Chinampa system farming (sometimes called floating gardens) is a form of ancient raised field agriculture, used by American communities beginning at least as early as the 10th century AD. The word chinampa is from a Nahuatl (native Aztec) word, chinamitl, meaning an area enclosed by hedges or canes. The term refers today long narrow garden beds, separated by canals. The garden land is built up from the wetland by stacking alternating layers of lake mud and thick mats of decaying vegetation; this process is typically characterized by exceptionally high yields per unit of land.
Ancient chinampa fields are difficult to identify archaeologically, if they've been abandoned and allowed to silt over: however, a wide variety of remote sensing techniques have been used with considerable success. Other information about chinampas includes archival colonial records and historic texts, ethnographic descriptions of historic period chinampa farming schemes, and ecological studies on modern ones. Historical mentions of chinampa gardening date to the early Spanish colonial period.
Ancient chinampa systems have been identified throughout the highland and lowland regions of both continents of the Americas, and are also currently in use in highland and lowland Mexico on both coasts; in Belize and Guatemala; in the Andean highlands and Amazonian lowlands. Chinampa fields are generally about 4 meters (13 feet) wide, but can be 400-900 m (1,300-3,000 ft) in length.
Farming on a Chinampa
The benefits of a chinampa system are that the water in the canals provides a consistent passive source of irrigation. Chinampa systems, as mapped by Morehart in 2012, include a complex of major and minor canals, which act both as freshwater arteries and provide access to and from the fields.
In addition, the upkeep of the raised beds involves continual excavation of soil from the canals, which is then redeposited atop the garden beds: the canal muck is organically rich from rotting vegetation and household wastes. Estimates of the productivity based on modern communities (described in Calnek 1972) suggest that 1 hectare (2.5 acres) of chinampa gardening in the basin of Mexico could provide an annual subsistence for 15-20 people.
Some scholars argue that one reason chinampa systems are so successful has to do with the diversity of species used within the plant beds. In a 1991 report, Jiménez-Osornio et al. described a system in San Andrés Mixquic, a small community located about 40 km (25 mi) from Mexico City, where an astonishing 146 different plant species were recorded, including 51 separate domesticated plants. Other scholars (Lumsden et al. 1987) point to a damping down of plant diseases, compared to ground-based agriculture.
Recent Ecological Studies
Ecological studies on modern chinampa soils in Mexico City have been concerned with the application of heavy metal pesticides such as methylparathion, an organophosphate which is extremely toxic to mammals and birds. Blanco-Jarvio and colleagues found that application of methylparathion negatively impacts the kinds of levels of nitrogen available in the chinampa soils, decreasing beneficial types and increasing those not-so-beneficial. However, removal of the pesticide has been successfully completed in the laboratory (Chávez-López et al), lending hope that damaged fields may yet be restored.
The first archaeological investigations into chinampa farming were in the 1940s, when Pedro Armillas identified relict Aztec chinampa fields in the Basin of Mexico, by examining aerial photographs. Additional surveys of central Mexico were conducted by William Sanders and colleagues in the 1970s, who identified additional fields associated with the various barrios of Tenochtitlan.
Chronological data suggests chinampas were built at the Aztec community of Xaltocan during the Middle Postclassic period, after significant political organization was in place. Morehart (2012) reported a ~1,500-2,000 ha (3,700-5,000 ac) chinampa system at the postclassic kingdom, by using a combination of aerial photographs, Landsat 7 data, and Quickbird VHR multi-spectral imagery, integrated into a GIS system.
Scholars such as Morehart suggest that the building and maintaining of extensive chinampa farms had to have involved organizational and administrative responsibilities that required top-down planning and construction. Ethnographic data from Tiwanaku in Bolivia has suggested that maintenance, at least, was managed at the local level.