Variability in the solubility of agricultural limestone from different sources and its pertinence for aquaculture

Samples of agricultural limestone were obtained from quarries in the USA as follows: Talking Rock, GA; Whitestone, GA; Austinville, VA; Bonham, TX; and Thomasville, PA, referred as GA‐1, GA‐2, VA, TX and PA respectively. The limestone products were tested initially for non‐equilibrium pH, concentrations of calcium and magnesium, neutralizing value (NV) and fineness rate. Laboratory solubility test of the products was conducted in which pH, specific conductance (SC), total alkalinity (TA), total and calcium hardness were measured weekly for 9 weeks. It was found that the agricultural limestone samples had comparable chemical compositions, that is NV (97–108%), Ca (19.8–32.1%), Mg (3.2–12.2%), pH of slurry (8.1–9.7), but somewhat different solubilities in water. Total alkalinity concentrations at equilibrium ranged from 30 to 60 mg L−1. It was possible to quickly estimate the relative solubility of different agricultural limestone samples by comparing their specific conductance under standardized conditions (2.0 g samples w/0.15–0.25 mm fineness; 3.5 L distilled water; 24 h). This procedure might be helpful in achieving better results when liming aquaculture ponds, that is choosing the agricultural limestones with the highest solubilities in water.