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Effects of Drying Treatments on Porosity of Soil Materials¹

ABSTRACT

The effects of three drying techniques on total porosity and pore size distribution of soil materials were studied by Hg intrusion porosimetry. The three soils investigated had different clay contents (21%, 35%, and 44%), but the clay fraction of each was dominated by montmorillonite. Some samples were dried in an oven at 40°C for 7 d; some samples were quick-frozen in liquid N and lyophilized; some samples were dried by acetone vapor exchange and immersion, followed by evaporation of the acetone. Both undisturbed and compacted samples were investigated. The three drying techniques caused a reduction in sample total porosity ranging from 3 to 52%. Freeze drying usually caused the least change in total porosity. Although materials highest in clay shrank the most, there was no other discernible relationship between shrinkage and clay content. Freeze-dried samples had the greatest volume of porosity in the 0.2- to 2- µm equivalent pore radius (epr) range, whereas acetone-dried samples had the greatest volume of porosity in the 0.02- to 0.2- and 0.2- to 2-µm epr ranges. Pore size distributions of oven-dried samples varied from soil to soil. The consistency of pore size distributions in freeze-dried materials strongly suggests that pores were deformed by ice crystals either during or after freezing of the samples. In the epr range of 0.002 to 0.02 µm, acetone-dried samples had porosities similar to oven-dried samples.

¹ Journal Paper no. J-11765 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA 50011. Project no. 2556. This paper was originally presented before Div. S-1, Soil Sci. Soc. Am., Las Vegas, on 29 Nov. 1984. Although the information reported in this article has been funded wholly or in part by the U.S. Environmental Protection Agency under assistance agreement CR-811093-01-0 to Iowa State Univ., it has not been subjected to the Agency's peer and administrative review and therefore does not necessarily reflect the views of the Agency and no official endorsement should be inferred.

² Assistant Professor, Graduate Research Assistant, and Associate Professor, Dep. of Agronomy, Iowa State Univ., Ames, IA 50011, respectively.

Received for publication March 4, 1985. Accepted for publication June 18, 1985.