Dynamic misting control techniques for poinsettia propagation.

摘要

This study presents the theoretical development and validation of two novel techniques for dynamically adjusting misting intervals during poinsettia (Euphorbia pulcherrima ‘Freedom Dark Red’ Willd. ex Klotzsch) propagation, namely, temperature based misting control and evapotranspiration based misting control. For the temperature based misting control, the “non-water-stressed baseline” concept was used to define a dynamic setpoint for misting control while plant feedback was monitored with an infrared thermometer. In the second method, the dynamic setpoint was determined by an equivalent canopy surface resistance to evapotranspiration (ET), which included the combined effects of stomatal resistance, water uptake resistance, propagation medium resistance and crop adaxial surface resistance. Mist was triggered when the measured crop temperature or estimated canopy surface resistance increased above a threshold value.; To calibrate the two misting control techniques, a series of controlled experiments were performed on fully rooted, rooted, partially rooted and unrooted poinsettia cuttings. The environmental system provided independent control of incident radiation, R_i, (0 to 300 WM−2) and air vapor pressure deficit, VPD_air, (0.5 to 2.5 kPa). After obtaining the required parameters, a comparative analysis was performed between a conventional static misting control (5 min OFF and 5 sec ON) and the two dynamic misting controls proposed in this study.; Misting intervals were shown to be sensitive to both R_i and VPD_air. An impressive reduction in water usage was observed in the chambers where misting was activated by either dynamic control technique. Under dark conditions and low VPD_air, the ET and the temperature based misting control required 10 and 8 times less water, respectively, compared to the static misting control. When plants were subjected to incident radiation of 300 Wm−2 and VPD_air of 1.8–2.1 kPa, water usage by both dynamic control techniques was about 50% of the static approach. Leaf temperatures were lower for plants propagated under static misting control. All poinsettia cuttings were successfully rooted in all misting control systems. Root dry matter and relative water content of poinsettia leaves were not affected significantly by misting control techniques. Both dynamic misting control methods proved to be promising alternatives for drastically reducing water usage during propagation of poinsettias and consequently, decreasing the quantity of runoff.