Monitoring leaf photosynthesis with canopy spectral reflectance in rice

Non-destructive and rapid method for assessment of leaf photosynthetic characteristics is needed to support photosynthesis modelling and growth monitoring in crop plants. We determined the quantitative relationships between leaf photosynthetic characteristics and canopy spectral reflectance under different water Supply and nitrogen application rates. The responses of reflectance at red radiation (wavelength 680 run) to different water contents and nitrogen rates were parallel to those of leaf net photosynthetic rate (PN). The relationships of reflectance at 680 nm and ratio index of R(81 0,680) (near infrared/red, NIR/R) to P-N of different leaf positions and leaf layers in rice indicated that the top two full leaves were the best leaf positions for quantitative monitoring of leaf P-N with remote sensing technique, and the ratio index R(8 10,680) was the best ratio index for evaluating leaf photosynthetic characteristics in rice. Testing of the models with independent data sets indicated that R(810,680) could well estimate P-N of top two leaves and canopy leaf photosynthetic potential in rice, with the root mean square error of 0.25, 0.16, and 4.38, respectively. Hence R(8 10,680) can be used to monitor leaf photosynthetic characteristics at different growth stages of rice under diverse growing conditions.