Intercropping is one of the traditional farming systems practiced by farmers in China for more than 2,000 years with some intriguing ecological principles. Previous studies have shown that intercropping enhances not only crop productivity but also the efficient utilization of resources, both above-ground and below-ground. Recent research efforts have made progress towards a better understanding of intercropping. Here, we reviewed the potential of intercropping to strengthen ecosystem services and functions at the agroecosystem level, propose research directions and highlight practical uses in modern agriculture.

Intercropping increased biodiversity, productivity and stability of agroecosystems. In addition, intercropping enhanced water use by separating in time the maximum water requirements for the different species and by separating spatially their hydraulic lift. The enhancement of nitrogen (N) acquisition was attributed to niche differentiation of N resources, in which cereals acquired more mineral N from the soil while legumes fixed more N from air N₂: cereals were more competitive than legumes in uptaking N, fostering symbiotic N₂ fixation in legumes. Some species facilitated the conversion of unavailable P into mobilized P, benefiting themselves and the neighboring species. For instance, the roots of fava beans released carboxylates or protons to help dissolving P compounds. Also, the roots of chickpeas released phytase or phosphates to decompose organic P in the soil, increasing P availability. There were inter-specific facilitations of iron (Fe) and zinc (Zn) when intercropping dicotyledonous or non-graminaceous species (with strategy I for Fe acquisition and non-Fe or Zn mobilization) and graminaceous monocotyledonous ones (with strategy II for Fe acquisition and Fe or Zn mobilization). This benefited micronutrient availability in intercropped non-Fe mobilizing or Zn-mobilizing species.

In the paper, we also identify some important research directions for the future of intercropping research and its practical uses. Research directions include crop diversity and agricultural sustainability, signal-controlled interspecific interactions between intercropped species, linking those interactions to above- and below-ground diversity and functional, structural and empirical models for intercropping. Intercropping can be used to develop ecologically intensive agriculture and organic farming, enhance fertilizer recovery and enrich edible crop parts with micronutrients. Finally, we identify the need to develop suitable machinery and to breed new crop varieties for intercropping.