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Title: OVERWINTER CHANGES TO NEAR-SURFACE BULK DENSITY, PENETRATION RESISTANCE AND INFILTRATION RATES IN COMPACTED SOIL

Author
item Halvorson, Jonathan
item GATTO, L - US ARMY CORPS/ENGINEERS
item McCool, Donald

Submitted to: Terramechanics Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2002
Publication Date: 2/2/2003
Citation: HALVORSON, J.J., GATTO, L.W., MCCOOL, D.K. OVERWINTER CHANGES TO NEAR-SURFACE BULK DENSITY, PENETRATION RESISTANCE AND INFILTRATION RATES IN COMPACTED SOIL. TERRAMECHANICS JOURNAL 40 (2003) 1-24.

Interpretive Summary: Heavy tracked vehicles such as military tanks can compact soil affecting vegetation and impeding water movement into the soil, thus increasing the potential for erosion. Although compaction can be reduced by freeze- thaw cycles, wetting and drying and soil biota, more information is needed about the rate of soil recovery. As part of a collaboration, between the Engineer Research and Development Center at the Cold Regions Research and Engineering Laboratory and the United States Department of Agriculture, Agricultural Research Service, we determined short-term dynamics of change in soil compacted by tracked military vehicles. We measured indicators of soil compaction such as soil bulk density (BD), penetration resistance (SPR), steady-state runoff (SSR) and saturated hydraulic conductivity (Kfs) soon after track formation and again after winter. BD was significantly increased in tank ruts and in simulated tracks but did not change appreciably overwinter. SPR was significantly greater in compacted soil with differences most pronounced near the surface. SPR ratios allowed us to compare samples collected at different dates and moisture conditions and showed that the greatest relative compaction and recovery occur near the soil surface and can be detected within a year after tracking. SSR from simulated rainfall and comparisons of Kfs in compacted soils of different ages indicated that significant soil recovery occurred after a single winter season even when it was not detectable by the other indices of soil compaction. Understanding of short-term changes in soil compaction is important for improving land management and models of soil erosion.

Technical Abstract: Earlier studies at Yakima Training Center (YTC), in Washington State, suggest freeze-thaw (FT)cycles ameliorate soil compacted by tracked military vehicles. However, we know little about the effects of soil FT over a single winter. We measured bulk density (BD), penetration resistance (SPR), and steady-state runoff (SSR) in soil newly tracked by an Abrams tank and in uncompacted soil, before and after a single winter at YTC. We also measured BD, SPR and saturated hydraulic conductivity (Kfs) in simulated tank tracks at Lind, Washington. Average BD was greater in tank tracks, at YTC and Lind, than in uncompacted soil soon after tracking but did not change significantly during the winter of 1997-1998. SPR was influenced by soil moisture, when soil was moist or tracks were newly formed, SPR was significantly higher in tank ruts than in uncompacted soil from 0 to about 10-15-cm depth. We observed highest SPR ratios (compacted rut:undisturbed) in fresh tracks near the surface and lower ratios with increasing track age or soil depth indicating that some soil recovery had occurred at YTC. Rainfall simulator data from YTC showed higher SSR rates in tank ruts than uncompacted soil both before and after winter. However, it took longer to reach SSR in tank ruts and the proportion of runoff was lower in May 1998 than in August 1997. At the Lind site, Kfs was lower in newly compacted soil than in one-year old compacted or uncompacted soil. Our data suggest that indices of water infiltration such as SSR or Kfs are more sensitive indicators of soil recovery after compaction than BD or SPR.