Abstract: The distribution characteristics of soil aggregates and their organic carbon in gravel-mulched land with different planting years (5, 10, 15, 20 and 30 years) were studied based on a long-term field trial. The results showed that the soil aggregate fraction showed a fluctuation (down-up-down) trend with the decrease of soil aggregate size. The soil aggregates were distributed mainly in the size of ＞5 mm for less than 10 years cultivation, and 0.05-0.25 mm for more than 15 years. The content of aggregates over 0.25 mm (R_0.25) and the mean weight diameter (MWD) of soil aggregates all decreased with the increase of cultivation time. The content of organic carbon within soil aggregates increased with the decrease of soil aggregate size in gravel-mulched land with diffe-rent planting years. However, the content of organic carbon within soil aggregates, contribution rates of different aggregate fractions to soil organic carbon and soil organic carbon storage of aggregate fractions decreased with planting time extension and soil depth. Soil organic carbon in the aggregate sizes over 1 mm was sensitive to long term gravel-mulched field planting. Organic carbon storage of aggregate fractions with 10, 15, 20 and 30 years of planting decreased by 8.0%, 24.4%, 27.5% and 31.4% in the soil depth of 0-10 cm, and 1.4%, 15.8%, 19.4% and 21.8% in the soil depth of 10-20 cm, respectively. In conclusion, the ability of soil carbon sequestration in arid gravel-mulched field was reduced with planting time extension. Therefore, soil fertility of gravel-mulched fields which were cultivated for more than 15 years need to be improved.

Key words: gravel-mulched field, soil organic carbon, soil organic carbon stock, soil aggregate