Screening of cover crops under conservation agriculture.
The practice of conventional tillage results in land degradation, reducing soil fertility due to soil erosion. Conservation agriculture aims at reducing soil disturbance which brings benefits of soil conservation. The call for promoting conservation agriculture in South Africa is important in order to reduce the negative impacts caused by frequent conventional soil tillage. Weeds compete for water, nutrients and light with the grown crops. The use of herbicide application to manage weeds has also become problematic due to herbicide resistance that has arisen. However, weed management remains one of the greatest problems that smallholder farmers are facing under conservation agriculture in South Africa. As such there is a need to introduce alternative methods that can be used to manage weeds under conservation agriculture without severe soil disturbances. The study was done in two contrasting agro ecological zones of KwaZulu-Natal, Bergville and Ukulinga. This study was aimed at evaluating three different cover crops for weed suppression and soil macrofauna abundance under conservation agriculture. Vigna unguilata (L.) Walp (cowpea), Lablab purpureus (dolichos lablab) and Mucuna prureins (L.) (velvet bean) were also evaluated for biomass production. The experiment was conducted in a randomised complete block design replicated three times. Herbicide treatment and bare plot served as controls. The data was analysed using the Genstat Stastical Package 17th edition. Poison distribution was used to analyse the soil macrofauna species abundance. Velvet bean produced the highest biomass in both Ukulinga (1.59 t/ha) and Bergville (0.72 t/ha). Cowpea had the lowest biomass accumulation in Bergville (0.59 t/ha) and lablab was the lowest in Ukulinga (0.88 t/ha). Lablab was effective in weed suppression in Bergville (P<0.05). Cowpea performed best in weed suppression in Ukulinga (P<0.05). Lablab showed to be the best in reducing weed species diversity and cowpea showed to be the best in reducing weed species diversity in Ukulinga. Cowpea showed to be effective in improving soil macrofauna abundance in Bergville with (39 species counts). Lablab proved to be the best in improving soil macrofauna species abundance in Ukulinga (57 species counts). Cowpea and lablab showed to be the highest in improving soil macrofauna diversity in Bergville. Lablab and Mucuna pruriens had the highest soil macrofauna species diversity in Ukulinga. It can be concluded that cowpea and lablab can be recommended for use under conservation agriculture to suppress weeds and to improve soil macrofauna species abundance and diversity in South Africa. Farmers will also improve their profit due to reduced herbicide use for weed control.