GASEOUS LOSSES OF APPLIED NITROGEN FROM A CORN FIELD DETERMINED BY 15N ABUNDANCE OF N2 AND N2O

Abstract

This study was carried out to investigate the magnitude of N loss through denitrification by 15N gas-flux method in a corn field where rape was incorporated with surface soils as green manure. To measure the in situ emissions of N2 and N2O, micro-plots with plastic barriers (0.70 m×0.30 m) were setup in triplicate in a corn field, (15NH4)2SO4 (70.7 atom% 15N) 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, 15N abundance in N2O and N2 was determined by mass spectrometry, and N2O concentrations were determined by gas chromatography. The 15N 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 N2 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 N2 and N2O were rather low. The 15N abundance of N2O was as high as 34.3 atom% 15N during the first week after fertilization and then decreased drastically to the background level. These temporal changes in 15N 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 15N mass balance was 86%, and 55% of the applied N still remained in soil profile as nitrate.