In this research, method for soil nitrogen fractionation proposed by Bremner (1965) was adopted to study the transformation
of nitrogen in the soil of long term fertilization experiment which has lasted for 16 years. The main results are as follows: When only chemical fertilizer was applied, the content of forms of nitrogen was slightly decreased. Even in the N treatment that the amount of nitrogen application had largely exceeded that the plant could used, but the extra N couldn't accumulated in the soil. Neither chemical fertilizer application had the effect on the content of soil nitrogen, nor had the effect on the nitrogen composition. Application of manure with chemical fertilizer significantly increased the contents of all forms of nitrogen, especially the content of amino acid N. The composition of nitrogen was also affected. Furthermore, application of manure with chemical fertilizer also affected the contents of forms of nitrogen in soil profile, as the amount of
manure application increased, the contents of
nitrogen forms increased, and the deeper layer of soil profile was affected. In the condition of our experiment, the deepest depth that fertilization affect was about 30 cm.