Potassium Fertilization of Bluegill Ponds

Abstract

Bluegill ponds at Auburn University, Alabama were treated with potassium (K) fertilizer at rates of 0, 0.125, 0.5, 1, 2, 4, and 8 Kg/ha with either one or two ponds per rate. Concentrations of potassium in pond water ranged from 2.34 to 38.9 mg/L by the end of the study and were correlated with potassium input. Chlorophyll a concentration and gross photosynthesis rate were not related to potassium input or concentration. Thus, it is not surprising that bluegill production, although highly variable among ponds (mean 416 ± 106 kg/ha; range 243 to 570 kg/ha) was not correlated with potassium application rate or concentration. The large degree of variation in bluegill production among ponds apparently was caused by differential survival of the initial fish stock and incomplete removal of small fish entangled in masses of filamentous algae during harvest. This study suggests that potassium fertilization is unnecessary in bluegill ponds with potassium concentration above 2.3 mg/L; the concentration in the control pond. Likewise, it should be unnecessary to use potassium fertilizer in sportfish ponds in the southern United States that contain more than 2.3 mg/L potassium. If potassium concentration in pond water is less than 2.3 mg/L or unknown, potassium fertilizer should be applied at 1 kg K/ha; equal to about 2 kg/ha of muriate of potash fertilizer. Pond bottom soil adsorbs potassium on cation exchange sites and serves as a source of this nutrient to the water column. In potassium deficient ponds, application of potassium for a few years should increase the concentration of this nutrient in bottom soil making further potassium fertilization unnecessary.