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Soil Moisture Effects on Poteassium Release Observed on Drying Soils with Organic Additives¹

ABSTRACT

A release of 223 ppm K occurred when Marshall subsoil samples were heated for 40 days in a drying oven at 110C. Most of this release can be attributed to the desiccation attained, not the heat, because similar heat treatments without drying increased the exchangeable K level by only 33 ppm.

The release of K associated with drying was entirely eliminated by adding organic compounds to the soil samples before they were dried. To attain this control of K release, however, it was necessary to dry the soil under conditions that ensured the presence of the organic compounds throughout the drying period. Otherwise, the effect of organic additives varied with the initial moisture level of the soil and the relative rates at which the water and organic additives were lost. Single additions of compounds with high boiling points were particularly effective in controlling K release, but even ethanol (boiling point 78C) prevented K release when it was maintained in the soil while the soil moisture was removed.

A practical method of controlling the release of K associated with drying involves the addition of 20 mmoles dextrose to 10 g soil. This treatment eliminates K release despite the presence of large amounts of water or the use of different drying rates.

¹ Journal paper no. J-5088 of the Iowa Agr. and Home Econ. Exp. Sta., Ames, Iowa. Project no. 1234.

² Former Graduate Assistant and Professor in Soils, respectively. The senior author is now Associate Professor, Department of Soil Science, Ontario Agricultural College, Guelph.

Received for publication May 10, 1965. Accepted for publication July 7, 1965.