Agricultural Water Management 156 (2015) 43–50 Contents lists available at ScienceDirect Agricultural Water Management jou rn al hom ep age: www.elsevier.com/locate/agwat Using field spectrometry and a plant probe accessory to determine leaf water content in commercial vineyards Ana Belén González-Fernández a,∗ , José Ramón Rodríguez-Pérez a , Victoriano Marcelo b , José B. Valenciano c a Geomatics Engineering Research Group, University of León, Av. Astorga s/n, 24401 Ponferrada, León, Spain b Department of Agrarian Engineering and Sciences, University of León, Av. Astorga s/n, 24401 Ponferrada, León, Spain c Department of Agrarian Engineering and Sciences, University of León, Av. Portugal 41, 24071 León, Spain a r t i c l e i n f o Article history: Received 20 September 2014 Accepted 30 March 2015 Keywords: Plant probe Water leaf content Reflectance Field spectroradiometer Continuum removal analysis Vegetation indices a b s t r a c t Vine water status is widely considered to be fundamental to grape yield and quality. Typical Mediter- ranean 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, Tem- pranillo 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 1200 nm, 1450 nm and 1950 nm intervals. To estimate vine water status, we recommend calculating the band area for 1450 nm because of its link to equivalent water thickness (R 2 = 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. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Controlling vine humidity levels is crucial to producing quality wines. An indirect method for measuring vine water content is to measure leaf water content (Kennedy et al., 2002). Mediterranean vineyards typically do not use irrigation systems but depend on Abbreviations: A, area of the three leaf disc; BA, band area; CR, continuum removal; DM, leaf dry weight (g); EWT, equivalent water thickness (kg/m 2 ); FM, leaf fresh weight (g); fWBI, floating position water band; FWHM, full width at half maximum; MBD, maximum band depth; NDII, normalized difference infrared index; NDVI, normalized difference vegetation index; NDWI, normalized difference water index; SIWSI, shortwave infrared water stress index; SLW, specific leaf weight (kg/m 2 ); SRWI, simple ratio water index; TSLW, total specific leaf fresh weight (kg/m 2 ); VI, vegetation index; WI, water index. ∗ Corresponding author. Tel.: +34 987 442000; fax: +34 987442070. E-mail addresses: agonf@unileon.es (A.B. González-Fernández), jr.rodriguez@unileon.es (J.R. Rodríguez-Pérez), v.marcelo@unileon.es (V. Marcelo), joseb.valenciano@unileon.es (J.B. Valenciano). climatic conditions and this explains why vines may experience water stress. Since water stress modifies the pigment composition of vine leaves (Flexas et al., 2010), reduces content in biochemical elements, turgor and total water potential and, in general, nega- tively affects plant growth; measuring leaf water content provides information on vine water content. Severe water stress reduces leaf area and, consequently, reduces photosynthesis and affects metabolism, resulting in stunted growth (Lisar et al., 2012) or even vine death (Shao et al., 2008). Leaf water content variations affect grape composition, must quality (Serrano et al., 2010) and yield (Leeuwen et al., 2009). Although a certain amount of water stress after veraison increases must quality (Chaves et al., 2010), water needs must particularly be met during and after bloom. In the period between bloom and veraison, water stress reduces must sugar content, with the resulting low alcohol content reflected in poor quality wines (Leeuwen et al., 2009). Mild water deficits have an impact on berry size, development and composition by increasing content in the tannins and anthocyanins that deter- mine wine quality. In fact, deficit irrigation is a strategy to improve http://dx.doi.org/10.1016/j.agwat.2015.03.024 0378-3774/© 2015 Elsevier B.V. All rights reserved.