Water use efficiency of a rice paddy field in Liaohe Delta, Northeast China

Abstract

Water use efficiency (WUE) of rice paddy fields is very important because of the increasing demand for crop production and increasing scarcity of water for irrigation. The seasonal dynamics of WUE and their environmental controls were determined in a rice paddy field in Liaohe Delta, Northeast China, based on 2-year period (2013–2014) eddy-covariance flux and meteorological measurements. The annual and growing-season ecosystem water use efficiency (eWUE) of the paddy field were 1.00gCkg−1 H2O and 1.35gCkg−1 H2O (two-year average), respectively. The seasonal variation of eWUE showed an asymmetric single-peak curve. The leaf area index (LAI) was the dominant regulator of evapotranspiration-based WUE; however, the VPD was the most important controlling factor of transpiration-based WUE. The significant positive control of LAI on evapotranspiration-based WUE was likely caused by its strong regulation of the ratio of transpiration (TR) to evapotranspiration (ET). The residual WUE (calculated from the WUE subtracted from the modeled WUE using the relationship between the WUE and LAI) was negatively correlated with net radiation (Rn). The WUE was generally higher under cloudy conditions than under clear conditions. Based on a comparison of the four WUE indicators, the separation of ET to TR and soil evaporation (ES), as well as the incorporation of the nonlinear effect of vapor pressure deficit (VPD) on WUE, would both greatly improve the performances of WUE indicators in rice paddy fields.