Transpiration Efficiency of Potato
1981
Tanner, C. B.
Wittwer (1979) recently has stressed the need for information on the number of kilograms of water needed to produce a kilogram of food. The objective of this study was to provide this information for potato, and in particular, to test the general proposal of Bierhuizen and Slatyer (1965) that transpiration efficiency (yield/transpiration) could be described by Y/T = k(e*−e), where k is a physico/physiologically-based constant and (e*−e) is the average daytime saturation deficit. Regression analysis of 3 years of field data, including periodic yield measurements and daily measurements of transpiration and saturation deficits, shows that during tuber bulking, k = 0.065 ± 0.007 mb for both tubers and total dry matter. This experimental k is in good agreement with a k derived from physiological data for potato. During early vine growth we found k = 0.055 ± 0.006 mb. These k values disagree with data of Rijtema and Endrodi (1970) which yield k = 0.015 mb. Sources of variability in k and the difference between the Wisconsin and Rijtema and Endrodi data are discussed. It is clear that since evapotranspiration is greater than transpiration, ET-efficiency is less than T-efficiency; therefore k ≈ 0.065 mb sets an upper limit of potato water-use efficiency for a given saturation deficit regime. Also potato water-use efficiency will be higher in humid regions than in semi-arid regions because of lower saturation deficits, particularly where advection exists.
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