A BICARBONATE TITRATION LIME REQUIREMENT METHOD FOR AQUACULTURE POND SOILS

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 1.0 N in potassium ion and 0.04 N in bicarbonate (2 mg CaCO₃ equivalent mL^-1).  This procedure, called the K-bicarbonate 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 relationship between the current lime requirement method and the K-bicarbonate method are shown in Fig. 1 in which the solid dots are for samples from ponds on the E. W. Shell Fisheries Center at Auburn, Alabama.  Open dots are for samples from major physiographic regions and soil associations in Alabama.