Effect of variable CO 2 enrichment on greenhouse production in mild winter climates

Abstract

Variable CO 2 enrichment was evaluated under the autumn–winter climatic conditions prevailing in a coastal zone of southern Spain. Two adjacent identical greenhouses were used: control (without CO 2 enrichment) and enriched. Pure CO 2 was supplied to a greenhouse cucumber crop, maintaining in the greenhouse the air CO 2 concentration at close to 700 μmol mol −1 when the greenhouse was closed and 350 μmol mol −1 when the vents were open. CO 2 dynamics, efficiency of radiation and CO 2 use, and crop responses were determined over the growing season and compared to those of a similar cucumber crop grown in a non-enriched greenhouse. While the average diurnal concentration remained above 400 μmol mol −1 in the enriched greenhouse, significant CO 2 depletion was observed in the unenriched compartment, where the CO 2 concentration fell below 300 μmol mol −1 during 60% of the daytime when the crop was fully developed (leaf area index (LAI) ≈ 3). In the unenriched greenhouse, the average diurnal CO 2 depletion as well as the average mean concentration were highly correlated to the radiation intercepted by the crop, i.e. to the potential for biomass production. The average efficiency of CO 2 enrichment, i.e. the ratio of the amount of CO 2 sequestrated in the crop to the amount of artificial CO 2 delivered, was about 2% with respect to vegetative biomass, and about 6% with respect to fruit biomass. CO 2 enrichment affected mainly fruit biomass and had only a slight effect on leaf area index and vegetative biomass. The average increase in fruit production for both dry and fresh matter due to CO 2 enrichment was 19%, which agrees well with previous results on the agricultural response of cucumber to moderate CO 2 enrichment.