Using field spectrometry and a plant probe accessory to determine leaf water content in commercial vineyards

Vine water status is widely considered to be fundamental to grape yield and quality. Typical Mediterranean vineyards experience seasonal droughts so water deficits need to be controlled. We evaluated the usefulness and effectiveness of a field spectroradiometer used to estimate vine water content at the leaf and canopy levels. The experiment was conducted in four commercial vineyards located in the Bierzo region (northwestern Spain) on four different grape varieties (Mencía, Cabernet Sauvignon, Tempranillo and Merlot). Data on spectral measurements and leaf variables (total specific leaf fresh weight, equivalent water thickness and specific leaf weight) were compiled during the growth phase up to berry set and veraison in 2009 and 2012 and the relationship between leaf variables, vegetation indices and continuum removal variables was studied. The results varied depending on the variety; also, at canopy level they were not suitable for determining water content. Equivalent water thickness and total specific leaf fresh weight for Tempranillo and Mencía were related to the normalized difference infrared and shortwave infrared water stress indices. Using the continuum removal variables, the best correlations for equivalent water thickness were achieved for band area and maximum band depth calculated for the 1200nm, 1450nm and 1950nm intervals. To estimate vine water status, we recommend calculating the band area for 1450nm because of its link to equivalent water thickness (R2=0.681 for Tempranillo). We demonstrate that yield spectroradiometry is a rapid and non-destructive method for estimating leaf water content in commercial vineyard at leaf level.