ABSTRACT
For numerous species, plant N concentration decreases as biomass accumulates throughout the growth cycle, while N accumulation continues. This dilution of nitrogen by carbon assimilates accounts for the allometric relationship between N uptake and biomass accumulation (Salette and Lemaire, 1981). The decline of the N concentration in vegetative aerial organs over time may be attributed to a decrease in the leaf/stem ratio and to remobilisation of nitrogen from shaded to illuminated parts of the canopy (Lemaire et al., 1992). The N concentration of the crop can be related to biomass production following a general equation presented below, which accounts for environmental and genotypic effects in nonlimiting conditions:
%Ncrop = α* (DMcrop) –β (Eq. 1)
with %Ncrop and DMcrop being the N concentration and biomass (in t.ha –1)
of the aerial parts of the crop respectively . This relationship, which was named the “dilution curve”, was fitted
for grasses, especially cereals. On these species, this curve is valid during the vegetative growth cycle. Later it was used for lucerne and then grain legumes.
