Conservation agriculture (CA) is a sustainable management system that optimises yield while reducing input costs. However, reduction in tillage intensity and frequency as practised under CA generally alters weed densities and composition. The objective of the study was to evaluate the effect of tillage, cropping system and fertiliser rate on weed density and diversity under CA systems compared with conventional tillage (CT). An on-station field trial with a split-plot, randomised complete block design, was used and included two tillage systems, three cropping systems and two fertiliser levels. Reduced tillage had significantly (p < 0.05) higher weed density (42 m−2) but lower weed biomass (154 g m−2) in contrast to CT with lower weed density (36 m−2) and higher weed biomass (242 g m−2). In a principal component analysis ordination, Datura ferox and Tribulus terrestris were more strongly associated with high fertiliser rate, whereas Zinnia peruviana was associated with CT. The increase in weed density and diversity under reduced tillage is likely to restrain the adoption of CA. Therefore, there is a need for alternative weed management options depending upon the weed spectrum, cropping system and fertiliser management.

Sweet sorghum (Sorghum bicolor L. Moench) is highly susceptible to weed competition during the early growth stages; hence, intercropping is considered to overcome the weed competition challenge. This study was conducted to determine the performance of sweet sorghum in legume intercropping systems under different weed management pressures. Three cropping systems (sole crop, inter-row, and intra-row intercropping) and three weed management levels (no weeding after crop emergency, ceasing weeding 50 days after crop emergency, and weeding throughout) were tested. Intercropping pattern had a significant (p < 0.05) impact on the plant and the number of leaves per plant, while other treatments remained insignificant during the 2017/18 growing season. During the 2018/19 growing season, the intercropping pattern had a significant (p < 0.05) effect on dry and fresh biomass and plant height at 60 days after emergence. An increase in weeding frequencies reduced Brix (◦Bx). Uncontrolled weed plots had the lowest sweet sorghum dry biomass accumulation, whereas the biomass increased as weeding frequencies increased but remained insignificant as weeding frequencies further increased from 50% to 100% in both seasons. Consequently, SS/DB intra-row intercropping and intermediate weeding are sufficient for optimum SS biomass production and sugar levels.

A better understanding of the dry bean (Phaseolus vulgaris L.) growth and yield response to weed competition under the intercropping system is critical for improving sustainable weed management strategies. A two-year trial was conducted with three types of crop arrangement (sole cropping, inter-row, and intra-row intercropping) combined with weeding frequency (no weeding, weeding over the first 50 days of crop growth, and weed-free). Effects of the treatments were tested on dry bean agronomic indicators in terms of the following: 100-grain weight, dry biomass, grain yield, grains per pod, pods per plant, plant height, number of leaves per plant, and chlorophyll content. The intercropping pattern significantly affected dry bean pods per plant, height, and chlorophyll content, while weeding frequency significantly affected all measured agronomic indicators for dry bean, except for chlorophyll content, during the 2017/18 growing season. The results showed that the significant measured agronomic indicators were the lowest under no weed control; however, they increased as weeding frequency increased. The 2018/19 growing season followed a similar trend; however, the interaction effect significantly affected dry bean 100-grain weight, dry biomass, and number of leaves per plant at 40 days after emergence. The dry bean/sweet sorghum or cowpea intra-row intercropping and intermediate weeding frequency displayed optimum productivity.