Distribution Of Nitrogen And Carbon In Black Soil And Red Soil Under Long-term Fertilization

Organic carbon and nitrogen is the core of soil fertility. Not only they affect the globalclimate changes but they are the basis of the sustainable agriculture. Therefore, it issignificant to discuss the influences of organic carbon and nitrogen and their relationshipsin soil. Fertilization is important for the accumulation of nutrients in soil, while themechanism of the interaction between carbon and nitrogen in the soil is uncertain. Toresolve this problem, based on the long-term fertilization experiments in black soil and redsoil, I studied the changes of the carbon and nitrogen and their components in each soil.The main results were given as follows:(1) Compared with no fertilizer(CK), NPK, NPKM, NPKS could significentlyincrease not only crop production but also the accumulation of organic carbon and nitrogenunder long-term fertilization in both soils. Therein, NPKM treatment produced the mostremarkable effect. Meanwhile, organic fertilizer could reduce the loss of nitrogen in thesoils and N exist mainly in the form of organic nitrogen, the soil C/N was reduced.(2) Compared with CK, long-term fertilization can change the ratio of DOC/TOC andDON/TN. DOC/TC of NPKM and NPKS treatment had no significant difference, butsignificantly higher than CK and NPK treatment. In the top black soil layer (0-20cm),soluble nitrogen accounted for1.07%~1.86%of the total nitrogen; and that was1.09%~1.72%in red soil surface layer. Contrasting with CK, the ratio of DON/TN in black andred soil increased by0.38%and0.07%respectively. In contrast with NPK, the ratio ofDON/TN in black and red soil increased by0.24%and0.26%, respectively. Microbialbiomass carbon(MBC) and Microbial biomass nitrogen(MBN) contents in black soilchanged along with the applications of organic fertilizer, and the increasing range wasNPKM＞NPKS＞NPK＞CK. The NPKM treatment of red soil also had a higher level ofMBC and MBN, which implied that the application of organic manure can increasemicroorganisms in different kinds of soil. The results deduced that nitrogen was moreeasily absorbed by the plant as using organic fertilizer.(3) The organic carbon was mainly preserved in the microaggregates with the sizes of 2-53μm for black soil while in those of <2μm for red soil. The accumulative organiccarbon contents in every size of soil microaggregates would significantly increase underthe long-term fertilization. It was also found that the distribution of nitrogen in the soilswas similar to that of organic carbon,64.4%-80.0%in2-53μm microaggregates for blacksoil and60.4%-62.7%in less than2μm microaggregates for red soil. Compared with CKtreatment, long-term fertilization would induce the ratio of N in the2-53μmmicroaggregates and increase that in the <2μm and53-250μm microaggregates for blacksoil. For the red soil, long-term fertilization would decrease the ratio of N in the53-250μm microaggregates and increase that in the250-2000μm microaggregates.(4) Under long-term fertilization condition, compared with CK，crop yields wereincreased at all fertilizations conditions. The highest was NPK treatment in black soil, andNPKM treatment in red soil. The use efficiency of organic-inorganic-mixed nitrogenfertilizers were17%and21%in black and red soil respectively, At the same time, theresidual rates of nitrogen in the soils were also improved, nitrogen losses were reduced.The nitrogen use efficiency of NPK treatment was higher than other treatments, howeverits residual rate was the lowest due to various reasons, indicating that the loss ratio ofnitrogen was also high.