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‘A’ Values of Potassium Related to Other Indexes of Soil Potassium Availability

ABSTRACT

A technique was developed to measure ‘A’ values of K with oat (Avena sativa) plants grown in the greenhouse and with the radioactive isotope ⁴²K. The isotope ⁴²K has a short half-life (12.42 ± .03 hours) and was applied to the soil as KCl (approximately 2 mc of ⁴²K/g of ³⁹K) 14 to 18 days after seeding. Plants were harvested to determine initial quantities of K at the time of tagged fertilizer application. Six days later the fertilized plants were harvested and the activity in the plant tissue was counted in a liquid scintillation spectrometer. For 11 soils the total of exchangeable K plus nonexchangeable K accounted for 56% of the variability in K uptake at the time of tracer application, whereas 92% of the variability in ‘A’ values was accounted for by these measurements. Results from the experiments indicated that both amounts of exchangeable and nonexchangable K should be used as availability indexes.

² Research Scientist, Canada Dep. of Agr., Res. Sta., Melfort, Sask.; Associate Professor of Soil Science, Univ. of Amherst Amherst, Mass., formerly Associate Professor of Soil Science, Macdonald College; and Assistant Professor of Physics, Macdonald College, McGill Univ., Quebec, Canada.

Received for publication September 19, 1966. Accepted for publication January 11, 1967.