Effect of dispersible clay on the physical properties of the B horizon of a red-brown earth

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Abstract
Three methods were compared for the determination of dispersible clay in the absence of chemical treatments. Treatment of the B horizon of a red-brown earth with a range of amounts (0-0.24% iron) of iron poly[Fe(III)-OH] cations of nominal molecular weight 10 000 to 50 000 allowed production of a range of dispersible clay contents from 0 to 70%. The samples of clay B horizon with decreasing contents of dispersible clay showed decreasing electrophoretic mobilities with zero mobility when the content of dispersible clay was zero. In such samples the clay particles were present in aggregates 50-250 mu m diameter according to sedimentation techniques. The amounts of dispersible clay present appeared to control various physical and mechanical properties of the soil such as swelling, porosity and water retention capacity, hydraulic conductivity, friability and modulus of rupture. It is suggested that the content of dispersible clay may be a useful quantitative characteristic of soils as it controls many other properties.