Soil Texture

Soil Texture

Definition of Soil Texture:Soil texture refers to the relative proportion of particles or it is the relative percentage by weight of the three soil separates viz., sand, silt and clay or simply refers to the size of soil particles.

The proportion of each size group in a given soil (the texture) can not be easily altered and it is considered as a basic property of a soil.

The soil separates are defined in terms of diameter in millimeters of the particles. Soil particles less than 2 mm in diameter are excluded from soil textural determinations.

Stones and gravels may influence the use and management of land because of tillage difficulties but these larger particles make little or no contribution to soil properties such as WHC and capacity to store plant nutrients and their supply.

Gravels: 2 – 4 mm
Pebbles: 4 – 64 mm
Cobbles: 64 – 256 mm
Boulders: > 256 mm

Particles less than 2 mm are called fine earth, normally considered in chemical and mechanical analysis.

Sand:

1. Usually consists of quartz but may also contain fragments of feldspar, mica and occasionally heavy minerals viz., zircon, Tourmaline and hornblende.
2. Has uniform dimensions
3. Can be represented as spherical
4. Not necessarily smooth and has jagged surface

Silt:

1. Particle size intermediate between sand and clay
2. Since the size is smaller, the surface area is more
3. Coated with clay
4. Has the physico- chemical properties as that of clay to a limited extent
5. Sand and Silt forms the SKELETON

Clay:

1. Particle size less than 0.002 mm
2. Plate like or needle like in shape
3. Belong to alumino silicate group of minerals
4. Some times considerable concentration of fine particles which does not belong to alumino silicates. (e.g.) iron oxide and CaCO3
5. These are secondary minerals derived from primary minerals in the rock
6. Flesh of the soil