Depth to high water table is the highest average depth from the soil surface to the zone of saturation during the wettest period of the year. This saturated zone must be more than 6 inches thick and persist for more than a few weeks. A shallow depth to high water table may not allow for sufficient filtration or retention of agricultural wastes or agricultural waste mineralization by-products. A high water table at a depth of less than 4 feet can limit plant and root growth and reduce the soil's agricultural waste adsorptive capacity.
Limitations for application of agricultural wastes are slight if the water table is at a depth of more than 4 feet, moderate at a depth of 2 to 4 feet, and severe if it is at a depth of less than 2 feet. Depth and type of water table, time of year, and duration data should be collected if agricultural wastes are to be applied to soils suspected of having a water table within 4 feet of the soil surface.
Agricultural wastes applied to soils that have moderate limitations because of the water table can overload the soil's retention capacity and percolate through the soil profile contaminating the water table. Reducing waste application rates on these soils helps to alleviate agricultural waste overloading and lessens the potential for ground water contamination.
The potential for contamination of shallow ground water is very high if agricultural wastes are applied to soils that have severe limitations. Careful application and management of agricultural wastes applied to these soils are recommended. Management should include frequent applications at very low rates.
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