Biomass Production and Water Use Efficiency of an Enriched Carbon Dioxide System Using Open Top Chambers.

Atmospheric carbon dioxide (CO₂) concentrations have steadily increased since the Industrial Revolution with levels reaching 392 ppm in 2013. Although elevated CO₂ levels are generally perceived as negatively impacting our environment, studies have shown that crop production and water use efficiency (WUE) increase under enriched CO₂ conditions. However, most of the experiments conducted to date have been performed in greenhouses. Therefore, the goal of our study was to evaluate the effects of elevated CO₂ and deficit irrigation on the biomass accumulation, yield, and WUE of fresh-market tomatoes grown in fields using open top chambers. The study was conducted over three years on a sandy loam soil in Central California. Sixteen open-top chambers (15ft W x 5ft L x 10ft H) received either ambient air or elevated CO₂. For the CO₂ enriched plots, mean daily CO₂ levels within the crop canopy was around 600 ppm during the 8 hours of application, whereas concentrations in the ambient plots averaged around 390 ppm. Subsurface drip irrigation was used to apply water at rates equivalent to 100% the evapotranspiration (ET) and 80% ET. Under elevated CO₂ concentrations, plant height and biomass increased by 7.5% and 22%, respectively; and marketable yield and WUE by 20%. While irrigation regime did not significantly influence plant biomass, tomatoes irrigated to satisfy 100% ET were 11% taller than those deficit irrigated (80% ET).  The current research highlights the potential of using agronomic crops to capture and utilize CO₂ emissions, because as much as 80% of the crop biomass is ultimately incorporated into the soil after harvest of the marketable product.