The influence of CO2 concentration and plant density on tomato yield and fruit quality

The survey was completed by 19 growers who completed a questionnaire and provided yield data. The survey provided the following findings: 

• Growing practices varied widely between growers and there was no standard system for CO2 enrichment across the UK.
• Setpoint for CO2enrichment ranged between 900-1500 ppm in the winter with no clear differences between those growers using gas to provide the CO2 and those using pure CO2.
• Several growers using pure CO2 (5 growers) were able to supply figures on CO2 usage during winter. Usage varied widely, ranging from 1.86 to 7.0 T/ha/week. There was no correlation between setpoint and usage.
• Summer CO2 setpoint varied widely ranging from 0 -1200 ppm.
• 7 out of the 19 growers surveyed reduced the CO2 enrichment setpoint as glasshouse ventilation percentage increased, reducing the CO2 setpoint to 100 – 450 ppm. Growers who did not reduce their CO2 setpoint with ventilation were growers who were burning gas to obtain their CO2.
• 5 out of the 19 growers surveyed had incorporated a change in CO2 setpoint with light.
• Summer CO2 use varied greatly, from 2.88 to 9.0 T/ha/week for those growers who were using summer enrichment.
• There was no correlation between summer usage and CO2 enrichment setpoint or between summer usage and reported achieved level. This may indicate that other factors have a greater effect in determining the amount of CO2 used, for example leakiness of the glasshouse.
• Of the eight growers burning gas to obtain their CO2 all had buffer tanks installed on the nursery. These tanks ranged in capacity from 54,000 to 135,000 l/ha.
• Information on the calibration of CO2 analysers indicated that there was no standard calibration method and no standard frequency of calibration. The wide variation in measured outside CO2 concentration suggests that the calibration of analysers as currently practiced may not be accurate.
• There was no clear correlation between summer yields (May - Early September) and either summer CO2 setpoints or measured achieved level.

Downloads

• PC 110 Survey Final report 
• PC 110a CO2 guidelines

• To collect information on current CO2 practices in terms of set points, achieved levels and methods of introduction.
• To provide information on cropping systems, growing environment and crop productivity.