The effect of maize-legume cropping system and nitrogen fertilization on yield, soil organic carbon and soil moisture.
Crop rotation and intercropping are regarded as better cropping in terms of yield improvement of both cereal and legume crops as compared to monocropping. A factorial experiment was carried out at three dryland localities of Northwest province (Potchefstroom, Rustenburg and Taung) from 2010/11 to 2012/13 planting seasons. The experiment consisted of three cropping systems, monocropping, intercropping and rotational cropping. Two rates of nitrogen fertilizer, zero and optimum levels based on soil analysis results prior to planting were applied on maize and cowpea plots. Soil moisture content was evaluated during three growth stages at different depths of the soil (0-15, 15-30, 30-60 and 60-90 cm) using gravimetric method. Parameters considered for the study included the followings: 100% tasseling/flowering, days to physiological maturity, plant height, number of leaves per plant, leaf area in maize, stem diameter in maize, ear length in maize, ear mass , kernel number per ear, hundred seed mass, grain yield in maize, LER, plant population at harvest and stover yield in maize, number of leaves and nodules per cowpea plant, pod length, seed per pod, pod mass at harvest, grain, field biomass yield at harvest, cowpea leaf, immature pod, seed protein content and maize seed protein, oil, starch and phosphorus content. The analysed soil chemical properties included soil organic carbon using Walkley Black method, soil Bray 1-P; N-NO3, N-NH4 and exchangeable K. Cropping system had significant effect (P < 0.05) on the growth and yield of maize. Cowpea-maize rotation and monocropping maize had tasseled earlier, reached days to physiological maturity earlier, had large leaf area, higher number of leaves per plant, ear mass, kernel number, seed mass, grain yield and stover yield. Maize-cowpea rotation and monocropping cowpea had significantly (P < 0.05) higher number of leaves per plant, seed per pod, pod mass, grain yield and field biomass yield than intercropped cowpea. Cropping system had significant effect (P < 0.05) on soil organic carbon; Bray 1-P and soil nitrate (N-NO3). The interaction effect of cropping system on cropping system x nitrogen x site on maize yield, cowpea growth, protein content and soil N-NO3 contributed towards significant of this study. The chapters of this thesis represent different studies presented as different articles. Chapter 1 is a general introduction to explain the study background and hypothesis. Chapter 2 is on the effect of maize-cowpea cropping system on soil moisture content. Chapter 3 is on crop rotation and intercropping cowpea with maize: maize growth and yield. Chapter 4 is on crop rotation and intercropping cowpea and maize: cowpea growth and yield. Chapter 5 is on the effect of crop rotation and intercropping on cowpea crude protein. Chapter 6 is on the maize seed quality in response to crop rotation, intercropping and nitrogen fertilization. Chapter 7 is on the effect of maize-cowpea cropping system on soil chemical composition. The last chapter 8 is a general discussion and conclusion.
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