Physical attributes of acric oxisols from the state of São Paulo - Brazil

Abstract

Physical attributes, i.e, water dispersible clay (WDC), available water (AW) and specific surface area (SSA) of surface and subsurface samples of three acne Oxisols from the São Paulo State - Brazil (two dusky red and one Una variant latosol) were studied. WDC decreased markedly with depth and their values were 0 and 2% for the B horizon. In that layer, electric charge density, surface potential and deltapH were close to zero, promoting colloid flocullation. Amounts of AW were low (<6%) in all samples, with exception of the surface layer from one of the dusky red latosols, for which available water was medium (6-12%). Those low values reflected strong microagreggationof the acric Oxisols, whose water retention and movement are similar to sandy soils. SSA had small values, varying from 42 to 104nrVg, as a result of a predominance of kaolinite and oxides in the soil clay fraction. A positive correlation was obtained between SSA and the amounts of organic carbon and iron oxides.