The Ecology of Maize
In Mexico, Central and South America, the crop plants known at the Three Sisters - corn, beans, and squash- have for thousands of years formed the basis of the diet of people living in these areas. The three plants are grown together (a polyculture). There are good ecological reasons benefits from growing these plants together.
Traditionally, the type of agriculture practiced in Latin America is called slash and burn. An area of forest is cut down, and the cut vegetation is left to dry in the field. After it is dry, the farmer sets fire to it. The leafy material burns quickly and the logs burn over several days until they turn to ash.
Within a week after the burn, farmers plant their fields. The nutrients that were in the slash are now available for the crop.
Corn and bean seeds are planted together in a single hole. Squash seeds are planted on small mounds of earth between the corn and beans. The corn germinates and grows quickly providing a support for the bean vines as they grow. The squash plants produce long vines that grow close to the ground. Within a few weeks, the squash plants produce many branches with large leaves that cover the ground surface and suppress the germination and growth of weeds. The beans provide another ecological benefit to the other crops growing in the field. Beans have a beneficial relationship with a bacterium, Rhizobium. This bacterium lives inside a fleshy nodule on the bean root. The bean provides this “home” for the bacterium and also provides carbohydrates as food/energy for the bacterium. The Rhizobium has the ability to take gaseous Nitrogen from the soil and transform it into a type of nitrogen that the bean plant uses as fertilizer.
The ancient cultures of Mexico also developed unique agricultural systems. One of these systems, called chinampas, was important in the Aztec city of Tenochitlan. The present day city of Mexico City occurs in the location of Tenochitlan. Before the arrival of the Spaniards, Tenochitlan was located in the Valley of Mexico- an area that was swampy and often flooded. To practice agriculture in this region, the Aztecs dug canals and built up earthen platforms with the mud. Many crop plants, including corn, beans, squash, tomatos, chilis, grew on these platforms.