The Atacama Desert in western South America is one of the most barren and driest landscapes on earth. Nevertheless, there were highly productive agricultural crops there centuries before the Inca Empire. Isotope analyzes of plant remains and skeletons have now revealed where they got their nutrients from. According to this, the people of the pre-Inca cultures of this area have already systematically collected guano from seabirds and brought it into the desert as fertilizer.
Archaeological studies show that people lived in the Atacama Desert a good thousand years ago. Large amounts of well-preserved plant remains from that time, including corn, beans, quinoa and other domesticated plants, testify to this. “Their frequency and diversity speak for an agricultural success that is difficult to explain in view of the dry, barren environment,” say Francisca Santana-Sagredo from the Catholic Pontifical University of Chile in Santiago and her colleagues.
Jump in nitrogen levels
But how did these people manage to farm in such a barren environment and harvest enough to support larger settlements? To find out, Santana-Sagredo and her team examined 246 plant samples from the period from 1000 to 1450 for their isotopic composition. The proportions of the different isotopes of carbon and nitrogen provide information about how well these plants were supplied with organic nutrients. The plant remains came from the Atacama Desert in northern Chile and were once grown there by people from previous cultures of the Incas. These crops included corn, quinoa, beans, lima beans, pumpkins, and chilli, among others.
The analyzes revealed a clear development over time: while the isotope values of crops from before 1000 differed only little from wild comparative plants, there was a jump from the year 1000 onwards. This indicates that the nitrogen supply of the cultivated plants increased sharply during this time. “The extent of this nitrogen accumulation cannot be explained by standard influences such as less rain or conventional tillage methods,” say Santana-Sagredo and her colleagues. Supplementary analyzes of human and animal skeletons from this period also show that these increased nitrogen levels were not a coincidence, but are also reflected in the diet of the people in this region.
Early import of guano
According to the scientists, these results suggest that the people of these pre-Inca cultures must have consciously applied nitrogen-rich fertilizers to their desert fields a good 1000 years ago. But what kind of fertilizer was this? And where did he come from? As the researchers explain, the most likely source of organic, nitrogen-rich material is the seashore. Because even then there was a rich population of seabirds, some of which nested in colonies on the coast and on islands – and accordingly produced a lot of guano. There are reports from the time of the Spanish conquest that the Incas collected this guano on a large scale and used it as fertilizer.
“Ethno-historical reports from the 16th to 19th centuries report that the local population used small boats to go to rocky islets off the coast of southern Peru and northern Chile to collect guano,” report Santana-Sagredo and her team. “These documents also describe how the guano was transported inland and then used there to improve the harvests.” At that time, the guano was so popular that it was sometimes even referred to as “white gold”. However, as the current study shows, guano mining and its use as fertilizer were not invented by the Incas. “At least 400 years before the Incas, sea birds brought guano in large quantities from the coast into the interior. This was associated with enormous effort, ”say the researchers. But this investment was worth it, as the rich harvests and growing population in the Ataca region at the time prove.
Source: Nature Plants, doi: 10.1038 / s41477-020-00835-4