# Tracing the allocation of water in rainfed rice ecosystem by partitioning evapotranspiration of rainfed rice (Oryza Sativa L.)

Bhone Nay-Htoon, Maren Dubbert, Xue Wei, Matthias Cuntz, Ko Jonghan, John Tenhunen, Christiane Werner

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Bhone Nay-Htoon, Maren Dubbert, Xue Wei, Matthias Cuntz, Ko Jonghan, et al. Tracing the allocation of water in rainfed rice ecosystem by partitioning evapotranspiration of rainfed rice (Oryza Sativa L.). EGU 2015, European Geophysical Union General Assembly 2015, Apr 2015, Vienne, Austria. 1p., 2015. [hal-02741491](https://hal.inrae.fr/hal-02741491)

HAL Id: hal-02741491

https://hal.inrae.fr/hal-02741491

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# Tracing the allocation of water in rainfed rice ecosystem by partitioning evapotranspiration of rainfed rice (Oryza Sativa L.)

Bhone Nay-Htoon (1), Maren Dubbert (1), Xue Wei (2), Matthias Cuntz (3), Jonghan Ko (4), John Tenhunen (2), and Christiane Werner (1)

(1) Department of Agro-Ecosystem Research, BayCEER, University of Bayreuth, Bayreuth, Germany, (2) Department of Plant Ecology, University of Bayreuth, Bayreuth, Germany, (3) Computation Hydrosystems, UFZ - Helmholtz Centre for Environmental Research, Leipzig, Germany, (4) Department of Applied Plant Science, Chonnam National University, Yongbon, South Korea

To understand productive and unproductive water use of crop production, partitioning evapotranspiration (*ET*) into evaporation (*E*) and transpiration (*T*) is important. Water movements within the eco-hydrologic cycle of agroecosystems can be traced by stable oxygen isotopes of water (δ¹⁸O) and plant transpiration and soil evaporation can also be estimated by tracing the δ¹⁸O. We quantified the contribution of transpiration to total ecosystem evapotranspiration of rainfed rice field by a stable oxygen isotope approach and FAO 56 dual crop modelling approach. Our study aims to provide quantification of ecosystem water cycle of rainfed rice by partitioning productive and unproductive water use since productivity and water use of rice which is a highly water demanding agroecosystem, is under intense research. Crop season total evapotranspiration fluxes from rainfed rice was mainly dominated by transpiration (*T* to *ET* contribution (*T*/*ET*) = 65%) and domination of transpiration over evaporation fluxes was noted since early vegetative stage (Leaf Area Index = 0.8 m² m⁻²) until harvesting. *T*/*ET* of rainfed rice fluctuated with changes in soil water content (SWC) and the highest *T*/*ET* was found at SWC of 0.34 m³ m⁻³, during seedling stage. Our results demonstrate that partitioning *ET* by FAO 56 dual crop model is in a good agreement with δ¹⁸O isotope based *ET* partitioning results. Using monthly mean values of leaf resistance and vegetation index derived crop coefficients instead of original fixed parameters of the FAO 56 dual crop model resulted better agreement with δ¹⁸O isotope based *ET* partitioning.