A Portable Chamber for Rapid Evapotranspiration Measurements on Field Plots¹

Abstract

Abstract The increased importance of water‐use efficiency in agricultural production has prompted the need for new techniques to measure evapotranspiration (ET) on field plots to evaluate the effects of new soil and water management practices on plant‐water use and stress. This note describes the design and performance of an inexpensive, portable chamber for rapid field measurement of ET. This chamber was constructed from aluminum conduit covered with Mylar film and mounted on a farm tractor for portability. The air within the chamber was mixed continuously with four strategically located fans. The ET rate was calculated from the air and wet‐bulb temperatures of a thermistor psychrometer before the chamber was lowered on the plot and 1 min later. The psychrometer's accuracy was checked by measuring the transpiration from a solution‐absorption system that accurately measured the change in solution level using an LVDT‐float system. When microclimatological conditions were changing slowly, transpiration was assumed to be equal to the absorption. The high correlation between measured absorption and transpiration rates indicated reasonable accuracy. The chamber's accuracy and rapidity of the measurement, portability, and relatively low cost makes it a useful tool in measuring ET under field conditions.