Bottom Soil and Water Quality Management in Shrimp Ponds

摘要

Marine shrimp farming has become an important component of aquaculture. Water and soil conditions have a great influence on the efficiency of shrimp production, and a review of water quality and bottom soil management will be provided. After a shrimppond has been drained for harvest, organic carbon analyses can indicate if organic matter concentrations are too low (< 0.5%) or too high (> 3 or 4%). Bottoms should be dried for 2 to 3 weeks to enhance oxidation of organic matter and other reduced substances. Soil pH should be measured and agricultural limestone applied to acidic pond bottoms. In soil with excessive organic matter, nitrogen fertilizers may be applied at 200 to 400 kg/ha to enhance microbial activity. Nitrate nitrogen is especially effective as a nitrogen source for treating pond bottoms because it also is a soil oxi-dant. Empty pond bottoms also may be tilled to 5 to 10 cm depth with a disk harrow to encourage oxidation. Once ponds have been filled with water, chemical fertilizer containing both nitrogen and phosphorus should be used to encourage natural productivity. Applications of 2 to 4 kg/ha of N and P_2O_5 at 2- to 3-day intervals are usually adequate. Within 1 or 2 weeks, natural food should be abundant and postlarvae can be stocked. Fertilization with 1-2 kg N and 0.5-1 kg P_2O_5 /ha at intervals of about 1 week should be continued for a few weeks. However, once feeding rates exceed 20 to 30 kg/ha per day, fertilization should be used cautiously because of the danger of causing excessive phytoplankton blooms. Mechanical aeration can be used to increase feeding rates and allow higher levels of shrimp production. Water exchange is widely used in shrimp farming, but water exchange often can be reduced to much lower levels thancommonly applied. Suggestions on the use of better practices to minimize possible adverse environmental effects of shrimp farming are provided.