Plant spacing effect on the nitrogen concentration of a crop

The nitrogen concentration of plants decreases as they grow, the decrease being more pronounced for densely planted crops. The common explanation to this is the decreasing ratio between the metabolically active biomass and the support biomass, the former being associated with the sunlit leaves. Based on this view of the crop, two simple models, termed here 'specific' and 'general', have been developed and fitted to existing data. The 'specific' model fits exponential functions to data of isolated plants and to each planting density separately. The 'general' model uses a single set of parameters for all planting densities. Both fit the available data rather well, but more data are needed to test them for a range of densities. Simulations with the 'general' model also agree qualitatively with the Shinozaki-Akira density-dependent yield-prediction formula. (C) 2003 Elsevier B.V. All rights reserved.