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from the issue of July 15, 2004
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Warming Hurts Rice Yield, Says Research
BY DAN MOSER, IANR NEWS SERVICE
Rice yields decline 15 percent for each degree of global warming, which could make it more difficult to feed Earth's growing population, according to research by an international team of scientists that includes a UNL agronomist.
The research, conducted in the Philippines, is significant because rice is the primary staple grain crop for one-third of the world's population.
Kenneth G. Cassman of UNL's Department of Agronomy and Horticulture collaborated with scientists from the International Rice Research Institute in the study. The team's results are published in the current edition of the Proceedings of the National Academy of Science.
The research used long-term climate data from the IRRI research farm to document a steady rise in temperature that was more pronounced at night than in the daytime. While the mean minimum nighttime temperature increased by 1.1 degree Celsius over 25 years, the maximum daytime temperature increased by only 0.35 degree.
The scientists examined the relationship between mean temperature during the growing season and rice yields and found that grain yield decreased by 10 percent for every 1 degree increase in nighttime temperature. In contrast, the much smaller increase in daytime temperature had no detectable effect on yield.
Because the rise in the minimum nighttime temperature was three times that of the mean maximum daytime temperature, researchers calculated that each 1 degree C in mean daytime temperature would decrease rice yield by 15 percent. The size of this yield reduction, based on field data, is greater than previous estimates of global warming effects on rice yields that were based on simulation modeling.
This report is the first to provide direct evidence of a link between temperature increase associated with global warming and yield reduction of a major cereal crop under field conditions.
This work has implications in Nebraska because yields of the major crops grown in the state also are sensitive to temperature regime, Cassman said. In particular, both wheat and corn yields are reduced by high temperatures during the grain filling period. In fact, recent UNL research indicates that year-to-year variation in corn yields can be partially explained by the effects of year-to-year variation in nighttime temperatures during the grain filling period.
The study
The full text of this article from the Proceedings of the National Academy of Science can be found at www.pnas.org/cgi/content/full/101/27/9971.
GO TO: ISSUE OF JULY 15
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