|Holland, Stephen -|
|Heitman, Josh -|
|Howard, Adam -|
|Giese, Gill -|
|Ben-Gal, Alon -|
|Agam, Nurit -|
|Kool, Dilia -|
|Havlin, John -|
Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 16, 2013
Publication Date: May 15, 2013
Citation: Holland, S., Heitman, J.L., Howard, A., Sauer, T.J., Giese, G., Ben-Gal, A., Agam, N., Kool, D., Havlin, J. 2013. Micro-Bowen ratio system for measuring evapotranspiration in a vineyard interrow. Agricultural and Forest Meteorology. 177:93-100. Interpretive Summary: Crop yield is often related to the availability of water. Especially where irrigation is practiced, water that evaporates from the soil is considered a loss because it is unavailable to the plants. To monior water use efficiency, it is important to be able to measure evaporation from the soil beneath a plant canopy. Techniques to measure soil water evaporation are either difficult or not very accurate. Recent improvements in sensors now make an old method called the micro-Bowen ratio worth reconsideration. New micro-Bowen ratio systems were placed over bare soil or short grass within a vineyard and in an open area in North Carolina. Evaporation was measured continuously and was compared with a weighing method and a micrometeorological technique. The micro-Bowen ratio method performed well when compared to other available methods. Some improvements of the measurement technique including better understanding of the measurement area are needed. This research is of interest to researchers interested in improving water use efficiency in sparse canopies like orchards and vineyards.
Technical Abstract: Sparse canopy systems such as vineyards are comprised of multiple components (e.g., vines, interrow soil and/or groundcover) that each contribute to system water and energy balance. Understanding component water and energy fluxes is critical for informing management decisions aimed at improving productivity and water use efficiency. Few methods are available to accurately and continuously measure component fluxes. We tested a novel micro-Bowen ratio (MBR) energy balance system for determining interrow evapotranspiration (ET) flux within a vineyard. Our objectives were to develop MBR methodology to measure ET flux from the vineyard interrow and to compare MBR ET measurements for bare soil and fescue interrow conditions to independent ET estimates. MBR methodology utilized measurement of air temperature and water vapor concentration at 1 and 6 cm heights within 2.7 m wide interrows. Measured ET rates were well correlated between MBR systems and micro-lysimeters for both fescue (R2 = 0.99) and bare surface (R2 = 0.89) interrow conditions, though MBR ET rates were larger than those determined from micro-lysimeters in both cases (20 and 60%, respectively). MBR daily ET estimates, determined by compositing measurements from fescue interrows and bare soil under vines, were also well correlated to (R2 = 0.70) and of similar magnitude as vineyard eddy covariance ET measurements during periods when the vines were dormant. Overall, MBR systems appeared to provide a reasonable approach to determine ET for the interrow component within the vineyard. Similar methodology may be useful to better understand components’ contributions to water and energy fluxes in other complex or sparse canopy systems.