Abstract: Abstract: 【Objective】 Investigate the spatial distribution characteristics of leaf nitrogen (N) and SPAD value, and determine the best leaf position for N diagnosis in rice with SPAD meter. 【Method】Based on the rice pot experiment involving five varieties (four were Japonica, one was Indica) and two N treatments and field experiment with different N treatments, the spatial differences of N and Chlorophyll content (SPAD value) in the four upper fully expanded leaves and their relationships with whole leaf and plant N concentration were investigated. Furthermore, the coefficient of variation (CV) of SPAD values at different leaf position was also compared. 【Result】Leaf N/ Chlorophyll content and SPAD value at different leaf position differed obviously, increasing N rates increased leaf N, chlorophyll content and SPAD value, and decreased the difference between different leaves. The fourth and third leaf from the top were more sensitive to N than the upper two leaves. The SPAD value of the third leaf from the top was most correlated with whole leaf and plant N concentration among the top four leaves at all growth stages. While the CV of SPAD value of the third leaf from the top was smallest at fore-and-aft spike differentiation under optimal N level. 【Conclusion】The third leaf from the top was the most ideal indicator when using SPAD value or leaf color difference to diagnose N status and make N fertilization recommendation at panicle initiation stage in rice.

Key words: Nitrogen diagnosis, spad, Leaf position, Nitrogen