Impact of soil amendments on maize yield and soil health in Uganda

Abstract Maize (Zea mays L.) is a critical crop for food security and economic well-being in Uganda, yet yields remain below the threshold among smallholder farmers (2–3 t/ha). This is attributed to nutrient-depleted ferralsols, as well as planting methods and land use types. Organic amendments, either alone or in combination with biochar, offer a sustainable alternative to conventional NPK fertilizers. This study compared eight treatments (Control, NPK, organic inputs alone, and organic + biochar combinations) to evaluate impacts on maize yield, soil chemical and biological properties, and economic viability for smallholder farmers. A randomized complete block design with three replications was used to measure yield, soil pH, organic matter, N, P, and K. Root colonization by arbuscular mycorrhizal fungi and soil enzyme activities (dehydrogenase, phosphatase). A cost-benefit analysis was carried out, including input costs, labor, revenue, profitability, and Benefit-Cost Ratio (BCR). The results indicate that treatments combining organic inputs with biochar (Bokashi + Biochar, Vermicompost + Biochar) and NPK delivered the highest yields (9.3–9.5 t/ha), outperforming the control (4.0 t/ha). These treatments significantly increased soil fertility indicators (organic matter, N, P, K) and microbial health. BCRs were favorable: NPK (5.7), Bokashi (1.9), Vermicompost (1.8), and combinations (≥ 1.4). Organic amendments combined with biochar achieved yields comparable to NPK under the conditions of this study, while improving soil chemical and biological properties. To support adoption by smallholders, local production of organic amendments and technical capacity must be strengthened. Graphical Abstract