Treated-cassava peel vermicomposts enhanced earthworm activities and cowpea growth in field plots

Abstract The peels of bitter cassava (Manihot utilissima) root, a major source of food carbohydrate in the tropics, though rich in nutrients, form toxic wastes lethal to soil invertebrates and can inhibit root growth. Recent investigations highlighted the ability of the earthworm, Eudrilus eugeniae (Eug) to partially detoxify the toxic wastes, and transform the cassava peels into valuable vermicompost. Vermicomposting and field investigations set up to assess the impact of three agricultural wastes: poultry dropping (Capo), cowdung (Caco), and guava (Psidium guajava) leaves (Cag) on Eug's ability to vermicompost cassava peel (Cas) and the biofertilizer value of the vermicomposts produced, highlighted the beneficial effects of the waste treatments and the efficacy of the biofertilizers in field plots cropped with cowpea. Cag and Caco induced 55% and 64% greater Eug fecundity than Cas alone while (Capo) induced a 23% reduction, Caco also induced 39% greater Eug biomass in compost cages. In the cowpea field all vermicomposts treatments similarly enhanced earthworm surface cast production, but differed in their effects on the diversity of the earthworm species: Capo and Cag induced 2120% and 390% greater Irridodrillus spp. (earthworm) cast production, while Cas depressed Irridodrillus surface activity. Capo induced 34% reduction on Aggrotoreutus nyongii (earthworm spp.) activity relative to Cas, though the vermicomposts enhanced this earthworm activity relative to the control. Cowpea aerial biomass increased significantly fivefold, twofold, and 1.6-fold with Capo, Cas and Cag, over the untreated field plots. Soil CEC was enhanced with Cag, and available phosphorous increased twofold with Capo.