Estimation of midday stem water potential in grapevine leaves (‘Cabernet Sauvignon’) using spectral reflectance indices

Water scarcity and the new production objectives put pressure on agriculture to make efficient use of water. For this, constant monitoring of physiological variables is required, which is commonly done using midday stem water potential (MSWP). However, this measurement in large areas is limited by the inability of performing a large number of measurements, meaning low spatial resolution and time consumption. As an alternative, the use of spectral reflectance (SR) is proposed, through the SR indices, which are based on the interaction between the visible (VIS), near infrared (NIR) and shortwave infrared (SWIR) regions of the electromagnetic spectrum. In order to develop correlations between SR indices (over 74) and MSWP, a study was conducted in a 5-year-old drip irrigated ‘Cabernet Sauvignon’ vineyard located in the Pencahue Valley, Chile, during 2018-19 season. In each experimental unit, measurements of MSWP and spectral signature with a pressure chamber and portable spectroradiometer were done, respectively. The indices that best correlated with MSWP were PRI_CI, PRI2 and NDSI40, with R² values of 0.57, 0.44 and 0.44, respectively.