Agriculture Reference
In-Depth Information
adsorbed to soil. A pesticide that is strongly adsorbed to soil would be less
likely to move to groundwater even if it is persistent.
Pesticide labeling usually does not tell about these properties of the pesti-
cide product. The Soil Conservation Service, Cooperative Extension Service,
your trade association, or your pesticide dealer may have specific information
about the characteristics of the pesticides you are using.
d.
Soil Factors
Soil is also an important factor in the breakdown and movement of pesti-
cides. Your local Soil Conservation Service can help determine the types of
soil in your area and how they affect breakdown and movement. The three
major soil characteristics that affect pesticides are texture, permeability, and
organic matter.
Soil texture
is an indication of the relative proportions of sand, silt, and
clay in the soil. Coarse, sandy soils generally allow water to carry the pesti-
cides rapidly downward. Finer textured soils generally allow water to move at
much slower rates. They contain more clay, and sometimes organic matter, to
which pesticides may cling.
Soil permeability
is a general measure of how fast water can move
downward in a particular soil. The more permeable soils must be managed
carefully to keep pesticides from reaching groundwater.
Soil organic matter
influences how much water the soil can hold before
it begins to move downward. Soil containing organic matter has greater abil-
ity to stop the movement of pesticides. Soils in which plants are growing are
more likely to prevent pesticide movement than bare soils.
e.
Geology
The distance from the soil surface to the water table is the measure of how
deep the ground water is in a given location. If the ground water is within a
few feet of the soil surface, pesticides are more likely to reach it than if it is
farther down. In humid areas, the water table may be only a few feet below
the surface of the soil. In arid areas, the water table may lie several hundred
feet below the soil surface. The depth to the water table does not stay the
same over the course of the year. It varies according to:
•
the amount of rain, snow, and irrigation water being added to the soil
surface
•
the amount of evaporation and plant uptake
•
whether the ground is frozen
