Continuous N-supplying capacity of the
fertile soil in the winter wheat /summer maize rotation system was studied in a three-year
experiment. Three N
fertilization treatments, including no N fertilization treatment, optimized N fertilization treatment by soil N_(min) testing and plant nitrate testing, and conventional N fertilization treatment, were involved in this field experiment. The results indicated, that the soil N-supplying capacity declined with time run, especially in the third year. However, this experimental
fertile soil maintained relatively high N-supplying capacity during whole three experimental years, and in summer maize growing season the soil N-supplying capacity was higher than that in the winter wheat growing season. The relative grain yield of no N fertilization treatment was 46%-76% in the winter wheat growing season and 69%-81% in the summer maize growing season. The calculated apparent N mineralization in each rotation period varied from 184 to 125 kg/hm~2 in the three experimental years, and the amount of soil N supplying which obtained from N uptake by crop at the no N fertilization treatment was 123-190 kg/hm~2. Because of taking soil N-supplying capacity in consideration, the optimized N fertilization treatment reached a same crops grain yield compared with the conventional N fertilization treatment, although its' N rate was much lower than that in the conventional N fertilization treatment. Moreover, soil residual N_(min) of the optimized N fertilization treatment was quite lower, which avoided the risk of N losses to the groundwater and atmosphere.