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Abdulelah Al-Faraj, George Meyer, and Jay B. Fitzgerald

A plant-based temperature control system for infrared heating to maintain the plant canopy at a desired temperature was evaluated under growth chamber conditions with possible projections to greenhouse environment. Benefits for using this system includes energy saving and plant protection. Infrared radiant heaters raised canopy temperatures to the optimum range which increased water use of New Guinea Impatiens over the same kind of plants grown with no radiant heat. Plant water use was 118% higher at an 18°C air temperature vs. 8°C air temperature and 33% higher at 24°C air temperature vs. 18°C air temperature. The degree of increase in plant water use was proportional to decrease (leaf air) temperature. The Penman-Monteith equation gave satisfactory results when the differential between leaf and air temperature was very low. At high (leaf-air) temperature deviation, the latent heat equation used to estimate stomatal resistance gave higher values for heated plants.

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Kyle R. Mankin and R. Peter Fynn

Nutrient uptake by New Guinea impatiens (Impatiens X hb.) `Equinox' was measured in a growth chamber under various combinations of light [photosynthetic photon flux (PPF)], air temperature, and nutrient solution concentration. Nitrate-N, P, K, Ca, and Mg ions were evaluated individually by measuring depletion of each nutrient from a constant-volume solution over 9 hours with constant environmental conditions. Individual nutrient uptake was not correlated to concurrent daily temperature environment, and only K and Mg showed a correlation with PPF. Uptake rates of N, P, K, Ca, and Mg increased significantly with increasing nutrient solution concentration. Estimated net assimilation rates of nutrients, based on measured shoot tissue concentrations of each nutrient and assuming that uptake occurred continuously at a rate proportional to canopy area, were correlated to average measured uptake rates for N, Ca, and Mg and were not correlated to average uptake rates for P and K. Although nutrient demand from plant growth may determine rates of nutrient uptake necessary over longer periods of time, short-term uptake was not related directly to daily fluctuations in environmental factors.