Soil Texture

Soil Texture relative proportions of sand, silt and clay. These fractions are defined in terms of the diameter in mm of the particles. Particles larger than 2 mm in diameter are excluded from soil texture determination. The size of particles in mineral soil is not readily subject to change. Thus, a sandy soil remains sandy, and a clayey soil remains clayey. Since the proportion of each size group in a given soil (the texture) cannot be easily altered, it is considered a basic property of a soil. To convey an idea of the textural make-up of soils and to give an indication of their physical properties, soil textural class names are used. Four broad groups of these classes are recognised: sands, silts, clays and loams. These broad textural classes are as follows: Sandy - soils containing more than 70% sand; Silt - soils containing more than 80% silt; Clay - soils containing more than 40% clay; Loams - intermediate mixture of sand, silt, and clay. Loam soils are considered to be the favourable texture for growing most agricultural crops. In addition to these general textural classes, in fact soils are technically divided into twelve textural classes. These are sand, loamy sand, sandy loam, loam, silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay and clay.

Differences in texture between topsoils and subsoils are found in some Noncalcareous Grey Floodplain soils on the Jamuna Floodplain formed in deposits that are less than 200 years old. On the Old Brahmaputra Floodplain and the Old Meghna Estuarine Floodplain, which are more than 200 years but probably not more than 2,000 years old, the prevalent Noncalcareous Dark Grey Floodplain soils commonly have differences in clay content of 5-15% between topsoils and subsoils, and differences of 20-30% are found in some acid basin clays. The discrepancies in texture between topsoils and subsoils could be due to the leaching of clay from the topsoil to the subsoil. Leaching of high floodplain ridge soils usually has not led to pronounced differences in texture between the topsoil and subsoil. In the older soils on the Old Himalayan Piedmont Plain, textures in the topsoil and subsoil are usually uniform. In Calcareous Brown Floodplain soils on the Ganges River Floodplain, there may actually be more clay in the topsoil than in the subsoil. [Md Mizanur Rahman Bhuiyan]