This paper examined the effects of biochar

polyacrylamide

and maize straw on the soil aggregate structure and distribution characteristic of organic carbon on sloping farmland in the purple hilly area

in order to provide the best choice for the protection of sloping farmland in the purple hilly area. Taking sloping farmland under different conservation practices

including CK (no-conservation practice)

BC (biochar addition alone)

PAM (application of polyacrylamide on the soil surface)

and SM (maize straw addition ) in purple hilly area as the research objects

the composition of soil aggregates and the content of organic carbon were determined by soil physiochemical analysis. The result showed that: (1) Soil aggregates in the studied area were mainly of the size of＞5 mm and 5 mm to 2 mm

which accounted for 58.18% to 40.12% and 30.34% to 24.46%

respectively. Compared with the CK

the three conservation practices were all effective in increasing the content of large soil aggregates

among which SM was most effective. Mean weight diameter (MWD) of soil aggregates under different conservation practices decreased with increasing soil depth

and followed the order of SM＞PAM＞BC＞CK

while the soil aggregate fractal dimension showed the opposite trend. (2) Organic carbon content of soil aggregates varied greatly with aggregate size

being the highest at 0.5 mm to 0.25 mm. Within the 0—30 cm soil depth

the average content of organic carbon in soil aggregates was in the order of SM＞PAM＞BC＞CK

and decreased with increasing soil depth. (3) The contribution rate of soil aggregates to organic carbon content was the greatest when they were the size of ＞5 mm (53.64% to 27.92%) and 5 mm to 2 mm(30.92% to 11.80%)

which accounted for 27.92% and 25.35% for average contribution

respectively. Aggregates in the size of ＞2 mm could be taken as the characteristic aggregates for organic carbon sequestration in soils in the purple hilly area. (4) The density of soil organic carbon in the studied area was in the order of SM＞PAM＞BC＞CK. The density of soil organic carbon and the difference among the three conservation practices decreased with increasing soil depth in the same treatment. The three conservation practices were effective in improving soil structure and increasing soil organic carbon content

among which the effect of SM was the best

showing that SM is a relatively ideal method for protection of sloping farmland in the studied area.