By dosing lilies with CO2 the light level can be reduced by one third while the quality remains the same. This conclusion was made by researchers who carried out trials with lighting in 2013 and 2014. However, growers wanted further confirmation because for years they have grown lilies under high light levels without any CO2-dosing. A trial carried out in June 2015 should remove any doubt. And the results bring further good news. Even more energy savings appear possible.
It is unusual. While CO2-dosing is the norm for most greenhouse crops in the Netherlands it is hardly used in the country’s 200 ha of artificially-lit lily production. In the past, research institute, PPO, showed that it had no effect on bloom weight, especially in the group of Orientals.
These findings appear to disagree with the results of photosynthesis measurements made by plant physiologists Sander Hogewoning and Govert Trouwborst of Plant Lighting and researchers at Plant Dynamics in 2012/2013. The Dutch specialists showed that photosynthesis significantly increased by dosing CO2 at 800 to 900 ppm. This insight was the reason for a greenhouse trial in 2013/2014. The trial showed that the duration of the lily crop, for both LAs and Orientals, was the same at 60 μmol SON-T lighting with CO2-dosing as with 90 μmol SON-T without CO2, which is the current practise in lily production.
Search for lower limit
To confirm these results and dig somewhat deeper, it was decided, together with the supervisory committee to carry out further research on two consecutive crops. “You have to bear in mind that for years growers have been told that CO2 on Orientals does not work. Therefore they want assurance. For us it was also important to know the lower limit for lighting with respect to quality and cropping duration,” says Hogewoning.
Trouwborst adds: “Growers wanted confirmation that lighting with 60 μmol leads to worse performance than lighting with 60 μmol and CO2. The first option was not taken into account during the previous trial. Only then can you be sure that the effect is due to the dosing.”
The research took place between October 2014 and March 2015 at the Improvement Centre in Bleiswijk, the Netherlands. As well as the two plant physiologists a large number of other experts were involved.
The researchers ran seven treatments on two crops in three trial greenhouses of 144 m2. The varieties on trial were Brindisi (LA), Robina (OT), Santander (Oriental) and White Heaven (Longiflorum) with a crop change in mid December. In greenhouse 1 three light levels of 45, 60 and 90 μmol/m2/s SON-T were combined without CO2-dosing; greenhouse 2 maintained the same light levels with 800 ppm CO2. The temperature regime was the same as that used in practise: ventilate at 17ºC and heat from 15ºC.
Set up to save 50%
Greenhouse 3 tested the so-called total concept for energy savings, which aimed to save 50% on energy. Earlier results in the area of energy savings were incorporated in one crop. “If you add up how much these measures can contribute, it is substantial,” says Hogewoning.
The first measure was to compensate the lower light intensity with CO2-dosing. The second was switching off the lights earlier when there was sufficient natural radiation. The third measure was to permanently switch off 40% of the lamps for several weeks at the beginning and end of the cultivation period. Hogewoning explains why: “The plant’s requirement for assimilates follows an S-curve. There is a high requirement in the middle of the cultivation period. Then you have to give plenty of light. But the plant needs far fewer assimilates at the start and at the end so you can turn the lights off.”
The fourth measure is temperature integration: ventilate later when the radiation is high and maintain a lower heating temperature at lower radiation. In this way the temperature, depending on the light intensity, can rise to 23ºC, but at low radiation the heating only comes on at 13ºC. However, the minimum night temperature remains at 15ºC to prevent too much stretching.
Good all round
In all treatments the effects on flower bloom weight, dry weight, stem length, weight/cm, turgidity, bud quality, cropping duration, bulb weight and vase life of the four different varieties were measured. The results of the first crop – from begin October to the beginning of December – were good in all respects. Light and CO2 had a positive effect on bloom weight. Only when the lighting was 45 μmol without any CO2 the blooms lighter in weight.
The researchers saw hardly any softening of flower stems; the only exception was the variety Brindisi at 45 μmol without CO2. “Also in greenhouse 3, which saved a lot of energy, good results were achieved across the board,” explains Hogewoning about the figures. “Certainly the good autumn meant there was a lot of natural light. Due to the high level of radiation we could allow the temperature in greenhouse 3 to be higher,” adds Trouwborst.
60 μmol with CO2 in winter
There was some concern about the second crop, from mid December to the beginning of March. How would the varieties cope with a lower level of natural light?
The results were similar to the first crop. But whereas during the first crop 45 μmol with CO2 was sufficient (except for Brindisi), in the second crop 60 μmol with CO2 was the lower limit for good quality. Without additional CO2, 60 μmol was too little to achieve top quality. “Then we saw too many soft flower stems. If you want to grow top quality for the entire year then you need to supplement 60 μmol with CO2 in the darker periods.” It is also important to confirm the conclusions drawn from the research in 2012/2013: when dosing with CO2 there is no additional benefit from dosing with 90 μmol compared with 60 μmol.
The results from the total energy savings concept showed that it came out on top, even in the darker period. “In the beginning the growers were most interested in greenhouses 1 and 2. Greenhouse 3 went a bit too far for them. They thought this was taking too big a risk. They were very surprised by the positive results. However, attention does need to be drawn to the number of softer flower stems and slightly too much stretch during the darker period.”
Application in practise
What do the conclusions mean for application in practise? Hogewoning: “For growers who strive for top quality, artificial lighting at 60 μmol with CO2-dosing is certainly possible. During open days I’ve heard growers say that they found the quality of flowers grown with artificial lighting of 45 μmol and CO2 quite spectacular. For DIY retailers the lilies don’t need to be so heavy.”
How growers respond to this research differs depending on the market segment. Certainly as a result of this research some growers have started to dose with CO2. Across the board this appears to be a good strategy, which saves energy and it has a positive effect on the strength of the crop.
The total concept approach seems to have a good chance of success. Calculations with models show that its application in a commercial greenhouse leads to a 45% saving on electricity. A crop does then use 1.5 m3 extra gas to compensate for the heat from the lights. The type of cogenerator and availability of CO2 will determine the economic return. In the end every grower will have to calculate for himself which strategy is most suitable.
If CO2 dosing is used in lily production the light level can be reduced by one third. A recently completed trial confirms the results. More energy savings are possible by using temperature integration and by adjusting the lighting further to suit the growth phase.
Text: Karin van Hoogstraten. Photos: Studio G.J. Vlekke