Abstract:Nitrogen (N) is one of the most important elements for plant growth and crop yield, however, excessive N fertilization and the relatively low N use efficiency (NUE) can results in the threat to environmental quality, but how to increase NUE has been an urgent problem still unsolved for agriculture development and environment protection, thus, it is important to study the diffusion and migration of N fertilizers to provide a theoretical basis for improving NUE and protecting the environment. A filed micro-plot experiment was carried out to study the effects of different fertilization methods and N fertilizers on the dynamics of soil N vertical diffusion and horizontal migration in lime concretion black soil, 3 fertilization methods (mixed uniformly with 12 cm top soil, placed in-hole at 12 cm depth, and placed in-furrow at 12 cm depth) and 2 nitrogen fertilizers (urea and ammonium phosphate) were designed, the concentrations of inorganic N (ammonium N and nitrate N) of different soil layers were determined at 30, 60 and 90 days after fertilization. The results showed that the concentrations of ammonium N and nitrate N in soils were in an order of placed in-hole at 12 cm depth > placed in-furrow at 12 cm depth > mixed uniformly with 12 cm top soil during 90 day treatment. With the point fertilization, the ammonium N of urea treatment was mainly concentrated in 6-18 cm along the vertical direction and in 0-7 cm alone horizontal distance, while the concentrated area of nitrate N reached the depth of 21 cm, and migrated to 15 cm away from fertilization point. Both the concentrations of ammonium N and nitrate N in soil declined obviously as the treatment time prolonged. The inorganic N of urea and ammonium phosphate point fertilization methods was mainly distributed in 6-18 cm soil, and the horizontal movement distance apart from the fertilization point was about 5-7 cm after 90 days. However, the inorganic N concentrations in soil 18 cm depth and 12 cm away from the ammonium phosphate fertilization point were 148.9 and 77.4 mg/kg, respectively, significantly higher than those of urea treatment (96.3 and 53.2 mg/kg, respectively). Moreover, the difference of inorganic N concentration between the two fertilizers was more apparent in the soil of fertilization point. It suggested that the capacity of ammonium phosphate in maintaining the high inorganic N concentration in soil under point fertilization method was better than that of urea. The results suggested that point fertilization could maintain higher inorganic N concentration in soil and reduce inorganic nitrogen losses. According to crop growth and fertilizer requirement, single basal application could supply the crop with a continuously high nutrient concentration during 90 days by optimizing the fertilizer placement and nitrogen species.