Characters of soil particulate organic matter under five-year application of N fertilizer and sheep manure in Leymus chinensis grassland of inner Mongolia

Chinese. 颗粒状土壤有机质（particulate organic matter，POM）是土壤有机质比较活跃的成分，受施肥、耕作及管理等多种因素的影响，本文研究连续5年施用氮肥和羊粪对内蒙古草原围栏封育的表层土壤颗粒状有机质的含量及其化学结构的影响。采用物理分组法获得游离态颗粒状有机质（FPOM）和包被态颗粒状有机质（OPOM），并用13C核磁共振法测定其化学结构。施用氮肥的土壤pH值降低了0.25～0.78个单位，微生物量碳降低了13%～27%，POM含量没有明显变化；而施用羊粪的土壤pH提高了0.47～0.59个单位，微生物量碳提高了19%，POM大幅度提高，特别是FPOM最多提高了96%。OPOM的化学结构几乎不受施肥的影响，但FPOM的化学结构在一定程度上受到施肥特别是羊粪的影响，烷基碳增多，而羰基碳减少。长期施肥特别是有机肥料，不仅引起草原土壤颗粒状有机质含量的变化，还导致其化学结构的改变，FPOM组分变化更加明显。

English. 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. 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. 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. 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.