Impact of various soil amendments on temporal NPK release, soil quality and maize yield in tropical Alfisols of Zaria, Nigeria

Sustainable crop production in tropical regions is challenged by poor soil fertility, necessitating effective soil amendment strategies. This study evaluated the temporal effects of five soil amendments-compost (CMP), biochar (BCH), co-composted biochar (C-BCH), a mixture of compost and biochar (CMP + BCH), and NPK fertilizer-on NPK release patterns, soil quality, and maize performance in the Alfisols of Zaria, Nigeria. The experiment followed a randomized complete block design with six treatments (including control) and three replications, applied at 15 t ha^{- 1} for organic treatments and recommended rate for NPK. Key soil quality indicators measured were organic carbon (OC), cation exchange capacity (CEC), pH, bulk density (ρb), and mean weight diameter (MWD). Nutrient release was monitored at bi-weekly intervals over 12 weeks, while maize growth and yield parameters were also evaluated. Statistical analysis (ANOVA, p < 0.05) showed that CMP initially released the most N, P, and K, but CMP + BCH significantly improved OC (1.89%), CEC (9.13 cmol kg^{- 1}), and MWD (1.36 mm), while maintaining near-neutral pH. These improvements translated into superior plant height (212.4 cm), leaf area (536.2 cm²), and grain yield (3.45 t ha^{- 1}). Among the Soil Quality Index (SQI) methods used, threshold and weighting methods aligned more with crop productivity, while the AHP method reflected long-term soil sustainability trends. CMP + BCH emerged as the most sustainable amendment under tropical conditions. Future research should investigate the long-term carbon sequestration potential of these amendments.