Many models have been constructed to describe the growth of the sugar beet crop up to harvesting. In general, these models have a complex physiological basis, requiring a large number of parameters yet relying on empirical functions with no mechanistic basis to partition assimilates within the crop. An important factor in considering the growth of the crop, both from an economic and environmental point of view, is the response of the crop to varying amounts of available nitrogen in the soil. In this paper, a model is described for crop growth using soil nitrogen content and solar radiation as driving functions. The parsimonious approach to construction resulted in a 14 parameter model, seven of which are associated with the driving variables. This is substantially fewer than for other crop models. The model contains a new dynamical way of describing partitioning of assimilates between shoot, storage root and fibrous roots. The partitioning model is derived from observations on the effect of soil nitrogen on crop growth. Interception of light is determined by foliage cover, which makes the model suitable for use with data collected from satellite imaging. The model fits well to three independent data sets with estimated parameters lying within biologically reasonable bounds. The model is used to test the sensitivity of yield to changes in soil nitrogen. (C) 1997 Annals of Botany Company.
