Crop yields decline in future greenhouse gas conditions.

Open-air field trials involving five major food crops grown under carbon-dioxide levels projected for the future are harvesting dramatically less bounty than those raised in earlier greenhouse and other enclosed test conditions. Scientists warn that global food supplies could be at risk without changes in production strategies.

The new findings are based on ongoing open-air research at the University of Illinois at Urbana-Champaign and results gleaned from five other temperate-climate locations around the world. According to the analysis, published in the June 30 issue of the journal Science, crop yields are running at about 50% below conclusions drawn previously from enclosed test conditions.

Results from the open-field experiments, using free-air concentration enrichment (FACE) technology, "indicate a much smaller C[O.sub.2] fertilization effect on yield than currently assumed for crops, such as rice, wheat and soybeans, and possibly little or no stimulation for crops that include maize and sorghum," says Stephen Long, a university plant biologist and crop scientist.

FACE technology, such as the SoyFACE project at Illinois, allows researchers to grow crops in open-air fields, using elevated levels of carbon dioxide that simulate the composition of the atmosphere projected for the year 2050. SoyFACE has added a unique element by introducing surface-level ozone, whose levels are also rising. Ozone is toxic to plants.

By 2050 carbon dioxide levels may be about 1.5 times greater than the current 380 parts per million, while daytime ozone levels during the growing season could peak on average at 80 parts per billion. They are now 60 parts per billion. Older studies, as reviewed by the Intergovernmental Panel on Climate Change, suggest that increased soil temperature and decreased soil moisture, which would reduce crop yields, likely will be offset in certain crops by the fertilization effect of rising C[O.sub.2], primarily because C[O.sub.2] increases photosynthesis and decreases crop water use. To date, for each crop tested yields have been well below (about half) the value predicted from chambers, the authors report.

The FACE experiments clearly show that much lower C[O.sub.2] fertilization factors should be used in model projections of future yields, the scientists say. They also called for research to examine simultaneous changes in C[O.sub.2], O3, temperature and soil moisture. While projections to 2050 may be too far out for commercial considerations, 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, according to the scientists.

Further information. Stephen Long, University of Illinois at Urbana-Champaign, Department of Crop Sciences, 1201 W. Gregory Dr., 379 ERML, MC-051, Urbana IL 61801; phone: [phone]; email: [e-mail].