Abstract: 【Objective】The paper was about the effects of nitrogen (N) fertilizer and sheep manure addition on particulate organic matter (POM) quantity and quality of surface soils. 【Method】Soil samples were collected from Leymus chinensis grassland plots in Inner Mongolia which was fenced and excluded from grazing since 1999. Based on physical fractionation, both free and occluded POMs were separated. The concentrations of C and N in these two fractions were determined and the composition was revealed by solid-state 13C NMR spectroscopy.【Result】The results showed that N fertilizer significantly reduced soil pH, soil microbial biomass C and OPOM. In contrast, sheep manure induced in obvious enhancements of soil pH, organic C, total N, soil microbial biomass C, FPOM and OPOM. Adding either N or manure resulted in a decrease of carbonyl C content in FPOM. Alkyl C content increased due to using manure. Furthermore, the ratio of alkyl C to O-Alkyl C increased in the manure FPOM, but decreased in the N FPOM. However, chemical structure of OPOM did not significantly change.【Conclusion】It is thus concluded that long-term utilization of either N or manure will result in significant changes of soil POM and chemical structure. In particular, FPOM is more sensitive to fertilizer.

Key words: N fertilizer, sheep manure, free POM, occluded POM, solid-state 13C NMR spectroscopy