High protein content in cowpea (Vigna unguiculata (L.) Walp.) is considered as major advantage for its use in nutritional components. In this way, an experiment was conducted to investigate the effect of cropping system, site, and nitrogen fertilization on cowpea crude protein. The study comprised of three cropping systems (Maize-cowpea rotation, monocropping cowpea and intercropped cowpea), three sites (Potchefstroom, Taung, and Rustenburg, South Africa) and two rates of nitrogen fertilizers applied in kg ha -1 at each site (0 and 20 at Potchefstroom, 0 and 17 at Rustenburg, 0 and 23 at Taung). Moreover, a factorial experiment randomized in complete block design with three replications was conducted during 2011/12 and 2012/13 planting seasons. The protein content was determined from green leaves harvested before flowering, immature green pods and seeds during reproductive stage and maturity. Results showed that cropping system had significant effect on cowpea leaf protein content (P < 0.05). Intercropped cowpea significantly gave higher leaf protein (26.7% more) content than rotational cowpea. Cowpea planted at Taung had significantly higher leaf protein (30.1% more) content as compared to cowpea planted at other sites. Application of nitrogen fertilizer contributed to higher protein content of immature pods. Moreover, cowpea protein content differs among the different locations due to different soil types and climatic conditions.

Maize seed quality during storage can decline to a level that may make the seed unacceptable for planting purpose. A factorial experiment randomized in complete block design with three replications was conducted during 2011/12 and 2012/13 planting seasons. The experiment comprised of three cropping systems (cowpea-maize rotation, monocropping maize and intercropped maize), three sites (Potchefstroom, Taung and Rustenburg) and two rates of nitrogen fertilizers applied in kg ha -1 at each site (0 and 95 at Potchefstroom, 0 and 92 at Rustenburg, 0 and 113.5 at Taung). The experiment was conducted to investigate the effect of cropping system, site and nitrogen fertilization on maize seed quality. Maize seeds harvested from Potchefstroom and Rustenburg had significantly (P < 0.05) higher oil content of 4.4% than maize seeds harvested from Taung. Maize plots applied with nitrogen fertilizer had significantly (P < 0.05) higher seeds protein content of 8.7% than maize plots without nitrogen fertilizer application. Maize seeds harvested from Potchefstroom had significantly (P < 0.05) higher starch content of 71.8% than maize seeds harvested from Rustenburg and Taung. Cowpea-maize rotation and intercropped maize had significantly (P < 0.05) higher seed phosphorus content of 0.50 and 0.52%, respectively than monocropped maize. In this study, site as factor played a vital role on quality of maize seeds. Maize seed quality was improved significantly by the interaction effect of site x season.

Cassava is an important starchy root crop grown globally in tropical and subtropical regions. The ability of cassava to withstand difficult growing conditions and long-term storability underground makes it a resilient crop, contributing to food and nutrient security. This study was conducted to evaluate the performance and adaptability of exotic cassava cultivars across different environments in South Africa and to recommend genotypes for cultivation. A total of 11 cassava cultivars were evaluated at six on-farm sites, using a randomized complete block design with three replications. There were highly significant (p < 0.001) variations between genotypes, environments, and their interaction for all yield and yield-related traits studied. This indicates the need to test the genotypes in multiple environments before effective selection and commercialization can be undertaken. MSAF2 and UKF4 showed the overall best performances for most of the traits, whilst UKF9 (49.5%) and P1/19 (48.5%) had the highest dry matter yield. UKF4 (102.7 t ha−1) had the highest yield and greatest root yield stability across environments. MSAF2 did not perform consistently across environments because it was highly susceptible to cassava mosaic disease (CMD). MSAF2 could be used as a donor parent to generate novel clones with large numbers of marketable roots, and high fresh root yields, if the other parent can provide effective resistance to CMD. Based on genotype and environmental mean, Mabuyeni (KwaZulu-Natal), Mandlakazi (Limpopo), and Shatale (Mpumalanga) were found to be better environments for cassava cultivation and testing. This study is a pioneer in cassava research using multiple environments in South Africa. It provides baseline information on the performance of currently available cassava clones, their adaptation to multiple sites, the identification of suitable test sites, and information on current genetic resources for a future breeding program.

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