Abstract:

Carbon (C), nitrogen (N) metabolism provides the substance basis of plant growth and development, and non-destructive, quick assessments of C, N content (%) and C/N with remote sensing are very necessary for the research of plant growth regulation, carbon and nitrogen cycling, and global climate change. In order to study the feasibility of the C, N content and C/N measurements with canopy reflectance spectra, canopy spectral reflectance (460–1 650 nm) data at tillering, heading and filling stage of rice (Oryza sativa L.) in field experiments with different N levels at two different sites were recorded with MSR-16 radiometer, and corresponding C, N content and C/N were also measured. Then the relation of C, N content and C/N in leaves and plant to reflectance of single band and all two-band combinations in the ratio vegetation index (RVI, λ₁/λ₂), normalized difference vegetation index NDVI (λ₁－λ₂)/(λ₁+λ₂), and difference vegetation index (DVI, λ₁－λ₂) were analyzed. Results showed that strong correlation existed between C, N contents and C/N in rice leaves/plant and spectral vegetation indices, the performance of RVIs was consistent with NDVIs, while a little difference with DVIs. Correlogram of C/N to different spectral vegetation indices was similar with that of N (Fig.2). Ratio and normalized difference vegetation index composed by 510 nm and 460 nm was significantly correlated with N content in leaves and plant, and data from three different development stages can be fitted with an uniform equation (Fig.3). While the relationship of C/N and vegetation indices at post-heading (including heading stage and filling stage) was better than that at whole growing stage, with the best index of ND(1650,710). Tests with other independent dataset showed that the estimation precision of N content and C/N in leaves and plant was 80.51%, 81.09%, 76.36% and 70.70%, with the RMSE of 0.20, 0.26, 1.64 and 3.95 respectively (Fig.4). This suggests that vegetation indices can be used to estimate N content and C/N in rice.

Key words: Rice, Canopy reflectance spectra, Nitrogen, Carbon, C/N, Vegetation index