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Soil Science Society of America Journal Abstract -

Use of Indigenous Soil-Rubidium Absorbed by Cotton Plants in Determining Labile Soil-Potassium Pool Sizes1


This article in SSSAJ

  1. Vol. 37 No. 4, p. 572-579
    Received: July 11, 1972
    Accepted: Apr 10, 1973

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  1. A. A. R. Hafez and
  2. P. R. Stout2



The rubidium/potassium (Rb/K) ratios of natural soils and of most soil-grown plants are higher than Rb/K ratios of many available fertilizer-grade potassium salts as revealed by analyses of 24 samples of commercial K-fertilizers. Low-Rb K-fertilizers of 0.02 mmoles Rb/mole K or lower may offer practicable means for field scale tracing of fertilizer-K absorbed by crop plants when growing under normal management regimes. Whenever K-fertilization results in lower Rb/K ratios appearing in fertilized plants, this dilution or “reversed-tagging” of indigenous soil-Rb with low Rb-containing K-fertilizers permits determinations of pool-sizes of labile soil-K. Four different soils were compared for NH4OAc extractable-K, HNO3 extractable-K, and the pool-size of labile-K as determined from Rb/K ratios of K-fertilized cotton plants (Gossupium hirsutum L.). A large pool size of labile-K does not necessarily mean that the K supplying power of a soil is large. The Rb/K ratios can also be used to calculate relative amounts of absorbed plant-K originating from the indigenous soil-pool vs. the plant-K derived from a K-fertilizer.

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