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This article in SSSAJ

  1. Vol. 16 No. 2, p. 210-214

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The Potassium Supplying Power of Representative Arkansas Soils1

  1. J. O. Legg and
  2. R. L. Beacher2



An evaluation of the potassium supplying power of soils, including both exchangeable and moderately available potassium, is of particular importance in predicting potash fertilizer needs for permanent pastures.

Greenhouse tests were conducted with 12 soils to measure the response of Ladino clover and common ryegrass mixtures to potash fertilization (100 pounds K2O per acre), other nutrients being supplied as needed. Laboratory data are presented to compare the plant growth response to potash fertilization with the general chemical nature of the soil exchange complex and the amounts of potassium extracted by normal nitric acid, sodium acetate, neutral ammonium acetate, and successive leachings with saturated carbonic acid.

All soils were considered low to moderately low in available potassium, ranging from 43 to 125 ppm exchangeable K and from 1.0% to 5.5% exchangeable potassium saturation. The amounts of potassium solubilized by boiling the soil in normal nitric acid were above 250 ppm in soils which did not respond to potash fertilization, and below 250 ppm in five soils in which plant growth was significantly increased by potash treatments. Two very sandy soils with less than 80 ppm of nitric acid-extractable K and approximately 5.0% exchangeable potassium saturation did not respond to potash fertilization. Lespedeza did not respond significantly to a field potash application on a sandy soil low in exchangeable potassium.

Results suggest that favorable response to potash fertilization may be expected on soils with exchange capacities above 5 me/100 gm. and nitric acid-extractable potassium levels below 250 ppm K, providing other nutrients are adequate. The amounts of potassium extracted by carbonic acid, neutral ammonium acetate, or sodium acetate (pH 4.8) were not sufficiently indicative of the potassium supplying power of these soils to be solely used as a sound basis in predicting the need of potash fertilization.

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