Nitrogen availability in black soils and its relations with crop yields under long-term applications of organic amendments

Based on a long-term field experiment,this paper studied the effects of long-term applications of organic amendments(straw and organic manure) on the nitrogen availability in black soils of Northeast China,and analyzed the relationships between the soil nitrogen supply and the crop biomass and yield.The applications of chemical fertilizer plus organic manure and of chemical fertilizer plus low amounts of straw increased the soil inorganic nitrogen and nitrate nitrogen significantly,and thereby,promoted the crop yields.The application of chemical fertilizer plus high amounts of straw increased the soil nitrogen mineralization rate,but the soil inorganic nitrogen content had less increase,as compared with the application of chemical fertilizer plus low amounts of straw,possibly due to the enhanced soil nitrogen transformation or nitrogen losses such as nitrate nitrogen leaching under high level of straw application.Our study suggested that it would be of importance to apply rational amount of organic amendments to improve the nitrogen availability in black soils,increase the crop yields,and protect the environment.