Effects of uniaxial stress on the physical properties of four Swedish soils

Abstract

The effects of uniaxial stress and soil water content at the time of compression on the degree of compactness (D), defined as the bulk density expressed as a percent of a reference bulk density, and on other soil physical properties were investigated. Stresses of 25, 50, 100, 200 and 400 kPa were applied to large, loose soil samples of light, heavy and humus-rich clays as well as loamy sand in a laboratory experiment. D increased approximately with the log of applied stress over the range of gravimetric water contents normally encountered during field work. Thus, a modified version of the compression model proposed by [Larson, W.E., Gupta, S.C., Useche, R.A., 1980. Compression of agricultural soils from eight soil orders. Soil Sci. Soc. Am. J., 44: 450-457] could be used to compute the stress that gives the optimal degree of compactness for crop growth. The soil compression index, which shows the susceptibility of a soil to compaction, was greatest for the heavy clay and about 30% less for the humus-rich clay, even though they had almost the same clay content. For the loamy sand, D was greatest in the driest sample (water content = 0.01 kg kg-1). In clayey soils, samples at a water content of < 0.20 kg kg-1 were not tested, and the maximum value of D was reached when the soils were compressed at or slightly below field capacity but, as the uniaxial stress increased, the soil water content at which maximum D was reached decreased. In wet clayey soils, soil matric tension was influenced by compaction. Stresses of 200 kPa and above caused the air permeability to fall below a value that is regarded to be critical with respect to crop growth.

Source or Periodical Title

Soil and Tillage Research

ISSN

1671987

Page

13-21

Document Type

Article

Subject

Compression index, Degree of compactness, Soil compaction, Uniaxial stress

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