The benefits of greenhouse CO2

European agriculture faces economic and environmental challenges, and part of the solution may involve increasing plant production by increasing CO2 concentrations. While promising, previous efforts have not yet cleared the cost hurdle associated with such methods.

The EU-funded CARBGROWTH (Maximisation of greenhouse horticulture production with low quality irrigation waters) project aimed to develop a CO2 injection system for greenhouses. The proposal was intended to increase production by 25 %, within cost constraints. The consortium addressed six objectives, involving determination of optimum growth conditions in terms of gas concentrations and salinity levels. Other goals included developing systems for gas exchange and recovery, and models of interior CO2 circulation. The ultimate goal was creation of new horticulture products compliant with EU legislation.

Experiments showed that increasing CO2 concentrations in the greenhouse environment improved sweet capsicum productivity under both saline and drought stress. Yet, results depended on substrate. The study demonstrated the feasibility of combined use of low-quality water and CO2, although higher-stress conditions did not mitigate growth. Tomato plants also responded well to increased CO2, yet severe stress could limit potential.

The team modelled convection and other movement of CO2 within greenhouses. The model accurately estimated CO2 distribution under various environmental conditions.

Results with sweet capsicum showed a 52.7 % growth increase at CO2 concentrations of 400 ppm and a 38.17 % increase at 800 ppm. Plants grown with salty water increased production even more, by 61.7 % and 59.2 %, respectively for the two concentration levels.

CARBGROWTH also successfully developed three devices: a solar water photoreactor, a gas treatment unit and a recirculation aquaculture system. Testing proved that in combination the systems could obtain and supply the nutrients needed for horticulture from a common greenhouse in conjunction with fish ponds. The project system thus achieved the proof-of-concept phase, with industrialisation being the next step.

Project estimates suggest an initial market growth of about 4 % per year, leading to an eventual penetration for the system of up to 20 % of the European greenhouse market.

CARBGROWTH systems are expected to improve European greenhouse horticulture productivity. Such outcomes mean improved profitability and competitiveness for European farmers.