Main conclusions of this study are addressed to agronomy, in general, and to crop modeling, in particular:

• As for the agronomic issues, it is clear that, to obtain the potential production, non-limiting water and mineral nutrition are not enough for some cultivated species (potato, sugar-beet, and sunflower). Soil type, its physical proprieties and soil management improving its physical proprieties play a determinant role in crop productivity.

• As for the crop productivity models, under non-limiting conditions of water and mineral soil nutrition, existing models simulate the biomass increase as a function of the absorbed radiation and of the RUE value characteristic of each crop. The validity of this hypothesis is restricted by the conclusions of the present work. Our result explains at least one of the possible reasons why predictions, provided by simulation models, do not always fit the observed data. Since some species demonstrate the RUE sensitivity to soil type, RUE values should be simulated accordingly.

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