Subsoils aggregation

Normally, clay in soil is not present as individual particles but is clustered to aggregates that consist wholly of clay or of a mixture of clay and other mineral and/or organic soil material. Mass transport of soil material along cracks and pores, common in cracking soils in regions with alternating wet and dry periods, does not necessarily enrich the subsoil horizons with clay. 

The conditions in subsoils for root growth are usually less favorable than in the topsoil. Limited extension of the root system, as already stated, is likely to be encountered in subsoils that are very high in clay content, poorly aggregated, or inadequately aerated. In addition, where pan layers exist, root growth may be greatly inhibited or entirely prevented. Most of these conditions could be alleviated if organic matter could be introduced but this is not feasible except where the subsoil is exposed. 

As the result of a 5-year field, laboratory and statistical study, Wischmeier and Man-nering (1969) concluded that the properties that contributed significantly to soil-loss variance included percentage of sand, silt, clay, and organic matter pH, structure and bulk density of plow layer and subsoil steepness and concavity or convexity of slope pore space filled by air residual effects of sod crops aggregation parent material and various interactions of these variables. ... 

Hardcore, aggregate bases or layers of drainage gravel, often to which polymers as polyester fibers are added, stabilize the soil and prevent objects from sinking into the subsoil. 

Several other applications of a. deal with the improvement of soils by means of soil conditioners, either to improve air or water permeability of the soil, to prevent the loss of water to the subsoil, or to increase aggregation of the soil particles, thus preventing splashing of soil onto the produce. Often such soil conditioners consist of - surfactantlike substances. 

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