Abstract
An ongoing study measuring grapevine (Vitis vinifera L., cv. Thompson Seedless) water use with a weighing lysimeter is being used to develop a model to simulate vine water use on both a diurnal and seasonal basis. A method to calculate the aerodynamic resistance (ra) of the vines was first determined. Subsequently, a model to predict canopy resistance (rc based solely upon intercepted photon flux density (PFD) was developed. The modeled values of ra and rcwere substituted into a resistance-energy balance equation to predict vine ET. The modeled parameters were validated against diurnal measurements of ET from the lysimeter. The greatest difference between modeled and measured rc occurred prior to 1000 h and subsequent to 1500 h each day. The model overestimated vine ET by 14 and 23% on 16 and 24 June, 1992, respectively. Ambient temperature and vapor pressure deficit were greater on 24 June than on 16 June. Refinements in calculating PFD interception by the vine's canopy early and late in the day and incorporating the effects of other environmental factors on grape stomatal conductance should improve the predictive capabilities of the model.
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