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Bray and Morgan Soil Extractants Modified for Testing Acid Soils from Different Parent Materials¹

Bray and Morgan soil extracting solutions were modified to increase their usefulness in testing acidic soils of different parent materials and ranges of fertility.

The Morgan extractant was changed by substituting NH₄ for Na. For equilibration type extractions, NH₄ removes more K from clay soils than does Na. Although the Morgan extractant satisfactorily removes K from sandy soils, its inability to remove a proportionate amount of K from clay soils makes it unsatisfactory for routine testing in areas where soils are variable.

The Morgan extractant removes some of the readily available P but gives little indication of the reserve or accumulated P in acid soils. But if NH₄F is added to the modified Morgan extractant to provide an 0.03 N F solution, a second extraction will give a measure of the accumulated P reserve. These two extractions made upon the same sample, or a second sample of the same soil, provide a better basis for assessing P availability in soils than either alone.

If the first extraction for the more available P is not desired, P and the more commonly determined exchangeable bases can be measured in a single extraction by the proposed solution of NH₄OAc + NH₄F. This procedure is recommended for states where two separate extractions presently are made for P and K.

Key Words: Phosphorus • Potassium • Adsorption • Soil test correlation

² Assistant Soil Scientist, Department of Plant and Soil Science, University of Vermont, Burlington, Vt. 05401.

Received for publication July 23, 1968.

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