Soil which fill the voids among sand grains. Silt is mineralogically like sand but with its higher specific surface area it is more chemically and physically active than sand. But it is the clay content of soil, with its very high specific surface area and generally large number of negative charges, that gives a soil its high retention capacity for water and nutrients. Clay soils also resist wind and water erosion better than silty and sandy soils, as the particles bond tightly to each other, and that with a strong mitigation effect of organic matter. Sand is the most stable of
Duplex soil is highly variable, with the top-soils ranging from coarse sand to clay loam and the subsoils from light to heavy clay. Some duplex soils are distinguished by the presence of an A2 bleached horizon, a character also used as a diagnostic key for the distinction between these type of soils. The diagnostic properties used by Northcote for the definition of duplex soils consider only the soil texture (texture contrast and type of boundary between horizons A and B) and the colour is used for their differentiation (i.e. brown, red and yellow duplex soils). Under the Australian Soil Classification they can