| In this experiment, the field capacity (FCv) and soil volumetric moisture content (WCv) were measured by three kinds of soil moisture instruments as frequency domain reflection (FDR), time domain reflection (TDR) and standing wave ratio (SWR) under field condition. The target relative soil moisture content was controlled as 80%, 70% and 70% in before the winter, jointing stage and anthesis stage, respectively. The soil depths for measuring soil moisture were set 20, 40 cm and 60 cm in each supplemental irrigation stage. The accuracy and stability of different instruments for soil moisture measuring during growing season of winter wheat has been researched to explore the effect and different reasons measuring soil moisture by different instruments to calculate irrigation quota for supplemental irrigation. The results showed that: The relative error was 0.4%～2.6% comparing the FCv-m measured by FDR and SWR with the FCm measured by the traditional method. The relative error between the WCv-m measured by TDR and the WCm measured by drying method has shown a significant positive correlation with the related soil depth temperature. It was high in sowing period, blossom stage and mature period, but was lower in before wintering and jointing stage. The relative error of WCv-m and WCm measured by SWR with the soil moisture content was a significant negative correlation, the measured accuracy was higher under the condition of higher soil moisture content. The measured accuracy and stability of FDR were total higher, which less affected by soil temperature and soil moisture in the growing season of winter wheat. Direct using the FCv and WCv measured by FDR to calculate the irrigation quota for supplemental irrigation have obtained the coincidence effect with the traditional drying method. |