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Future Rice Yields in India
Reference
Krishnan, P., Swain, D.K., Bhaskar, B.C., Nayak, S.K. and Dash, R.N. 2007. Impact of elevated CO2 and temperature on rice yield and methods of adaptation as evaluated by crop simulation studies. Agriculture, Ecosystems and Environment 122: 233-242.

What was done
Two popular models of rice growth ORYZA1 (Kropff et al., 1994) and INFOCROP (Aggarwal et al., 2006) were calibrated for the indica rice variety IR 36 at ten different sites in eastern India and then used to predict rice yields for the ten sites for five 1C incremental increases in temperature above typical ambient conditions, as well as for one 20-ppm and three 100-ppm incremental increases in atmospheric CO2 concentration culminating at a value of 700 ppm.

What was learned
The authors report that "for every 1C increase in temperature, [the] ORYZA1 and INFOCROP rice models predicted average yield changes of -7.20 and -6.66%, respectively, at the current level of CO2 (380 ppm)," but that "increases in the CO2 concentration up to 700 ppm led to ... average yield increases [our italics] of about 30.73% by ORYZA1 and 56.37% by INFOCROP," which they "attributed to greater tillering and more grain-bearing panicles." In addition, they note that the limitation on rice yields that is sometimes imposed by spikelet sterility at high temperatures can be "largely overcome by the selection of genotypes that possess a higher potential of spikelet fertility at high temperatures."

What it means
In spite of the potential for enhanced global warming in the years and decades ahead - due to either anthropogenic- or non-anthropogenic-induced forcing - the world's rice farmers should be able to meet the needs of the planet's expanding human population ... if (1) the air's CO2 content continues to rise and (2) judicious use of plant breeding is made.

References
Aggarwal, P.K., Kalra, N., Chander, S. and Pathak, H. 2006. InfoCrop: A dynamic simulation model for the assessment of crop yields, losses due to pests, and environmental impact of agro-ecosystems in tropical environments. I. Model description. Agricultural Systems 89: 1-25.

Kropff, M.J., Van Laar, H.H. and Mathews, R.B. 1994. ORYZA1: An ecophysiological model for irrigated rice production. In: SARP Research Proceedings. IRRI, Wagningen, The Netherlands.

Reviewed 14 November 2007