Use of a new sigmoid growth equation to estimate organ area indices from canopy area index in winter oilseed rape (Brassica napus L.)

In oilseed rape, the formation of organ area indices (AI), in particular of leaves and pods, is a key process determining seed yield. However, analyses of AI dynamics in rapeseed are rare in literature. This is because destructive measurements of organ area are usually labour-intensive and often impaired by large sampling errors. Here, we present a new approach for estimating AI of different organs from total canopy area index using a model that is based on combining growth equations. The proposed model provides a compact and robust tool for describing the time courses of area indices of aerial organs from the beginning of shooting until ripening. Key characteristics of AI development are defined by the model in unique way. The model was successfully tested against sets of data either taken from literature or from own experiments, including different years, locations, cultivars, and levels of nitrogen fertilisation. Data from non-destructive measurements of total canopy area index were used for adjusting the model to different scenarios. The performance of the model can be further improved specifying parameter values for different growth conditions and cultivars. Nevertheless, the model in its present form together with given parameterisation complies well with key characteristics of AI formation and may be used to reduce laborious destructive measurements.