Below canopy radiation divergence in a vineyard – implications on inter-row surface energy balance

Authors: Kustas, William - Bill; AGAM, N. - Ben Gurion University Of Negev; Alfieri, Joseph; McKee, Lynn; Prueger, John; HIPPS, L.E. - Utah State University; HOWARD, A. - North Carolina State University; HEITMAN, J. - North Carolina State University

Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2018
Publication Date: 10/19/2018
Citation: Kustas, W.P., Agam, N., Alfieri, J.G., McKee, L.G., Prueger, J.H., Hipps, L., Howard, A., Heitman, J. 2018. Below canopy radiation divergence in a vineyard – implications on inter-row surface energy balance. Irrigation Science. https://doi.org/10.1007/s00271-018-0601-0.
DOI: https://doi.org/10.1007/s00271-018-0601-0

Interpretive Summary: The architecture of wine-grape vineyards is characterized by tall plants with most of the biomass in the upper one-half to one-third of the plant height, and widely spaced rows. The canopy architecture and wide row spacing facilitates sunlight interception, air flow, and field operations. It also results in two distinct management zones: the vines, and the interrow that is often planted with a cover crop. Any water management tool for vineyards must consider how these two systems interact to affect water and energy exchange. The trellis design as well as ground cover and vine management will influence both the radiation and the energy exchange of the interrow with the overstory vine canopy, resulting in the interrow acting as an energy source or sink Moreover, with vineyards increasingly being established in arid areas, water becomes a limiting factor and there is much greater interest in understanding and quantifying the contribution of evaporation (E) relative to transpiration (T), which will have a correlation to grape yield and quality. The objective of this work was to describe the radiation reaching the vineyard floor by conducting extensive radiation measurements, and to relate the radiation patterns to below canopy energy fluxes using three micro-Bowen ratio systems. These measurements provided insight to the relative importance of radiation and local soil water and plant dynamics in the exchange of water and heat from the vine canopy and interrow systems. These measurements are being used to improve remote sensing and land surface models estimating E and T contributions from vineyards, which will ultimately improve water management and water use effciiency in vineyards while maintaining grape yield and quality.

Technical Abstract: Vineyards canopy architecture and row structure pose unique challenges in modeling the radiation partitioning and energy exchange between the vine canopy and the interrow area. The vines are often pruned and manipulated to be strongly clumped while mechanical harvesting requires wide rows, often with vine height to vine spacing ratio >1. This paper estimates the intercepted radiation by the canopy, and the effect of this interception on the below-canopy surface energy balance and evapotranspiration (ET). Measurements were conducted in an east-west oriented vineyard in CA during Intensive Observation Periods (IOPs) as part of the Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX). Below canopy incoming short wave radiation was measured at multiple positions across the interrow, and the surface energy balance/evapotranspiration (ET) below the vine rows was measured for one growing season using three micro-Bowen ratio (MBR)systems one in the center of the interrow and one underneath a vine row south and the other north of the MBR in the center of the interrow. A significant spatial and temporal variability in radiation was observed since the vines were not significantly pruned or manipulated so they were allowed to grow randomly into the interrow. However, when averaged over the sensor array, the values appeared to give reliable average radiation extinction conditions that agreed with model estimates. The variation in the surface energy fluxes were dominated by the amount of transmitted radiation, while soil moisture was a 2nd order affect. Daily estimates of ET from the three micro-Bowen ratio systems, weighted by their respective representative sampling area, yielded estimates similar to values computed by the correlation-based flux partitioning method, which utilizes high frequency eddy covariance data.