Effect of slope and aspect on vine water use and stress

Abstract

While evapotranspiration (ET) and crop coefficient (Kc) information for wine grapes grown on flat terrain are widely published, there is little information available on ET and Kc for vines grown on slopes and even less on the impact of water stress on vine ET. Therefore, our objective was to measure ET and stem water potential (SWP) in pilot studies conducted on North and South facing sloped vineyards to evaluate differences in vine water use to improve irrigation management on the basis of vineyard topography. We  conducted  our  study  in  El  Dorado  County,  CA  in  vineyards  where  the  growers  managed  the  irrigation. Site A (2013) was Merlot grafted on Chenin blanc root, planted in 1973, on about 10% slope. Vine spacing: 2.4 x 3.6m, soil granitic. Site B (2014) was Cabernet sauv. on 3309 rootstock, planted in 2000 on about 35% slope. Vine spacing: 1.5 x 1.8m, soil metasedimentary. On each site slope the ET was determined using the residual of the energy balance method using eddy covariance and surface renewal to measure sensible heat flux. Reference evapotranspiration (ET₀) from local CIMIS stations was used with the measured ET to calculate crop coefficients. Midday SWP measurements were taken periodically from 6-10 vines on each slope. Results from both vineyards showed that as the season progressed, vine SWP became more negative as Kc and ET decreased. The S. facing vineyards had higher net radiation and crop water use (ET) ; in site A (10 May – 12 Oct) the cumulative ET (N.) was 354mm compared to 453 mm (S.) while in site B (8 Aug. to 10 Nov.) the cumulative ET (N.) was 95 mm compared to 221 mm (S.). SWP was the same for vines on N. and S. blocks in site A; but was more negative in the N. facing block in site B. 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 more specific site evaluation.