EFFECT OF ALUMINUM AND IRON-OXIDES AND ORGANIC-MATTER ON FLOCCULATION AND DISPERSION OF ARID ZONE SOILS

We investigated the structural stabilities of eight arid zone soils using percent optical transmittance as a measure of flocculation-dispersion behavior. The soils were sodium saturated and their stabilities determined in sodium chloride solutions of varying concentrations. We treated the soils with hypochlorite for organic matter removal, with oxalate for removal of amorphous aluminum and iron oxides, and with dithionite for removal of crystalline aluminum and iron oxides. The removal of amorphous and/or crystalline oxides increased the clay dispersivity. This indicated that amorphous and crystalline oxides play important, stabilizing roles in soil structure. The removal of organic matter decreased the clay dispersivity. This indicated that dissolved organic matter enhances clay dispersion. The well-known positive effect of organic matter on soil tructure probably occurs through binding of soil particles by roots and hyphae at the aggregate level, but at the clay-particle level the negative charge of organic anions enhances clay dispersion. © 1990 Williams and Wilkins.