Vermicompost-assisted Azotobacter and Bacillus inoculation enables partial substitution of mineral NPK and improves maize yield, nutrient uptake, soil fertility, and biological activity

Abstract

Reducing dependence on mineral fertilizers requires integrated nutrient management (INM) strategies that sustain maize productivity while improving soil functioning. A field experiment evaluated nine combinations of mineral NPK, farmyard manure, vermicompost, and Azotobacter-Bacillus inoculation in a randomized block design with three replications. The 75% NPK treatments integrated with either FYM or vermicompost and inoculation formed the leading treatment group. T7 (75% NPK + 5 t vermicompost ha⁻¹ + Azotobacter–Bacillus) recorded the highest observed grain yield (40.8 q ha⁻¹), stover yield (62.5 q ha⁻¹), and total N, P, and K uptake (121.0, 31.3, and 92.2 kg ha⁻¹, respectively), but these responses did not differ significantly from T6. Microbial biomass carbon and dehydrogenase activity were also highest under T7 (112 mg kg⁻¹ and 4.4 µg TPF g⁻¹ h⁻¹, respectively) and remained statistically comparable with T6. Available soil K was the only variable across nutrient uptake, soil fertility, micronutrient availability, and biological activity that differed significantly between T7 and T6. Relative to sole 100% NPK, T7 increased microbial biomass carbon by 32.9% and dehydrogenase activity by 51.7%. T7 generated gross returns of ₹99,340 ha⁻¹ (US$1,263.79 ha⁻¹), net returns of ₹59,722 ha⁻¹ (US$759.78 ha⁻¹), and economic efficiency of ₹567.66 ha⁻¹ day⁻¹ (US$7.22 ha⁻¹ day⁻¹). Principal component analysis associated the 75% NPK-based treatments with greater water-holding capacity, soil organic carbon, nutrient availability, and microbial activity. Thus, the complete 75% NPK-based organic-biological treatment packages provided effective fertilizer-saving options under the tested conditions.