Abstract:

【Objective】Under the same nitrogen application condition, the variation of carbon and nitrogen in yellow clayey soil and its relationship with NO3--N accumulation under long-term fertilization were studied to illustrate the main factors affecting the NO3--N accumulation. 【Method】The changes of soil organic carbon(SOC), total nitrogen(TN), microbial biomass carbon(SMBC), microbial biomass nitrogen(SMBN), recovery efficiency of nitrogen and the correlation among accumulated amount of NO3--N in a yellow clayey soil after fertilization were analyzed based on a 25 year long - term fertilizer experiment in yellow clayey soil in Nanchang County, Nanchang, China. In an experiment carried out in 1984 at this site, 8 different treatments were designed in an early rice-late rice rotation system. The treatments were no fertilizer(CK), nitrogen fertilizers deficiency (PK)，potassium fertilizers deficiency (NP), phosphorus fertilizers deficiency (NK), balanced chemical fertilizers application (NPK), 70% chemical fertilizers substituted by 30% organic manure in balanced chemical fertilizers application (70F+30M), 50% chemical fertilizers substituted by 50% organic manure in balanced chemical fertilizers application (50F+50M), 30% chemical fertilizers substituted by 70% organic manure in balanced chemical fertilizers application (70F+30M).【Result】Two main results were found from this experiment. First, in the double rice-cropping syetem areas, combined application of organic manure and chemical fertilizers were better than inorganic fertilizers for improving the SOC, TN, available N, SMBC and SMBN, in which combined application of high amount (70%) or low amount (30%) of organic manure was the best. Second, the content and accumulated amount of NO3--N of the combined high amount or low amount of organic fertilizer treatments were more than chemical fertilizers in the soil profile under the same nitrogen condition. The content and accumulated amount of NO3--N of the same ratio of organic manure
combined with chemical fertilizers treatments which greatly reduced the accumulated amount of NO3--N in the soil were equal with no fertilization. 【Conclusion】High amount and the same ratio of organic manure combined with chemical fertilizers is the best to improve soil quality and decrease the accumulated amount of NO3--N in soil, respectively. In consideration of soil quality and environmental protection, the ratio of organic manure combined with chemical fertilizers should be used in the region. Factors affecting NO3--N accumulation are SOC, TN, SMBC and SMBN under the same nitrogen conditions, and SMBC is the most important and direct factor.