Mixed crops are multiple crops that co-occur on the field. This can range from herbal pastures over crop mosaics to crops in lines. Aim is the positive influence of the crops on each other. This can occur in a direct way in which the combination of crops leads to higher total yield than the individual crops, but also indirect. For example clover in grass can fixate nitrogen, diversity of roots in herbal leys lead to a better soil structure or beneficial insects can always find shelter because parts of the soil are always covered.
An interesting project about mixed crops is Strip cropping (The Netherlands). The strip cropping project is using new large-scale strip trials to see if crop diversity can fulfill its promise of creating a robust, plant-based food production system. Here (English) you can find a presentation with the results of the project
An other interesting project about mixed crops is ReMIX. The aim of the project is to redesign European cropping systems based on species MIXtures. ReMIX will exploit the benefits of species mixtures to design more diverse and resilient arable cropping systems, making use of agro-ecology principles and adopting the EIP-Agri multi-actor approach.
Here you can find the results of the project (French).