Abstract

Loss of soil fertility, reduction in soil productivity and water scarcity is the major limitation of rain fed area of Pakistan. Applications of biochar on low fertile and degraded soil enhance soil fertility, nutrients uptake and water retention thus improves soil productivity. Field study was conducted to examine the effect of biochar on biological nitrogen fixation (BNF) by mash bean (Vigna mungo. L), soil nutrients availability and soil water retention. Biochar was applied at 0, 0.25 and 0.5 t ha^-1 along with and without chemical fertilizer (20, 50, 50 kg ha^-1 NPK) with four replications. Crop was harvested at maturity and soil samples were collected from each experimental plot before sowing and after harvesting and was analyzed for soil ECe, soil pH, total nitrogen, phosphorus, potassium, soil infiltration rate, soil aggregate stability, soil water retention and cation exchange capacity (CEC). Biological nitrogen fixation was determined by xylem-sap method and xylem sap was extracted at pod filling stage. Soil treated with biochar @ 0.5 t ha^-1+chemical fertilizer (NPK 20, 50, 50 kg ha^-1 respectively) showed maximum pH (7.78) and soil electrical conductivity (0.67 ds m^-1). Application of biochar and chemical fertilizer to soil (0.5 t ha^-1+NPK 20,50,50 kg ha^-1) increases total N from 3.9 mg kg^-1 to 18 mg kg^-1, Phosphorus from 4 mg kg^-1 to 18.5 mg kg^-1, potassium from 98 mg kg^-1 to 143 mg kg^-1 and soil CEC from 6.6 Cmolc kg^-1 to 11.2 Cmolc kg^-1. Biochar @ 0.5 t ha^-1 stabilized soil aggregates (34%) and improves soil infiltration rates (164 mm h-1) without impacting any significant effect on soil water retention. Biochar applied @ 0.5 t ha^-1 along with chemical fertilizer (NPK 20, 50, 50 kg ha^-1 respectively) showed maximum increase in BNF (24 kg N ha^-1), biomass yield (2.7 t ha^-1) and grain yield (1.8 t ha^-1). The study concluded that biochar application (0.5 t ha^-1) along with chemical fertilizer increase availability of nutrients (NPK), soil pH and ECe where as sole application of biochar (0.5 t ha^-1) promoted aggregation and infiltration rate. The significant increase was observed in case of BNF (40%), grain yield (77%) and biomass yield (64%) of mash bean. It is recommended that biochar application to soil along with chemical fertilizer improve soil productivity and BNF by mash bean.

Keywords: Biochar; Water retention; Biological nitrogen fixation; Soil aggregates