Impact of Soil Amendments on Maize Yield and Soil Health in Uganda

Maize ( Zea mays L.) is a critical crop for food security and economic wellbeing in Uganda, yet yields remain below the threshold among smallholder farmers (2–3 t/ha). This is attributed to nutrient-depleted ferralsols given planting methods and land use types. Organic amendments such as Bokashi, vermicompost, and bio-compost, alone or combined with biochar offer a sustainable alternative to conventional NPK fertilizer. 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 with biochar are competitive with NPK in yield and profitability, while enhancing soil health. To support adoption by smallholders, local production of organic amendments and technical capacity must be strengthened.