Page 511 - Moving the Earth_ The Workbook of Excavation

PIT OPERATION

PIT OPERATION 10.17

Testing. One test of topsoil is the observation of the type and condition of vegetation it supports
before stripping. The vigor of weed growth on piled topsoil is an excellent index to its quality.
Laboratory or field tests can be made for humus content, grain size, acidity, and available plant
food. Humus is measured by the ignition test to be described for peat, and grain size on screens
used for testing sand and gravel.
The test for acid-alkaline balance is commonly made by pressing litmus paper against the
damp soil, and comparing its new color with a chart. If the soil is dry, distilled water should be
used to dampen it, as tap or pond water may give a false reading.
Acidity is expressed in terms of pH (percentage of free hydrogen ions). A reading of 7.0 is neutral,
lower readings increasingly acid, and higher ones alkaline. Most plants will grow under quite a
wide range of conditions. A slightly acid condition is desirable for most of them.
Excessive acidity is readily corrected by the addition of lime, which can be spread on the field
before plowing or disking. Soils are made more acid by mixing with humus, oak leaves, or aluminum
sulfate.
Kits obtained at garden supply stores can be used to measure available or soluble nitrogen, potash
(potassium oxide), and phosphorus or phosphorus oxide. It should be remembered, however, that
these chemicals are often taken up by plants, or leached out by rain, as fast as they become soluble.
The real measure of prolonged fertility is the insoluble reserves that are gradually made available
by soil organisms, plants, and weathering. Except for humus, which is rich in nitrogen, and often
in the other plant-supporting chemicals, such reserves are difficult to measure.

Preparation for Stripping. The cost of properly preparing a field from which topsoil is to be
sold is usually a small part of the total expense, and should increase the value of the soil so that it
will either command a higher price or be more readily salable at a standard price.
Aside from clearing, field preparation may not be necessary if the soil is to be left piled long
enough to rot the vegetation—usually 4 to 6 weeks of warm weather for sod—or if digging is to
be done by a chain bucket loader. Plowed land is more easily and cheaply piled by a bulldozer
than solid fields.
The field should be plowed to the full depth of the topsoil, if possible, or at least deeply enough
to turn up most of the roots of the grass or crop. However, turning up of subsoil should be kept to
a minimum, particularly if it is of a conspicuously different color. Therefore, if the topsoil depth
is variable, or plow depth hard to control, it may be necessary to plow very lightly.
After plowing, the field should be thoroughly disked so that the vegetation is chopped up and
well mixed with the soil. It is then ready for stripping.
If soil is to be removed in a wet season, it may be necessary to leave some strips of sod intact
to support trucks.
Noxious weeds can be reduced or eliminated by planting and turning under one or more vig-
orous, close-growing cover crops. Buckwheat is particularly effective at smothering out.
Nitrogen Deficiency. When vegetation is turned under and mixed with soil, there is an immediate
and rapid increase in the number of the microorganisms which cause it to decay. For their growth they
need nitrogen. If the crop is a legume, such as clover or vetch, they will be able to obtain it as they
break down the plant material; otherwise they obtain it, or as much as they can get, from the soil.
This is likely to result in temporary total exhaustion of available nitrogen. When the vegeta-
tion has decayed so that it no longer provides sufficient food, most of the organisms die and their
nitrogen is largely returned to the soil.
During the interval, which is 2 or 3 weeks for fresh green material in warm weather, and longer
when the material is dry or coarse, when soil moisture is deficient, or when the weather is cold,
any crop which is planted will be starved for nitrogen and make little or no growth. This effect is
most severe when conditions favor rapid decay.

Packing Soil. The value of topsoil is reduced or lost if it is packed into lumps. Except for a few
very light and friable soil types, varying degrees of damage will be done if it is worked wet, or
trucked over except when thoroughly dry.