was a result of N dilution. The N dilution is the result of two processes: (i) self-shading of leaves that induces a nonuniform
leaf N content from the top canopy layers with high N concentration to the shaded layers with low N concentration; and
(ii) an increase in the proportion of plant structural and storage tissues with a lower nitrogen concentration, even when crops grow with non-limiting N supply (see Ple´net and Lemaire, 2000).