Effects of particle sizes on the N2O emission of soil irrigated with nitrogen in freezing and thawing process

Through simulated experiments in fridge, the effects of soil particle sizes (1 cm and 0.25 mm) irrigated with three kinds of nitrogen forms (ammonium, nitrate and amide-N) and three concentrations (40, 200 and 800 mg/L) on the fluvio-aquatic soil N2O emission flux in freezing and thawing process were conducted. The results showed that: before soil freezing, the N2O emission fluxes of coarse soil were smaller than those of the fine particle with the exception of nitrate concentration of more than 200 mg/L. And fine soil could reach stable N2O emission flux earlier than coarse soil in the freezing stage. The fine soils could also reach N2O emission peaks earlier than coarse soils in the thawing stage, but the peak values of N2O emission were mostly smaller than those of the coarse soil. With nitrogen concentration increasing, the coarse soils of the average cumulative soil N2O emissions (three kinds of nitrogen forms) increased by 45.46%, 7.81% and 46.87% compared with the fine soils, respectively. The paper proposed irrigation with nitrogen in winter should try to avoid nitrate fertilizer, reduce the ammonium nitrogen fertilizer concentration, and break the coarse particle size of soil after irrigation with nitrogen in winter in order to reduce N2O emissions.