Phosphorus and nitrogen budget for inland, saline water shrimp ponds in Alabama

Abstract

Phosphorus and nitrogen budgets were prepared for ponds in an inland low-salinity shrimp farm in the Blackland Prairie region of Alabama. The study was conducted during the first crop in three ponds which were newly constructed and had never before contained water. Ponds were not fertilized, and the main input of phosphorus and nitrogen in feed averaged 47 kg/ha and 208.5 kg/ha respectively. These inputs respectively accounted for 98.9% and 95.5% of total input for phosphorus and nitrogen, other inputs of phosphorus and nitrogen were post larvae, well water, rainfall and runoff that combined averaged 0.5 kg/ha for phosphorus and 9.8 kg/ha for nitrogen. The major output of phosphorus and nitrogen was shrimp harvest which averaged 5.2 kg/ha for phosphorus and 45.7 kg/ha for nitrogen. Only 10.9% of phosphorus and 21% of nitrogen applied in feed was incorporated into shrimp. Other losses of phosphorus and nitrogen that resulted from water outflows (seepage and harvest effluent) accounted for 3.2 kg/ha for phosphorus and 7.8 kg/ha for nitrogen. It was difficult to measure the phosphorus and nitrogen increase in the bottom soil over a single crop especially for these new ponds. Phosphorus adsorption by bottom soil is the major pathway of phosphorus loss from pond water, and the difference between the inputs and outputs is thought to result from adsorption by bottom soils. For nitrogen, the discrepancy between input and output was caused by absorption by the bottom soil, denitrification and NH3 volatilization. Nitrogen loss caused by denitrification and NH3 volatilization was not measured in this study. Reuse of the water removed from ponds at harvest is a practical way to reduce the nutrient load to the environment and to save water.