Page 359 - FRUTAS DEL TRÓPICO

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iRRigating efficiently: wateRshed management stRategies

A method is available for estimating the combined evaporation and transpiration or eva-
potranspiration (ET) using climate data and coefficients instead of using direct measurements,

expressed as:

ET = ET K (3)
A O C

Climate data is used to calculate a reference potential evapotranspiration (ET0). Actual

evapotranspiration (ETA) is the product of ET0 and a cropping coefficient (Kc). The most

commonly used methods for estimating ET0 are the Penman-Monteith, Priestly-Taylor, and

Penman methods. These methods use only climatic data to estimate ET0 on a daily or monthly

basis. Because of the availability of climatic inputs for the estimating ET0, the limiting factor
for calculating ETA is generally an appropriate Kc. Cropping coefficients are a function of crop

maturity and therefore could be considered dependent on heat units (or cumulative solar

radiation). Cropping coefficients from literature or other references should be used with con-

sideration to the physical and atmospheric conditions of their origin.

Drainage and runoff

Drainage refers to the movement of water through the soil profile into groundwater reser-

voirs and drainage water is considered no longer available to the crop. Measuring drainage

may not be feasible; however, drainage may be estimated by understanding soil characte-

ristics. Gravelly soils generally have the greatest infiltration and drainage rates and clay soils
have the lowest infiltration and drainage rates. Infiltration and drainage rates are not only in-

fluenced by the soil texture but also by other factors such as compaction, shrinkage cracks,

crusts, aggregation and structure, water content, organic matter, and pores. Hence, soils

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