NITROGEN MOVEMENT IN THE SOIL PROFILE AS INFLUENCED BY LONG-TERM DIFFERENT FERTILIZATION

摘要

Nitrate contamination of surface and ground waters in Shaanxi province, China, has made it necessary to evaluate the impact of fertilizer N management on the accumulation and movement of NO_3-N in the soil. A long-term winter wheat - summer maize experiment with different fertilizer treatments was conducted to determine (ⅰ) the distribution and accumulation of NO_3-N in the soil profile, down to 400 cm depth, and (ⅱ) to estimate the movement of NO_3-N in different years. The results show that recovery of fertilizer N by 23 successive crops plus inorganic N in the soil profile ranging from 37.1 to 61.7%. The application of fertilizer N and NK without P resulted in a much larger NO_3-N concentration in the soil profile compared to the application of N with P or PK. With an annual application of 352 kg N·ha~(-1) alone or with K, peaks in NO_3-N accumulation occurred at 280 cm or 160 cm soil depth. However, with the application of NP or NPK, no peaks in NO_3-N distribution were discernible, with the exception of the surface 20 cm, NO_3-N concentrations were smaller at each sampling depth compared to the concentrations measured in the N and NK treatments. The annual application of 4500 kg·ha~(-1) maize stalk along with NPK led to a smaller NO_3-N content in the sub- soil. The amount of NO_3-N accumulation in the soil profile decreased as the cumulative N uptake by the crops increased. There were discernible movements of NO_3-N in the treatments of N and NK within a four-year interval, but not in the treatments of NP, NPK or NPK with organic materials. To minimize N leaching losses, fertilizer management must be balanced in a way that meets the needs of the growing crop.