研究了不同土壤水氮条件下小麦（Triticum aestivum）抽穗后叶片碳氮状况及其比例与叶片叶色（SPAD值）的关系。结果表明，小麦中后期叶片氮含量和可溶性糖含量与顶部3张叶片叶色（SPAD值）均呈显著的指数正相关，其相关程度大小为L1>L2>L3，但与不同叶位叶色间的差值或比值相关并不显著；而叶片碳氮比与各叶位叶色相关不显著，但与顶1叶和顶3叶的叶色差值呈极显著直线相关，据此建立了基于叶色特征的叶片氮含量、可溶性糖含量和碳氮比监测模型，检验结果显示，顶1叶叶色和顶1叶与顶3叶叶色的差值可用来有效地评估小麦叶片的碳、氮含量及碳氮比状况。
Non-destructive monitoring of crop carbon, nitrogen and carbon to nitrogen ratios (C/N) is important for precision fertilizer management. This research was conducted to determine the relationships of leaf carbon, leaf nitrogen, and leaf C/N ratios to post-heading leaf color (SPAD values) in wheat (Triticum aestivum) under different nitrogen and water supply levels. The results showed that leaf soluble sugar content were positively exponentially related to leaf color in the top three leaves, but there were no significant relationships between color differences or ratios among different leaf positions. Similar trends were found for leaf nitrogen status. The correlation sequence was: L1>L2>L3 (correlation coefficients were 0.92, 0.86 and 0.71 for leaf nitrogen content and 0.84, 0.77 and 0.49 for leaf soluble sugar content, respectively). The best leaf position for monitoring leaf nitrogen and carbon status was the first leaf from the top in wheat (LSSC=4.080 8e0.026 9SPADL1, R2=707 5; LNC=0.697 2e0.026 1SPADL1, R2=837 6), with a RMSE of 0.22 and 0.04, respectively, for model testing. In addition, leaf carbon to nitrogen ratios were not significantly related to leaf colors in different leaf positions but were linearly significantly related with color difference between L1 and L3 in wheat (C/N=0.071 3×(SPADL1－SPADL3)+4.459), with a RMSE of 0.07 for model testing. These results indicate that the leaf color of L1 and color differences between L1 and L3 are good indicators of leaf soluble sugar content, nitrogen content and C/N in wheat leaves.