SIMULATED WATER-USE AND CANOPY RESISTANCE OF NEW-GUINEA IMPATIENS (IMPATIENS X HB) IN SINGLE POTS USING INFRARED HEATING

A plant-based temperature, infrared thermometer (IRT) control system w as tested for a prototype greenhouse infrared heating system, using wa ter use and canopy resistance of New Guinea Impatiens as performance i ndicators. Infrared heaters were used to raise canopy temperature of N ew Guinea Impatiens to a literature-based optimum level, which resulte d in higher daily water use than plants receiving no radiant heat. The increase in plant water use was proportional to the decrease in the l eaf-air temperature difference. Plants with canopy temperature close t o 24 degrees C had increased water use of 118%, when air temperature w as increased from 8 degrees to 18 degrees C, and 33% when the air temp erature was increased to 24 degrees C. A modified Monteith equation us ing canopy temperature predicted evapotranspiration very well, especia lly when the leaf-air temperature difference was 6 degrees C or less. Canopy resistance values were predicted to be higher for heated plants at higher leaf-air temperature differences and vapor pressure deficit s (VPD) using a separate canopy energy analysis.