JXB Advance Access originally published online on September 12, 2006
Journal of Experimental Botany 2007 58(4):827-838; doi:10.1093/jxb/erl115
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Field Applications for Stress Monitoring |
Use of thermal and visible imagery for estimating crop water status of irrigated grapevine*
1Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization (ARO), The Volcani Center, PO Box 6, 50250 Bet Dagan, Israel
2Institute of Agricultural Engineering, Agricultural Research Organization (ARO), The Volcani Center, PO Box 6, 50250 Bet Dagan, Israel
3Crop Ecology Laboratory, Migal, PO Box 831, 11016 Kiryat Shmona, Israel
4Golan Research Institute PO Box 97, 12900 Katzrin, Israel
5The J Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Sede-Boker Campus 84990, Israel
To whom correspondence should be addressed. E-mail: marmoeller{at}yahoo.de
Achieving high quality wine grapes depends on the ability to maintain mild to moderate levels of water stress in the crop during the growing season. This study investigates the use of thermal imaging for monitoring water stress. Experiments were conducted on a wine-grape (Vitis vinifera cv. Merlot) vineyard in northern Israel. Irrigation treatments included mild, moderate, and severe stress. Thermal and visible (RGB) images of the crop were taken on four days at midday with a FLIR thermal imaging system and a digital camera, respectively, both mounted on a truck-crane 15 m above the canopy. Aluminium crosses were used to match visible and thermal images in post-processing and an artificial wet surface was used to estimate the reference wet temperature (Twet). Monitored crop parameters included stem water potential (
stem), leaf conductance (gL), and leaf area index (LAI). Meteorological parameters were measured at 2 m height. CWSI was highly correlated with gL and moderately correlated with stem. The CWSI-gL relationship was very stable throughout the season, but for that of CWSI-stem both intercept and slope varied considerably. The latter presumably reflects the non-direct nature of the physiological relationship between CWSI and stem. The highest R2 for the CWSI to gL relationship, 0.91 (n=12), was obtained when CWSI was computed using temperatures from the centre of the canopy, Twet from the artificial wet surface, and reference dry temperature from air temperature plus 5 °C. Using Twet calculated from the inverted Penman–Monteith equation and estimated from an artificially wetted part of the canopy also yielded crop water-stress estimates highly correlated with gL (R2=0.89 and 0.82, respectively), while a crop water-stress index using ‘theoretical’ reference temperatures computed from climate data showed significant deviations in the late season. Parameter variability and robustness of the different CWSI estimates are discussed. Future research should aim at developing thermal imaging into an irrigation scheduling tool applicable to different crops.
Key words: Canopy temperature, CWSI, energy balance, infrared thermography, irrigation scheduling, stem water potential, stomatal conductance, Vitis vinifera
* Contribution No. 610/06 from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel.
Received 1 May 2006; Accepted 5 July 2006
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