While evapotranspiration (ET) and crop coefficient (K_cc) information for winegrapes grown on flat terrain are widely published, there is little information for vines grown on slopes. We measured ET and stem water potential (SWP) in sloped vineyards to evaluate differences in vine water use; our goal was to improve irrigation management on the basis of topography. Site A (10 May to 12 Oct 2013) was Merlot on Chenin blanc root, planted in 1973 in a granitic soil on a 10% slope. Site B (8 Aug to 10 Nov 2014 and 8 April to 18 Oct 2015) was Cabernet Sauvignon on 3309 rootstock, planted in 2000 on metasedimentary soil with an 18% slope. On each slope, the ET was determined using the residual of the energy balance method and eddy covariance to measure sensible heat flux. ET_o from local CIMIS stations was used with the measured ET to calculate crop coefficients. Midday SWP measurements were taken periodically. Vine SWP became more negative as K_c and ET decreased. SWP was similar for vines in the north and south blocks at site A, but became more negative in the north-facing block at site B in both years. At both sites in 2014, greater daily net radiation and ET was observed on the south-facing slope; at site B in 2015, greater daily net radiation and ET was observed on the south-facing slope in spring and fall and on the north-facing slope in June. At both sites, the cumulative vine water use (ET) was greater on the south slope than the north, and cumulative ET on both slopes was greater than measured precipitation + applied irrigation. We conclude that vines on south-facing slopes used more water due to higher net radiation; however, factors contributing to vine stress are complex and require specific site evaluation.

Funding Support: In-kind from authors