Fractal features of soil aggregate structure in slope farmland with different de-farming patterns in south Sichuan Province of China

By using fractal model,this paper studied the fractal dimension of soil aggregate structure (D) in the slope farmland (CK),its 5-year de-farmed Neosinocalamus affinis plantation (NAP),Bambusa pervariabilis×Dendrocalamopsis oldhami plantation (BDP),Alnus crenastogyne + Neosinocalamus affinis plantation (ANP),and abandoned farmland (AFL) in south Sichuan Province of China,and analyzed the relationships between the D and soil physical and chemical properties. In the de-farmed plantations and abandoned farmland,the contents of 0.25 mm soil aggregates and water-stable aggregates were increased significantly,compared with those in the slope farmland. The D was 1.377-2.826,being in the order of NAPBDPANPAFLCK,and decreased with the increasing contents of 0.25 mm soil aggregates and water-stable aggregates. Comparing with CK,de-farming increased the soil natural water content,capillary porosity,and contents of soil organic matter,total N,alkali-hydrolysable N,total P,and total K,and decreased soil bulk density,non-capillary porosity,and aeration porosity. There were close relationships between the fractal dimension of soil aggregate structure and the soil physical and chemical properties. All the results suggested that the de-farming of slope farmland was beneficial to the increase of the contents of 0.25 mm soil aggregates and water-stable aggregates,and the enhancement of soil structure stability. The D could be used as an ideal index to evaluate soil fertility,and planting Neosinocalamus affinis on the de-farming slope farmland was a good measure for the improvement of soil fertility in the research area.