川南坡地不同退耕模式对土壤团粒结构分形特征的影响

运用分形模型，研究了川南坡地及其退耕成慈竹林、杂交竹林、桤木+慈竹混交林和弃耕地5年后土壤团粒结构分形维数，探讨了分形维数与土壤理化性质之间的关系.结果表明：退耕后，不同退耕模式样地＞0.25 mm的土壤团聚体和水稳性团聚体含量均显著增加，团粒结构分形维数介于1.377～2.826，为慈竹林＜杂交竹林＜桤木+慈竹混交林＜弃耕地＜农耕地，并随＞0.25 mm的土壤团聚体及水稳性团聚体含量的增加而降低；土壤自然含水量、毛管孔隙、有机质、全氮、碱解氮、全磷和全钾含量增加，而土壤容重、非毛管孔隙和通气度降低.退耕后的慈竹林、杂交竹林、桤木+慈竹混交林和弃耕地的土壤团粒结构分形维数与土壤理化性质相关性较好.农耕地退耕对增加＞0.25 mm的土壤团聚体及水稳性团聚体含量和提高土壤结构稳定性具有较好的作用；土壤团粒结构分形维数可以作为坡地退耕后土壤肥力变化的理想指标，在研究区坡地退耕种植慈竹具有较好的培肥改土效益.

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 ofChina, and analyzed the relationships between the Dand 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 NAP＜BDP＜ANP＜AFL＜CK, 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 onthe de-farming slope farmland was a good measure for the improvement of soil fertility in the research area.