MONITORING LEAF CARBON AND NITROGEN STATUS IN WHEAT WITH LEAF COLOR CHARACTERISTICS

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: L 1L 2L 3 (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 8 e 0.026 9SPADL 1 , R 2=707 5; LNC=0.697 2e 0.026 1SPADL 1 , R 2=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 L 1 and L 3 in wheat (C/N=0.071 3×(SPADL 1-SPADL 3)+4.459), with a RMSE of 0.07 for model testing. These results indicate that the leaf color of L 1 and color differences between L 1 and L 3 are good indicators of leaf soluble sugar content, nitrogen content and C/N in wheat leaves.