Fig. 6. The use of old (A and B) and new (C) Cate-Nelson procedures to determine the critical N concentration of shoot tissue at different crop stages for optimum relative grain yield of the pearl millet hybrid HGM 100. Arrows in A and B would represent accurate diagnoses of deficient or adequate levels of N. Intersection of the vertical line with the y axis represents the critical N value in A and B, whereas the highest coefficient of determination (r²) value produced by a shoot N concentration represents the critical value in C.