![]() The volumetric expression of water content is used most often. Water content can be quantified on both a gravimetric (g water/g soil) and volumetric (ml water/ml soil) basis. Water held in a soil is described by the term water content. Infiltration and permeability describe the manner by which water moves into and through soil. If the percolating water carries chemicals such as nitrates or pesticides, these water reservoirs may become contaminated. Water that percolates deep in the soil may reach a perched water table or groundwater aquifer. It also refers to the movement of water below the root zone. This is the mechanism by which water reaches the subsoil and rooting zone of plants. Permeability is generally rated from very rapid to very slow ( Table 2.4). Permeability also varies with soil texture and structure. Organic matter, especially crop residue and decaying roots, promotes aggregation so that larger soil pores develop, allowing water to infiltrate more readily. Low infiltration rates lead to ponding on nearly level ground and runoff on sloping ground. Infiltration rates can be near zero for very clayey and compacted soils, or more than 10 inches per hour for sandy and well aggregated soils. It also serves as the storage compartment for water. Pore space in soil is the conduit that allows water to infiltrate and percolate. ![]() Movement of water into soil is called infiltration, and the downward movement of water within the soil is called percolation, permeability or hydraulic conductivity. Soil acts as a sponge to take up and retain water.
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