Soil concentration profiles and diffusion and emission of nitrous oxide influenced by the application of biochar in a rice-wheat annual rotation system

Field experiments were carried out to determine biochar effects on nitrous oxide (N2O) concentration profiles, diffusion, and emissions in paddy soil under rice-wheat annual rotation in southeastern China. An in situ soil gas device was adapted to measure N2O concentrations at depths of 7, 15, 30, and 50 cm. Five treatments were installed as N0B0, N0B1, N1B0, N1B1, and N1B2 (B0, B1, and B2 designated as biochar at 0, 20, and 40 t ha−1, respectively, while N0 and N1 as nitrogen at 0 and 250 kg N ha−1 crop−1, respectively). The results showed that N2O concentrations were higher in the 15 and 30 cm depths than other depths. With positive diffusive fluxes, the 7 cm in the rice season and 15 cm in the wheat season were main production sites. The surface N2O emissions and topsoil diffusive fluxes showed good agreement. N application strongly increased soil N2O profiles and surface emissions. Relative to N1B0, N1B1 decreased N2O concentration, surface emissions, and diffusive fluxes by 25.2, 31.8, and 26.5 %, respectively, while N1B2 decreased them averagely by 40.7, 43.2, and 44.2 %, correspondingly. Therefore, the gas gradient method is effective for estimating N2O emissions, and biochar can decrease N2O production when N was applied.