Simulated water use and canopy resistance of New Guinea impatiens (Impatiens X hb.) in single pots using infrared heating

Abstract

A plant-based temperature, infrared thermometer (IRT) control system was tested for a prototype greenhouse infrared heating system, using water use and canopy resistance of New Guinea Impatiens as performance indicators. Infrared heaters were used to raise canopy temperature of New Guinea Impatiens to a literature-based optimum level, which resulted in higher daily water use than plants receiving no radiant heat. The increase in plant water use was proportional to the decrease in the leaf-air temperature difference. Plants with canopy temperature close to 24°C had increased water use of 118%, when air temperature was increased from 8° to 18°C, and 33% when the air temperature was increased to 24°C. A modified Monteith equation using canopy temperature predicted evapotranspiration very well, especially when the leaf air temperature difference was 6°C or less. Canopy resistance values were predicted to be higher for heated plants at higher leaf-air temperature differences and vapor pressure deficits (VPD) using a separate canopy energy analysis.