Abstract:

【Objective】 Crop nitrogen status is an important index for evaluating the growth status and forecasting grain yield. Non-destructive and fast monitoring of leaf nitrogen status can play a significant role in precision nitrogen management in wheat production. The primary objective of this study was to explore the optimum wavebands, vegetation indices and quantitative models for estimating leaf nitrogen content (LNC) in wheat by precise analysis on canopy hyperspectral information in relation to leaf nitrogen status. 【Method】 On the basis of detailed data from 4-year field experiments under varied nitrogen rates and wheat cultivars, a systematic analysis was undertaken on quantitative relationships of LNCs to major hyperspectral indices composed of any two wavebands with original reflectance and its derivative within the full spectral range of 350-2 500 nm. 【Result】 The results showed that the optimum wavebands for LNC were 690 nm, 691 nm, 700 nm and 711 nm in the red edge range, and 1350 nm in the near-infrared range. The derived key hyperspectral parameters were NDSI (R1350, R700) and NDSI (FD700, FD690) as Normalized Difference Spectral Index, RSI (R700, R1350) and RSI (FD691, FD711) as Ratio Spectral Index, and SAVI (R1350, R700)(L=0.09) and SAVI (FD700, FD690)(L=-0.01) as Soil Adjusted Spectral Index. The LNC monitoring models developed from these spectral indices gave the coefficients of determination (R2) no less than 0.842. Testing of the derived equations with independent experiment data produced R2 values over 0.758 and RRMSE lower than 0.266, with best performance from the model based on RSI (FD691, FD711) and SAVI (FD700, FD690)(L=-0.01). 【Conclusion】 Overall, the method of discovering the optimum bands and constructing the spectra indices and building the model based on the systematic precise analysis methods can enhance the precision and reliability of the N monitoring model, and provide new waveband choice and technical approach for non-destructive and fast monitoring of the canopy nitrogen status in wheat.

Key words: wheat, optimum waveband, hyperspectral index, leaf nitrogen content