Competition and facilitation processes between sweet pepper and associated crops in additive intercropping system

Organic vegetable farms have a frequent recourse to intercropping in order to produce a diversity of vegetable on a small plot with high-yields. Additive row intercropping is a promising pattern to introduce a secondary crop into a main crop without drastically modifying other practices. However, the need for references on the design of intercropping systems, their performances and functioning is strong especially for production under walk-in shelter. Yield advantage in intercropping system results from two contrasted interaction processes between intercrops: competition and facilitation for resources. The objectives of this study were to compare the growth and the productivity of a sweet pepper intercropped with different secondary crops (French bean, parsley and onion) to that of a sweet pepper in sole crop and to reveal competition and facilitation processes at work with regards to soil resources and organisms. We set up an on-station field experiment in a completely randomized block design with three replicates and four treatments. All crops were planted at the same time and except intercropping, cultural practices were the same for all treatments: we used the same sweet pepper density, amounts of water, organic fertilizer, organic pesticides and similar pruning and trellising methods for all systems. We measured marketable yields of main and secondary crops as well as growth, root necrosis and mycorrhization of sweet pepper and monitored water and nitrate availability in soil. According to the secondary crop species, marketable yields of sweet pepper in intercropping systems were reduced from 21 to 28% compared to sole crop but this reduction was compensated by production of secondary cash crops. Soil resources monitoring suggests that water was a limiting factor, but nitrate was not. Roots of sweet pepper were more intensely colonized by arbuscular mycorrhizal fungi in intercropping systems but no significant effects were detected on root necrosis.