Multiple Methods to Partition Evapotranspiration in a Maize Field

Abstract

Partitioning evapotranspiration (ET) into soil evaporation E and plant transpiration T is important, but it is still a theoretical and technical challenge. The isotopic technique is considered to be an effective method, but it is difficult to quantify the isotopic composition of transpiration ST and evaporation dE directly and continuously; few previous studies determined STsuccessfully under a non-steady state (NSS). Here, multiple methods were used to partition ET in a maize field and a new flow-through chamber system was refined to provide direct and continuous measurement of 67-and SE. An eddy covariance and lysimeter (EC-L)-based method and two isotope-based methods [isotope combined with the Craig-Gordon model (Iso-CG) and isotope using chamber measurement (Iso-M)] were applied to partition ET. Results showed the transpiration fraction F j in Iso-CG was consistent with EC-L at both diurnal and growing season time scales, but Fr calculated by Iso-M was less than Iso-CG and EC-L. The chamber system method presented here to determine ST under NSS and isotope steady state (ISS) was robust, but there could be some de viation in measuring SE. The Fr varied from 52% to 91%, with a mean of 78% during the entire growing season, and it was well described by a function of LAI, with a nonlinear relationship of FT = 0.71LAI014. The results demonstrated the feasibility of the isotope-based chamber system to partition ET. This tech nique and its further development may enable field ET partitioning accurately and continuously and improve understanding of water cycling through the soil-plant-atmosphere continuum.

Seasonal variability in evapotranspiration partitioning and its relationship with crop development and water use efficiency of winter wheat

“…This study indicated that the seasonal changes in F T could be effectively described through a power-law function of the LAI. This relationship was similar to those obtained in recent studies at both the global and the field scale Wei et al, 2015;Wu et al, 2017;Lu et al, 2017). The strong correlation between F T and LAI confirmed that F T was controlled by LAI at seasonal timescale (Wang and Yamanaka, 2014;Wei et al, 2015;Wei et al, 2018 Kang et al (2003), respectively.…”

“…CC BY 4.0 License. productive component of the crop yield, while E was described as the non-productive water loss (Agam et al, 2012;Van Halsema and Vincent, 2012;Ding et al, 2017). A positive linear function has generally been used to describe the relationship between the yield and T provided that water was the main limiting factor on the yield (Hanks, 1983;Ben-Gal and Shani, 2002;Tolk and Howell, 2009).…”

“…Conventional hydrometric methods employed various techniques to directly measure ET (e.g., the eddy covariance technique, micro Bowen ratio energy balance method, and the weighing lysimeter approach) in addition to E (via a micro-lysimeter) or T (using sap flow sensors) (Mitchell et al, 2009;Cavanaugh et al, 2011;Liu et al, 2002;Zhang et al, 2003;Sun et al, 2006). Simulation models such as the Shuttleworth-Wallace model, the Food and Agriculture Organization (FAO) dual crop coefficient model, the HYDRUS-1D model, and the hybrid dual-source model (TVET) have also been used to simultaneously calculate E and T (Li et al, 2010;Zhang et al, 2013;Ding et al, 2017;Sutanto et al, 2012;Guan and Wilson, 2009). Since various fractionation processes such as condensation and evaporation leave characteristic imprint on the isotopic composition of water, the stable water isotopes of 18 O and D are considered ideal (natural) tracers for separating E and T from ET and tracking water through the soil based on distinct Hydrol.…”

“…At the daily scale, the ratio of T within ET (F T ) varied over a wide range of 0.2-1 within a rice paddy field during a complete growing season in Mase, Tsukuba (Wei et al, 2015). The daily F T also changed greatly (0.52-0.96) throughout the growing season of maize in northwestern China (Wen et al, 2016;Wu et al, 2017). Substantial differences in F T were discovered between the late filling stage (0.83) and the stage of wax ripeness (0.6) in an irrigated field of winter wheat in the North China Plain (NCP) (Zhang et al, 2011).…”

“…However, Kang et al (2003) proposed that F T and the LAI exhibited a saturation relationship for wheat and maize in a semi-arid region of Northwest China. Several recent studies identified a power-law correlation between F T and the LAI for agricultural systems at both the global scale and in certain croplands Wei et al, 2015;Wu et al, 2017;Lu et al, 2017;Zhao et al, 2018). In addition, numerous possibilities were suggested for high F T even under low LAI conditions.…”