Studies On The Water Use Efficiency Of Alfalfa In Taiyuan Basin

As quality forage, Alfalfa is cultivated in the large-scale of various regions, especially arid and semi-arid regions in northwest of China. Water use efficiency of alfalfa has extremely important practical significance because of water consumption and water shortage in northwest region.Currently on the water use efficiency of alfalfa, the study is almost the leaves and yield levels while the study about ecological systems level is rarely reported. Net ecosystem CO2 exchange, actual evaporation and other environmental factors were measured by LI-6400 portable photosynthesis system in this study. Diurnal and monthly change about the water use efficiency of alfalfa and the correlation between the water use efficiency of alfalfa and the photosynthesis, respiration, net ecosystem CO2 exchange, temperature of soil, temperature of air, temperature of eradiate and other environmental factors were analyzed, and the main conclusion is that:The water use efficiency varies violent fluctuations from 06:30 to 10:00 am, shows a sharp rise in first, then the sharp decline. It decrease slowly and steadily from 10:00 to 17:30, declines sharp with the disappearance of Photosynthesis after 17:30, the peak appears between 7:30 to 9:30. The water use efficiency increases slowly without the influence of informal weather from July to October.Difference analysis about the water use efficiency and other factors shows that it is different among these factors. The water use efficiency varies complicated with the relatively change between the net ecosystem CO2 exchange and evaporation. But both the difference of water use efficiency and net ecosystem CO2 exchange are not significant.Correlation analysis of the water use efficiency with other factors shows that the correlation of the water use efficiency with 10cm soil temperature is better than air temperature and infrared radiation temperature. The correlation of the water use efficiency with NEE, GPP and VPD is significant, while the correlation of the water use efficiency with actual evaporation is not significant. It is mean that net ecosystem CO2 exchange has a greater impact on the water use efficiency than actual evaporation.