Modelling nitrogen and light sharing in pea-wheat intercrops to design decision rules for N fertilisation according to farmers' expectations

Cereal-legume intercropping has gained increased interest in Europe. Nevertheless, performance and especially the percentage of each species at harvest are often considered highly variable. Nitrogen (N) fertilisation can be a relevant driving factor affecting the percentage of each species at harvest. Soil N availability influences competition for light and nitrogen in cereal-legume intercrops. However, management of N fertilisation still remains unclear for intercrops. Few references on the effects of a range of strategies of N fertilisation are available to guide farmers with relevant decision rules considering their expectations. Here, a modelling approach was proposed to simulate interactions between light and N acquisition of a pea-wheat intercrop and to test different scenarios for the management of such intercrops. A model (Azodyn-IC) was built resulting from the combination of two existing individual-crop models (AZODYN and AFISOL) and by applying rules of light and soil inorganic nitrogen sharing between the intercropped pea and wheat. Evaluation of the model outputs with experimental data showed satisfactory predictions of the studied variables (N accumulation, LAI, and crop dry weight). The model validated both resource sharing and light-N interactions. Furthermore, the model was able to respond to increases in inorganic N availability based upon straightforward formalisms. Simulating unmeasured variables, such as root growth and light interception and use by each species, improved our understanding of the relative dominance of each species for acquiring resources. Eventually, the model was used to simulate different scenarios of N fertilisation over 26 years of climatic data to account for climatic variability. We demonstrated the interest of such a modelling approach to design decision rules of N fertilisation according to farmers' expectations.