Discovery of a unique drainage and irrigation system that gave way to the “Neolithic Revolution” in the Amazon

A pre-Columbian society in the Amazon developed a sophisticated agricultural engineering system that allowed them to produce maize throughout the year, according to a recent discovery by a team of researchers from the Institute of Environmental Science and Technology (ICTA-UAB) and the Department of Prehistory at the Universitat Autònoma de Barcelona, (Spain); the Universities of Exeter, Nottingham, Oxford, Reading and Southampton (UK); the University of São Paulo (Brazil) and Bolivian collaborators. This finding contradicts previous theories that dismissed the possibility of intensive monoculture agriculture in the region.

The study, published today in the journal Nature, describes how the pre-Hispanic Casarabe society of the Llanos de Moxos in Bolivia designed and implemented an innovative landscape engineering system, including the construction of extensive drainage canals and farm ponds. This advancement allowed the transformation of flooded tropical savannahs into highly productive fields, thereby driving the development of the “Neolithic Revolution” in the Amazon, understood as the process towards an economy based on grain production.

This region, inhabited by the Casarabe people between 500 and 1400 A.D., is a tropical lowland savannah marked by intense rainy seasons and flooding, as well as very dry seasons. The discovery, led by Umberto Lombardo, an environmental archaeologist at the UAB, has identified a unique agricultural infrastructure previously undocumented anywhere else in the world.. This system enabled them 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 reservoirs. These ponds enabled pot-irrigation, allowing maize cultivation to continue throughout the dry season.

This dual water management system enabled at least two harvests of maize per year, ensuring a stable food supply 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 traditional slash-and-burn techniques used to create fertile fields. Instead, the Casarabe people preserved nearby forests for other purposes, such as obtaining firewood and medicinal plants, while implementing practices that maximized the efficient use of water and soil in the seasonally flooded savannas.

These conclusions were made possible through meticulous fieldwork combining techniques such as microbotanical analysis, remote sensing, and environmental archaeology. The analysis of 178 phytolith (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 pre-Columbian 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-Columbian civilizations but also offers valuable lessons for modern agricultural sustainability. 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.