‘A’ Values of Potassium Related to Other Indexes of Soil Potassium Availability
1967
Nuttall, W. F. | Warkentin, B. P. | Carter, A. L.
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.
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