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A New Approach to Soil Testing: III. Differential Adsorption of Potassium¹

ABSTRACT

Donnán type ratios were used to develop an index to account for the differential adsorption of K in two widely different soils of the Rayne and Hublersburg series. This index was used to calculate an adjusted K requirement for the soils using the approach of Baker. Three corn hybrids (Zea mays L.) were grown in the two soils treated with different levels of K and multiple regression analysis was used to relate soil test variables to plant K content.

Most of the variation in the index, K_E/S, was associated with soil effects, making the index useful in characterizing the two soils with respect to differential K adsorption and in calculating soil K requirements. Over 60% of the variation in plant K content was explained by the soil K requirement calculated from the index. Compared with a critical K level of 98 ppm exchangeable K for soils with a CEC of 10 meq/100 g and a K_E/S of 1.0, the comparable critical values for K were 71 ppm for the Rayne and 114 ppm for the Hublersburg.

¹ Contribution from the Dep. of Agronomy, Pennsylvania Agric. Exp. Stn., Pennsylvania State Univ., University Park, PA 16802, Journal series no. 5314.

² Soil Scientist, USDA-ARS, Morgantown, W. Va., and Professor of Soil Chemistry, respectively.

Received for publication June 23, 1977. Accepted for publication November 1, 1977.