Report of the Committee on Transpiration and Evaporation, 1943–44

Abstract

In the following statements the members of this Committee have outlined at least a partial summary of current progress in research on transpiration and evaporation. E. A. COLMAN—Last year's Committee report described an analysis, then under way, of the annual soil‐water cycles in the four types of lysimeters which form the San Dimas installation. This study was carried on in order to determine the extent to which vegetation water‐economy data obtained in one kind of lysimeter would agree with that obtained in other kinds. The analysis has been completed and a manuscript prepared for publication under the title of “A study of the relative performance of four types of lysimeters”. It was shown that when compared on the same dates a linear relationship existed between the water‐content of confined lysimeters 24 inches and 38 inches deep, but between them and the confined lysimeters 72 inches deep, no definite relationship was found. Comparisons between the confined lysimeters and a six‐foot deep block of the same soil provided with free‐draining soil‐to‐soil seepage‐contact, showed no unique or predictable relationship between them. In Short, the soil‐water cycle in one type of lysimeter is not related with any degree of assurance to the cycle in any other kind. These findings indicate that serious difficulties may be encountered in any lysimeter‐study of vegetation water‐economy if an attempt is made to compare results from lysimeters of different depth or type since the findings might be influenced by the characteristics of the lysimeters themselves.