Influence Of Grazing Intensity On The Soil Organic Carbon Fractions And The Carbon, Nitrogen Characteristic Of Meadow Steppe In Zhaosu

The influence of grazing intensity，including CK (0cattle/hm2), light grazing (0.38cattle/hm2),moderate grazing (0.64cattle/hm2) and heavy grazing (0.90cattle/hm2), on the soil organic carbon, soiltotal nitrogen, soil microbial biomass carbon and soil microbial biomass nitrogen, soil readily oxidizablecarbon, soil light fraction organic carbon, soil light fraction nitrogen, soil particulate organic carbon andsoil particulate nitrogen in Zhaosu Meadow Steppe by plot grazing experiment was studied during2010-2011. The main results are summarized as follows:1. During the short grazing period, the change of aboveground standing crop, soil organic carboncontent and soil total nitrogen content were not obvious under different grazing intensities（P>0.05）.2. The content of soil microbial biomass carbon and soil microbial quotient of0-30cm appeared thetrend of first increasing then decreasing following the increase of grazing intensity. During the shortgrazing period, the change of soil microbial biomass carbon content was significantly different underdifferent grazing intensities（P<0.05）, which indicated that the response to grazing of soil microbialbiomass carbon was more sensitively than that of soil organic carbon. The content of soil microbialbiomass carbon under moderate grazing was higher than that of CK, light grazing and heavy grazing（P<0.05）.3. At0-10cm layer, grazing reduced the content of soil microbial biomass nitrogen, and the content ofsoil microbial biomass nitrogen appeared the trend of first increasing then decreasing following theincrease of grazing intensity. The content of soil microbial biomass nitrogen of0-10cm under light grazingwas obviously lower than that of other grazing intensities（P<0.05）. The content of soil microbial biomassnitrogen of10-30cm appeared the trend of increasing following the increase of grazing intensity.4. At0-10cm layer, grazing increased the content of soil readily oxidizable carbon, and the content ofsoil readily oxidizable carbon appeared the trend of first increasing then decreasing following the increaseof grazing intensity. At0-10cm layer, the difference of soil readily oxidizable carbon content underdifferent grazing intensities was not significant（P>0.05）.5. At0-30cm layer, the proportion of soil light fraction component, the content soil light fractionorganic carbon and soil light fraction nitrogen under different grazing intensities were all not significantlydifferent（P>0.05）. At0-10cm and20-30cm layer, the proportion of soil light fraction component, thecontent of soil light fraction organic carbon and soil light fraction nitrogen which were all highest undermoderate grazing appeared the trend of first increasing then decreasing following the increase of grazingintensity. At10-20cm layer, grazing reduced the proportion of soil light fraction component, while thecontent of soil light fraction organic carbon and soil light fraction nitrogen appeared the trend of firstincreasing then decreasing following the increase of grazing intensity.6. At0-10cm layer, grazing increased the proportion of soil particulate component, and the proportionof soil particulate component under moderate grazing was higher than that of other grazing intensities（P<0.05）. The difference of the proportion of soil particulate component of10-30cm, soil particulateorganic carbon of0-30cm, and soil particulate nitrogen of0-20cm under different grazing intensities wasnot significant（P>0.05）. At20-30cm layer, soil particulate nitrogen under heavy grazing was higher thanthat of other grazing intensities（P<0.05）.7. Correlation analysis showed that the relation between MBC,MBN,ROC and stocking rates wassignificant, and they have reached a very significant positive correlation（P<0.01）, in addition, thecorrelation of MBC, MBN, ROC and TOC, TN was also very significant （P<0.01）. Therefore, we couldchoose MBC, MBN, ROC as grazing sensitive factor and early indicator to indicate the impact of grazingon the soil.