Fig. 6. Linear regression of cotton leaf N concentrations with the values of a specific reflectance ratio (R₅₁₇/R₄₁₃) that had the greatest r² value with leaf N. Leaf N concentrations were expressed on both (left) a leaf dry weight basis and (right) a leaf area basis. Data were pooled across the studies, treatments, replications, and sampling dates (n = 120 in 2001 and n = 156 in 2002). MC, mepiquat chloride.