Conserving soil moisture for soybean growth as a climate change adaptation strategy.

Abstract

Low crop productivity among smallholder farmers in rural areas is mainly associated with low and variable rainfall as well as factors such as soil fertility. Climate change projections show that rainfall is going to become more variable and hence a major constraint to rain-fed rural cropping systems. There is a need to assist farmers in these areas to cope with current challenges and develop long-term adaptation to climate change. Therefore, the aim of this study was to evaluate the use of soil water conservation strategies and nitrogen fixing legumes as part of climate smart agricultural practices. Specifically, the study evaluated the effect of mulching and fertiliser levels on growth and yield of soybean under rain-fed conditions in the Swayimane rural area of KwaZulu-Natal. The experimental design was a split-plot [hay-mulch (HM) and non-mulch (NM)] arranged in randomised complete blocks (0%, 50% and 100% of recommended fertiliser) replicated three times. Data collected included soil water content, plant height, leaf number, leaf area index (LAI), chlorophyll content index (CCI) and stomatal conductance (SC).Yield and yield components were determined at harvest. The results showed that the use of hay-mulch was effective (P<0.05) in retaining soil water in the root zone. Soil water content in the non-mulched plots frequently reached permanent wilting point hence exposing plants to intermittent water stress. However, mulching had no significant effect on plant growth (plant height, LAI) and SC. Highly significant (P<0.01) differences were observed in CCI, with hay-mulch having a higher CCI compared to non-mulch. Interestingly, plants in non-mulched plots had higher (P<0.05) leaf number compared to plants in mulched plots; this was partly due to a fungal disease that affected plants in mulched plots. Consistent with results of growth, there were no differences in yield of soybean plants grown under mulched relative to non-mulched plots. Subsequent to harvesting the soybean, the seeds were subjected to seed quality tests to assess the effect of production environment on seed quality of progeny. Results of seed quality showed highly significant differences (P<0.001) with progeny from non-mulched plots having relatively higher seed quality (germination percentage, mean germination time and germination velocity index). Overall, the study concluded that while mulching was effective in retaining soil water in the root zone, this did not translate to improved growth and yield as well as subsequent seed quality. The lower soil temperatures experienced under mulching may have inadvertently suppressed growth. Further research is still required over several seasons to confirm these findings and develop firm recommendations on the appropriate use of mulch.