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The Potassium Supplying Power of Several Western Oregon Soils¹

ABSTRACT

Soil samples from 20 sites representing 7 soil series were intensively cropped with Ladino clover in the greenhouse. The amounts of total and nonexchangeable potassium removed by the clover were determined. These values were then compared with the amounts of total and nonexchangeable postassium extracted by boiling 1N HNO₃ and the amount of exchangeable potassium present in the soils before and after cropping.

The soils varied widely in their potassium supplying power. The total amount of potassium extracted by HNO₃ was highly correlated with the amount of potassium removed from the soils by 10 successive cuttings of Ladino clover in the greenhouse (r = 0.959). The amount of potassium released from nonexchangeable forms by HNO₃ was highly correlated with the amount released during greenhouse cropping (r = 0.937). The correlation coefficient for the total amount of potassium removed by the clover and the amount of exchangeable potassium in the soils before cropping was 0.852. The correlation between the amount of potassium released from nonexchangeable forms during cropping and the amount of exchangeable potassium before cropping was very low (r = 0.174).

Total potassium in the HNO₃ extract and potassium released from nonexchangeable forms by HNO₃ appeared to be better indexes than exchangeable potassium before cropping to potassium release and removal by intensive cropping with Ladino clover in the greenhouse.

¹ Technical Paper No. 931. Oregon Agr. Exp. Sta. This work includes a portion of a thesis presented by the senior author in partial fulfillment of the requirements for the Ph.D. degree at Oregon State College. This investigation was supported in part by a grant from the American Potash Institute. Presented before Div. II, Soil Sci. Soc. of Amer., Davis, Calif., Aug. 16, 1955.

² Research Assistant in Soils and Professor of Soils, respectively.

Received for publication September 13, 1955. Accepted for publication December 2, 1955.