30 JUNE 2014 • WORLD AQUACULTURE • WWW.WAS.ORG Ponds are limed to neutralize the acidity of bottom soils and to improve productivity. “Liming” refers to the application of various acid-neutralizing compounds of calcium or calcium and magnesium. The material most commonly used to lime ponds is finely crushed agricultural limestone, or agricultural lime. Liming ponds has three important benefits. Liming may enhance the effect of fertilization. Liming helps prevent wide swings in pH. Liming also adds calcium and magnesium, which are important in animal physiology (Wurts and Masser 2013). There has been some interest in the potential use of pelleted lime and liquid lime products for liming ponds. Pelletized lime and “liquid lime” (lime suspensions) have been available for farm and home use for many years. Typically higher quality, finely ground agriculture limestone, “ag lime”, is used to make both. To form pellets, the lime particles are held together with lignosulfonates (less than 10 percent). Liquid lime is formulated by suspending finely ground lime particles in water, with a small amount of clay and dispersant added to the mixture. Sufficient quantities of either product must be used to match the acid neutralizing effectiveness of a bulk agricultural lime application. Practicality of Liquid Lime Suspensions and Pelleted Lime for Liming Ponds William A. Wurts Neutralizing Value of Agricultural Lime Commercial liming materials vary in their ability to neutralize soil acidity — their neutralizing value (NV). Liming rates are dependent on the neutralizing value, which is dependent on purity and particle size. Pure calcium carbonate is the standard used for assigning relative neutralizing values to each of the liming compounds. Calcium carbonate is considered to have an acid neutralizing value of 100 percent. Agricultural limestone may have neutralizing values between 85 and 109 percent depending on its specific chemical composition, calcium carbonate or calcium magnesium carbonate. Finely crushed agricultural limestone is composed of particles of different sizes. Small particles react faster and dissolve more rapidly and completely than large particles. Therefore, the neutralizing efficiency (NE) of agricultural limestone depends on the fineness of the mixture. The particle fineness and associated neutralizing efficiency are determined by passing limestone through a series of sieves. Particles that pass through a 20-mesh sieve but are retained by a 60-mesh sieve have a NE of 52.2 percent. Those passing through a 60-mesh sieve have a NE of 100 Pelletized limestone from two different sources.
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