Airborne Thermal Imagery to Detect the Seasonal Evolution of Crop Water Status in Peach, Nectarine and Saturn Peach Orchards

Abstract

In the current scenario of worldwide limited water supplies, conserving water is a major concern in agricultural areas. Characterizing within-orchard spatial heterogeneity in water requirements would assist in improving irrigation water use efficiency and conserve water. The crop water stress index (CWSI) has been successfully used as a crop water status indicator in several fruit tree species. In this study, the CWSI was developed in three Prunus persica L. cultivars at different phenological stages of the 2012 to 2014 growing seasons, using canopy temperature measurements of well-watered trees. The CWSI was then remotely estimated using high-resolution thermal imagery acquired from an airborne platform and related to leaf water potential (Ψ L ) throughout the season. The feasibility of mapping within-orchard spatial variability of Ψ L from thermal imagery was also explored. Results indicated that CWSI can be calculated using a common non-water-stressed baseline (NWSB), upper and lower limits for the entire growing season and for the three studied cultivars. Nevertheless, a phenological effect was detected in the CWSI vs. Ψ L relationships. For a specific given CWSI value, Ψ L was more negative as the crop developed. This different seasonal response followed the same trend for the three studied cultivars. The approach presented in this study demonstrated that CWSI is a feasible method to assess the spatial variability of tree water status in heterogeneous orchards, and to derive Ψ L maps throughout a complete growing season. A sensitivity analysis of varying pixel size showed that a pixel size of 0.8 m or less was needed for precise Ψ L mapping of peach and nectarine orchards with a tree crown area between 3.0 to 5.0 m 2 .

Selecting Canopy Zones and Thresholding Approaches to Assess Grapevine Water Status by Using Aerial and Ground-Based Thermal Imaging

“…Some authors proposed that phenological stages could have affected the CWSI accuracy of water stress prediction. Möller et al [26] found that in vineyards at the end of the growing season, leaves were in a senescence condition and may not have been representative of complete canopy conditions, and Bellvert et al [39] found differences between varieties and the phenological stage in vineyards, as well as peach and nectarine orchards [41].…”

Plant-Based Methods for Irrigation Scheduling of Woody Crops

“…Still, the method has been mostly used for research purposes only. Recently, however, the development of both cheaper image acquisition systems and user-friendly, powerful data image processing packages has substantially increased the potential of the method for irrigation scheduling in commercial orchards [55,56]. Thermal readings can be made both at the plant level (ground-based imagery) [55,57] and from above the crop (airborne imagery), after installing the sensors on towers or cranes [58,59], on unmanned aerial vehicles (UAVs), also known as remote piloted aerial systems (RPAS) [60], planes [61] or satellites [62,63].…”

“…Ground-based and airborne thermal images can be combined to assess within-orchard spatial heterogeneity in water status, as demonstrated with grape [64] and olive plants [65]. The principles of thermal sensing are described elsewhere [66,67] and nice examples on both the linking between thermal imaging to main physiological indicators [68] and the use of thermal imaging for irrigation scheduling [56,60,66,69] can be found in the literature.…”

“…Most authors using thermal images taken from UAVs and planes reported robust relationships between the derived CWSI and main physiological variables related to water stress, such as stomatal conductance and stem or leaf water potential [56,64,65], and claimed that the approach was suitable for characterizing plant water status variability in woody crops. Remote sensing data acquired by satellite sensors can be used to derive daily evapotranspiration (ET) maps.…”

Remote Sensing for Irrigation of Horticultural Crops

“…Recently, Bellvert et al [172] measured the CWSI in three peach cultivars (Prunus persica L.) throughout different growing seasons. They measured the canopy temperature of well-watered trees using high-resolution thermal imagery obtained from an airborne platform and related it to leaf water potential (ψ L ) as a water stress indicator.…”