A process-based model is the mathematical (and normally computer-based) representation of one or several processes characterizing the functioning of well-delimited biological systems of fundamental or economical interest. Examples include models of biochemical pathways or population dynamics models (single species or mixed). Usually, such models consist of a set of ordinary or partial differential equations that define the essence of each process (temporal patterns of key parameters), as well as their inputs and outputs, as a function of first principles (generic PBM) or else empirical knowledge (descriptive PBM). Outputs of one process can serve as input to other processes. Such a modeling paradigm was heavily employed in the case of crop modeling: A crop model describes the growth and development (phenology from germination to harvest) of a crop, at the level of the field, the canopy, or the plant (Goudriaan and van Laar 1994). In doing...