Abstract: The field experiment was carried out in two winter wheat growing seasons during 2007–2009. Winter wheat canopy reflectances in the 656 nm and 770 nm wavelengths were obtained by GreenSeeker at over-wintering stage, reviving stage, jointing stage, early-filling stage, and last-filling stage, respectively, in order to compute NDVI [(NIR₇₇₀-R₆₅₆)/(NIR₇₇₀+R₆₅₆)]. Yields were collected at harvest stage and compared among different nitrogen application rates. Canopy NDVI changes were analyzed with nitrogen increasing and growth, respectively. Furthermore, correlation analysis was done between yield and canopy NDVI. Yield estimation models were established for winter wheat based on canopy NDVI. Results showed that, winter wheat yield changed in parabola shape with N increasing. Wheat canopy NDVI value presented almost changeless before reviving stage, but great increase from reviving stage to early-filling stage with N increasing. In the whole growth stage, canopy NDVI value presented a trend of “low–high–low”. The correlation between canopy NDVI and yield was positive in the whole growth stage with different N rates and gradually became higher with growth, and up to the highest at the late-filling stage. The yield estimation models based on canopy NDVI at early-filling stage (P=0.005) and late-filling stage (P<0.001) were greatly significant. Regression validated between predicted and measured values was significant at early-filling stage (P=0.0129) and greatly significant at late-filling stage (P=0.0002). So, it is feasible that using canopy NDVI at early-filling stage and late-filling stage estimates winter wheat yield, especially at late-filling stage.

Key words: Winter wheat, Nitrogen application rate, Yield, Canopy NDVI, Estimation models