Predicting Canopy Temperatures without and with Infrared Heating of Open-Field Plots and Energy Requirements for Such Infrared Heating.

In order to determine the likely effect of global warming on agricultural productivity while avoiding experimental artifacts, there is a need to conduct warming research under conditions that are representative of future open fields, i.e., temperature free-air controlled enhancement (T-FACE) experiments. One promising approach is to deploy arrays of infrared (IR) heaters over experimental plots. However, in order to plan such IR field experiments, it is desired to predict the consequent vegetation canopy temperatures and the costs for electrical (or other) energy needed to achieve the warming. The first step is to calculate the canopy temperature of ambient reference plots with no heating, Tcr. The second step, albeit tiny, is to set the temperature of the heated plot, Tch, equal to Tcr plus the desired degree of warming. The third step to compute how much more thermal radiation from IR heaters would be required to balance the surface energy flows of the heated plot. Fourth, if the IR radiation requirement computed from Step 3 exceeds the capacity of the IR heater system, then Step 1 needs to be repeated but with the maximum heater radiation imposed. Prediction of the canopy temperatures using an energy balance approach requires an accurate method for determining aerodynamic and canopy resistances to sensible and latent heat transfer. Several such approaches exist in the literature, which were tested against data from a 2-year Hot Serial Cereal T-FACE experiment on wheat at Maricopa, Arizona.