In many crop growth simulation models, leaf area index is often predicted from available carbon for leaf growth with little attention being paid to its response to nitrogen. The quantitative analysis presented by Yin et al. (pp. 893-903) shows that the relationship between leaf area index and canopy nitrogen content is linear for young canopies and logarithmic for established canopies. This finding, combined with the existing carbon-based approach, promises a robust model for predicting a temporal course of crop leaf area index under the framework of carbon-nitrogen interaction.