Recalibrating plant water status of winter wheat based on nitrogen nutrition index using thermal images

Accurate and timely assessment of crop water status is imperative for in-season irrigation scheduling in crop production. The canopy water stress index and water deficit index have been widely used to appraise crop water status using spatial thermal images. However, the inter-relationships of CWSI, WDI and crop nitrogen status have been rarely investigated. Therefore, the present study was conducted to compare the differences between the CWSI and WDI values of winter wheat across different N and irrigation treatments, to examine the effect of crop N status on CWSI and WDI, and to recalibrate the CWSI and WDI values for better assessment of water status in winter wheat using nitrogen nutrition index. The result demonstrated that CWSI and WDI values decreased with the increasing irrigation rates within the same N treatments. However, both indices could not be used for assessing plant water status under different N treatments at the same I treatments. The increase in CWSI and WDI values with decreasing N rates indicated that there is a significant effect of plant N status on CWSI and WDI values. The pure canopy foliage temperature and mixed soil canopy temperature showed a significantly negative relationship with NNI across different N treatments. The recalibrated Tc and Ts values were lower than the original values under the N-limiting treatments. Using the recalibrated Tc and Ts value, the CWSI and WDI values were recalculated, which can better signify plant water status under different N conditions.