Diversification and combination of crops is one of the principles of regeneration agriculture. By planting two, three or more plants side by side on the same plot, many benefits can be obtained. The plants play a structuring and nourishing role for the soil, while helping each other.
One family of plants is systematically associated with crops: that of beans, which are called legumes (or fabaceae). They have the power to capture nitrogen from the air that cannot be assimilated by other plants and return it to the soil, through the degradation of their roots and leaves. By leaving these plants on the soil, we increase the content of organic matter and nitrogen. This feeds the fauna of the soil (earthworms, insects...) and allows to reduce the contribution of fertilizers.
We can also combine squash, whose large leaves provide shade and preserve soil moisture. This benefits corn and bean crops, for example.
Generally speaking, the choice of species is based on the needs of the population and local crops.
The advantages of crop association are:
Increase the carbon and nitrogen content of the soil
Preserve soil moisture
Promote infiltration and water retention (through root action)
Improve soil structure
Increase biodiversity in fauna and flora
Diagram: the effects of nitrogen from legumes on other plants.
Diagram: example of Milpa (maize-squash-beans)
Le Monde : https://www.youtube.com/watch?v=qtiNAKNG_Wg