In order to explore the reason for low yield of planosol, the difference of mechanical composition of soil, soil hardness, density and permeability were studied. The results showed that the mechanical composition of planosol had the feature that upper layer was loose and down layer was clay. Topsoil and albic horizon were mainly powder,especially the content of rough powder and the middle size powder was 17.5% -42.5% higher than those of illuvial horizon. Soil clay particle content was insufficient 1/2 of illuvial horizon. The permeability of topsoil of albic was good, solid fraction of albic horizon and illuvial horizon were higher, gas fraction was lower,the permeability of albic soil layer and illuvial horizon was bad. Albic horizon had high hardness, high density, shallow depth, and it could hander the growth of crop root.%为明确白浆土低产原因，对白浆土不同土层的机械组成、土壤硬度、透水性和水浸容重进行了比较研究。结果表明：白浆土机械组成呈上轻下粘的“二层性”特点。耕层和白浆层以粉粒为主，特别是粗粉粒和中粉粒含量比淀积层高17．5％～42．5％，粘粒含量不足淀积层的1／2；白浆土耕层通透性良好，白浆层和淀积层固相率高、气相率低；白浆层和淀积层土壤透水性不良；白浆层土壤硬度大，容重高，埋藏深度浅，是作物根系生长的障碍层次。
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