HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Lagerwerff, J. V. Articles by Moses, S. W. Search for Related Content PubMed Articles by Lagerwerff, J. V. Articles by Moses, S. W. GeoRef GeoRef Citation Agricola Articles by Lagerwerff, J. V. Articles by Moses, S. W.

Detection and Determination of Gypsum in Soils¹

ABSTRACT

A rapid, semiquantitative method (I) and a quantitative method (II) are proposed for the determination of gypsum in soils. Method I involves the determination of the degree of gypsum-unsaturation of an aqueous soil extract nearly saturated with gypsum, i.e., sufficiently dilute to dissolve all gypsum initially present. The unsaturation is determined by electrical conductivity (EC) measurements before and after saturating the extract with reagent CaSO₄·2H₂O. Increasing the water content of the soil in preparation of the dilute soil extract causes an exchange of adsorbed cations for Ca²⁺ from gypsum, and the formation of an equivalent amount of sulfate salts of cations other than Ca²⁺ ("exchange error"). The error is equal to the difference between the observed and calculated contents of salts-other-than-gypsum in the dilute extract. It has been estimated from EC measurements.

Method II is a modification of an existing method, where gypsum is precipitated in the dilute soil extract by acetone. The exchange error is avoided by determining gypsum on the basis of sulfate associated with calcium. The method minimizes several potential errors, such as those due to acetone and ions occluded in the gypsum precipitate.

For a group of gypsiferous soils, errors due to Ca²⁺-exchange and acetone occlusion averaged about –22% and –3%, respectively. Gypsum contents, and recovery of added amounts of gypsum, as determined independently by Methods I and II, compare favorably for the soils studied.

¹ Contribution from U. S. Salinity Laboratory, Soil and Water Conservation Research Division, ARS, USDA, Riverside, Calif., in cooperation with the 17 Western States and Hawaii.

² Soil Scientist, Physical Science Technician, and Laboratory Assistant, respectively, U. S. Salinity Laboratory, Riverside, Calif. The senior author is now with the U. S. Soils Laboratory, Beltsville, Md.

Received for publication January 16, 1965. Accepted for publication March 23, 1965.