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A Comparison of Several Methods for Evaluating the Potassium Status of Some Mississippi Soils¹

ABSTRACT

Potassium was extracted from soils by growing five sunflower plants (Helianthus annuus L. Var. Mammoth Russian) in 500 g. of soil in the greenhouse for 10 weeks. Adequate fertility was provided by adding periodically in small aliquots 1,400 ml. of a nutrient solution complete except for K. In preliminary experiments the effects of length of cropping period, addition of fertilizer K, and day length and temperature were studied.

Seventeen representative Mississippi soils were obtained, and total K removal by sunflower was compared to removal by various chemical methods. Chemical methods compared were exchangeable K by N NH₄OAc, 0.5N NH₄Cl in 0.25N HCl and 0.5N HCl for 15 minutes, and K released by boiling N NHO₃, heating to 500° C., and continuous percolation with distilled water. The best correlations were obtained with those methods measuring exchangeable K.

In another experiment correlation coefficients between K extracted by sunflower and exchangeable K by N NH₄OAc for 29 surface soils and 22 subsoils were 0.899 and 0.928, respectively. The same correlation for upland surface soils was 0.977; for terrace and bottom surface soils, 0.929.

A Kaufman sandy loam, continuously fertilized for 30 years with a complete fertilizer was found to accumulate both exchangeable and nonexchangeable K. The uptake of K by sunflower correlated equally well with K extracted by N NH₄OAc or boiling N HNO₃.

¹ Contribution from Department of Agronomy, Mississippi Agr. Exp. Sta. (No. 694). Presented before Div. IV, Soil Science Society of America, Aug. 7, 1958, at Lafayette, Ind.

² Associate Agronomist.

Received for publication September 29, 1958. Accepted for publication March 27, 1959.