The nutrient type and amount contributed from vermicompost varies depending on the source material, earthworm type used, agro-ecology and farmers’ management. These call for crop, soil and site specific study. This study, therefore, aimed at determining: (i) the optimal vermicompost application rate/s for wheat and maize production; and (ii) the role of vermicompost on soil fertility improvements. Field experiments in three agro-climatic zones (highland, midland and lowlands) were established on wheat and maize crops following a randomized complete block design. The treatments were vermicompost (2.5, 5.0, 7.5 and 10 t ha−1), conventional compost (10 t ha−1), and recommended rates of Nitrogen and Phosphorus (NP = 100 kg DAP and 50 kg Urea) fertilizers. Our results revealed that the studied soil chemical properties, primarily, organic carbon (OC %), N (%) and available P (mg kg−1) increased with increasing vermicompost rate. The 10 t ha−1 vermicompost treated plots had 157-210%, 64-81% and 100-242% higher soil total nitrogen content as compared to the control, 10 t ha−1 conventional compost and NP fertilizer treatments, respectively. Application of 10 t ha−1 vermicompost also resulted in a 1.5-fold and 43-63% grain yield increment of both tested crops compared to the control and NP treated plots, respectively. However, the highest net benefit was obtained from 5 t ha−1 vermicompost for maize (86% increase) and 10 t ha−1 of vermicompost for wheat (152% increase compared to the control). In conclusion, vermicompost at 5 t ha−1 for maize and 10 t ha−1 for wheat can be recommended to sustainably manage farm productivity.
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