Effects of Elevated CO₂ on Crop Water Relations

Working in a 20-hectare field near the German city of Braunschweig in southeastern Lower Saxony, Burkart et al. (2011) conducted a free-air CO₂ enrichment (FACE) experiment (enriching the air above portions of the field to a CO₂ concentration of 550 ppm) that was begun in 1999, in which they studied two rotation cycles (six years in total) of a typical local crop rotation that went from winter barley (Hordeum vulgare) to a cover crop of Italian ryegrass (Lolium multiflorum) to sugar beet (Beta vulgaris) to winter wheat (Triticum aestivum), during which time they measured a number of soil, plant and atmospheric properties. And throughout their long-term study, they managed the crops in accordance with "current local farming practices," in which "field irrigation was applied in order to avoid drought stress during the main growing season, keeping soil water content above 50% of maximum plant available soil water content."

Averaged across the two rotation cycles, Burkart et al. determined that the approximate 47% increase in the air's CO₂ content they supplied to portions of the field reduced canopy stomatal conductance by 9%, 17% and 12% in barley, sugar beet and wheat, respectively, and that it likewise reduced canopy transpiration by 9%, 18% and 12% in the same three crops. And as a consequence of the lower canopy transpirational water loss, they found that the CO₂ increase "increased plant water available soil water content in the course of the season by ca. 15 mm ... for all crops and years."

In discussing the implications of their findings, the five German scientists say the cumulative increase of soil moisture due to CO₂ enrichment found in their study suggests that in a future atmosphere, "CO₂-related water savings may improve crop water status and reduce the need for irrigation in Central Europe," which could prove a huge boon to the inhabitants of the continent.