Effects of Nitrogen Fertilizer Level on Chlorophyll Fluorescence Characteristics in Flag Leaf of Super Hybrid Rice at Late Growth Stage

To compare the effects of slow-release nitrogen fertilizer at six different levels on the flag leaf chlorophyll fluorescence characteristics of super hybrid rice, a field fertilization experiment was conducted with super hybrid rice Y Liangyou 1 as a test material. The photosynthetic electron transport rate (ETR), effective quantum yield (EQY), photochemical quenching coefficient (qP), and non-photochemical quenching coefficient (NPQ) of flag leaves were measured at the initial heading, full heading, 10 d after full heading and 20 d after full heading stages. Results showed that the values of ETR, EQY and qP increased with rice development from initial heading to 20 d after full heading, whereas the NPQ decreased. During the measured stages, ETR, EQY and qP increased initially and then decreased as nitrogen application amount increased, but they peaked at different nitrogen fertilizer levels. The maximum ETR and EQY values appeared at the treatment of 135 kg/hm2 N. In conclusion, the optimum nitrogen amount for chlorophyll fluorescence characteristics of super hybrid rice was 135-180 kg/hm2.