Fig. 1. Leaf N concentrations versus relative yields from N fertilization trials conducted in LA, MS, AR, and AL in 1996 and 1997. Results are presented for growth stages of first pin-head square (a), early bloom (b), mid-bloom (c), and cut-out (d). Our recommended critical values are presented as the vertical dotted line for early and mid-bloom growth stages. Correct diagnoses using these critical values are found in the bottom left and top right quadrants. At first pin-head square, some sites are represented as open squares (Brewton, AL), open triangles (Columbia, LA), and open diamonds (St. Joseph, LA).