Maize is the most important cereal crop grown in areas of South Africa by both small-scale and commercial farmers. Maize monocropping without sufficient input and declining soil nitrogen content are some of the factors that limit yield. The objective of the study was to evaluate the effect of different cowpea cultivars and populations on growth, yield and yield components of succeeding maize. The effects of cropping systems on soil N content were also observed. Field experiments were conducted during the 2005/2006 and 2006/2007 growing seasons at Potchefstroom and Taung in North West province. The trial consisted of four cowpea cultivars: PAN 311 (short duration cowpea cultivar), CH 84, Bechuana white (medium duration cowpea cultivar) and TVU 1124 (long duration cowpea cultivar) and, four planting densities (10 000, 15 000, 20 000 and 40 000 plants ha-1). Maize was used as sequential test crop to determine the residual effect of previous cowpea treatments. Cowpea grain yield increased as planting density increased at both localities. TVU 1124 gave highest grain yield of all cowpea cultivars at both localities. Total dry matter yield also increased with increasing planting density. After cowpea soil NO3- and NH4+ content increased with increasing density. Similarly, soil NO3- content of maize following cowpea showed a considerable improvement, compared to maize monocropping. The highest soil NO3- and NH4+ content was observed when maize followed Bechuana White. Significant differences were also observed in soil microbial activities among the cultivars. Maize grain yields and plant height responded positively to the previous cowpea crop, compared with maize monocropping at both locations, but especially at Taung. Maize stover yield, cob length and KNC significantly responded to maize and cowpea rotation compared to maize monocropping at Taung. These results further confirm the potential of using cowpea to contribute soil N to subsequent maize crops in a rotational system. Copyright / Dissertation (MScAgric)--University of Pretoria, 2010. / Plant Production and Soil Science / unrestricted

La pollution de l’environnement est un problème croissant à l’échelle mondiale. La phytoremédiation est une technique in situ qui utilise les plantes et les micro-organismes qui leur sont associés pour extraire, dégrader ou immobiliser les contaminants environnementaux. Il s’agit d’une méthode moins coûteuse et moins nocive pour l’environnement que les autres techniques de restauration conventionnelles. Le cuivre est un élément trace (ET) souvent trouvé dans les friches industrielles ; il est peu mobile en raison de sa forte liaison avec la matière organique et les particules d’argile. Lorsqu’il est présent en excès, il est nocif pour la flore et la faune. Nous avons mené une expérience en conteneurs impliquant deux espèces distinctes, Brassica napus L., une plante agricole cultivée en grande quantité au Canada et Salix nigra 'S05', une espèce ligneuse à croissance rapide originaire du sud-est du Canada qui ont été cultivées ensemble ou séparément. Le but était de comparer leur potentiel de phytoremédiation de sol contaminé avec du cuivre suivant différentes concentrations. Pour les deux espèces, le cuivre était présent en plus grande quantité dans les racines. Nous avons constaté que la polyculture, en plus de produire le plus de biomasse en général, permettrait la stabilisation et l’extraction maximale de Cu et que l’arrachage de la plante entière serait le moyen le plus efficace d’assurer l’élimination maximale de Cu du sol. De nouvelles expériences devront être effectuées, car le déracinement des plantes présente de nouveaux défis et de nombreux autres facteurs doivent être étudiés et pris en considération. / Environmental pollution is a growing problem on a global scale. Phytoremediation, an approach that uses plants and their associated microorganisms to extract, degrade or immobilise environmental contaminants, is cheaper and less harmful to the environment compared to other conventional remediation techniques such as excavation. Furthermore, phytoremediation can help restore the ecological integrity of an ecosystem and allows for the revegetation of the sites. Copper is a trace element (TE) often found in brownfields which has a low mobility partly due to its strong bond with organic matter and clay particles. When present in excess, Cu is harmful to both flora and fauna. We experimented with two distinct species, B. napus L., an crop species which is grown in large quantities in Canada and S. nigra ‘S05’, a fast-growing woody species native to south eastern Canada in order to compare their phytoremediation potential in various levels of copper-contaminated soil when grown together or in monoculture. For both species, the copper was present in greater quantities in the roots as expected. We observed that the polyculture, in addition to producing the most overall biomass, would allow for the maximum stabilization and extraction of Cu of all treatments and that the removal of the entire plant would be the most efficient way of ensuring Cu removal from the soil. Further experiments will have to be done since the uprooting of plants would present new challenges and multiple other factors would have to be studied and taken into consideration.