Soil and canopy energy balances in a west Texas vineyard

Water use in vineyards i controlled by energy absorbed by plants and the soil surface. An 8 day field experiment was conducted ina commercial vineyard near Lamesa, TX, to evaluate soil and canopy energy balances, and to examine nergy exchange between canopy and soil. Grape-vines in the vineyard were wrapped tightly to trellis wires, creating compact hedgerows that were 3 m apart and of 1.6 m height and 0.4 m width, with little foliage below 1 m above the soil surface. The Bowen ratio method was used to measure the vineyard energy balance including total latent heat flux (AE). Latent heat flux from the canopy (,~Ec) was determined from sap flow measurements of transpiration. Soil latent heat flux (AEs) was calculated as the difference between AE and AE c. These measurements were combined with measurements of soil net irradiance to partition the vineyard energy balance into soil and canopy components. During the study, AEs accounted for 44-68 % of AE. Unstable conditions predominated during the study, with the soil generating sensible heat that was transferred to the canopy, producing values of AE c that were greater than canopy net irradiance. Within-row advection of sensible heat was 17-36 % of AEc. Although the canopy was cooler than within- and above-canopy air