Loamy Sand (Nunn)
Sandy Loam (Greeley)
Sandy Loam (Akron)
Silty Clay (Grand Junction)
Clay Loam (Fort Collins)
Water Content at Time of Compaction (g/cm3)
0
0.04
0.08
0.12
0.01
0.02
0.01
0.02
0.01
0.02
0.03
0.01
0.02
100
10
1
0.1
0.43 kg/cm2
0.87 kg/cm2
1.73 kg/cm2
0.01
3.46 kg/cm2
0.001
40
30
20
10
0
1.8
1.6
1.4
1.2
1.0
0.0
0.5
1.0
0.5
1.0
0.5
1.0
0.5
1.0
0.5
Water Content at Time of Compaction as a Fraction of Field Capacity
LG-32
Figure 3. Effects of compacting loads and water content on infiltration rate, compaction, and bulk density. (After
Akram and Kemper 1979.)
The above results may differ because of the real
not reduce bulk density of compacted Nicollet
variability in nature and the absence of standard-
clay loam in Minnesota at 2030 cm depth, even
ized methods for characterizing soil compactness
after 9 years. Akram and Kemper (1979) reported
(Soane and van Ouwerkerk 1994), although soil
that FT reduced soil compaction in different soils
bulk density, total porosity, void ratio, specific vol-
and, as a result, infiltration rates increased after
ume, and unit weight are generally considered to
FT. Infiltration increased most after one FT cycle in
be fundamental criteria that define the degree of
a loamy sand, after two cycles in one sandy loam
compaction.
and three cycles in another sandy loam, and infil-
tration was still increasing in a clay loam after four
cycles (Fig. 4).
Vehicular ruts
Vehicles can rut a soil surface, depending on
Voorhees et al. (1978, 1986) suggested that the
vehicle load in relation to soil conditions at the time
persistence of soil compaction in agricultural
of trafficking (Richmond et al. 1995). Ruts are
fields, despite FT cycling, may be partly attribut-
potential sites of high soil erosion when aligned
able to increasing tractor weight. FT loosened the
directly up and down slope and are hydraulically
soil to about 20 cm but compaction persisted be-
similar to natural rills in the erosivity of the flows
low 20 to 90 cm depth where it was unaffected by
in them. Water flow is faster and more turbulent in
FT (Fig. 5); however, this persistence was in part
natural rills than it is in overland sheet wash
soil-dependent. Voorhees (1983) reported that soil
(Evans 1980) and it has more energy to detach and
FT and wetting and drying reduced soil pene-
transport sediment.
tration resistance by 2050% and that the FT was
Voorhees et al. (1979) reported that the ruts left
more effective in reducing resistance when the soil
was wetter at freezeup.
by wheeled vehicles can act as channels to concen-
4
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