Extraction of Potassium from Soils by Sulfuric Acid

Methods of extracting potassium from soils by use of sulfuric acid have been developed. The amounts of K extracted from several Ohio and New York soils by these methods were compared with those extracted by neutral 1 N NH 4 OAc and boiling 1 N HNO 3 methods as means of furnishing a reliable index to the “plant‐available” K of soils. Using H 2 SO 4 method 1, amounts of K were extracted which were highly correlated with amounts of K extracted from soils by cropping. The correlation coefficient thus obtained was significantly different at the 1% level from the coefficients obtained by using ammonium acetate or boiling nitric acid. The sulfuric acid methods developed are simple to use and, since an exact quantity of heat energy is furnished to the soil extraction system, these methods theoretically furnish a means of releasing a constant amount of non‐exchangeable K, due to breakdown of primary and secondary minerals, as well as the exchangeable K from a particular soil.