Growing Season Water Use Efficiency and Evapotranspiration Determined by Eddy Covariance and Surface Renewal of a Soybean-Corn Rotation Behind a Tree Windbreak in Nebraska

Abstract:

Tree windbreaks in the U.S. Great Plains are used to alleviate moisture stress by decreasing wind speed and water evaporation. The presence of a tree windbreak leads to a more complex energy and water balance situation than a crop grown in an open field. The objective of this study is to investigate the WUE and evapotranspiration with eddy covariance and surface renewal methods over the growing season for a soybean-corn rotation field sheltered by a tree windbreak.

An eddy covariance (EC) system was installed near the north edge of the field, 200 m away from a tree windbreak, to maximize fetch for prevailing wind direction in 2018 and 2019, Mead, NE. A fine wire thermocouple was installed at the same height as the CSAT to measure sensible heat flux by the surface renewal method (SR). The net radiation and soil heat flux together with soil temperature and water content were measured close to the EC tower. EC is recognized as the standard micrometeorology method to measure sensible and latent heat flux, however, its cost, complexity of application and measurement requirements such as fetch and landscape homogeneity frequently limit its use. Thermocouples are relatively cheap and the SR method has the potential to be less restrictive to fetch requirements than EC as the sensors can be deployed closer to the canopy or ground.

Preliminary results show that the sensible and latent heat flux measured with EC and SR method were comparable. The surface energy balance closure was about 0.90 and 0.94 over the soybean (2018) and corn (2019) growing season, respectively. The ET from EC tended to be larger than the ET from the surface renewal method.