Environmental Engineering Reference
In-Depth Information
Soil compaction is one of the most common problems on abandoned lands (Luce 1997). Soil
compaction can result from trampling by livestock, repeated pedestrian foot traffic, the use of
heavy equipment associated with agricultural and forestry practices, or unrestricted vehicle traf-
fic and parking. Soil compaction is the process of increasing the density of soil by packing soil
particles closer together, causing a reduction in the volume of air. Soil water acts as a lubricant
increasing compaction when a load is imposed on the soil. By packing primary soil particles (sand,
silt, clay) and soil aggregates closer together, the balance between solids and air-filled and wa-
ter-filled pore spaces is dramatically altered. Compaction usually eliminates the largest soil pores
first. When a large portion of the initial soil air is forced out of the upper plant root zone, water
movement and root penetration are destroyed. Also, compacted soil will tend to hold chemicals at
the surface because penetration by water is slower. Discing, deep soil ripping, soil imprinting, and
other physical actions can usually remove this problem (Montalvo, McMillan, and Allen 2002).
Salinity in the soil can be common on farmlands, especially in locations where cattle were
concentrated, such as holding pens and small pastures. Looking at existing vegetation to deter-
mine if there is a salinity problem is not al-
ways reliable. Unless you know the age of
the existing vegetation, it will be difficult to
assess the soil condition because it may have
changed after the plants became established
and their root systems were lower than the
salt penetration.
Salinity is typically expressed as electro-
conductivity (EC) and is shown as a whole
number. For most native vegetation, an EC
of 2 or lower is preferred. High salinity will
negatively affect seed germination. An EC
of 4 will cause plants to show negative signs.
We highly recommended that a soil test
be conducted on your site very early in the
analysis process. Past usage of the site or ad-
jacent land uses will be a guidepost for how
intensive your sampling should be. Contact-
ing local farmers, farmer advisers, agricultur-
al offices, and soil conservation offices should
be helpful. At a minimum, testing should be
conducted for pH, salinity, EC, percentage of
organic matter content, texture, macronutri-
ents and micronutrients, and any other chem-
icals that are known locally to be of concern.
Failure to conduct even the simplest soil test
can lead to significant consequences (fig. 7-4).
FIGURE 7-4. Conducting basic soil sampling for
every project site can yield valuable information for
design decisions.
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