Percolation Generally percolation means slow movement of water through the pores in soil or permeable rock. In pedology, downward movement through soil of the water from rainfall or irrigation and the substances carried by it. The ability of soil to absorb water is known as soil percolation. Soil texture determines how quickly water will be absorbed in the drainfield. Soils containing a balance of coarse and fine particles are the best types for' percolation of water.

Field data on the Ganges River Floodplain show that percolation rates of medium textured soils vary between 0.2 and 2 cm per hour, and those of silty clay and clay soils between 1 and 8 cm per hour.

The low rates in medium textured soils are attributed to the ease with which silty topsoils slake when wetted. The high rates measured in some clay soils are attributed to surface cracking and strong structural development in lower soil layers. The low rates for medium textured soils probably hold true for medium textured soils on other floodplains and for many cultivated terrace soils (forested terrace soils may have much higher infiltration rates). The high rates measured for clay soils on the Ganges River Floodplain may be higher than those occurring in basin clays on other floodplains where the soils have less pronounced shrink -swell properties. [Md Khurshid Alam]