From a practical view point, the application of evaporation equation based on the general unsaturated flow equation has some liitations. Therefore, a rapid and simple method was developed and valuated to determine evaporation rate from bare soil surfaces in absence of a water’ table.
Soil samples of a fine sand with various lengths were subjected to artificial potential evaporation from the top. T1ie ratio of real to potential evaporation versus volumetric water content at the surface was plotted for varying soil depths by which the coefficient of real evaporation was determined.
In general, the ratio E/EO versus soil surface water content was constant in initial stage of evaporation. In the falling rate stage (second and third stage), however, evaporation decreased linearly. In the initial stage, evaporation was controlled by potential rate whereas soil hydrolic ‘properties, namely coefficient of unsaturated hydraulic conductivity , were major limiting factors in the falling rate stage.
Based on the results, a standard graph indicating the relation between Es/EQ and soil surface water content was developed for the fine sand used in the experiment. This relationship can be used to determine the coefficient of real evaporation. Similar standard graphs could be developed accordingly.
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