Dynamics of different soil nitrogen pools after appIying different types of nitrogen fertilizers

The dynamics of different soil nitrogen pools after applying different types of nitrogen fertilizers were studied by pot experiment．The results show that the wheat biomass and nitrogen uptake have no significant difference by mixed application of Urea，NH₄HCO₃，(NH₄)₂SO₄，and Ca(N()₃)₂ with the same rate of nitrogen applied．Nitrifications of ammonia and urea type nitrogen fertilizers were completed in 14 days．The sOil microbiomass N decreases with crop growth under Urea，NH₄₃，and(NH₄)₂SO₄ treatments，which may be caused by crop uptake．The utilization of old fixed NH₄⁺ by crop is weak．Soil fixed NH₄⁺ is increased after the application of nitrogen fertilizers，and this kind of fixed NH₄⁺ can be uptaken by crop in growing period．The apparent nitrogen recovery rate，loss rate and fixed rate have no significant difference among four nitrogen fertilizer type.