Intercropping is the cultivation of more than one crop species on a single parcel of land.Intercropping seeks to exploit species complementarities to capture more of the available light, water and nutrient resources, and thus increase combined crop yield[1].Intercropping is well known in China, where smallholder farmers practice a great diversity of species combinations to increase their yields[2].Figure 1 illustrates intercropping as done by a farmer in Gansu Province, China, who chose to combine wheat, soybean and maize.This three-way combination offers several species complementarities.First, the growing period of wheat ends earlier than that of soybean and maize, so the soybean and maize can use all the light, water and nutrient resources of the land after wheat harvest.With the wheat covering only around half of the area, the plants will still produce about 70％ of the normal yield for wheat grown as a sole crop, because the wheat has virtually no competition for resources early on, resulting in greater capture of light, water and nutrient resources in the intercrop than in a sole crop[3].Furthermore, soybean and maize have a complementarity for nitrogen acquisition, with maize requiring nitrogen from soil, but soybean being able to fix it from the air.Therefore.this combination can reduce fertilizer requirements[4].