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Potassium -Sulfuric Acid Extraction

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As the exchangeable K of soils is removed by cropping or leaching, some K from the mineral reserve becomes exchangeable K. Soils with low exchangeable K content need not be deficient, as the mineral reserve may be able to supply K for plant growth. Extraction of K with H2SO4 removes an amount of K that seems to be correlated with the removal by extensive cropping. The method has a detection limit of 1 mg kg-1 (on a soil basis) and is generally reproducible within 10%.

Brown, A. L., Quick, J. and deBoer, G. J. 1973. Potassium deficiency by soil analysis. p. 13-14. Cal. Agr. June.