Plant water status: evaluating stress using soil-plant indices in Vitis vinifera cv. Mencía

Abstract

The aim of the research is to determine the water status of a vineyard of cv. Mencia under rainfed conditions and establish relationships between the different indicators of water stress. During the year 2012, we selected 10 vines of two different plots (Ladredo and Meixemán) located in the Ribeira Sacra (Doade-Lugo, Galicia) in NW Spain. The study area is characterized by steep slope viticulture (heroic viticulture) with strong insolation and non-irrigated. It is therefore important to evaluate the degree of water stress as a basis for producing quality products. Water status assessment was performed by combining measurements of soil water content (θ) with Time Domain Reflectometry (TDR-100) and several leaf water status indices at noon using  a water activity meter (WP4, Decagon Device Inc.). Leaf indices studied were: leaf water potential (Ψ), osmotic potential (Ψ_o) and  turgor pressure (P_t). The results showed the presence of intra- and inter-plot differences, and even differences between individual vines within the same terrace, where Ladredo appeared to have a higher water status (less stress) (0.116 m³ m^-3, Ψ= -1.66 MPa, Ψ_o=-2.29) than Meixemán (0.096 m³ m^-3, Ψ = -1.85 MPa, Ψ_o = -2.40). We found  a linear relationship between  leaf indices and soil water content, with the following adjustment coefficients (r²): Ψ vs θ: 0.91, Ψ_o vs θ: 0.91, Pt vs θ: 0.69. The establishment of these relationships will provide information about the actual water status of vineyards at  each moment of the season based on  measurements of soil water content and without having to resort to more difficult methods, such as water activity meters.