Influence Factors and Characteristics of Transpiration and Evaporation in Water-saving Irrigation Paddy Field under Different Temporal Scales

Liu Xiaoyin;Wang Guanyi;Yang Shihong;Xu Junzeng;Wang Yijiang;State Key Laboratory of Hydrology-water Resources and Hydraulic Engineering,Hohai University;College of Water Conservancy and Hydropower Engineering,Hohai University;Kunshan Water Conservancy Engineering Quality and Safety Supervision and Water Technology Popularization Station;

water-saving irrigation paddy field;;transpiration;;evaporation;;mini-lysimeter;;temporal scale

Rice evapotranspiration and soil evaporation were measured by using canopy mini-lysimeter system in rice growth period in 2015 with water saving irrigation in the South China Plain. The characteristics of diurnal variation in typical days and daily variation during the whole growth period for evapotranspiration( ET),transpiration( T) and evaporation( E) were analyzed. The ratio of E to ET was also discussed. In addition,the correlations between T,as well as E,and related factors at hourly and daily scales were studied based on multiple linear regression method. The results illustrated that the diurnal variations of ET and T were basically consistent,which presented as the singlet trend of inverted"U"shape obviously. At the stage of tillering,E was also varied diurnally in unimodel shape,whilethere was no obviously diurnal variation after tillering stage. Positive and negative fluctuations of ET at night indicated that the influence of water vapor condensation on measurement of mini-lysimeter cannot be ignored. The daily variation trend of T was also similar to ET,and the two values were increased firstly and then decreased,with peak value occurred at late tillering stage. Moreover,rice evapotranspiration was soil evaporation primarily before late tillering stage,and later transpiration was dominant. The ratio of E to ET was varied from 1 to 0. 19 with the growth of rice,and it was increased slightly in the ripening stage with value of 0. 23. The main factors that affected transpiration and evaporation of water saving irrigation paddy fields were not identical at hourly and daily temporal scales. Net radiation( Rn) and leaf area index( LAI) were the main influence factors for rice transpiration at hourly and daily scales,respectively,while LAI and vapor pressure difference( D) were the main influence factors for soil evaporation at the two scales,respectively. LAI had significant effect on transpiration and evaporation at both temporal scales( α < 0. 001),albeit in varying degrees. The analysis of scale difference had important and practical significance to the research of water management and water transformation in the field.