Actual Evapotranspiration as Determined from Soil-Water and Canopy Characteristics and Potential Evapotranspiration

摘要

Transpiration and evaporation from a sparsely populated onion field were computed separately from measured evapotranspiration, potential evaporation, stomatal resistances and leaf area indices. Transpiration also was calculated independently from measured stomatal resistance, air vapor pressure, plant-temperature and wind. Daily transpiration estimates found by these two methods agree within 5 percent. The transpiration was only about 25 percent of total evapotranspiration. This field, which was at 1/3-normal population, would transpire at proportionately greater rate if population were increased to normal; however, measurements show that soil evaporation decreases so that evapotranspiration would increase only about 15 percent. The portion of transpiration accounted for by each plant part was 3 percent for umbels, 42 percent for leaves and 55 percent for scapes. (Author)