Maize Stover Biochar Accelerated Urea Hydrolysis and Short-term Nitrogen Turnover in Soil

A soil incubation experiment was conducted to investigate the effect of biochar application (2% w/w) on urea hydrolysis and inorganic nitrogen accumulation. Fresh biochars were produced from maize stover that was pyrolyzed at 300 °C, 500 °C, and 700 °C. Then the matured biochars were obtained via a 50 days maturing process. Biochar prepared at 700 °C strongly accelerated the urea hydrolysis and increased soil pH. Fresh biochar, especially when pyrolyzed at low temperature, contained a relatively high concentration of labile carbon and 43% to 64% could be oxidized within 40 days of maturing incubation. The labile carbon in fresh biochars led to microbes thriving and resulted in an accelerated shortterm nitrogen (N) turnover, i.e., at an early stage of incubation, fresh biochar increased mineralization of soil organic N by 79 mg·kg−1 to 449 mg·kg−1. However, a reduction of soil available N contents induced by microbial immobilization effect was observed at the end of incubation. The authors concluded that aged biochar was suitable for simultaneous soil amendment with urea rather than newly produced biochar. This is because aged biochar can avoid high soil available N accumulation; thus it can decrease the risk of inorganic N leaching loss.