Measurement of Evaporation and Transportation with Lysimeters

SIXTEEN hydraulically weighed lysimeters with surface dimensions of 76 cm x 152 cm were used to measure soil evaporation (E), plant transpiration (T), and evapotranspiration (ET) from irrigated corn during the growing season. Polyethylene film, gravel, and plywood/soil covers were used to suppress soil evaporation from the lysimeters used to measure transpiration. Soil evaporation was measured in uncropped lysimeters that were either shaded or not shaded by the surrounding crop canopy. Summation of the E and T measurements overestimated measured ET by 12% to 24%. Water vapor losses through each of the lysimeter covering materials were measured in the laboratory. Water vapor conductances were used to estimate the lysimeter cover losses in the field. The water vapor losses through the polyethylene film, gravel and plywood/soil covers in the field were estimated to be 11%, 12%, and 6% of the measured transpiration, respectively. Soil evaporation field data were also adjusted since the crop surrounding the lysimeters for the E measurements had 102 cm rows rather than the 76 cm rows used for the ET and T measurements. The summation of the adjusted E and T data were within 1 % to 10% of the measured ET.