A bicarbonate titration method for lime requirement to neutralize exchangeable acidity of pond bottom soils

• Acidic ions on bottom soil samples are exchanged for K + in a KCl-KHCO3 solution.
• Alkalinity loss (as CaCO3) from the KCl-KHCO3 solution is the soil lime requirement.
• The K-bicarbonate method provided lime requirements similar to those obtained by the current method.
• The K-bicarbonate method is economical and does not require a pH meter, or a hazardous chemical.

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 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.