Portable Canopy Chamber Measurement of Evapotranspiration in Corn, Soybean and Reconstructed Prairie.

Increasing energy demands promote biofuel production in the US, which leads to a transformation from row crop production to bioenergy production with perennial plants in the Midwest. This transformation may impact the field water balance, and it is important to understand how the different cropping systems affect the field water balance. Evapotranspiration (ET) is a vital component of a field water balance; however, accurate determination of ET can be difficult. The objectives of this study are to quantify the seasonal and diurnal trends of ET in three cropping systems with a portable canopy chamber and to measure and compare field water balance components, i.e., soil water storage, drainage and rainfall, for the cropping systems. Corn and soybean in a corn-soybean rotation and reconstructed prairie were studied at the Comparison of Bio-fuel Systems (COBS) research site in central Iowa. Portable canopy chambers were used to measure ET during the 2014 growing season. Three different chamber sizes were used to match crop growth stages. Diurnal measurements of ET were collected once a week. Leaf area index (LAI) was measured as a plant indicator to determine its proportional relationship with ET. Potential evaporation was also estimated with weather data to compare with the chamber ET. We collected 14 diurnal data sets during the 2014 crop growing season. The measured ET values were consistent with ET values calculated with field water balance. During the early growing season, the ET flux from reconstructed prairie was largest, because of early growth of prairie. During the middle growing season, the ET flux from corn was the largest, because corn had the largest LAI. During the late growing season, ET flux from soybean was a little larger than for corn and prairie, because the corn and prairie matured earlier than soybean. Potential evaporation was generally larger than measured ET. It is valid to use the portable canopy chambers to measure the ET in the different cropping systems.