Page 123 - Soil Degradation, Conservation and Remediation

4.5 Principles of Wind Erosion Control 111

the wind erosion rate decreases exponentially. The measurements of threshold velocity
and wind erosion in wind tunnel tests under various vegetation conditions showed
that the threshold velocity increases with vegetation coverage, and that wind erosion
rate decreases sharply as vegetation coverage increases (Liu et al. 1992). Quantitative
relationships between the crop residues and wind erosion were reported early
by Chepil (1944). Several latter workers observed that crop residues and stubbles
effectively reduce wind erosion. Amounts of wheat straw needed to protect most
erodible dune sand and less erodible soils against strong winds were established.
Standing stubble is much more effective than flattened stubble. Standing sorghum
stubble with rows perpendicular to wind direction controlled wind erosion much more
effectively than rows parallel to wind direction (Englehorn et al. 1952). Siddoway
et al. (1965) quantified the specific properties of vegetative covers influencing soil
erodibility and developed regression equations relating soil loss by wind to selected
amounts, kinds, and orientation of vegetative covers, wind velocity, and soil cloddiness.
They found a complex relation between the relative effectiveness of different kinds
and orientation of residue. The relative value of kinds and orientations of residue to
control erosion must be qualified by soil, wind velocity, and variable characteristics
of the residues. Generally they concluded that (1) fine-textured residues are more
effective than coarse-textured residues, (2) any orientation of residue except flattened
decreases wind erosion, and (3) fine-leafed crops, like grasses and cereals, provide a
high degree of erosion control per unit weight. Craig and Turelle (1964) presented
equivalent vegetative cover for additional crops, including a figure for converting
quantity of various crop residues (peanuts, soybeans, shredded cotton, sesame, standing
cotton stalks) to quantity of equivalent flat small grain residue. Hayes (1966) suggests
that if any residue is not represented, a curve for a residue most like it can be used.

4.5 Principles of Wind Erosion Control

As early as in 1910, a USDA Farmers’ Bulletin listed actions to control soil blowing
as follows:

• Increase the water content of the soil.
• Increase the amount of humus (organic matter).
• Provide a cover of growing vegetation.
• Leave the stubble of the previous crop still standing on the land.
• Provide an artificial cover of straw and brush lines.
• Plant windbreaks to protect fields.
• Leave the soil surface in small clods instead of in a finely pulverized condition.
• Roughen the surface by proper cultivation at right angles to the direction of
dangerous winds.
Lyles et al. (1983) extracted the following four principles of wind erosion control
from the above list:

1. Establish and maintain vegetation or vegetative residues.
2. Produce or bring to the surface non-erodible aggregates or clods.