Rice Today - adron.sr

with irrigation. It is a highly stylizedexample that shows simulationresults for only one variety (IR72).It used 9 years of daily weatherdata 2 to compute average andrelative yields (with and withoutirrigation) over this period. Manyother known sources of variation,such as local hydrological processesand differences in soil types, are nottaken into account in this example.It nevertheless shows some basicfacts about rice and water. Thereare some places where you cannotgrow much rice without irrigation.This does not necessarily meanthat water stress is an importantproblem there. In fact, some of themost productive rice areas are foundthere, including the Punjab in Indiaand the Nile Valley in Egypt. On theother hand, if water becomes scarcein these regions—as is happening inmany areas—water-saving irrigationtechnologies and appropriatevarieties would be very useful.Most areas with a relative riceyield of below 50% have little rainfed(nonirrigated) rice production. 3But this does not mean there is noirrigated rice in wetter areas wherefarmers could produce a reasonablerice crop without irrigation. Forexample, in southeastern China,farmers could produce rice withoutirrigation. However, supplementalirrigation increases production,particularly in dry years, and allowsfor the production of rice or anothercrop outside the main rainy season.The map shows the relationbetween maximum rainfed yield(in the rainy season) and yield ofirrigated rice in the off-season (anyseason that would allow the highestyield if irrigation were available). Ittherefore reflects a yield increasepartly by reduced water stress andpartly by shifting toward growingseasons with more solar radiationand perhaps lower temperatures.Drought tolerance would seemparticularly relevant in areas withpredominant rainfed productionwith a moderate to large yieldreduction (50–70% relative yield).Such areas include Bangladesh andeastern India. Current research 4aims to refine the approach byimproving the data used to run themodels, and by running modelsfor different rice ecosystems andfor different varieties to contrastexisting versus new droughttolerantvarieties, and to contrastcurrent cropping practices versuswater-saving technologies.Dr. Hijmans is a geographer in theIRRI Social Sciences Division.2Estimated from satellite observations byNASA, data available athttp://earth-www.larc.nasa.gov/cgibin/cgiwrap/solar/agro.cgi.3Compare this map with the rice areaby ecosystem map on pages 20-21 ofRice Today Vol. 6, No. 3 (www.irri.org/publications/today/pdfs/6-3/20-21.pdf).4Together with colleagues at theInternational Food Policy ResearchInstitute and the University of Minnesota,see www.harvestchoice.org.Rice Today October-December 2008 13RT7-4 (p1-23)_FA.indd 1310/9/2008 8:24:17 AM