Some Meteorological Aspects of Evapotranspiration

Abstract

During the past decade increasing attention has been given to various engineering type equations designed to estimate, from available climatic data, the amount of water used by plants. Some of the basic assumptions involved in these equations are examined in the ligh to frecent advances in knowledge of the physical processes at the earth‐atmosphere interface. It is found that the majority of equations involving the concept of potential evapotranspiration or consumptive use tend to assume a homogeneous soil moisture regime infinite in horizontal extent. Therefore, it has been difficult to apply these equations to irrigation practice, which obviously must create isolated areas of above normal moisture. Consequently, the problem is approached from the strictly physical point of view, and it is shown that a solution can be obtained, provided that sufficient knowledge of soil interactions is available.

An Analysis of Actual Evapotranspiration

“…DE VRIES (1962) proposed some theoretical considerations in order to calculate evapotranspiration in an irrigated area. HALSTEAD and COVEY (1957) give also indications for the calculation of the oasis effect. The possibilities for calculation are highly depending on the size of the oasis.…”

A quantitative analysis of plant growth: the effect of environmental stresses on foliar expansion in castor beans

“…Mathe¬ matically, this is identical with d In G/ . It was adopted for ' dt use in this study as discussed under development of equations [10], [11], and [12]. It should be again stressed that it was essential to use the trend in total leaf area on the control As shown in Figure 64, where Q = -this function expressed the relationship very closely.…”

“…Relative growth in areal expansion of leaves as a function of total leaf area attained by the "control" plants As pointed out in the discussion of equation [12], the constants derived in equation [36] were locked into the appli¬ cation of equation [12] for the data in each of the experimental treatments. This mathematical manipulation enabled the observed values of In Q in each of the five treatments other than the con¬ trol to be treated as deviations from control.…”

“…In each of the treatments, other than the control, there was marked dispersion of the day-to-day observations from the general trend. Table 55 presents the constants attained for each treatment by use of equation [12] as modified by equation [36]. The term "now light" indicates the relationship to light occurring on the day the growth increment took place; and "old light" the relationship to light occurring on the day previous the specified growth increment.…”

“…Use of equation [37] was far more effective in accounting for the variance in In Q than equation [12].…”