Maize (Zea mays L.) productivity and profitability response to inorganic N-P nutrients, biochar and vermicompost levels in acidic soils of Northwestern Ethiopia

Maize (Zea mays L.) is sensitive to abiotic factors that can severely diminish crop yields. The combined use of organic and inorganic sources of nutrients enhances soil fertility and crop productivity. However, site and crop-specific integration levels are essential for optimal outcomes. This study aimed to identify the optimal N/P₂O₅, biochar (BC), and vermicompost (VC) combination to improve the physiological traits, growth, yield components, and yield of maize (BH-661) under rainfed agriculture. A field experiment was conducted over two consecutive growing seasons (2023/24 and 2024/25) to identify the optimal combination of N/P₂O₅, BC, and VC for improving physiological traits, growth, yield components, and yield of maize. The experiment was arranged in a 3 × 3 × 3 RCBD design with three replicates. Treatments included three levels each of N/P₂O₅ (0/0, 120/69, 240/138 kg ha⁻¹), BC (0, 4, 8 t ha⁻¹), and VC (0, 5.02, 10.04 t ha⁻¹). Data were collected on days to 90% physiological maturity (DPM), number of leaves per plant (NLPP), plant height (PH), ear length (EL), ear number per plant (ENPP), grain number per ear (GNPE), number of rows per ear (NRPE), thousand grain weight (TGW), biological yield (BY), and grain yield (GY). The analysis of variance (ANOVA) indicated that maize phenology, growth, yield components and GY were significantly different (p < 0.01). The highest GY (12.13 t ha⁻¹), PH (320.5 cm), and GNPE (647.11) were recorded under integrated applications, particularly the combined application of 120 kg N ha⁻¹ + 69 kg P2O5 ha⁻¹ + 8 t BC ha⁻¹ + 10.04 t VC ha⁻¹ (T24) in soils that received a uniform lime application of 0.63 t CaCO3 ha⁻¹. The lowest values were observed in the control (T1). Notably, 120/69 kg N/P₂O₅ ha⁻¹ + 4 t BC ha⁻¹ + 5.02 t VC ha⁻¹ (T14) consistently produced high economic yields (12.09 t ha⁻¹) and the highest net benefit (289,124 ETB ha⁻¹) with a marginal rate of return of 149.067%. Combining 120/69 kg N/P₂O₅ ha⁻¹, 4 t BC ha⁻¹, and 5.05 t VC ha⁻¹ (T14) is recommended to enhance maize yield and profitability in the area. Further multi-season, multi-location studies with additional data on physiological, molecular and nutritional traits are needed to validate and consolidate these findings.