Soil Texture

Soil texture refers to the proportion of the various particle-size classes (fractions) in a given soil volume and is described as soil textural class

The names for the particle-size classes correspond closely with commonly used standard terminology, including that of the system used by the United States Department of Agriculture (USDA). However, many national systems describing particle-size and textural classes use more or less the same names but different grain fractions of sand, silt and clay, and textural classes.

Field estimation of textural classes The textural class can be estimated in the field by simple field tests and feeling the constituents of the soil. For this, the soil sample must be in a moist to weak wet state. Gravel and other constituents > 2 mm must be removed.

Field estimation of textural classes Clay: soils fingers, is cohesive (sticky), is formable, has a high plasticity Silt: soils fingers, is non-sticky, only weakly formable Sand: cannot be formed, does not soil fingers and feels very grainy

Particle-size classes

Soil Texture

Subdivision of the sand fraction Sands, loamy sands and sandy loams are subdivided according to the proportions of very coarse to coarse, medium, fine and very fine sands in the sand fraction. The proportions are calculated from the particle-size distribution, taking the total of the sand fraction as being 100 percent

Subdivision of the sand fraction

Important diagnostic characteristics derived from the textural class are: A texture that is loamy sand or coarser to a depth of ≥ 100 cm → Arenosol.

Determination of soil grain size composition Gravimetric methods - Sieve methods - Sedimentation of soil suspension - sieve hydrometer method (Bouyoucosa) - weight method (pipetting method ) Optical methods - Laser diffraction

sieve hydrometer method 1. Remove the graval particles by sieve 2. Weigh 40 grams of soil )particles below 1mm diameter 3. Prepare of soil solution (700cm3 water + 20 Calgon +40 grams of soil) 4. Mix the suspension for 5 minutes 5. Transfer the suspension to the cylinder and leave it for 10 minutes

sieve hydrometer method 6. Prepare control probe (water + calgon) 7. Measure the temperature of soil suspension in cylinder 8. Measure the density of soil suspension after 10 minutes of sedimentation 9. Make the calculation (density of soil suspension minus density of control probe)

sieve hydrometer method 10. Make the density measurements after (specified) sedimentations times 11. Use the sieve metods to separate sand’s fractions 12. Dry the sand’s fractions and then weigh it and mutliply (x2,5)

Laser Metod It consists of measuring the angle of refraction of laser light passing through the soil suspension

measuring apparent weight of float submerged in suspension Density of suspension is determined, on the basis of apparent weight changes of the float submerged in soil suspension The weight of the float suspended on a thin line, at a given depth in the suspension, is measured with a sensitive dynamometer and registered on a recording device

measuring apparent weight of float submerged in suspension The Stokes equation is used to calculate the content of soil fractions with equivalent diameters in the range of 0.001mm to 0.1 mm