Prehistoric people developed rich agriculture using natural fertilizers in Atacama – 01/29/2021 – Science

Centuries before contact with Europeans, indigenous groups turned part of the Atacama Desert in Chile into a rich agricultural area, from which corn, pumpkin and beans could be harvested in abundance. The secret behind this productivity was the use of guano, a natural fertilizer given to the natives on the Pacific coast.

This surprising scenario of intensive pre-Columbian agriculture is being rediscovered thanks to the particular chemical composition of desert cultures. The vegetables grown in Atacama, according to a study recently published in the journal Nature Plants, have a typically marine signature on their nitrogen atoms – which makes sense when you consider that guano is nothing more than the accumulation of bird droppings fish-eaters.

This chemical signature is even reflected in the composition of the bones of people who lived in the desert around AD 1000, study coordinator Francisca Santana Sagredo of the School of Anthropology at the Pontifical Catholic University of Chile told Folha. “The levels are similar to the Inuit [popularmente conhecidos como esquimós, que só comiam animais marinhos]- and they are even bigger, ”she says.

The food production in prehistoric Atacama was already known to archaeologists. According to the researcher, one factor that made agriculture possible in the area was the presence of rivers in some desert valleys, as well as water sources in oases and certain underground springs. “It is also likely that agricultural activities took place in areas that are now drier but have had water in the past,” she explains.

However, the availability of springs did not solve another critical problem in the region: the lack of nutrients in the soil. For example, lama dung, an animal domesticated by the Andean peoples about 4,000 years ago, could be used to remedy this.

However, everything indicates that this was not the “magic ingredient” of Atacama farming. The key to this conclusion is nitrogen-15 content, a heavier variant of the chemical element (its normal, lighter form is nitrogen-14 – the difference is that nitrogen-15 carries an extra particle in its core). It turns out that nitrogen-15 builds up in the body more and more as it rises from the trophic level – that is, from plants to herbivores, from herbivores to the carnivores that eat them, from those carnivores to the carnivores that they eat eat etc.

The presence of nitrogen-15 in crops and human skeletons in Atacama is so high that it would be impossible to explain it with the use of llamakot (a mere herbivore) as fertilizer. But it is fully compatible with the use of guano. Precisely because it comes from the excrement of waterfowl, which normally eat carnivorous fish that are built into a complex marine food chain, the fertilizer is very rich in nitrogen-15.

To gain access to the resource, the desert dwellers likely had to join a regional trade network that traversed about 100 km of territory towards the coast and reached islands with large colonies of birds such as pelicans and gannets (see infographic), the main “producers”. “From guano. The control of the transport and distribution of fertilizers must have contributed to the formation of complex societies with hierarchies and inequalities and a relatively high demographic density, says the Chilean researcher.

The strange thing is that the Atacama system heralded something that would become more prominent worldwide in the 19th century. Before the invention of artificial fertilizer, guano from Chile, Peru and other regions of the world became a globally coveted agricultural resource known as “white gold” “.

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