Study On The WUE Of Rice In The Middle And Lower Reaches Of The Yangtze River

This paper analyzes the variation characteristics of the WUE of paddy rice plant in the middle and lower reaches of the Yangtze River, which is important to make full use of the limited water resources, to make ensure a high and stable rice yield, to strengthen water-save management and improve the adaptability of rice production to climate change.The field and pot experiments were carried out to study on the effects of environmental factors on water use efficiency of paddy rice. With meteorological data, rice plant growth data observed in the middle and lower reaches of the Yangtze River from1981to2010, the temporal and spatial variation of the major meteorological elements and water use efficiency of paddy rice during rice growth season are statistically calculated at the study area. The main results are as follows:(1)The total net solar radiation shows a decreasing trend, while the average temperature has a significantly increasing trend during growth period duration of rice at the study area. For three types of rice cultivation, the total solar net radiation and precipitation is strongest for single cropping rice and lowest for later season rice, the mean temperature of single cropping rice is strongest. The total solar net radiation of single cropping rice is stronger in southern area than that in northern area, and has a tendency of increases from the south to the north for double croping rice area. The average temperature in the single cropping rice area increases from the western to the eastern in Hubei province, and decreases from southwest to northeast in Jiangsu and Anhui province. For double cropping rice, the high temperature area in the early rice growing season lies in the southern region and the low temperature area distributes in the northern. For the average temperature of the later season rice a center of high value is in middle area. The total precipitation of rice growing season in single and double cropping rice appears an overall trend of high in north and low in south.(2)Analyses on the relationships between leaf water use efficiency of rice and environmental factors including carbon dioxide concentration, high temperature, light intensity and soil moisture under pot condition were made. The results were as follows:LWUE of rice increases with the increase of light intensity and carbon dioxide concentration, and it exsits a significant quadratic equation between them, The LWUE of rice will decreased after the temperature increasing4～5℃. Appropriate soil drought can raise LWUE, but the optimal ranges to raise different cultivar’s leaf water use efficiency under deferent stages are different. The LWUE can attain the maximum value when the soil moisture is between66%and68%of saturated soil moisture, otherwise the LWUE of rice would be inhibited when the soil moisture is too low. With the different rice growing stages, the relative soil water content which the LWUE of rice begin to declined are different, booting-heading stage>filling stage>jointing stage>tillering stage. High concentration of CO2would be promote the LWUE of rice, and the WUE increase of Nanjing44is higher than Liangyoupeijiu, a higher concentration of CO2would be compensation the effect of drought and synergistic reaction of drought and high temperature, especially the early growth period (such as the tillering stage and the jointing stage). Generally, The LWUE of rice in different growth period appears a trend of high in filling stage, moderate in booting-heading stage and low in tillering stage. The diurnal variation of LWUE showed a curves like "L", and the LWUE in the morning was higher than that in the afternoon.(3)With field experiment data, the water use efficiency of rice at yield level was estimated, and the impact of warming, drought on yield and water use efficiency was also analyzed. The results show that the treatment of warming and drought would reduce the yield of rice, and yield loss of the Nanjing44under drought were greater than CK, then yield of the Liangyoupeijiu loss under the high temperature treatment were greater than CK. The response of WUEy to temperature is more significant than to drought. The WUEy of the Liangyoupeijiu was reduced more than Nanjing44under water-stress, and just on the contrary under a higher temperature.(4) Compared the results from the crop coefficient--Reference Crop Evapotranspiration method with the results from the ORYZA2000model for the past three decades,we can found, the WUE with this two algorithms were increased during the past three decades, but this trend is not significant for early rice. The WUE of the early season rice is lower than the later season rice, and the WUE increase from southwestern area to northeastern area in double cropping rice region. The WUE of single cropping rice is lower than double cropping rice calculated by crop coefficient--Reference Crop Evapotranspiration method, and the WUE reduce from northwest to southeast in single cropping rice region, the WUE of single cropping rice is higher than double cropping rice calculated by ORYZA2000model method, and the WUE increase from northwest to southeast in single cropping rice of Hubei, the WUE in Jiangsu and Anhui province single cropping rice growing season reduce from north to south.