Biochar addition mitigates nitrogen loss induced by straw incorporation and nitrogen fertilizer application

Biochar has been shown to be potentially beneficial for enhancing yields and soil properties, and diminishing nitrogen (N) losses. However, it remains unclear how biochar regulates soil carbon (C) and N to mitigate N losses induced by straw mixing with N fertilizer in dryland soils. Therefore, we investigated the effects of straw mixing (S-1), S(1)with biochar (SB) and no straw inputs (S-0), and routine urea application rates (N-1) and 70% of routine rates (N-0.7) on yields and N losses, and identify the relationship between N losses and soil C and N compounds. Results showed that N(0.7)and N(1)were suitable for the maize and wheat seasons, respectively, contributing to mitigating N losses without reducing crop yields. Moreover, in the maize season, N-0.7-SB significantly mitigated the straw-induced NH3-N and N2O-N emissions by 106% and 81%, respectively. In the wheat season, N-1-SB reduced the straw-induced NH3-N and N2O-N emissions by 35% and 66%, respectively. In addition, N-0.7-SB sharply reduced soil inorganic N (SIN) storage in the maize season. Furthermore, the NH3-N and N2O-N emission rates were negatively correlated with dissolved organic carbon/SIN content (0-20 cm) (DOC/SIN0-20). N losses (N2O-N and NH3-N emissions and SIN storage) were positively correlated with SIN0-20, but negatively correlated with soil organic carbon / SIN0-20(SOC/ SIN0-20). This study provides further evidence that biochar with an appropriate N application rate decreased SIN(0-20)and increased DOC/SIN0-20, thus reducing SIN storage and the straw-induced gaseous N emissions without decreasing crop yields.