Potassium adsorption by bottom soils in ponds for inland culture of marine shrimp in Alabama

Potassium is applied to correct ionic imbalance in pond water for inland culture of marine shrimp in Alabama. This study evaluated the loss of potassium through adsorption by bottom soil. Adsorption by bottom soils of potassium added in fertilizers continued over 4 yr. Exchangeable potassium concentration in bottom soils did not increase after the first year, but potassium loss to bottom soil continued over 4 yr. Laboratory work on soil-water systems contacted bottom soil with potassium-enriched pond water for 8 mo: nonexchangeable potassium fixation accounted for 75% of potassium adsorption. Soil total potassium adsorption averaged 518 mg/kg. Bottom soil samples exposed to consecutive 50 mg/L potassium solutions (potassium chloride in distilled water) and agitated by shaker led potassium adsorption by soil to decline from 406 mg/kg in first exposure to 70 mg/kg in sixth exposure. During the next six exposures, potassium adsorption was similar, between 61 and 95 mg/kg in each exposure, averaging 1804 mg/kg of potassium. Pond soils contain smectite clay, have a large capacity to adsorb potassium by nonexchange processes, and remove added potassium from water for years. The only reliable way to determine when potassium fertilizer may be added to Alabama inland shrimp ponds is to monitor potassium concentration in water.