Ontogenetic decline in the nitrogen concentration of field grown white cabbage—Relation to growth components

The plant nitrogen concentration (PNC) declines ontogenetically with growth and the rate of decline can be determined by repeated sampling. Alternatively, the rate of decline can more easily be derived from weight-leaf-area relations. To investigate these possible ways to determine the rate of decline in PNC, the relations of PNC to growth and leaf area were examined in a multi-N-rate and multi-harvest experiment with white cabbage. The experiment was conducted in Uppsala, Sweden (59°49′N, 17°39′E). The rates of decline in PNC, leaf area ratio (LAR) and relative growth rate (RGR) could be described by the exponent b of biomass (W) of the power function y = aWb. The rate of decline in PNC during the linear growth phase (from 49 to 97 days after transplanting, DAT) was associated with a corresponding decline in LAR, with b = −0.3 in both cases, whereas by definition RGR declined with b = −1. This offers a possibility to predict the decline in PNC from the decline in LAR.