Growing season surface energy balance by eddy covariance and surface renewal of a soybean-corn rotation behind a tree windbreak in Nebraska

Authors: TONG, BING - Orise Fellow; Sauer, Thomas; DOLD, CHRISTIAN - Juelich Research Center; WEDIN, DAVID - University Of Nebraska; SUYKER, ANDY - University Of Nebraska

Submitted to: Agricultural and Forest Meteorology Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2020
Publication Date: N/A
Citation: N/A

Interpretive Summary: 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 surface energy balance 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 to measure the sensible heat flux (H) by the surface renewal method (SR). Thermocouples are much cheaper than EC systems 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. The net radiation and soil heat flux together with soil temperature and water content were measured close to the EC tower. Four micromet measurements towers were installed, positioned on a transect parallel with the prevailing wind direction to measure canopy and soil conditions as influenced by the windbreak on the south side of the field and instrumented to measure wind speed and direction, canopy and air temperature, relative humidity, NDVI, and soil water content. A tower on the south side of the windbreak measured wind speed, wind direction, air temperature, and relative humidity to characterize those parameters upwind of the windbreak. Reference heights for aerial sensors were 2.5 m for soybean and around 3.5 m for corn. Preliminary results show that most of wind came from the southeast, and when wind direction was from south, the wind speed increased with distance from the windbreak. The sensible and latent heat flux measured with EC and SR methods were comparable. The surface energy balance closure was about 0.90 and 0.94 over the soybean and corn growing season, in 2018 and 2019, respectively.

Technical 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 surface energy balance 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 to measure the sensible heat flux (H) by the surface renewal method (SR). Thermocouples are much cheaper than EC systems 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. The net radiation and soil heat flux together with soil temperature and water content were measured close to the EC tower. Four micromet measurements towers were installed, positioned on a transect parallel with the prevailing wind direction to measure canopy and soil conditions as influenced by the windbreak on the south side of the field and instrumented to measure wind speed and direction, canopy and air temperature, relative humidity, NDVI, and soil water content. A tower on the south side of the windbreak measured wind speed, wind direction, air temperature, and relative humidity to characterize those parameters upwind of the windbreak. Reference heights for aerial sensors were 2.5 m for soybean and around 3.5 m for corn. Preliminary results show that most of wind came from the southeast, and when wind direction was from south, the wind speed increased with distance from the windbreak. The sensible and latent heat flux measured with EC and SR methods were comparable. The surface energy balance closure was about 0.90 and 0.94 over the soybean and corn growing season, in 2018 and 2019, respectively.