Effect Of Organic Fertilizer On The Soil Nitrate Accumulation And Its Environmental Impact

In the past, people thought commonly that organic fertilizer application was the beneficial agriculture measure to reduce NO₃^--N leaching as well as NO₃^--N accumulation of soil and vegetables . But in recent years, studies had found that unreasonable organic fertilizer application also caused NO₃^--N accumulation of soil and vegetables. In this paper, indoor culture experiment, pot experiment and outdoor simulating soil column were carried out to study the effects of different organic fertilizers,combined application of organic and inorganic fertilizers on NO₃^--N accumulation of soil and vegetable(ssp chinensis Makino) as well as soil NO₃^--N leaching, aimed at offering the theoretical basis on rational application organic fertilizer. The main results were as follows.1. Effects of organic fertilizers on nitrogen transformation in vegetable soil1.1 Effects of different organic fertilizers on nitrogen transformation in soil varied with the C / N ratio of organic fertilizers. Soil NO₃^--N content was no significant difference between cow dung application treatment and CK. Comparing with CK,soil NO₃^--N content of soybean cake application and pig dung application treatments increased 5.03 times and 1.34 times respectively, while the soil NO₃^--N content of mushroom residue application treatment decreased 0.94 times. There was no significant difference of soil NH₄⁺-N content between soybean cake , cow dung and pig dung application treatment and CK, while application of mushroom residue reduced soil NH₄⁺-N content .1.2 Combined application of organic fertilizer and urea could increase the activity of urease, and accelerated the urea decomposition in the soil. Comparing with urea application, combined application of soybean cake and urea increased soil NO₃^--N content by 28.57%, while combined application of mushroom residue and urea reduced 44.12% . Comparing with application ammonium sulphate, combined application of soybean cake and ammonium sulphate increased soil NO₃^--N content by 23.77%, while the combined application of mushroom residue and ammonium sulphate reduced 39.78%. Effects of the combined application of organic and inorganic fertilizers on soil NH₄⁺-N content were small, the soil NH₄⁺-N content of all treatments was less than 10 mg/kg at the end of the culture experiment.2. Effects of organic fertilizers on NO₃^--N accumulation in vegetable2.1 Effects of organic fertilizer application on the growth and the NO₃^--N content of vegetable varied with the C / N ratio of organic fertilizers. Comparing with no organic fertilizer application (CK), application of high C/N ratio mushroom residue ( 0.2-0.4gN /Kg soil) decreased significantly the biomass of vegetable by 98.53%-99.16.While application of low C/N ratio soybean cake ( 0.2-0.4gN /Kg soil) increased the biomass of vegetable ,the NO₃^--N and NO₂^--N content of leaves by 303.52%-315.77%,19.75-66.25 times and13.68%-130.47% respectively, and the NO₃^--N and NO₂^--N content of vegetable increased with the increase of soybean cake amount.2.2 Effects of combined application of organic and inorganic fertilizers on NO₃^--N content of vegetable depended on C / N ratio of organic fertilizers. Comparing with urea application,combined application of soybean cake and urea increased vegetable NO₃^--N content by 200.94%, while combined application of mushroom residue and urea reduced vegetable NO₃^--N content by 87.64%. As compared with ammonium sulphate application,combined application of soybean cake and ammonium sulphate increased vegetable NO₃^--N content by 228.53%, while combined application of mushroom residue and urea reduced vegetable NO₃^--N content by 81.27%.2.3 Correlation analysis showed that vegetable NO₃^--N content was very significant positive correlations with the NO₃^--N content of the soil , the NO₂^--N content of leaves and the nitrate reductase activity of leaves.3 Effects of organic fertilizers on NO₃^--N leaching in vegetable soil3.1 Effects of organic fertilizer application on NO₃^--N leaching in vegetable soil depended on C / N ratio of organic fertilizer. Comparing with CK, application of low C/N soybean cake ( 0.2-0.4gN /Kg soil) increased NO₃^--N leaching amount by 58.41%-120.23%,application of high C/N mushroom residue ( 0.2-0.4gN /Kg soil),reduced NO₃^--N leaching amount by 39.09%- 46.56%.3.2 Effects of combined application of organic and inorganic fertilizers on vegetable soil NO₃^--N leaching depended on the C / N ratio organic fertilizers. Comparing with urea application, combined application of soybean cake and urea increased NO₃^--N leaching amount by 15.43%, while combined application of mushroom residue and urea reduced 21.31%. Comparing with application ammonium sulphate, combined application of soybean cake and ammonium sulphate increased NO₃^--N leaching amount by 7.33%, while the combined application of mushroom residue and ammonium sulphate reduced 13.46%.3.3Application low C/N soybean cake could cause NO₃^--N leaching, while application high C/N mushroom residue could Inhibit NO₃^--N leaching. Comparing with chemical fertilizers(urea, ammonium sulphate)application, combined application of chemical fertilizer and soybean cake led to soil NO₃^--N accumulation, while combined application of chemical fertilizer and mushroom residue reduced the soil NO₃^--N accumulation,.Soil NO₃^--N accumulation, particularly in deep soil layer would increase NO₃^--N leaching.