Bluegill yield in response to nitrogen and phosphorus versus phosphorus-only fertilization in ponds at different times since sediment removal

Nitrogen often is omitted in fertilization of sportfish ponds in the southeastern United States that have been fertilized for several years with both nitrogen and phosphorus. This practice was tested in 40-yr-old research ponds at the Auburn University E. W. Shell Fisheries Center from which sediment had been removed 2 to 9 yr earlier to restore bottoms nearly to their original soil composition. In ponds from which sediment had been removed 8 yr before, there was no difference (P > 0.05) in harvest weight of bluegill (Lepomis macrochirus) between ponds receiving nitrogen plus phosphorus fertilization (6 kg N and 3 kg P2O5 ha(-1) application(-1)) and those fertilized only with phosphorus (3 kg P2O5 ha(-1) application(-1)). Grass carp controlled aquatic macrophytes effectively in most ponds and did not interfere with bluegill yield. No correlation (R-2 = 0.040, P > 0.05) was found between time since sediment removal and bluegill yield in 13 ponds treated only with phosphate fertilizer at 3 kg P2O5 ha(-1) application(-1). Concentrations of soluble reactive phosphorus and total ammonia nitrogen in the water column were correlated (R-2 = 0.312 and R-2 = 0.514, respectively, P < 0.05) with time since sediment removal. An earlier study showed that nitrogen fertilization was necessary in sportfish ponds the year following sediment removal. In the present study, there was much variation in production among ponds treated with nitrogen plus phosphorus as well as those treated only with phosphorus as typically encountered in pond fertilization trials. Nevertheless, results suggest that nitrogen fertilization of sportfish ponds possibly can be ceased after only 2 years of fertilization with nitrogen and phosphorus. Statement of relevance This research work provides useful information for pond managers when developing a fertilization schedule. The results of the present study do suggest that after 2 yr of nitrogen plus phosphorus fertilization, pond manager might cease nitrogen fertilization and assess the response of the phytoplankton bloom. Omitting nitrogen fertilization from ponds lessens fertilizer cost and reduces possible nitrogen pollution of nearby natural waters. (C) 2015 Elsevier B.V. All rights reserved.