Fig. 4. Influence of average N nutrition index (NNI) on the relative values of (A) crop dry weight, (B) cumulative intercepted photosynthetically active radiation (PAR), (C) light use efficiency (LUE), and (D) harvest index of potato at about 52 d after emergence (DAE) in 1997 and 47 DAE in 1998. The values are relative to maximum or critical values given in Table 4. Points represent individual replicates. Solid regression lines include all points, except those indicated by arrows. Dotted lines represent separate years.