Fluorescence, PRI and canopy temperature for water stress detection in cereal crops

Narrow-band multispectral remote sensing techniques and thermal imagery were investigated for waterstress detection in cereal crops. Visible and near infrared AISA Eagle (Specim, Finland) and thermal AHS-160 (Sensytech Inc., USA) imageries were acquired with an airborne survey on a farm-level experimentalsite where maize (Zea mays L.) and sorghum (Sorghum bicolor L.) were grown with three different irrigationtreatments. Vegetation biophysical and eco-physiological measurements were collected concurrentlywith the airborne campaign. Leaf fluorescence yield ( F/Fm ) resulted to be a good indirect measureof water stress. Therefore, F/Fm measurements were compared against remotely sensed indicators:(i) the Photochemical Reflectance Index (PRI), (ii) the sun-induced chlorophyll fluorescence at 760 nm(F760), retrieved by the Fraunhofer line depth method and (iii) the canopy temperature (TC) calculateddecoupling soil and vegetation contributions. TCwas related to F/Fm with the highest determinationcoefficient (R2= 0.65), followed by PRI586(reference band at 586 nm) (R2= 0.51). The relationship withF760was significant but weaker (R2= 0.36). The coefficient of determination increased up to 0.54 whenpigment concentration was considered by multiplying F/Fm and chlorophyll content, confirming theclose relationship between passive fluorescence signal, pigment content and light photosystem efficiency.PRI586, F760and TCmaps were produced in maize and sorghum plots. The differences in the averagevalues of PRI586, F760and TCextracted from the plots with different water treatments showed that watertreatments were well discriminated in maize plots by the three remotely sensed indicators. This wasconfirmed by the visual observation of the PRI586, F760and TCmaps, while in sorghum plots, F760and TCappeared more sensitive to water stress compared to PRI586.