Abstract: Hydrogen and oxygen isotope tracing is an important means in studying the hydrological cycle in soil-plant-atmosphere continuum (SPAC). Isotope ratio infrared spectroscopy (IRIS), with its unique superiorities, has been widely applied to investigate the stable isotopes of water from different sources, but some discrepancies in the measurement results are reported between IRIS and isotope ratio mass spectrometry (IRMS). In this paper, 19 water samples including 6 plant waters, 4 soil waters, 1 groundwater, and 8 rain waters were collected, with their hydrogen and oxygen isotopes measured by IRIS and IRMS. It was observed that all the samples except plant waters presented a well agreement in the measured results between IRIS and IRMS. The plant waters were contaminated during the cryogenic vacuum distillation process. By using the spectral contamination identifier, the δ_D values were well corrected, whereas the δ¹⁸O values still showed minor difference, as compared with those measured by IRMS. It was suggested that IRIS could be applied to replace IRMS to measure the stable isotopes of liquid waters which are not contaminated.

Key words: cotton, infrared thermal imager, canopy temperature,  , crop water stress index.