Non-water-stressed baseline as a tool for dynamic control of a misting system for propagation of poinsettias

A technique is presented for dynamically adjusting misting intervals during propagation of vegetative cuttings. A crop setpoint temperature for activation of misting was defined by a "non-water-stressed baseline" concept, using infrared thermometry to acquire canopy temperature for plant feedback. The critical crop setpoint temperature was calculated from instantaneous values of air temperature, incident radiation, and air vapor pressure deficit (VPD_air). Misting was activated when the actual crop temperature exceeded the critical crop setpoint temperature. The dynamic control was shown to have the potential to reduce the amount of applied water from 9 to 12 times during low levels of VPD_air (0.8 to 1.1 kPa) and under dark conditions when compared to a conventional on/off misting interval of 5 s each 5 min. In addition, misting intervals were reduced three-fold, from 30 to 11 min, when incident radiation increased from 0 to 100 W m^-2 and VPD_air was maintained in the range from 2.3 to 2.6 kPa. Further increases in radiation levels from 200 to 300 W m^-2 did not appreciably change the misting frequency. The dynamic misting control provides a large potential for increasing the period between misting events under dark conditions and with low to moderate levels of incident radiation. It automatically increases misting frequency as VPD_air and/or radiation increase.