Using a decision support system (Vintel®) to determine the relationship between soil water content and whole-grapevine transpiration
Vintel is a decision support system that provides irrigation recommendations in grapevine to maintain a desired predawn leaf water potential (Ψpd). Ψpd is calculated from the fraction of transpirable soil water (FTSW). FTSW is computed daily using a soil-plant-atmosphere continuum model with sub-models for vine growth, light interception, transpiration, soil evaporation, water run-off and cover crop evapotranspiration. This work focuses on vine transpiration, that is calculated from light interception and then modulated to account for the stomatal response to water deficit using a bi-linear response to FTSW reported in the literature. If FTSW is higher than 0.4 no reduction in transpiration is considered. Below this threshold, relative transpiration is reduced linearly with FTSW from one to zero. This approach produced satisfactory results with Vintel users that irrigate frequently but FTSW and Ψpd values decreased too rapidly when vines were subjected to long periods of water deprivation (a common practice in wine regions). To understand this issue, Ψpd, early-morning, mid-morning and midday leaf conductance (gs) were measured during 2017 and 2018 in four vineyards in the South of France. The vineyards included Grenache, Cinsault and Syrah grafted onto SO4 and Syrah grafted onto 140 Ruggeri. Each vineyard was grown under irrigated and non-irrigated conditions and eight measurements of Ψpd and gs were performed between budbreak and harvest for each plot, year and irrigation treatment. Independently of the hour of measurement, relative gs was lower than that expected using the bi-linear function with the 0.4 threshold. For this reason, Vintel predictions of Ψpd were improved using a sigmoid relationship that starts decreasing vine transpiration around FTSW values of 0.6 and slowed down as FTSW values get close to zero. This research opens an interesting discussion about the existence or not of a unique response of vine transpiration to water stress.
Lopez, G., Juillion, P., Becel, C., Bourget, R., Chopard, J., Fumey, D., Guaus, A., Gelly, M. and Hublart, P. (2022). Using a decision support system (Vintel®) to determine the relationship between soil water content and whole-grapevine transpiration. Acta Hortic. 1335, 275-282
crop modeling, irrigation scheduling, plant physiology, precision agriculture, Vitis vinifera, water stress