Abstract: Aimed to understand the translocation and transformation characteristics of applied fertilizer nitrogen in paddy soil, a simulated soil column experiment was conducted in laboratory to study the variations of soil mineral nitrogen along the profile under the application of 360 mg·kg^-1 (3 folds of conventional application rate) of urea- and ammonium sulfate nitrogen. In the experimental period, the soil NH₄⁺-N and NO₃^--N contents in the control (no fertilization) had less change, and no significant differences among different soil layers. Applying urea- and ammonium sulfate nitrogen resulted in a significant increase of soil NH₄⁺-N and NO₃^--N in 0-50 mm layer, being 186.0-2882.1 mg·kg^-1 and 268.7-351.5 mg·kg^-1, and 4.8-242 times and 5.7-316 times of those in CK, respectively. However, the NH₄⁺-N and NO₃^--N contents below 50 mm soil depth were similar to those in CK, indicating that the translocation and transformation of applied fertilizer nitrogen mainly occurred in 0-50 mm soil layer. The translocation of fertilizer nitrogen mostly occurred in the first 14 days after fertilization. In the whole experimental period, the NH₄⁺-N and NO₃^--N contents in each soil layer under the application of ammonium sulfate were 0.7-2.0 times of those under the application of urea, and the nitrification rate was 0.9-1.4 times of that, suggesting the higher transformation rate of applied ammonium sulfate in paddy soil, as compared with applied urea.

Key words: simulated soil column, paddy soil, fertilizer nitrogen, translocation, transformation, fertilizer micro-region