Abstract:

It is very important for using non-destructive method to determine nitrogen status and growth characters of crop plants. Remote sensing has been successfully applied in assessing crop biophysical and biochemical variables, such as leaf area index, chlorophyll, nitrogen and so on. Chlorophyll fluorescence is a new non-destructive instrumentation for predicting leaf nitrogen content of crop. In this study, two experiments were carried out at Nanjing to investigate the correlative relationship of leaf nitrogen content to fluorescence parameters in wheat (Triticum aestivum L.). Experiment one was conducted with two cultivars (Ningmai 9 and Huaimai 20) and five nitrogen rates of 0, 75, 150, 225 and 300 kg ha^-1 in 2003. Experiment two included two cultivars (Ningmai 9 and Yumai 34) with three nitrogen rates of 0, 90, 270 kg ha^-1 in 2004. The change patterns of leaf nitrogen contents and fluorescence parameters across growth stages in different wheat cultivars were determined under different nitrogen levels, the correlative relationships of leaf nitrogen contents to fluorescence parameters were established, and the regression equations for predicting leaf nitrogen contents were formulated. The results showed that the leaf nitrogen contents and fluorescence parameters at different leaf positions of wheat increased with raised nitrogen applications. From booting to maturity, fluorescence parameters Fv/Fm and Fv/Fo of wheat leaves initially increased and then decreased with growth process of time. Leaf nitrogen contents of different leaf positions in wheat had significant positive correlations with fluorescence parameters Fm，F_v，F_v/F_m，F_v/F_o，F_s and F_o’, especially the correlation in the 1st and 2nd leaves from top was the best. Nitrogen contents of two top leaves in different wheat cultivars were significantly related to F_v/F_m and F_v/F_o, with average R₂ of 0.66 and 0.61, respectively. For different types of cultivar with low, medium and high grain protein contents, an integrated regression equation could be used to describe the dynamic change pattern of leaf nitrogen contents at the two top leaves with fluorescence parameter (F_v/F_o).

Key words: Wheat(Triticum aestivum L.), Leaf position, Leaf nitrogen content, Fluorescence parameter