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  • Author or Editor: Glen H. Smerage x
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Abstract

A dynamic heat transfer model was developed for simulation of freeze protection of young citrus trees by tree wraps and microsprinkler irrigation. Heat exchange at the surface of the tree wrap was a function of heat input from irrigation and heat losses to evaporation, radiation, and convection. A finite difference form of a transient heat conduction equation was used to calculate rates of trunk temperature change as a result of heat exchange at the wrap surface. Predicted trunk temperatures were generally within 1 SE of observed means when simulating the effects of tree wraps without irrigation, with high correlation (r = 0.99) between observed and predicted minimum temperatures. When simulating the effects of microsprinkler irrigation combined with tree wraps, however, predicted trunk temperatures were generally 1° to 3°C lower than observed means (r = 0.81). Under-prediction of trunk temperature was attributed to underestimation of sensible heat transfer from the irrigation water and/or inaccuracies in parameters associated with irrigation. The behavior of the real and model systems was qualitatively similar in a majority of validation trials. Thus, the simulation model could be used to analyze factors affecting freeze protection.

Open Access

Abstract

Computer simulation was used to study factors affecting freeze protection of young citrus trees using tree wraps and microsprinkler irrigation. Simulation results suggest tree wraps provide 1° to 2°C more freeze protection when air temperature decreased linearly rather than exponentially with time toward a minimum value. Tree wraps provided greater freeze protection when air temperature decreased rapidly (0.75°/hr) than slowly (0.5° or 0.25°/hr). Thus, variation in rate and pattern of air temperature decrease among freeze nights may be responsible for inconsistent levels of freeze protection observed with tree wraps. Changing irrigation water temperature from 12° to 7° or 17° produced changes in trunk temperature under radiative, but not advective, freeze conditions. Simulated positioning of the microsprinklers to maximize coverage of the wrap surface with water provided better freeze protection than positioning that resulted in increased water interception. Increasing windspeed from 0 to 10 m·s−1 reduced temperature of an irrigated wrapped trunk by 5°. Without irrigation, temperature of a wrapped trunk was largely unaffected by windspeed. Reducing humidity from 80% to 20% had a negligible effect on trunk temperature of irrigated wrapped trees under radiative and advective freeze conditions.

Open Access