Experiments on the Pond Lime Requirement Test and the Effect of Organic Matter on Dissolution of Agricultural Limestone in Aquaculture Ponds

Abstract

Three investigations were performed related to limestone in aquaculture. The first investigation studied the lime requirement of ponds can be determined by direct titration with standard sulfuric acid of the amount of alkalinity neutralized by the exchangeable acidity displaced from a bottom soil sample equilibrated with a solution of 1.0 N in potassium ion and 0.04 N in bicarbonate (2 mg CaCO3 equivalent mL−1 ). This procedure, called the Kbicarbonate method here, provided precise estimates of lime requirement that were 9.6% to 27.2% (average = 12.9%) greater than those obtained by the method currently recommended for use on pond soils. It is likely that the K-bicarbonate method neutralizes more of the exchangeable acidity in pond bottom soil samples than does the current method recommended for pond bottom soils and thereby provides a more reliable estimate of lime requirement. Moreover, the K bicarbonate method does not require a hazardous chemical, a mechanical shaker, or a pH meter as does the current method for pond lime requirement. The cost per analysis also is cheaper by the K-bicarbonate method than with the method currently recommended for pond soils. The second study assessed the influence of single, initial chicken manure applications of 0, 1,000, 2,000, and 4,000 kg/ha on the solubility of agricultural limestone in ponds fertilized with chemical fertilizers. The two higher manure application rates resulted in greater alkalinity (P < 0.05) than achieved in control ponds. However, control ponds with alkalinity concentrations iii of about 40 mg/L did not differ (P > 0.05) in chlorophyll a concentration from the 2,000 and 4,000 kg/ha manure treatments. Although net yield of tilapia (Oreochromis niloticus) was numerically higher in ponds of the 2,000 and 4,000 kg/ha manure treatments, it did not differ from the control (P > 0.05) Laboratory soil-water systems to which organic matter concentrations in soil were increased by 0.0, 0.5, 1.0, 2.0, and 4.0% were established by adding dry, chopped ryegrass (Lolium perenne) shoots to sandy soil containing 0.06% organic matter. Agricultural limestone was added to the systems, and pH, alkalinity, and hardness was monitored for 65 d. The pH, alkalinity and hardness of water increased with increasing soil organic matter concentration. The amounts of carbon dioxide released by microbial respiration increased as soil organic matter concentrations increased. Greater carbon dioxide concentrations resulted in more rapid and greater solubility of agricultural limestone. Although organic matter in pond soils would not decompose as rapidly as ryegrass, results indicate that greater soil organic matter concentrations in ponds would favor the rate and extent of agricultural limestone dissolution