COMPARISON OF A STANDARD CLIMATIC REGIME AND A 24-HOUR TEMPERATURE INTEGRATION REGIME IN POT PELARGONIUM CULTURE

The production of pelargonium occurs between February and May, this period of the year is favourable to a temperature integration (TI) regime. From 2009 to 2011, trials were carried out in two identical, 90 m²-sized greenhouses, to evaluate the energy saving potential of the TI and to measure its effects on plants. Temperature integration is based on the plants’ capacity to tolerate variations around an optimum temperature. The excess of solar energy during sunny days is compensated by decreasing consequently the night setpoint temperature. Pelargonium were grown either under a standard regime with fixed setpoints (T_night: 12°C, T_day: 15°C, T_ventilation: 18°C), or under a TI-regime (5°Cnight<12°C, T_day: 15°C, 18°Cventilation<23°C depending on radiation). The objective was to obtain similar average temperatures over a 24-h period in the two greenhouses. TI started at rooting. The following measurements and counts were made: length of the main stem, number of open flowers, fresh and dry weight of the aerial part. Energy consumption was monitored with thermal energy meters (Multical^® 601 by Kamstrup) with Pt 500 sensors, located at the entry of each greenhouse. The same average temperature over a 24-h period was achieved with a difference of 0.1 to 0.3°C between the two regimes. In 2009, the energy saved with TI was low (2.5%). In 2010 and 2011, the temperature increase speed was reduced to 1°C/h in the TI greenhouse. With this change, energy saving of TI reached 32% in 2010 and 40% in 2011. The percentages are high but represent only 10 kWh/m². Depending on the year and cultivar, the main stem elongation was significantly higher with TI, but TI had no effect on the flowering, fresh and dry weight.