Spatial distribution of leaf N content and SPAD value and determination of the suitable leaf for N diagnosis in rice

chinois. 研究分析水稻氮素和SPAD值的叶位分布特点，并试图提出SPAD计诊断氮素营养状况的最佳测定叶位。在95-38、武育粳3号、镇稻5394、9915等4个粳型品种和1个籼型品种R161-10的盆播氮肥试验和宁粳2号大田氮肥试验的基础上，研究水稻氮素和叶绿素含量（SPAD值）随叶位的空间分布特征，并对不同叶位叶片的含氮率、叶绿素含量、SPAD值之间及其与总叶片含氮率和植株含氮率之间的相关性进行分析，比较不同叶位叶片SPAD测定值的变异系数。水稻不同叶位叶片含氮率、叶绿素含量、SPAD值均存在差异，增加施氮量能提高叶片含氮率、叶绿素含量和SPAD值，同时减少叶位间的差异；SPAD值对氮素的敏感性顺序为顶4叶、顶3叶和顶2叶，而顶1叶的敏感性排序因品种不同而不同；穗分化期、齐穗期和成熟期均以顶3叶与总叶片及植株含氮率相关系数最高；且适宜氮素水平下，穗分化期顶3叶SPAD值的变异系数最小。以某一特定叶片的SPAD值或以叶色差的大小来诊断水稻氮素营养状况和推荐水稻穗肥施用时，顶3叶是较为理想的指示叶或参照叶。

anglais. In order to investigate the spatial distribution characteristics of leaf nitrogen (N) and SPAD (Soil Plant Analysis Development) value, and to determine the best leaf position for N diagnosis in rice with SPAD meter. 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 compared. The results showed that leaf N/ Chlorophyll content and SPAD value at different leaf position differed obviously, leaf N, chlorophyll content and SPAD value increased and their difference between different position leaves decreased at high N rates. The sensitivity of the forth leaf from the top to N was highest, then third and second, while the first leaf varied within the varieties. 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 through the panicle initiation stage, full-heading stage and mature stage. The CV of SPAD value of the third leaf from the top was smallest at fore-and-aft spike differentiation under optimal N level. It was suggested that 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.