Effects of biochar, vermicompost, and inorganic N-P nutrients on soil physical properties, maize growth, and yield, Northwest Ethiopia

Soil degradation in Northwest Ethiopia, driven by acidity and nutrient depletion, severely limits maize productivity. This study evaluated the integrated use of biochar (BC), vermicompost (VC; applied on a nitrogen-equivalent basis), and inorganic nitrogen-phosphorus (N-P) nutrients to rehabilitate acidic soils over two growing seasons (2023/24–2024/25). Treatments markedly improved key soil physical properties: bulk density decreased by up to 10.8%, while gravimetric moisture content increased substantially. These improvements directly enhanced maize growth, increasing leaf area index by 26% and harvest index to over 50%. The highest grain yield (12.13 t ha−1) was achieved with high amendment rates (8 t BC + 10.04 t VC + 120–30.2 kg N-P ha−1), representing a 176% increase over the control. However, economic analysis revealed that moderate integrated application (4 t BC + 5.02 t VC + 120–30.2 kg N-P ha−1) delivered near-optimal yield (12.09 t ha−1) with superior economic returns, optimizing the cost-benefit ratio. A strong predictive model coefficient of determination (R2 = 0.906) confirmed soil and crop parameters as reliable yield indicators. We recommend this moderate, integrated package as a suitable agronomic and economically viable strategy for sustainable maize intensification in acidic and drought-prone agroecosystems.