Energy and ET Partitioning in a Drip-Irrigated Vineyard Subject to Local and within-Field Advection.

Vineyards are increasingly cultivated in arid areas. While vineyards are traditionally rain-fed, under arid conditions irrigation is indispensable and precise water management is necessary to optimize grape yields and quality. Vineyards are characterized by an elevated canopy with large areas of exposed bare soil in between, where evaporation from the soil (E) may considerably contribute to evapotranspiration (ET). As E and transpiration (T) respond differently to environmental conditions, separate assessment of interrow and vine canopy fluxes is necessary to adequately determine their contributions to total energy and water exchange under different climate and management conditions. This is a challenging task and largely unresolved due to limitations in measurement techniques. Furthermore, ET in irrigated fields in arid environments can be enhanced by advection of sensible heat (H) from surrounding dry areas, while large differences between wet and dry areas within a field may cause additional within-field advection. To obtain greater understanding of the ET partitioning in vineyards, the objectives of this study were the following: 1) use a below canopy energy balance approach to study the effects of canopy growth, irrigation, and changes in atmospheric conditions on ET partitioning; and 2) understand how local and within field advection affect ET partitioning.

The research was conducted over a season (bud break till harvest) in a drip-irrigated wine-grape vineyard located in an arid region. Field ET was measured using eddy covariance. A below canopy energy balance approach was applied both at the wet irrigated area underneath the vine row and in the dry midrow to continuously estimate E. At daily intervals E was comparable to microlysimeter measurements. However, instances of underestimation of up to 16% suggest advection of energy from the midrow to the below-vine position. Advection was also evident from the bare row into the canopy. Canopy H was negative, particularly on days with high T, despite positive H fluxes at field level. Seasonal partitioning indicated that total E amounted to 9−11% of ET.