Micro-Bowen ratio system for measuring evapotranspiration in a vineyard interrow

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.