三峡库区有限顺坡耕作坡耕地表土颗粒分形特征

Fractal features of soil particles on sloping farmland under downslope tillage system with limited slopelength in the Three Gorges Reservoir Area

在三峡库区忠县境内选择水平沟模式、埂坎模式、地埂植物篱模式以及无措施的4种典型坡耕地采集了48个表土（0 ～ 20 cm）样本,利用分形维数研究不同模式有限顺坡耕作坡耕地的表土颗粒组成、分形特征及相互关系.结果表明：4种模式坡耕地土壤颗粒黏粒体积分数均较低（均值8.03％～11.47％）,粉粒较高（均值62.39％～83.24％）.无措施、水平沟模式、埂坎模式坡耕地的砂粒体积分数为22.95％ ～29.58％,而地埂植物篱模式坡耕地的砂粒均值仅5.29％.4种模式坡耕地表土的粒径体积分形维数分别为无措施2.579 ～ 2.708、水平沟模式2.603～2.706、埂坎模式2.581 ～2.701、地埂植物篱模式2.610～2.827.粒径分形维数均值表现为地埂植物篱模式（2.737）＞水平沟模式（2.674）＞埂坎模式（2.659）＞无措施坡耕地（2.654）.4种模式坡耕地表土的粒径分形维数与黏粒（＜0.002 mm）体积分数呈显著的线性正相关关系,与砂粒（＞0.05 mm）体积分数呈显著的线性负相关关系;但与粉粒（0.002 ～0.05 mm）体积分数线性关系差异较大.其中,无措施、水平沟模式、埂坎模式呈显著的线性正相关关系,而地埂植物篱模式二者相关性不显著.

Forty eight topsoil （0-20 cm） samples were collected from four kinds of typical sloping farmlands with horizontal ditch （HD）,terrace ridge and bank （TR）,terrace hedgerow （TH）,and none conservation measures （NC） in Zhongxian County of the Three Gorges Reservoir Area.The surface soil particles,their fractal characteristics and their relationship with each other were studied using fractal dimension.The results showed that there was low volume of clay particles （8.03％-11.47％） while high volume of silty particles （62.39％-83.24％） in all surface soils on the four kinds of sloping farmlands.The sandy particles in the topsoil on sloping farmlands with HD,TR and NC were 22.95％-29.58％ ; however,it accounted for only 5.29％ in the TH sloping farmland topsoils.The volume fractal dimension for the surface soil particles on the HD,TR,TH and NC farmlands was 2.579-2.708,2.603-2.706,2.581-2.701,2.610-2.827,respectively.The mean volume fractal dimension ordered from high to low as TH （2.737）,HD （2.674）,TR （2.659） and NC （2.654）.The fractal dimension for the four patterns had significant linear positive correlation with clay particles （＜ 0.002mm） volume percentage,and had significant linear negative relationship with silty particles （0.002-0.05 mm） volume percentage.However,the fractal dimension for the NC,HD and TR patterns was positively correlated to the sand particles （＞ 0.05 mm） volume percentage,while there was no significant correlation between them for the TH pattern.