Fig. 9. The use of old (A and B) and new (C) Cate–Nelson procedures to determine the critical N content of shoot tissue at different crop stages for optimum relative protein yield (ha^-1) of the pearl millet hybrid HGM 100. Arrows in A and B 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.