Leaf reflectance response to deficit irrigation in olive trees

Multispectral signatures from leaves at different spectral bands are increasingly used for characterize plants and their response to biotic and abiotic environmental factors.
As the increase of water scarcity and consequent adoption of deficit irrigation treatments, this type of analysis can be useful for monitoring the water status of the plants.
Therefore, the aim of this work is to assess the influence of different irrigation treatments on reflectance to VIS-NIR radiation of olive leaves (Olea europaea L, ‘Cobrançosa’). The study was conducted in an olive orchard located in Alfândega da Fé (northeast of Portugal), under five irrigation treatments: full-irrigated (FI) with 100% of estimated Evapotranspiration (ET), sustained deficit irrigation (SDI60 and SDI30 of ET) and regulated deficit irrigation (RDI100 and RDI60 of ET). Reflectance (RVIS-NIR) was evaluated using a near infrared spectroscopy (400-1000 nm) in 15 leaves from five random olive trees of each irrigation strategy.
The measurements were performed in the middle of June, before irrigation cut off; in cut off irrigation period (OFF; during pit hardening); after shift irrigation (third week of August) and in late irrigation period (LI; early autumn). The results showed that in all sampling dates, leaves from FI had lower RVIS-NIR than deficit irrigation treatments with differences found in VIS spectrum (540-590nm) and in the near infrared spectrum (740-820 nm). However, no significant differences were observed in radiation wavelength absorbed by photosynthetic pigments (420-500 and 610-720 nm), except in OFF and LI periods in which SDI30 and RDI60 had higher RVIS-NIR at 610-720 nm.
The most discriminatory reflectance difference between FI and deficit irrigations was verified in SDI30 and RDI at OFF and LI irrigation, where SDI30 had an increase of 28% at 760 nm when compared with FI values.
In these periods, the relative water content (RWC) was 92, 86, 76, 85 and 70% for FI, SDI60, SDI30, RDI100 and RDI60 respectively.
We also observed a relationship between mean reflectance at different wavelength with RWC and ΨMD, especially in the mean green reflectance.
Thus, multispectral reflectance appears as useful and potential strategy to monitor water status and a promising tool for irrigation management.

IV International Symposium on Horticulture in Europe – SHE2021

P. Marques, L. Canas, A. Fernandes-Silva

irrigation management, precision agriculture, spectroscopy

https://doi.org/10.17660/ActaHortic.2021.1327.82