Assessing plant water status in Merlot vineyards using Worldview-3 multispectral images in central Spain

Water status in vineyards is a determining factor, given its relationship with productive and physiological parameters such as vegetative growth, berry ripening, yield and overall wine quality. In-field measurements, through a pressure chamber, provide very accurate and reliable measurements of midday stem water potential (Ψ_stem), a direct method for determining a plant’s water status by quantifying the tension with which water is retained in the leaf. Despite the robustness of this method, it is not practically applied to extensive commercial vineyards as it is a labour-intensive practice which can narrowly evaluate the significant intra-field variability. Remote sensing offers large-scale information at a single point in time without the need to be physically present in the field. This study aims to assess the use of multispectral imagery from Worldview-3, a commercial satellite, as a tool to indirectly estimate water status in the vineyard through different Vegetation Indexes (VI).

This research was carried out in a commercial Merlot vineyard in Yepes (Toledo), an arid area in central Spain where rainfall and irrigation water availability is scarce. The vines were established in 2002 and arranged on a trellis with a plantation spacing of 2.6 x 1.1 m. Five different irrigation doses were tested to obtain variability in vine water status. Drip irrigation emitters were identical in all treatments ( 2 l h^-1), but distances between emitters were adjusted to modify irrigation levels. Treatments were designed as follows: T1 (100% dose) emitters every 0.25 m, T2 (50%) emitters every 0.5 m, T3 (25%) emitters every 1.0 m, T4 (0%) no emitters and T5 (25%) underground emitters every 1.0 m. The results will be discussed in the context of deficit irrigation.