Intercropping to Maximize Root–Root Interactions in Agricultural Plants

Intercropping is a traditional farming practice involving two or more crop species, or genotypes, growing together, and coexisting for a period of time. Compared with the monoculture, intercropping systems provide several advantages driven mainly by interspecific root–root interactions. Therefore, how root–root interactions can be used to sustainably intensify agricultural production by optimizing intercropping systems both agronomically and ecologically becomes essential. First, we summarized the distribution of intercropping in the world. Second, we discussed in detail the importance and the main drivers of root–root interactions in intercropping, including yield advantages, complementarity, facilitation of nutrient acquisition. Third, we focused on the effects of intercropping systems on below-ground processes, considering root distribution, biological nitrogen fixation, and phosphorus and micronutrient acquisition. Finally, we described the competition-recovery principles and plasticity mechanisms. By maximizing facilitative root–root interactions in intercropping, we can optimize and sustainably intensify agricultural production.