Background
Shimono et al. write that "by 2050, the world's population will have increased by about 37%, from the current level of 6.7 billion to an estimated 9.2 billion (UN, 2009), with a corresponding increase in global food demand." They also state that "about 0.6 billion Mg of rice is produced annually from an area of 1.5 million km², making rice one of the most important crops for supporting human life," especially, as noted by Pritchard and Amthor (2005), since it supplies the planet's human population with an estimated 20% of their energy needs (on a caloric basis) and 14% of their protein requirements (on a weight basis).

Within this context, the six scientists further note that "rice production depends heavily on water availability," stating that "irrigated lowlands account for 55% of the total area of harvested rice and typically produce two to three times the crop yield of rice grown under non-irrigated conditions (IRRI, 2002)." And because the demand for ever greater quantities of water will continue to rise, due to our need to adequately feed our growing numbers, they conclude that "efficient use of water will thus be essential for future rice production."

What was done
In an attempt to determine how the agricultural enterprise may be impacted in this regard by the ongoing rise in the air's CO2 content, the Japanese researchers conducted a two-year free-air CO2 enrichment or FACE study in fields at Shizukuishi, Iwate (Japan) to learn how elevated CO2 may reduce crop water use via its impact on the leaf stomatal conductance (gs) of three varieties of rice (Oryza sativa L.): early-maturing Kirara397, intermediate-maturing Akitakomachi, and latest-maturing Hitomebore.

What was learned
In response to the 53% increase in daytime atmospheric CO2 concentration employed in their experiments, Shimono et al. report that "the reduction in gs due to elevated CO2 was similar across measurements, averaging around 20% in the morning, 24% around noon and 23% in the afternoon across all growth stages." And they add that "there was no significant CO2 x cultivar interaction."

What it means
With the concomitant increase in grain yield that also results from atmospheric CO2 enrichment (see Rice in the Plant Growth Data section of our website), it should be apparent to all that a continuation of the historical and still-ongoing rise in the air's CO2 content will play a major role in enabling us to meet our food needs at the mid-point of the current century, without having to lay claim to all of the planet's remaining fresh water resources and much of its undeveloped land and thereby driving many of the species with which we share the terrestrial biosphere to extinction for lack of land and water to meet their needs, as is also explained in greater detail in several of the items we have archived under the heading of Food in our Subject Index.

References
IRRI (International Rice Research Institute). 2002. Rice Almanac: Source Book for the Most Important Economic Activity on Earth. CABI Publishing, Oxnon, United Kingdom.

Pritchard, S.G. and Amthor, J.S. 2005. Crops and Environmental Change. Food Production Press, New York, New York, USA.

UN (United Nations). 2009. The 2006 World Population Prospects. The 2008 Revision Population Database. United Nations, New York, New Your, USA. [WWW document]. URL http://esa.un.org/unpp/.