Monitoring nitrogen accumulation in wheat leaf with red edge characteristics parameters

Three field experiments were conducted with different nitrogen application rates and wheat cultivars across three growing seasons, and time-course measurements were taken on canopy spectral reflectance, leaf dry weight and leaf nitrogen concentration under the various treatments. The primary objective of this study was to explore the optimum red edge characteristics parameters and quantitative models for estimating leaf nitrogen accumulation in wheat (Triticum aestivum L.). The results showed that the first derivative of the reflectance spectra changes regularly with increasing N rates in red edge region, and canopy spectral reflectance changes complexly. The analyses on relationships between the vegetable indices reported to leaf N accumulation indicated that red edge spectral parameters related most significantly to leaf N accumulation, differed among red edge spectral parameters. An integrated linear regression equation of leaf N accumulation to GM2, SR705 and FD742 described the dynamic pattern of change in leaf N accumulation in wheat, giving the determination of coefficients（R2）as 0.854, 0.848 and 0.873, respectively, and the standard errors (SE) as 1.136, 1.160 and 1.059, respectively. The two peak spectral parameters in red edge region were constructed on analysis of red edge characteristics, and differential vegetation index of two peak in red edge region LSDr_REPLE was highly correlated with leaf N accumulation with 0.868 of R2 and 1.080 of SE. When independent data were fit to the derived equations, the average relative error (RE) values as 17.6%, 17.0%, 14.9% and 14.5% between measured and estimated N accumulation using spectral parameters GM2, SR705, FD742 and LSDr_REPLE, respectively, indicating a good fit and better in LSDr_REPLE. The result indicated that those models could be used to reliably estimate the leaf N states in wheat, and especially LSDr_REPLE of new extracted parameters could indicate further steadily dynamic changes in leaf N accumulation.