Production of Sunfish Lepomis spp. in Ponds Treated with Controlled-Release Fertilizers

Abstract.– Controlled-release fertilizer in pond water released nutrients according to the pattern reported for exposure in soil. A single application of controlled-release fertilizer (13% N, 13% P₂O_5, 13% K₂O) was compared with multiple applications of conventional, liquid fertilizer (10% N, 34% P₂O₅, 0% K₂O) for augmenting sunfish production in ponds. Liquid fertilizer was used at an annual phosphorus input rate of 39.3 kg/ha; controlled-release fertilizer was applied at 19.7, 9.8, and 4.9 kg phosphorus/ha per yr. Phytoplankton abundance inferred from chlorophyll u and Secchi disk visibility estimates and phytoplankton photosynthesis measured by the oxygen, light-dark bottle method were similar in ponds treated with liquid fertilizer and in ponds that received controlled-release fertilizers at the two highest rates. Net sunfish production did not differ among ponds treated with 39.3 kg phosphorus/ha in liquid fertilizer or 19.7 and 9.8 kg phosphorus/ha applied in controlled-release fertilizer. Controlled-release fertilizer used in this study contained more nitrogen and potassium than needed, but a custom, controlled-release fertilizer with the proper ratio of nutrients can be made. This fertilizer would have the advantage of requiring only a single application at the beginning of the growing season, and amounts of soluble reactive phosphorus in outflow from ponds could be reduced by using controlled-release fertilizers.