"The physical and chemical behaviour of soil is influenced strongly by its particle size distribution. The relative proportions of clay, silt and sand can tell you a lot about the physical and chemical behaviour of your soils. “ (McKenzie et al, 2004)
You can test particle size distribution via a laboratory, or you can do a field texture estimate.
Field texture can give you a rough estimate of particle size distribution. Field texture is a measure of the behaviour of a small handful of soil when moistened and kneaded into a ball (the bolus) and pressed out to form a ribbon between the thumb and forefinger. The feel of the soil, and length of the ribbon able to be formed is then a measure of the approximate clay content of your soil. See the table below.
Broad Field Texture Classes
|Field Texture Group
||Approximate clay content
||Nil to slight coherence. Ribbon of 0-15mm
|| Less than 10%
||Coherent but very sandy to touch.Ribbon of 15-25mm
||Coherent, spongy and smooth feel with no obvious sandiness. Ribbon of about 25mm
|| Plastic blous. Smooth to touch. Ribbon of 50-75mm
|Medium to heavy clay
|| Plastic bolus. Smooth to touch. Handles like normal to stiff plasticine. Firm resistance to shear and ribbon of 75mm or more.
|| 40% or more
Table (McKenzie et al, 2004 page 7)
(McKenzie, N; Jacquier, D; Isbell, R; Brown, K, Australian Soils and Landscapes – An illustrated compendium, 2004, CSIRO Publishing)