PRACTICAL ASPECTS OF CHEMISTRY IN POND AQUACULTURE

Relationships among liming, fertilization, water and soil chemistry, p hytoplankton response, and aquatic animal production are still poorly understood. There is considerable confusion about critical nutrients a nd fertilizer formulations for pond fertilization. The literature does not support the high application rates of nitrogen often used. Nitrat e is more desirable than ammonium or urea as a source of fertilizer ni trogen. Problems in ponds with water and soil quality that are related to feeding result primarily from high inputs of feed. Organic matter is decomposed mostly to stable humus during a growing season, and ther e is little accumulation of highly decomposable organic matter from on e crop to the next. High input of fresh organic matter to the bottom d uring. a crop period can cause high oxygen demand in sediment, but sed iment removal between growth cycles does not greatly reduce soil oxyge n demand for the next crop. Organic matter resuspension without erosio n of mineral soil has the potential for improving bottom soil conditio n during crops. This can possibly be achieved by new approaches to mec hanically induced aeration and water circulation and the use of sodium nitrate as a soil oxidant. Chemical precipitation of phosphorus by ap plication of aluminum, iron, or calcium ions has the potential for red ucing phytoplankton blooms that result from feeding. The most importan t principle regarding water quality and soil management is that a pond has a finite capacity to assimilate nutrients and organic matter. Whe n this capacity is exceeded, water and soil quality deteriorate. Sedim ent removal and water exchange only transfer pollution problems from p ond environments to surrounding environments.