Characters of Soil Particulate Organic Matter Under Five-Year Application of N Fertilizer and Sheep Manure in Leymus Chinensis Grassland of Inner Mongolia

【Objective】 Soil particulate organic matter, being an active portion of soil organic matter, is largely controlled by the factors such as fertilization, cultivation, management and so on. This paper studies on the effects of 5-year application of N fertilizer and sheep manure on soil particulate organic matter (POM) including its quantity and chemical structure. 【Method】Soil samples were collected from Leymus chinensis grassland plots in Inner Mongolia which was fenced and excluded from grazing since 1999 and applied N fertilizer and sheep manure for 5 years. Both free and occluded POMs were separated with physical fractionation method. The concentrations of C and N in these two fractions were determined. And the chemical structure was also revealed by solid-state 13C NMR spectroscopy. 【Result】N fertilizer reduced soil pH by 0.25-0.78 units, soil microbial biomass C by 13%-27%, and OPOM by 11%-27%. However, sheep manure enhanced soil pH by 0.47-0.59 units and soil microbial biomass C by 19%. POM was also largely increased due to using sheep manure. In particular, FPOM was enhanced by 96% compared with the control soil. It was found that the chemical structure of OPOM was little influenced by fertilization. In contrary, the chemical structure of FPOM significantly changed due to application of either N fertilizer or sheep manure for 5 years. It was found that alkyl C content increased, but carbonyl C decreased. 【Conclusion】It is obvious that long-term application of fertilizer, particularly organic fertilizer, not only resulted in the change of POM content, but chemical structure as well. And FPOM is much more sensitive to fertilization than OPOM fraction.