A field test of a soil-based measure of evapotranspiration
1993
KIRSCH, SCOTT W.
The zero flux plane (ZFP) method for estimating actual evapotranspiration (ET), derived from the work of Richards et al. (1956. Soil Sci. Soc. Am. Proc. 20:310–314) and Arya et al. (1975. Soil Sci. Soc. Am. Proc. 39:424–430), was field tested as suggested by M. L. Sharma (1985. Academic Press, New York). The ZFP method requires total hydraulic head and soil water content data from the upper few feet of a soil. The total hydraulic head data, derived from tensiometers, is used to identify the “zero flux plane.” This plane separates the region of the soil where water flow is upward from the region where flow is downward. When the ZFP is below the root zone, only water above the zero flux plane is available for ET. Combining this knowledge with water content data allows estimation, using an equation given here that is based on information from Arya et al. (1975), of actual water lost from the region above the ZFP for the period of interest.Where applicable, several advantages make the ZFP method theoretically more attractive than other techniques for estimating ET: (i) it is based on measurements made directly in the controlling medium, the soil; (ii) it intrinsically integrates the effect of atmospheric, soil and plant processes which affect water movement in the soil and hence ET; and (iii) it is simple, relatively inexpensive, and conceptually sound.
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