S. Zolnier, R.S. Gates, R.G. Anderson, R.L. Geneve
Department of Biosystems and Agricultural Engineering and Department of Horticulture
University of Kentucky, Lexington KY USA 40546

Keywords: evapotranspiration, water conservation

Abstract:  Poinsettia cuttings were propagated under static and dynamic misting control techniques. The static control was based on a fixed on/off misting interval of 5 sec each 5 minutes. Static control was compared to two dynamic regimes, one based on evapotranspiration and the other based on an infrared sensor’s measurement of canopy surface temperature. These control techniques were evaluated in three environmentally controlled chambers. Poinsettia cuttings were subjected to several combinations of incident radiation and air vapor pressure deficit (VPD). Under dark conditions, four ranges of air VPD were used (0.8-1.1, 1.3-1.6, 1.8-2.1 and 2.3-2.6 kPa). Under light conditions, three levels of incident radiation (100, 200 and 300 W m-2) were combined with three ranges of air VPD (1.3-1.6, 1.8-2.1 and 2.3-2.6 kPa). An impressive reduction in water usage was observed in the chambers where poinsettia cuttings rooted normally and where misting was activated by either dynamic control technique. Under dark conditions, dynamic control decreased water use to 10 to 13% of water use by static control and under conditions of high light and high VPD, water use was decreased by 10% to 50%. Less water usage decreases costs, reduces runoff and should lessen disease problems during poinsettia propagation.

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