Applying stable isotopes to determine seasonal variability in evapotranspiration partitioning of winter wheat for optimizing agricultural management practices

Abstract

The partitioning of evapotranspiration (ET) into soil evaporation (E) and crop transpiration (T) is fundamental for accurately monitoring agro-hydrological processes, assessing crop productivity, and optimizing water management practices. In this study, the isotope tracing technique was used to partition ET of winter wheat under different irrigation (100, 160 and 240 mm) and fertilization (105, 210 and 315 kg N ha−1) treatments during the 2014 and 2015 growing seasons in Beijing, China. The correlations between seasonal ET partitioning and the leaf area index (LAI), grain yield, and water use efficiency (WUE, ratio of crop yield and ET) were investigated and agricultural management practices were optimized. The fraction of T in ET (FT) between the greening and harvest seasons was 0.82 on average and did not vary significantly among the treatments (p > 0.05). However, the values of FT during the individual growth periods ranged from 0.51 to 0.98, and they were remarkably distinct for all treatments. The seasonal variability in FT could be effectively explained via a power-law function of the LAI (FT = 0.61 LAI0.21, R2 = 0.66, p < 0.01). There was no significant relationship between FT and the grain yield or WUE (p > 0.05). The total T during the jointing-heading and heading-filling periods (Tjf) had significantly quadratic relationships with the crop yield and WUE (p < 0.01). Both the crop yield and the WUE had high values under the Tjf range of 117.5–155.8 mm. Furthermore, the WUE was higher under larger ratio of E in ET (FE) during the greening-jointing period and lower FE during the filling-harvest period. Two irrigations during the greening-jointing (20 mm) and heading-filling (80 mm) stages and one fertilization (105 kg ha−1 N) during the greening-jointing stage were determined as appropriate irrigation and fertilization schedules.