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The purpose of this investigation was to establish relationships between potential evapotranspiration and several elements of weather, potential evapotranspiration as influenced by the surroundings and irrigation of the surroundings, and potential evapotranspiration of Kentucky bluegrass, sweet corn, and celery. High correlations were found between measured potential evapotranspiration (PE) of bluegrass and open‐pan evaporation, atmometer evaporation, average temperature, solar radiation, and duration of sunshine when data were grouped into between‐rain periods. When the same data were grouped into seven‐day periods, relatively low correlations were obtained. Uniform surroundings, watered daily, were found to reduce measured PE of bluegrass 23.2 pct below bluegrass in non‐uniform surroundings which were not watered. Measured PE exceeded evapotranspiration computed by the Thornthwaite empirical formula by 10 to 70 pct and appeared more closely associated with amount of rainfall than with mean temperature. Water use by sweet corn was found to be 22.2 pct higher than use by bluegrass. Although the surrounding area of celery was watered each day, PE was 11.0 pct greater than that of bluegrass, the surrounding area of which was not watered. When compared with PE of bluegrass which received daily irrigation of surroundings, water use by celery was 36.8 pct greater.
The authors cite the need for re‐examination of methods because of inconsistencies and indicate that they have followed Mather's [1951] method of installing and operating modified evapotranspirometers. While it is stated that two plants were grown in each of the corn and celery tanks, no mention is made of tank size or how the number of plants was selected. It is believed that the results would have been quite different had one or three plants been grown in each tank. Suomi [1953] and King and others [1956] have shown that the effective area of an evapotranspirometer cannot be assumed to equal the actual area, even when great care has been exercised with respect to plant density.
It was of interest to note that the authors chose to derive solar radiation from black‐minus‐white atmometer values in preference to sunshine duration. Since the correlation analysis (Table 1) indicates that sunshine duration per se is the better index, radiation data derived therefrom [Hamen and others, 1954] would undoubtedly be superior.
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