A pre-Columbian society in the Amazon rainforest developed a sophisticated agricultural irrigation system that allowed them to produce maize throughout the year, according to a discovery by an international team of researchers.

Extensive drainage canals and farm ponds were designed and engineered by indigenous people living in the plains of Llanos de Moxos in Bolivia, according to a study published in the journal Nature. The researchers describe how Casarabe communities transformed of flooded tropical savannahs into highly productive fields, driving a 'Neolithic Revolution' in the Amazon, and movement towards an economy based on grain production.

This finding contradicts previous theories that dismissed the possibility of intensive monoculture agriculture in the region.

Evidence of people living in the Llanos dates back to 8000 BC, while the region was inhabited by the Casarabe people between 500 and 1400 AD. It is a tropical lowland savannah marked by intense rainy seasons and flooding, as well as very dry seasons.

The discovery by the team led by Umberto Lombardo, an environmental archaeologist at the Universitat Autònoma de Barcelona (UAB), has identified a unique agricultural infrastructure previously undocumented anywhere else in the world. This system enabled farmers to drain excess water from flooded fields during the rainy season, facilitating agricultural productivity.

In addition to the drainage canals, the Casarabe people constructed clusters of farm ponds that served as water storage reservoirs, enabling pot-irrigation, which allowed maize cultivation to continue throughout the dry season. Pot irrigation is highly efficient and involves using buried porous clay pots filled with water to provide controlled irrigation directly into soil and to plants.

This dual water management system made at least two harvests of maize per year possible, ensuring a stable food supply all-year-round, which was essential for sustaining a relatively large population.

"This intensive agricultural strategy indicates that maize was not only cultivated but was likely the staple crop of the Casarabe culture," explains Lombardo.

This agricultural model did not rely on the slash-and-burn techniques traditionally used to create fertile fields in the Amazon. Instead, the Casarabe people preserved nearby forests for other purposes, such as obtaining firewood and medicinal plants, while implementing practices that maximised the efficient use of water and soil in the seasonally flooded savannahs.

The researchers' conclusions were made possible through meticulous fieldwork combining techniques such as microbotanical analysis, remote-sensing and environmental archaeology. The analysis of 178 plant microfossils and pollen samples from a farm pond confirmed the presence of maize in the fields and the crucial role of maize monoculture in the diet of this indigenous society.

"The data shows the absence of other types of crops," Lombardo adds. "We can document that this is the first grain-based agrarian economy in the Amazon, where until now it was believed that agriculture was based on agroforestry polyculture and not on large-scale monocultures.

"Now we know that this was not the case in Llanos de Moxos", says Lombardo, who asserts that this innovative piece of engineering allowed for the transformation of a challenging environment into a productive system that ensured food stability and supported the development of a growing population.

The research not only sheds light on the technological capabilities of pre-colonial civilisations, but also offers valuable lessons for modern agricultural sustainability. The researchers say this discovery is a testament to the ingenuity and adaptability of the Casarabe people, who thrived due to their ability to design long-term sustainable agricultural solutions in an adverse environment.

The international research team was drawn from institutions in Europe and Latin America, including the Institute of Environmental Science & Technology (ICTA-UAB) and the department of prehistory at the Universitat Autònoma de Barcelona in Spain; the Universities of Exeter, Nottingham, Oxford, Reading and Southampton in the UK; the University of São Paulo in Brazil, along with Bolivian collaborators.