Red edge characteristics and monitoring SPAD and LAI for rice with high temperature stress

For promoting the application of hyper-spectral technique on growth monitoring and disease evaluation in rice, the high-temperature stress experiments for two rice cultivars Yangdao 6 and Nanjing 43 were conducted in this paper, and canopy hyper-spectral reflectance, red edge parameters, soil and plant analyzer development (SPAD) value and leaf area index (LAI) of two rice cultivars at different growth stages were measured under high-temperature stress on booting stage. The results showed that SPAD value and LAI of two rice cultivars presented a tendency from rising to falling with development of growth stages, wherein both of them were up to peak value on flowering stage and turned lower value on early heading and ripening stages. The SPAD value and LAI would be reduced with the elevation of stress temperature. There were ‘red shift’ phenomena before flowering and ‘blue shift’ phenomena after flowering for the red edge position, red edge slope and red edge area of canopy spectrum. With the elevation of stress temperature, the ‘blue shift’ phenomena were also presented for those three red edge parameters. The SPAD value and LAI of rice flag leaves at different growth stages were significantly or very significantly correlative to the red edge feature variables. Therefore, the model based on red edge position could be more reliable for predicting SPAD value and LAI of rice flag leaves compared with red edge slope.