Agriculture Reference
In-Depth Information
Figure
9.15.
Murphy well house. The well, bottom left, round hole and lid, and associated
pump, unseen in back, and pipes that serve as the water source for Steve's farm.
goes to pay for pumping water. Steve does not use water from his well to irrigate any
plants. He relies entirely on rain for all his crops.
9.11
WATER AND SOIL
Soil cannot be separated from water and water cannot be separated from soil. Water is
constantly being added to and removed from soil, and the moisture available for crops
is different in different parts of the world, as seen in Figure 9.16. Rain falling on soil
adds water that either runs off the surface or infiltrates and percolates through the soil
profile. Some water falling on soil will be held in pores against the pull of gravity.
Some of this water will be lost by evaporation from the surface of the soil, and
some will be lost by transpiration from the leaves of plants. As discussed earlier
the total process is called evapotranspiration.
Several things happen as water percolates through soil. Microorganisms
decompose organic contaminants dissolved in the water, and solid components,
both organic and inorganic, are filtered out because of the tortuosity of the path
of the water through soil pores. However, as water passes through soil, it also
dissolves both organic and inorganic components from soil to become part of the
soil solution. When taken up by plants, many of these components are used as
plant nutrients.
