235 POTASSIUM, SODIUM, CALCIUM, AND MAGNESIUM IN SATURATED PASTE EXTRACT
Saturated Paste Extract: K, Na, Ca, Mg
Amounts of soluble calcium and magnesium in the saturated paste extract by ICP-AES. Amounts of soluble potassium and sodium in the saturated paste extract by emission spectrometry.
Summary: This method quantitatively determines the concentration (meq L-1) of dissolved K, Na, Ca, and Mg in the saturated paste extract using inductively coupled plasma emission spectrometry (ICP) for Ca and Mg and emission spectrophotometry (AA) for K and Na. These four ions generally are the dominant cations in the saturated paste extract of soils. Concentration of soluble Na, Ca, and Mg is used to determine the sodium absorption ratio (SAR) of soils. Extract solutions containing greater than 10,000 mg L-1 (1.0% w/v, estimated from ECe) will require dilution since solutions this concentrated with salt may impair instrument operation. The detection limits for these cations are approximately 0.1 meq L-1 on a solution basis.
Knudsen, D., Peterson, G. A. and Pratt, P. F. 1982. Lithium, sodium and potassium. p. 225-246. In: A. L. Page et al. (ed.) Methods of soil analysis: Part 2. Chemical and microbiological properties. ASA Monograph Number 9.
Soltanpour, P. N., Benton Jones, Jr., J. and Workman, S. M. 1982. Optical emission spectrometry. p. 29-65. In: A. L. Page et al. (ed.) Methods of soil analysis: Part 2. Chemical and microbiological properties. Monograph Number 9 (Second Edition). ASA, Madison, WI.