Characterisation of Chamaecytisus tagasaste, Moringa oleifera and Vachellia karroo Vermicomposts and Their Potential to Improve Soil Fertility

Abstract

Poor soil fertility and land degradation limit crop production among smallholder farmers. The practice of agroforestry with leguminous trees has proven to be sustainable as it bolsters nutrient supply through nitrogen fixation and nutrient cycling. The beneficiation of agroforestry species could add even more value by using tree based waste materials as mulch or vermicomposting. A study was conducted to investigate the impact of vermicomposting on chemical and biological characteristics of three agroforestry species; Chamaecytisus tagasaste, Vachellia karroo and Moringa oleifera. Eisenia fetida earthworms were added to the leaves and small twigs of the three trees in worm composting bins. The worms were allowed to feed on the feedstocks for six weeks under laboratory conditions. The results showed that vermicomposting significantly enhanced macronutrient nutrient content in all the three feedstocks. The findings also showed that the quality of the vermicompost depends on the feedstock type. M. oleifera had the best quality vermicomposts with a significantly higher composition of macronutrients which ranged between 50 and 170% higher for Ca, K, Mg and P. Vermicomposting increased Mo while other micronutrients such as Zn, Mn, Fe and B significantly decreased with vermicomposting time. In addition, vermicomposting increased E. fetida reproduction with more than a 450% increase in earthworm numbers in all three feedstocks. In conclusion, vermicompost have potential to be used to improve soil fertility and thus reduce the use of synthetic fertilisers in crop production.