Assessment of the possible interactions between soil and plant water status in a Vitis vinifera cv. Merlot vineyard

[摘要] ENGLISH ABSTRACT: Irrigation scheduling decisions are based either on the direct measurement of soil water status(SWS) or on physiological measurements like plant water status (PWS). Soil based measurementsare quick and easily automated, but the plant response for a particular quantity of soil moisturevaries as a complex function of evaporative demand.A plant-based approach measures the plant stress response directly, but is an integration ofenvironmental effects as well. In contrary to soil-based methods, plant based measurements canindicate when to irrigate, but not the quantity.Pre-dawn leaf water potential (ΨPD) is determined mostly by the soil moisture level, and can serveas a measure of static water stress in plants and an index of bulk soil water availability or even asan estimate of soil water potential at the root surface. Therefore it should be possible to establish alink between SWS and PWS, but it is largely unknown how stable the link in a heterogeneousvineyard would be, and how the grapevine vegetative and reproductive response relates to thislink.Plant water status plays a large role in determining vigour and yield of the plant. The levels of PWSare influenced by irrigation, but it was mostly affected by the season and vine location in thevineyard. More negative plant water potentials reduced vigour, but had a less pronounced effect onyield, while also reducing overall wine quality.Vigour variability in the vineyard was largely attributed to soil heterogeneity, which seemed to havea strong effect on SWS. SWS measurements were calibrated according to the observed variability,increasing the accuracy of measurements significantly. Soil water content values were used toestablish a link between SWS and PWS. This link was determined over time using nine plots,consisting of rain-fed and irrigated regimes, in variable vigour areas. A non-linear relationship wasfound between ΨPD and percentage extraction of plant available water for rain-fed plots. Whenirrigation was applied, no correlation could be found.In this study, for Merlot in the Stellenbosch region, PWS differences affected vigour, and to alesser extent yield, as well as wine quality. More negative plant water potentials reduced vigourmore in high vigour areas than in lower vigour areas, which in turn led to unbalanced vegetative:reproductive ratios. This disturbed vine balance may have had a bigger impact on wine quality thanPWS levels. Therefore a well-managed and balanced vine is able to withstand more stress, withless detrimental effects. This study also highlights the danger of limiting the assessment of soil andplant water status conditions to point measurements in vineyards with high levels of vigourvariability.

[发布机构] Stellenbosch University