关键词: 土壤团聚体, 有机碳, 退耕地

Abstract: Soil can be source or sink of atmospheric C depending on land use,cropping system and management practices. Soil aggregate,which has significant influence on soil physical and chemical properties,is an important process of C sequestration. The distribution and stability of soil aggregates are important indicators of soil physical quality,reflecting the impact of land use and soil management on aggregation or degradation. Although soil organic carbon content in aggregates was mainly controlled by land use and soil management,abandoned cropland is considered to be an important factor affecting soil organic content in cropland. In this study,the stability and organic carbon of soil aggregates were studied under different abandoned cropland modes by the method of field investigation and laboratory analysis. The results showed that: 1) Under the condition of dry sieve,soil aggregates were dominated by >5 mm particle size and the changes of soil aggregates were from decreasing to increasing and decreasing again with the decreasing of particle size for all the abandoned cropland modes. Under the condition of wet sieve,soil aggregates were dominated by <0.25 mm particle size and the changes of soil aggregates were from decreasing to increasing with the decreasing of particle size for all the abandoned cropland modes. The contents of dry and wet sieve aggregates had the great difference under different soil layers for all the abandoned cropland modes,and the difference was more obvious under the condition of wet sieve. 2) Under the condition of dry sieve,the average weighted diameter and the geometric mean diameters of soil aggregates were the highest for the conversion of farmland to Eucalyptus plantation and were the lowest for the conversion of farmland to tea plantations in the surface (0-20 cm) layer,and the results were opponent in the subsurface (20-40 cm) layer. Under the condition of wet sieve,the average weighted diameter and the geometric mean diameters of soil aggregates were the highest for the conversion of farmland to eucalyptus plantation and were the lowest for the abandoned farmland in the surface (0-20 cm) layer,and the average weighted diameter and the geometric mean diameters of soil aggregates were the highest conversion of farmland to tea plantations in the subsurface (20-40 cm) layer. 3) The organic carbon contents of different particle sizes in the surface (0-20 cm) layer were higher than those of the subsurface (20-40 cm) layer,and the organic carbon content reduced gradually with the decreasing particle size for all the abandoned cropland modes. The organic carbon contents of soil aggregates were the highest for the conversion of farmland to eucalyptus plantation in the surface (0-20 cm) layer and the highest for the abandoned farmland in the subsurface (20-40 cm) layer.

Key words: soil aggregate, organic carbon, abandoned cropland