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A Modification of the Hydrometer Method of Mechanical Analysis for Certain Western Forest Soils¹

ABSTRACT

Difficulty in getting complete dispersion of the sample for mechanical analysis has been experienced with many western forest soils. In this study four different methods of dispersing the samples were investigated. Samples were pretreated with hydrogen peroxide to destroy the organic matter. A 5% Calgon solution was used as the dispersing agent. Two methods of dispersion involved the use of a standard milkshake mixer and two methods the use of a reciprocating shaker. Dispersion methods were as follows: first, dispersing for 30 minutes with a standard mixer; second, dispersion with a mixer equipped with a larger paddle; third, shaking for 12 hours on a reciprocating shaker; and fourth, addition of sodium hydroxide to the dispersing agent and shaking on the reciprocating shaker. The data revealed that dispersion was poorest with the standard mixer, and best with the reciprocating shaker. The increase in the clay content of the soils that had been dispersed on the shaker resulted from a better dispersal of the silt and sand size aggregates. For latosolic soils the addition of sodium hydroxide gave better dispersion than shaking without sodium hydroxide. With Western Brown Forest soils there was no difference with or without sodium hydroxide.

¹ Technical Paper No. 1037, Oregon Agr. Exp. Sta. Joint Contribution from the Oregon Agr. and Forest Exp. Sta. Presented before Div. V-A Soil Science Society of America, Cincinnati, Ohio, November 13, 1956.

² Associate Forest Soil Scientist, Oregon State College. The author wishes to acknowledge the services of Dr. R. G. Peterson for the statistical analysis and of Mr. C. T. Dyrness and J. E. Andre for portions of the laboratory work.

Received for publication April 1, 1957. Accepted for publication May 17, 1957.