This method estimates the quantitative concentration of sulfate sulfur (SO4-S) in the soil by extraction with monocalcium phosphate. This method for extractable sulfur as SO4-S follows the procedure originally outlined by Schulte and Eik (1988) with the following exception: (1) elimination of activated carbon and (2) determination of S by ICP-AES. The ICP-AES determines all sulfur, both organic and inorganic. This method is inappropriate for soil containing greater than 4% organic matter. The method is quantitative only for the time of sampling since sulfur is constantly being mineralized in the soil. The method has a detection limit of approximately 0.5 mg/kg sulfur as sulfate and is generally reproducible within 8%.
Schulte, E. E. and Eik, K. 1988. Recommended sulfate-sulfur test. p. 17-19. In: Recommended chemical soil test procedures for north central region. North Dakota Agric Exp Sta Bull No. 499 (revised).