Soil has a major influence on water and air movement, biological activity, root growth and seedling emergence.
It is enhanced by:[1][2] the precipitation of oxides, hydroxides, carbonates and silicates; the products of biological activity (such as biofilms, fungal hyphae and glycoproteins); ionic bridging between negatively charged particles (both clay minerals and organic compounds) by multivalent cations; and interactions between organic compounds (hydrogen bonding and hydrophobic bonding).
The decline of soil structure under irrigation is usually related to the breakdown of aggregates and dispersion of clay material as a result of rapid wetting.
The ESP will increase if irrigation causes salty water (even of low concentration) to gain access to the soil.
A special form, lenticular platy structure, is recognized for plates that are thickest in the middle and thin toward the edges.
Platy structure tends to impede the downward movement of water and plant roots through the soil.
The vertical cracks result from freezing and thawing and wetting and drying as well as the downward movement of water and roots.
In the columnar structure, the units are similar to prisms and are bounded by flat or slightly rounded vertical faces.
The strongest blocky structure is formed as a result of swelling and shrinking of the clay minerals which produce cracks.
Sometimes the surface of dried-up sloughs and ponds shows characteristic cracking and peeling due to clays.
Cultivation, earthworms, frost action and rodents mix the soil and decrease the size of the peds.
[6] The NSW Department of Land and Water Conservation suggests that in cropping systems, wheat yields can be increased by 10 kg/ha for every extra millimetre of rain that is able to infiltrate due to soil structure.
[4] Hardsetting soils lose their structure when wet and then set hard as they dry out to form a structureless mass that is very difficult to cultivate.
It may have occasional cracks, typically at a spacing of >0.1 m. Air dry hardset soil is hard and brittle, and it is not possible to push a forefinger into the profile face.