26 July 2006
Crop Yields Set To Plunge
by Kate Melville
Past research indicated that rising levels of greenhouse gases could benefit crop yields, but that theory now looks to be incorrect. Worrying new research from the University of Illinois (UI) suggests that rising carbon dioxide levels could in fact trigger serious food shortages. The researchers based their findings on open-air field trials involving five major food crops grown under carbon-dioxide levels that are expected to occur in the near future. They found that crop yields plunged dramatically and warned that future global food supplies could be at risk without changes in food production methodologies.
Importantly, the results were gleaned from a half-dozen test locations around the world, rather than a single research plot. According to the analysis, published in the journal Science, crop yields are running at about 50 percent below those from enclosed (rather than open-air) test conditions.
UI researcher, Stephen P. Long, said the results "indicate a much smaller CO2 fertilization effect on yield than currently assumed for C3 crops, such as rice, wheat and soybeans, and possibly little or no stimulation for C4 crops that include maize and sorghum."
The research project used Free-Air Concentration Enrichment (FACE) technology, which allowed the scientists to grow the test crops in open-air fields, with elevated levels of carbon dioxide simulating the composition of the atmosphere projected for the year 2050. Additionally, the researchers added a unique element by introducing surface-level ozone, which also is rising. This project is the first to test both the effects of future ozone and CO2 levels on crops in the open-air. Previous studies had all been carried out in greenhouses or controlled environmental chambers.
The older studies suggested that increased soil temperature and decreased soil moisture (which would reduce crop yields) would likely be offset by the fertilization effect of rising CO2, primarily because CO2 increases photosynthesis and decreases crop water use. But plants grown in enclosures can differ greatly from those grown in farm fields and FACE has been the only technology that has tested effects in real-world situations.
With the new study, for each crop tested, yields have been "well below [about half] the value predicted from chambers," the researchers reported. The results encompassed grain yield, total biomass and effects on photosynthesis. In fact, in three key production measures, 11 out of 12 factors scrutinized were lower than the chamber equivalents. "The FACE experiments clearly show that much lower CO2 fertilization factors should be used in model projections of future yields," the researchers said.
And while projections to 2050 may be too far out for commercial considerations, the researchers believe action is required now. "It must not be seen as too far in the future for public sector research and development, given the long lead times that may be needed to avoid global food shortage," they concluded.
Source: University of Illinois at Urbana-Champaign