Intercropping consists in growing distinct crops on the same plot at the same time. It may play a role in the transition towards a more sustainable agriculture, thanks to its many advantages, e.g. higher yield, lesser use of pesticides. Intercropping has experienced a particular boom in recent years in the market gardening sector and there are now countless mainstream market gardening books dealing with it. However, its use by professional market gardeners remains low. The most likely reason is that Intercropping management is more complex than the image conveyed by mainstream books and very little objective data is available to help market gardeners in its relevant implementation.

In this thesis, we tackle the issue of intercropping in market gardening with the objective of providing market gardeners with knowledge and reliable information enlighting management choices. We begin by listing the interactions observed in intercropping, both between the associated crops and with their environment, and present these interactions as networks. We then investigate the prediction of intercropping outcome based on complementarity principles by comparing the results of a series of intercrops in on-field trials. We show the importance of the difference in sowing date, growth dynamics and maximum soil coverage between associated crops in the determination of yield gain and yield gain asymmetry in intercrops. Finally, we address the issue of inter-site variability of yield by comparing the growth and outcome of specific intercrops in different farms, using participatory on-farm trials. We explain the participatory methodology we used and show the consistency of intercrops relative outcome across a gradient of environmental conditions and crop management practices.

Our approach was purposely exploratory and aimed at taking an overview of our subject. This thesis paves the way for the scientific study of intercropping in market gardening and highlights some key points about the use of intercropping by market gardeners.