The phenomenon that peppers have a 30% lower efficiency of photosynthesis in the spring, in getting used to the high CO2 concentration, disappears within six days. Dosing above 800 ppm also has little added value. This was apparent from research carried out by Plant Lighting and TTO which was presented during the Masterclass CO2 specifically for pepper growers on Friday, September 25th at Demokwekerij Westland.
Earlier research has shown that if peppers are used to a high CO2 concentration of 1000 ppm (the 'winter situation'), the efficiency of photosynthesis is 30% lower than when the CO2 concentration lowers in the glasshouse in the spring. In the new research from Plant Lighting and TTO, it appears that this adaptation will disappear within six days. Another dosing strategy in order to avoid this phenomenon is therefore not necessary. However, it appears that a dosage above 800 ppm has substantially no effect on photosynthesis in peppers.
In addition, research has been done on 6 CO2 dosing in the summer. From measurements taken at a test farm, it has now been discovered that when the right conditions are applied, photosynthesis in peppers is maintained even on very hot summer days. The farm in question used a diffuse coating, and was able to keep the vents closed more often because of a lower leaf temperature (in the head). The moisture deficit thus remained more resilient. The VPD remained below 2 kPa. Also dosing was more useful because the stomata remained open. The question from those present at the masterclass was whether this was possible without a diffuse coating.
Plan of action effective CO2 dosing
Peter Geelen from Plantmonitoring.nl presented a plan of action of effective CO2 dosing, particularly in the summer months, at the master class organized by TTO, LTO Glaskracht Netherlands, Inno-Agro and Demokwekerij Westland. The first step is to keep the stomata open. Moisture plays an important role. Because of the open stomata, the plant can cool itself by evaporation, thus more energy can be removed from the glasshouse and the CO2 can be better used for the photosynthesis process. The second step is to keep the vents more closed, with the additional result that the CO2 losses remain limited and the VD rises less. The third step is that the dosing strategy is adapted to the level of light.
The final step is that use of assimilates is adjusted to the production of assimilates. This requires a constant tuning of the daily temperature on the light content and maintaining a lower plant load. The four steps thus form a coherent whole with each strengthening the other. One can easily start with an infrared camera to identify when the stomata are going to close.
Source: Dennis Medema, LTO Glaskracht, via Kas als Energiebron