Organic nutrient sources and biochar technology on microbial biomass carbon and soil enzyme activity in maize-black gram cropping system

Since studies on biochar stability in agricultural soils are very limited, the microbial biomass carbon and soil enzyme activity influenced by biochar addition to field condition remains uncertain. Results of this study revealed that microbial biomass carbon and different soil enzyme activity were significantly influenced by both manure alone and combined biochar-manure application. The microbial biomass carbon was highest in vermicompost (355.28 mg kg⁻¹ soil) and lowest in pig manure (343.62 mg kg⁻¹ soil). Among combined biochar-manure treatment, the MBC was highest in goat manure 5 t ha⁻¹ + biochar 5 t ha⁻¹ (476.58 mg kg⁻¹ soil) and lowest in FYM @ 10 t ha⁻¹ + biochar 5 t ha⁻¹ (458.53 mg kg⁻¹ soil) than control (301.43 mg kg⁻¹ soil). The dehydrogenase activity increased significantly with increase in biochar application rate. But acid phosphatase activity decreased with increase in biochar application rate. Urease activity was highest in poultry manure and lowest in pig manure. Vermicompost with biochar resulted maximum increase in protease and lowest in FYM with biochar. The specific UV absorbance (SUVA) increased with biochar application at 2.5 t ha⁻¹ and then again slightly decreased at 5.0 t ha⁻¹ significantly. Among the biochar-manure treatment, the fluorescein diacetate was highest in FYM @ 10 t ha⁻¹ + biochar 5 t ha⁻¹ (66.29 mg of fluorescein kg⁻¹ oven dry soil h⁻¹) and lowest in poultry manure 5 t ha⁻¹ + biochar 5 t ha⁻¹ (56.36 mg of fluorescein kg⁻¹ oven dry soil h⁻¹) than control from initial value (16.38 mg of fluorescein kg⁻¹ oven dry soil h⁻¹). The vermicompost with biochar resulted maximum increase in invertase activity and lowest in goat manure with biochar. Finally, the microbial quotient decreased significantly with increase in biochar application rate. This is the first time report of examining microbial biomass carbon and soil enzyme activity using combined biochar and organic manure under an acidic hilly soil.