THE CO₂ FACTOR IN MODELLING PHOTOSYNTHESIS AND GROWTH OF GREENHOUSE CROPS

A model for the growth and development of a cucumber crop, at a CO₂ concentration of 340 vpm, was validated for three crops grown at different times in winter and spring.
The results from the model were in agreement with the experimental date.
As next step predictions were made for the effects of CO₂ concentration on crop production.
A realistic assessment of this problem requires not only knowledge about different physiological parameters but also about physical processes like ventilation and the calculation of the CO₂ supply.
In the model it is assumed that CO₂ is supplied by the combustion of natural gas in the heating system.

The amount of CO₂ generated by the heating system appeared to be sufficient to elevate the CO₂ concentration over a level of 340 vpm in january and february.
Afterwards the heat demand decreases and consequently not enough CO₂ is available.
The combined effect of an increased irradiance (increase of photosynthesis) and a decreased heat demand (less CO₂ supply) results in CO₂ concentrations in the greenhouse considerably below ambient.
For a crop with a leaf area index of 3 the loss of net CO₂ assimilation due to CO₂ depletion was calculated to be about 15% in early spring (Schapendonk and Gaastra, 1984a). When long term effects of CO₂ are taken into account for a crop planted early february the fruit production losses due to CO₂ depletion were about 6900 kg/ha (11% of the total potential production when CO₂ depletion is prevented). The costs of preventing CO₂ depletion are calculated to be equivalent to 1421 m³ natural gas that have to be combusted additive to the normal heating purposes.
The data presented apply for a period of 63 days after planting.
Elevating the CO₂ concentration to 1000 vpm would cost the equivalent of 16081 m³ of natural gas.
The simulated profit, compared with a crop that did not receive additional CO₂ was 38500 kg/ha over this period.
The amount of CO₂ that was lost through ventilation was accounted for.

Symposium on CO2 Enrichment

A.H.C.M. Schapendonk, W. van Tilburg

https://doi.org/10.17660/ActaHortic.1984.162.7