HEAVY NITROGEN FERTILIZER APPLICATION AND LOSSES IN THE ANTHROSOLS OF THE GUANZHONG REGION, SHAANXI, CHINA

摘要

To estimate fertilizer over-consumption and the fate of nitrogen (N) from fertilizer in the wheat and maize rotation system used in the Guanzhong area, Shaanxi, China, an investigation including a laboratory and four field experiments was carried out. The results suggest that over-consumption of pure N fertilizers amounts to 90 million kg per year in this area, which includes 1.7 million ha of arable land. There was no correlation between the amount of N fertilizer applied and the yield of either wheat or maize, as a result of over-application of N fertilizer to previous crops. In our study of Anthrosols, 85% of the N fertilizer was readily transformed to NO_3~-. Most of the nitrate was still located in the top 1 m after a year and large quantities were subsequently lost from the soil profile, although only 5 kg NO_3-N·ha~(-1)·yr~(-1) leached out from the profile at a depth of 8 m. N_2O-N concentration was determined within the soil profile and fluxes were both calculated from the data and measured at the soil surface. The highest net production was found at 5 to 20 cm depth and the highest emission fluxes occurred after rainfall or irrigation, accounting for about one kg N_2O-N·ha~(-1)y~(-1).