[Distribution of organic carbon pools in different sizes of soil aggregates in Loess Plateau].

According to the types of vegetation and soil, 22 soil profile samples (0 - 20 cm, 20 - 40 cm and 40 - 60 cm) were collected from different regions of Loess Plateau to approach the distribution of organic carbon pools in different sizes of soil aggregates. The results showed that the organic carbon content and storage in all sizes of soil aggregates were decreased with increasing soil depth. For each soil layer, the organic carbon content had an increasing trend in the aggregates with the sizes from > 5 mm, 2 - 5 mm, 1 - 2 mm to 0.25 - 1 mm, and a descreasing trend from 0.25 - 1 mm to < 0. 25 mm. Because of the different proportions of each size of soil aggregates, the organic carbon storage and content in different sizes of soil aggregates were not the same, i. e., the storage was decreased with the sizes from > 5 mm, 2 - 5 mm to 1 - 2 mm, while increased from 1 - 2 mm, 0.25 - 1 mm to < 0. 25 mm. Except Eum-Orthic Anthrosols had the highest organic carbon content in its aggregate of < 0.25, Ust-Sandiic Entisols, Los-Orthic Entisols and Hap-Ustic Isohumisols had a peak value in their aggregate of 0.25 - 1 mm. The organic carbon storage was the highest in the aggregate of < 0.25 mm in Ust-Sandiic Entisols and Los-Orthic Entisols, and in the aggregate of > 5 mm in Hap-Ustic Isohumisols and Eum-Orthic Anthrosols. The soil organic carbon content and storage under different types of vegetation had the trend of natural forestland > bare land > artificial forest land > farming land.