoogste graanobrengs is ook gekry onder die minimumen geen-bewerkingsbehandelings vir 2010 en 2011. Wisselbou en bewerkingsmetodes het geen duidelike invloed op koringkwaliteit gehad nie. Dit is ‘n weerspieëling van die belangrike invloed van omgewingsfaktore gedurende die korrelvulstadium van koring. Omgewingsfaktore soos reënval en temperatuur het betekenisvolle effekte in beide jare van die studie gehad, maar die belang van ‘n wisselbou wat ‘n stikstofbinder soos medics insluit, was reeds in hierdie vroeë stadiums van die langtermynproef opvallend. Die positiewe effek van minimum- en geen-bewerking was ook duidelik sigbaar gedurende die verloop van die studie. / The Western Cape Agricultural Trust for the opportunity and the finances to do this study