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A Double Buffer Method for the Determination of Lime Requirement of Acid Soils¹

ABSTRACT

A buffer method to take into consideration both the acidity and buffering property of individual acid soils was investigated. The buffer was composed of tris, imidazol, chromate, and pyridine in a 0.2M CaCl₂ solution. It was prepared so that each addition of 0.1 meq of a strong acid to 50 ml of this buffer would reduce the pH by 0.1 unit within the pH range of 8.0 and 5.4. Two buffers of the same composition, one adjusted to pH 7.00 and the other to pH 6.00, were added to two separate soil samples. After shaking for 1 hour the pH was determined. The depression of the buffer pH measured the soil acidity neutralized to the equilibrium pH in these systems. The soil acidity to be neutralized from the equilibrium pH to the desired pH was determined by the buffering property of soil which, in turn, was defined by dividing the difference in soil acidity neutralized in the two buffer systems by the difference of the two equilibrium pH values. This is to represent the acidity released by the soil at each increment of pH. The lime required to raise the soil to the desired pH was calculated from the sum of these two acidity portions. The results from this method were highly correlated with and comparable to those by the lime incubation and BaCl₂-triethanolamine methods.

¹ Contribution from the Department of Soil Science, Florida Agr. Exp. Sta., IFAS, Univ. of Florida, Gainesville, Fla. 32611, as a Journal Series Paper no. 5190. Presented before Div. S-2, Soil Sci. Soc. Amer. at Las Vegas, Nevada, 14 Nov. 1973.

² Professor (Chemist).

Received for publication November 16, 1973. Accepted for publication January 11, 1974.