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360 Frutas del trópico
that are characterized by high infiltration rates should receive smaller irrigation volumes at
a higher frequency than low infiltration soils.
Runoff or surface runoff is the portion of precipitation that moves over land and out of
the field. One method for estimating the portion of precipitation that becomes surface runoff
is the Soil Conservation Service (CSC) curve number (CN) method (SCS, 1972; 1985). The
CN method calculates runoff volume as a function of precipitation, soil group, and land use. In
an efficient irrigation system, there is no surface runoff from irrigated waters.
Soil moisture sensors
A more direct method for determining soil moisture for irrigation purposes is the use of soil
moisture sensors. Three terms are often used when describing soil moisture: saturation, field
capacity, and wilting point. Saturation refers to a soil moisture level that has almost all of the
soil pores filled with water. Field capacity refers to a soil moisture level that results when all
the gravitational water has been drained and no further movement of water due to gravity is
significant. The wilting point describes a soil moisture level where there is no longer moisture
present that is available to the plant. Yield reductions are often associated with crops that are
subject to wilting point soil moisture levels.
The ability of a plant to use water within the soil is dependent on the tension associated
with the water, or soil moisture tension. Soil moisture tension is often expressed as a unit of
pressure, such as bars. As soil moisture tension increases, the energy required by the plant to
absorb the water from the soil increases.
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