Soil classification systems recognise several soil groupings based upon the particle size and their proportions. Commonly, Sand, Silt and Clay, large, medium and small particles.
Crudely Clay soils contain at least 40% small particles; Loam soils contain a mixture of small and medium particles ranging between 15% and 39% and Sandy soils contain small and medium particles up to a maximum of 14%.
Besides nutrients, the soil acts also as a water and air reservoir. Soil porosity retains water and air in the spaces between the particles that compose the soil. Each type of soil has different capabilities of retaining water, air and nutrients that plants need.
Sandy soils are well drained and aerated due to large particles as well as large spaces between the particles that compose these soils. Sandy soils usually drain very well being able to retain a small amount of water and because of this sandy soil has a reduced capacity to retain water and nutrients.
Clay soils exhibit diametrically opposite characteristics from sandy soils. Clay soils suffer from lack of drainage and aeration. The lack of aeration and drainage is caused by the small size of particles that compose these types of soil as well as the small spaces between particles which allow them to retain large amounts of water and nutrients at the same time.
Water infiltration rates vary depending on soil type:
Sandy soils have a high infiltration rate of 19 to 25 mm/hr.
Loamy soils, an infiltration rate of 9 to 13 mm/hr.
Clay soils the lowest infiltration rate of 3 to 8 mm/hr.
Compact the soil in any way and the infiltration rate is dramatically reduced especially on a soil with a high clay content.
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