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A Chemical Method for the Rating of Agricultural Limestones Used as Soil Amendments¹

ABSTRACT

A method for the calibration of the efficiency of both calcitic and dolomitic limestone in relation to their rapidity in correcting acidity in soils is proposed. The procedure is as follows:

Exactly 1.0 gm. of the limestone to be tested is added to 250 ml. of boiling 0.07 N disodium ethylene-diaminetetraacetate which is contained in a 500-ml. Erlenmeyer flask connected to a reflux condenser. After refluxing 20 minutes, 10 ml. of ammonia buffer solution (pH 10) is rapidly added. The solution is immediately titrated with 1.0 N magnesium sulphate solution using Eriochrome black T as indicator. The end point is attained when the color of the indicator changes from blue to wine red. Time and rate of heating must be controlled precisely.

Limestone samples are calibrated from these titration results by comparing them to the reaction of calcite under identical conditions.

When the results of this test for 19 commercial limestone samples were compared with the pH change of soil suspensions treated with the same materials, a correlation of 0.96 was obtained. A field test of nine commercial samples showed a correlation with this test of 0.79.

¹ Paper No. A484, Contribution No. 2580 of the Maryland Agr. Exp. Station (department of agronomy). Part of dissertation submitted by the senior author (now at University of Cairo, Egypt) in partial fulfillment of the requirements for the degree of doctor of philosophy.

Received for publication October 18, 1954.