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Atmospheric CO2 Enrichment: Boosting Rice Yields of Asia
Kim, H.-Y., Lieffering, M., Kobayashi, K., Okada, M., Mitchell, M.W. and Gumpertz, M.  2003.  Effects of free-air CO2 enrichment and nitrogen supply on the yield of temperate paddy rice crops.  Field Crops Research 83: 261-270.

"On the basis of both area and tonnage harvested," according to the authors, "Oryza sativa L. (rice) is the most important crop in Asia, providing a significant proportion of the people's dietary needs (Alexandratos, 1995)."  Hence, they say that "in view of the expected growth in Asia's population, there is a need to determine how the predicted increase in the levels of atmospheric CO2 will affect rice yield."

What was done
In order to determine the interactive effects of elevated CO2 and nitrogen (N) availability on the grain yield of rice crops grown under temperate flooded paddy conditions, Kim et al. grew rice crops from the seedling stage to maturity at atmospheric CO2 concentrations of ambient and ambient plus 200 ppm using FACE technology and three levels of applied nitrogen -- low (LN, 4 g N m-2), medium (MN, 8 and 9 g N m-2), and high (HN, 15 g N m-2) -- for three cropping seasons (1998-2000).

What was learned
The authors report that "the yield response to elevated CO2 in crops supplied with MN (+14.6%) or HN (+15.2%) was about twice that of crops supplied with LN (+7.4%)," confirming the importance of N availability to the response of rice to atmospheric CO2 enrichment previously determined by Kim et al. (2001) and Kobaysahi et al. (2001).

What it means
In terms of the more common increase in CO2 concentration used to express plant responses to atmospheric CO2 enrichment, i.e., 300 ppm, the results of Kim et al. suggest we could likely expect something on the order of a 22% increase in rice yield for the MN treatment, which they say is "similar to that recommended to local farmers."  Such a yield increase, courtesy of the ongoing rise in the air's CO2 content, would go a long way towards helping the people of Asia meet the future dietary needs of their expanding population.

Alexandratos, N.  1995.  World Agriculture: Towards 2010.  Food and Agriculture Organization, Wiley, Chinchester.

Kim, H.-Y., Lieffering, M., Miura, S., Kobayashi, K. and Okada, M.  2001.  Growth and nitrogen uptake of CO2-enriched rice under field conditions.  New Phytologist 150: 223-229.

Kobayashi, K., Lieffering, M. and Kim, H.-Y.  2001.  Growth and yield of paddy rice under free-air CO2 enrichment.  In: Shiyomi, M. and Koizumi, H. (Eds.), Structure and Function in Agroecosystem Design and Management.  CRC Press, Boca Raton, FL, USA, pp. 371-395.

Reviewed 14 January 2004