Estimation of Water Stress in Grapevines Using Proximal and Remote Sensing Methods

Abstract

Abstract:In light of climate change and its impacts on plant physiology, optimizing water usage and improving irrigation practices play a crucial role in crop management. In recent years, new optical remote sensing techniques have become widespread since they allow a non-invasive evaluation of plant water stress dynamics in a timely manner. Unmanned aerial vehicles (UAV) currently represent one of the most advanced platforms for remote sensing applications. In this study, remote and proximal sensing measurements were compared with plant physiological variables, with the aim of testing innovative services and support systems to farmers for optimizing irrigation practices and scheduling. The experiment, conducted in two vineyards located in Sardinia, Italy, consisted of two regulated deficit irrigation (RDI) treatments and two reference treatments maintained under stress and well-watered conditions. Indicators of crop water status (Crop Water Stress Index-CWSI-and linear thermal index) were calculated from UAV images and ground infrared thermal images and then related to physiological measurements. The CWSI values for moderate water deficit (RDI-1) were 0.72, 0.28 and 0.43 for 'Vermentino', 'Cabernet' and 'Cagnulari' respectively, while for severe (RDI-2) water deficit the values were 0.90, 0.34 and 0.51. The highest differences for net photosynthetic rate (Pn) and stomatal conductance (Gs) between RDI-1 and RDI-2 were observed in 'Vermentino'. The highest significant correlations were found between CWSI with Pn (R = −0.80), with Φ PSII (R = −0.49) and with Fv'/Fm' (R = −0.48) on 'Cagnulari', while a unique significant correlation between CWSI and non-photochemical quenching (NPQ) (R = 0.47) was found on 'Vermentino'. Pn, as well as the efficiency of light use by the photosystem II (PSII), declined under stress conditions and when CWSI values increased. Under the experimental water stress conditions, grapevines were able to recover their efficiency during the night, activating a photosynthetic protection mechanism such as thermal energy dissipation (NPQ) to prevent irreversible damage to the photosystem. The results presented here demonstrate that CWSI values derived from remote and proximal sensors could be valuable indicators for the assessment of the spatial variability of crop water status in Mediterranean vineyards.

A Review of Current and Potential Applications of Remote Sensing to Study the Water Status of Horticultural Crops

“…In the context of precision agriculture, the application of UAS, their future prospects, and knowledge gaps are discussed in [53,[78][79][80][81]. While many horticultural crops have been studied using UAS technology, the most studied horticultural crops are vineyards [31,[82][83][84], citrus [85,86], peach [32,33], olive [18,87,88], pistachio [89,90], and almond [91][92][93][94], among others [95][96][97][98][99]. Some of the UAS types used for water status studies of horticultural crops are shown in Figure 2.…”

“…Thus, such stress is reflected in the vegetation profile and easily captured by indices, such as NDVI. For this reason, NDVI has shown correlations with a wide array of crops response including vigour, chlorophyll content, leaf area index (LAI), crop water stress, and occasionally yield [34,[82][83][84]127]. The rededge band covers the portion of the electromagnetic spectrum between the red and NIR bands where reflectance increases drastically.…”

“…A crop's biophysical and biochemical attributes can be approximated using different indices and quantitative products. For example, CWSI is used to proxy leaf water potential (Ψ leaf ), stem water potential (Ψ stem ), g s , and net photosynthesis (P n ) [83,100,195]. With regard to horticultural crops, water status has been assessed using a number of spectral and thermal indices ( Table 2).…”

Evaluating Remotely-Sensed Grapevine (Vitis vinifera L.) Water Stress Responses Across a Viticultural Region

“…The advantage of the remote sensing approach is that large areas can be rapidly profiled obviating the need for a large number of measurements of individual vines that are time-and labour-intensive [18,25,26]. With the advent of high-resolution thermal cameras, sub-meter spatial resolution is now feasible from airborne platforms [27] allowing for the characterisation of water status of sub-blocks and even individual vines. Using an Unmanned Aerial Vehicle (UAV), Zarco-Tejada and co-workers evaluated a multispectral and thermal index and found a strong correlation with both g s and Ψ l in 'Thompson Seedless' grapevines in California [24].…”

“…Bellvert and colleagues mapped CWSI across an 11-ha Pinot Noir vineyard in Spain, finding a stronger correlation between CWSI and Ψ l at solar noon (1230 h) than in the morning (0930 h) [18]. Recently, Matese and co-workers determined CWSI and I g values under various irrigation regimes in two Italian vineyards planted with CAS and 'Cagnulari' [27]. All of the above-mentioned studies were undertaken using UAV platforms, which are limited by range (flight time) and therefore not suited to characterising entire viticultural regions or even large vineyard blocks.…”