Gaseous losses of applied nitrogen from a corn field determined by N-15 abundance of N-2 and N2O

This study was carried out to investigate the magnitude of N loss through denitrification by N-15 gas-flux method in a corn field where rape was incorporated with surface soils as green manure. To measure the in situ emissions of N-2 and N2O, micro-plots with plastic barriers (0.70 m X 0.30 m) were setup in triplicate in a corn field, ((NH4)-N-15)(2)SO4 (70.7 atom% N-15) was mixed thoroughly with the 0-10 cm topsoil inside the plots at a rate equivalent to 150 kg N ha(-1). The gas samples were taken periodically by using a static chamber method, N-15 abundance in N2O and N-2 was determined by mass spectrometry, and N2O concentrations were determined by gas chromatography. The N-15 mass balance in the micro-plots was estimated at harvest. The total amount of gaseous N losses was about 10.8% of the applied fertilizer N, and N2O emissions accounted for only 2.9% of the gaseous N loss. The average emission rates of N-2 and N2O during the corn-growing period were 13.4 and 0.041 mg N m(-2) d(-1), respectively. However, after 30-40 days from the sowing, both the fluxes of N-2 and N2O were rather low. The N abundance of N2O was as high as 34.3 atom% N during the first week after fertilization and then decreased drastically to the background level. These temporal changes in N-15 abundance of N2O coincided well with those in nitrate contained in the soil. At harvest time, the recovery of the applied fertilizer N calculated from N-15 mass balance was 86%, and 55% of the applied N still remained in soil profile as nitrate.