Effects of long-term fertilization on organic nitrogen forms and their distribution in profile of a brown soil.

【Objective】 Soil organic nitrogen(N) is the main form of soil nitrogen,which is affected by fertilization practices.【Method】 The Bremner method was employed to analyze soil organic N fractionation.After 29-year fertilization treatments,the changes of N supply capacity in a brown soil were studied in this paper.【Result】 Compared with the control,neither single chemical fertilizer had the effect on the content of soil organic N,nor had the effect on the nitrogen composition.Application of manure with chemical fertilizer significantly increased the contents of all forms of hydrolysable organic N,especially the content of amino acid N.The contents of different forms of soil organic N in all treatments followed the order of amino acid N non-hydrolysable Nammonia Nunidentified hydrolysable Namino sugar N.The distributions of all forms of organic N were similar,and decreased with layers' depth.The basic rule is organic-inorganic fertilizer treatmentsingle organic manure fertilizer treatmentsingle chemical fertilizer treatment and the control.【Conclusion】 Manure plus chemical fertilizer increased the content of most organic N,and was considered the best way for maintaining the soil fertility and sustainable agriculture.