ProCrop 1999

SALT ACCUMULATION PROCESSES

The weathering of geologic materials has given rise to our present soils and left the salts that impact crop growth and yield. Lack of leaching has kept the salts from leaving. The pattern of saline soils across the state results from years of natural salt redistribution. However, farming practices can influence the spread and severity of saline soil acreage.

Leaching of salts into a shallow water table over time has created shallow saline groundwater in wide areas of the state. Water flows downgrade due to gravity. Salts are often concentrated at or near the surface by capillary flow. In capillary flow, water moves from where the soil is saturated, or nearly so, to drier soil independent of gravity, much like water moving into a dry sponge from a puddle of water on a table. Evaporation then dries the soil and "pulls" water by capillary flow from the wet soil zone. When the water evaporates, salts are left behind.

In clay soils, this rise can reach 4 to 5 feet above the water table. In sandy soils, which have larger pore sizes between soil particles, the pull is less, perhaps reaching 2.5 to 3 feet above the water table. Water movement toward the surface through capillary rise provides a continuous supply of salts which accumulate in the root zone or at the soil surface when the capillary water evaporates.

Groundwater produces a crop production paradox. Crops can use some residual groundwater to supplement precipitation received during the growing season. However, groundwater too close to the surface can carry salts as well as water into the crop root zone, causing yield reductions and crop failures. Management of these soils must somehow balance seasonal water needs with salt reduction.

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