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Physical Properties: Porosity
Soil porosity refers to that part of a soil volume that is not
occupied by soil particles or organic matter. Pore spaces are filled
with either air, other gases, or water. Large pores (macropores)
allow the ready movement of air and the drainage of water. They
are also large enough to accommodate plant roots and the wide range
of tiny animals that inhabit the soil. Large pore spaces permit
fast infiltration and percolation of water through a soil or soil
horizon. Small pores (micropores) exhibit attractive forces strong
enough to hold water in the pore. They are the water retention system
of the soil which provides water storage for plant roots. During
precipitation, macropores conduct water into the soil where it fills
the micropores. At field capacity all pores small enough to retain
water against the pull of gravity are filled (Brady
and Weil, 1999; Munshower,
1994).
Clay soils have numerous micropores and hold large quantities of
water, but since they have few macropores they produce very slow
infiltration rates. The pores in the clays may be so small and hold
water so tenaciously that the water is not available to plants.
Sandy soils with numerous macropores but few micropores have higher
infiltration and percolation rates but a lower water-holding capacity
than other soil textures. A lower water-holding capacity can mean
less available water for plant roots. For revegetation purposes,
plants perform best in intermediate soil textures (loams) where
soils contain mixtures of micro- and macropores (Munshower,
1994).
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| Health & Safety | Sampling
| Analytical | Data
Quality
Site Assessment | Prediction
| Construction | GIS
| Monitoring & Assessment
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