选用美棉33B和泗棉3号两个叶色深浅差异明显的品种，设置氮素水平（0、120、240、360和480 kg hm-2纯氮）试验，研究棉花主茎叶SPAD值的叶位分布，对棉花进行氮素营养诊断。结果表明，棉花主茎顶部4张定型叶片的SPAD值对施氮水平反应的敏感程度存在显著差异，随施氮量增加，棉花主茎顶1、2、3、4定型叶SPAD值的大小位次发生明显变化，其中以顶1定型叶对施氮量增加的响应最为敏感，顶4定型叶最为迟钝。利用顶1定型叶与顶4定型叶SPAD值的相对差值，可较精确地诊断棉花的氮素营养水平，并能克服品种和生育时期不同的影响，是一种具有普适性的棉花氮素营养诊断指标。
The objective of this research was to investigate the positional distribution of SPAD values of the main-stem leaves and their relationships with the nitrogen content of cotton (Gossypium) leaves. The plant and leaf samples were analyzed for concentrations of N and SPAD values from the field experiments in 2004 and 2005 on the farm of Jiangsu Academy of Agricultural Sciences with two cotton cultivars and five N fertilization rates applied. The five N rates were 0, 120, 240, 360, and 480 kg ha-1 and the two cotton cultivars were Meimian 33B and Simian 3 which have obvious difference in leaf greenness. The results showed that the SPAD values of the two cultivars increased significantly with N rate increasing, and they all could be used as indices for diagnosis of the plant nitrogen nutrition. The leaf SPAD values at different positions on main stem of two cultivars responded differently to the N rate increasing, of which the 1st fully-expanded leaf from the top on the main stem (SL1) were more sensitive while the 4th fully-expanded leaf (SL4) responded slowest. The differences of SPAD values between SL4 and SL1 of the two cultivars decreased with N rate increasing. They could be well characterized by the relative positional difference index (PDI) reflecting the greenness difference between the SL1 and the SL4. The PDI was related to plant leaves nitrogen concentrations, which could be combined in a linear regression for Meimian 33B and Simian 3. In particular, the PDI can accurately indicate plant leaves nitrogen status of cotton varieties under varied nitrogen supply levels over different growth stages. It was concluded that PDI can be an ideal indicator of cotton nitrogen status.
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