Closing the Loop: Crop Yield Response and Soil Health Implications of Human Excreta-Derived Fertilizer Application in Dryland Agriculture

William Musazura^1*Nqobile Nkomo¹Benton Otieno²Taruvinga Badza¹Alfred Oduor Odindo¹Steven Ojwach³

• ¹Crop Science, School of Agricultural, Earth & Environmental Sciences, University of KwaZulu-Natal, P. Bag X01, Scottsville, Pietermaritzburg, South Africa
• ²WASH R&D, Chemical Engineering Basement, Entrance 3, Rick Turner Road, Howard College, University of KwaZulu-Natal, Glenwood, Durban, South Africa
• ³Chemistry Department, School of Chemistry and Physics, University of KwaZulu-Natal, P. Bag X01, Scottsville, Pietermaritzburg, South Africa

This study evaluated the potential of human excreta-derived amendments, specifically, sewage sludge-based co-compost and urine, to improve soil fertility and crop productivity in dryland agriculture without compromising public health. A field experiment was conducted at the Bishopstowe Agricultural Living Lab using a randomized complete block design with five treatments (urine, urine + co-compost, chicken manure, no fertilizer, and conventional fertilizer) and four replications. Chili (Capsicum annuum) yield, soil N mineralization, ammonium and nitrate-N concentrations, urease activity, β-glucosidase activity, alkaline and acid phosphatase activity, microbial community, and active carbon did not differ significantly among treatments (P > 0.05). In contrast, organic C and extractable P were significantly higher in the urine + co-compost and chicken manure treatments. Although the co-compost exhibited high organic C content, associated microbial activity was significantly lower than that observed under chicken manure. Groundwater contamination by Escherichia coli and nitrate was not significantly affected by the application of excreta-derived amendments over the six-month trial. These findings provided insight into the impacts of human excreta-derived fertilizers on crop yields, soil health, and environmental integrity for resilient and sustainable food systems. However, good management practices, including salinity control and adherence to WHO sanitation safety guidelines, should be implemented. The study was constrained by its short duration (six months) and single-site design. Long-term (>2 years) and multilocation experiments are recommended to comprehensively assess the agronomic, soil health, and environmental implications of excreta-derived amendments in dryland agriculture.