Variation characteristics of rice water requirement in middle and lower reaches of Yangtze River during 1961－2007

Based on ground observation data from 91 meteorology stations during 1961－2007 and phenology data of single cropping rice and double cropping rice from 63 agrometeorology experimental stations during 1981－2006 well spread over the middle and lower reaches of the Yangtze river, using the U.S. Department of Agriculture Soil Conservation method and some methods recommended by Food and Agriculture Organization, the effective precipitation and rice water requirement were calculated and water use efficiency(WUE) of the supply irrigation(Is) for the double cropping rice and single cropping rice were analyzed. The results indicated that in study area, effective precipitation of the early season rice and single cropping rice were increasing, but the late season rice decreased along with global climate changes in study period. The early season rice, late season rice and single cropping rice water requirement showed a downward trend, and water requirement of single cropping rice and late season rice significant reduced. The supply irrigation water requirement of single cropping rice was less 125 mm than double cropping rice, but water use efficiency of double cropping rice was higher than that of single cropping rice at the study area. So from the perspective of WUE increasing, it is preferable to plant double cropping rice in the middle and lower reaches of the Yangtze river.