Plants with an insufficient N supply having the same number of leaves exhibited lower growth and had lighter colored leaves. Moreover, at harvest time, the color value a* showed that heads with optimal N supply in combination with optimal and excessive S supply were significantly more green than the heads with insufficient N supply (Tab. 1).
The color values L*, b*, and color saturation C*, as well as the hue angle of the broccoli heads did not differ significantly as their variability was quite high. Especially the broccoli plants subjected to insufficient S supply showed a strong non- homogeneity of the single heads in their yellow color (value b* minimum 7.7 – maximum 19.3). The color differences between broccoli heads may be explained by reduced chlorophyll concentration that is associated with S deficiency as reported for spinach (Dietz, 1989). However, as the outer product quality is very strongly determined by the head color due to consumers preferring very green broccoli, yellow values do not correspond to consumer preference (Schonhof et al., 2004).