Abstract
The increasing water shortages are leading to develop new tools to better manage irrigation monitoring and scheduling for high water use efficiency. This results in a need of systems for rapid water status monitoring to better manage crop and irrigation scheduling for a high water use efficiency.
The objective of this preliminary work was to predict the grapevine water status in a rapid and non-destructive way using two portable optical devices (vis/NIR, 400-1000 nm; and NIR, 1000-2000 nm) for measurements directly on the leaves.
The measurements were performed on 72 leaf samples (cv. Cabernet Sauvignon) in a glasshouse under environmental controlled conditions (temperature and relative humidity). As references, a Scholander pressure chamber was used to measure the leaf water potential (Ψ) immediately after spectral acquisitions. Measurements were made around midday (10.00 to 14.00 hours, solar time) on three leaves for each plant chosen from the mid-upper part of the canopy. Moreover, the leaf total water content was quantified weighing each fresh leaf sample before the water potential measurement and after the drying process.
Principal component analysis (PCA) was performed on vis/NIR and NIR spectra to examine sample groupings, and partial least square (PLS) regression algorithm was used to correlate samples spectra and reference data. Regarding the vis/NIR results, PLS models showed for the prediction of leaf water potential Rcv2= 0.67 and RPD = 1.7, and for the prediction of total water content Rcal2 = 0.72 and RPD = 1.9. Slightly better results were obtained for NIR spectroscopy; PLS models achieved good prediction performance for total water content (Rcv2= 0.91 and = 3.4) and acceptable results for leaf water potential (Rcal2 = 0.63 and RPD = 1.8).
The study could provide the sector with portable optical systems for a quick evaluation of grapevine water status directly in field. Therefore, vis/NIR and NIR spectroscopy might support winegrowers for prompt decisions about the irrigation scheduling.
