Valorizing agricultural wastes through composting vermicomposting and anaerobic digestion for sustainable soil fertility management in Ethiopian smallholder systems

The strategic use of agricultural organic waste, either directly or processed into high-value organic fertilizers (OFs), is crucial for sustainable agricultural land management, particularly in sub-Saharan Africa, including Ethiopia. This strategy addresses soil organic matter (SOM) depletion and rising chemical fertilizer costs, which pose significant challenges to smallholder farmers. Focus has shifted to underutilized agricultural feedstock such as crop residues and animal manure to counter the decline in soil organic carbon and nutrients caused by competing uses like fuel, construction, and livestock feed. Despite the urgency to recycle organic resources through methods like composting and vermicomposting, challenges persist due to limited information. This review aims to (i) highlight available organic resources for valorization in different agro-ecologies, (ii) showcase technologies for converting organic waste into valuable bio-products and assess their characteristics, focusing on nutrient composition, fertilizer replacement value, and impact on crop yield and soil health, and (iii) discuss current gaps and future prospects tailored to Ethiopian conditions. Recent valorization strategies such as vermicomposting convert underutilized organic matter into high-quality amendments with higher nutrient and microbial composition compared to other methods like thermophilic composting. The combined use of organic and chemical fertilizers consistently leads to significant increases in crop yields in various agro-ecological contexts compared to using organic or chemical fertilizers alone. However, the long-term effects on soil health metrics and agricultural productivity need further investigation in Ethiopian farming. Overall, valorizing organic waste into value-added bio-products (OFs) promotes sustainable agricultural land management practices. Collaborative efforts among governments, research institutes, agricultural experts, and local communities are essential to formulate and implement effective strategies that prioritize soil health through the large-scale adoption of valorization methods for producing OFs

Zerihun Getachew Gebrehana; Mesfin, T.; Cherenet, M.; Gebremikael, M.T.; Ebrahim, M.; Degefie, T.; Abera, W.; Tamene, L.