Adaptation of the crop model STICS to intercropping.: Theoretical basis and parameterisation

Given the complexity of intercropping systems, models can be especially helpful to analyse them comprehensively. The present work puts forward a modelling approach based on an extension of sole crop models, considering the system to be composed of two species instead of one. The chosen sole crop model is STICS and its adaptation to intercropping relies first on a simplified definition of the complex agronomic system, which is subdivided into three sub-systems: the dominant canopy, and the shaded and sunlit parts of the understorey canopy. It is assumed that no inversion of dominancy occurs during the cycle of the shorter duration crop. Each of the sub-systems is embedded in a different light microclimate, estimated from a radiative balance module, assuming that a simple geometric shape can represent the dominant canopy. This radiative balance pilots the differential behaviours of the sub-systems in terms of growth, LAI dynamics, water and nitrogen uptakes and stress indices. The estimation of the water requirements for both crops relies on light partitioning coupled to a resistive scheme and applied at a daily time-step. In the soil, the horizontal differentiation is neglected in favour of the vertical one. As far as below-ground competition for water and nitrogen is concerned, it is assumed that the interactions between the two root systems result from the influence of the soil on each crop root profile through its water content dynamics. Data sets from three different intercrops, two annual and one perennial systems grown in French Antilles, were used for parameterisation of the model and verification of its consistency. The intercrop-specific modules of the model are described and discussed in comparison with the other existing models.