Biochar improves soil quality and N2-fixation and reduces net ecosystem CO2 exchange in a dryland legume-cereal cropping system

Biochar, a product of the pyrolysis of organic material, has received wide attention as a means to improve soil fertility, crop productivity, and carbon sequestration to mitigate climate change. This study was conducted in an arid zone agricultural region to investigate the impacts of biochar on soil quality, N-2-fixation, and net ecosystem CO2 exchange (NEE) for a legume-cereal crop rotation (2013-15). Biochar was produced by pyrolysis of sugarcane bagasse and applied at rates of 0%, 0.25%, and 0.5% carbon (C) equivalent, with and without chemical fertilizer (23 kg N, 45 kg P and 25 kg K ha(-1)). In terms of soil quality, biochar applications increased soil organic carbon (SOC), total nitrogen (TN), and decreased soil bulk density. The yield of mash bean and wheat crop was significantly enhanced in response to biochar treatment with and without chemical fertilizer during both the years of study. N-2-fixation in mash bean increased by 83% in biochar-only (0.5% C) amended soil and by 127% with chemical fertilizer. In the first year of mash bean, no difference was observed in NEE, while a significant decrease was observed in the second year attributed to priming effect of fresh biochar. Wheat NEE decreased by 144% and 200% in the first year, and by 283% and 265% in the second year, in unfertilized soil amended with 0.25 and 0.5% biochar, respectively, as compared to the controls. In treatments with chemical fertilizer, wheat NEE decreased by 311% and 344% in the first year, and by 293% and 292% in the second year, as compared to their respective controls. Biochar treatment increased biomass yield (BY) and grain yield (GY) in both mash bean and wheat crops during both the years with and without chemical fertilizer. These results indicate that sugarcane -bagasse biochar applications in arid soils with low organic carbon may increase crop productivity and N-2-fixation of legumes while reducing the NEE of legume-cereal cropping systems.