Abstract:

In order to improve the method of nitrogen spectral diagnosis, we conducted a experiment with two winter wheat (Triticum aestivum L.) cultivars Jing 411(low protein content) and Zhongyou 9507(high protein content) under nitrogen application levels of 0, 100, 200, and 400 kg N ha^-1. The wheat canopy spectral reflectance over 350–2 500 nm and canopy leaf nitrogen contents (CLNC) were measured at tillering, jointing, heading, milking, and mature stages. Seven vegetation indices (VIs) with view angles of 0°, 30°, 60°, 90°, 120°, 150°, and 180° to the vertical line to wheat row were compared with corresponding CLNC. The results indicated that CLNC had most significant correlations with RVI[670,890] among seven spectrum vegetation indices, especially in the view angles of 0°, 30°, and 90°, and the predicting models for CLNC were further established on the basis of the correlations. The coefficient of determination (R²) of three models were sequenced as: 0°＞30°＞90°. Root mean square error (RMSE) and R2 between measured and estimated CLNC were employed to test the model reliability and predicting accuracy. RMSE and R² were different in different view angles and cultivars, the model based on the view angle of 0°had RSME of 0.2915 and R² of 0.902 for Jing 411, and RSME of 0.3824 and R² of 0.872 for Zhongyou 9507. There were lower RMSE and higher R² in the model established based on the view angle of 0°than in that of other angles. The correlation was different between canopy spectral reflectance and CLNC in different cultivars, indicating that different predicting models should be selected based on different cultivars.

Key words: Canopy leaf nitrogen content(CLNC), Observational angle RVI, Model, Winter wheat (Triticum aestivum L.)