‘White gold’ guano fertilizer drove agricultural intensification in the Atacama Desert from ad 1000

Abstract

The archaeological record shows that large pre-Inca agricultural systems supported settlements for centuries around the ravines and oases of northern Chile's hyperarid Atacama Desert. This raises questions about how such productivity was achieved and sustained, and its social implications. Using isotopic data of well-preserved ancient plant remains from Atacama sites, we show a dramatic increase in crop nitrogen isotope values (d 15 N) from ~AD 1000. Maize was most affected, with d 15 N values as high as +30‰, with human bone collagen following a similar trend; moreover, their carbon isotope values (d 13 C) suggest a significant increase in the consumption of maize at the same time. We attribute the shift to extremely high d 15 N values -the highest in the world for archaeological plants -to the use of seabird guano to fertilise crops. Guano -"white gold" as it came to be called -thus sustained agricultural intensification, supporting a substantial population in an otherwise extreme environment.

High- and low-latitude forcings drive Atacama Desert rainfall variations over the past 16,000 years

“…had major impacts on human societies that thrived in the Atacama hyperarid core ( 9 , 57 ). Major technological improvements for coastal and inland food procurement and processing, coupled with major sociocultural changes including investments in permanent hamlets with solid and multifunctional architectures, irrigated and fertilized desert farming, major population growth, and increased social complexity and inequalities, were all accelerated during these Late Holocene pluvials ( 9 , 65 , 66 ).…”

Pre-Columbian transregional captive rearing of Amazonian parrots in the Atacama Desert

“…Given that neotropical parrots are primarily frugivores and granivores (55), the consumption of marine resources is unlikely. Furthermore, whereas a few wild edible plants from the hyperarid Pacific desert coast (around 90 km to the west) have a relatively high carbon and nitrogen isotopic composition, it is unlikely that consuming these plants alone could produce the observed extreme values (58). A more plausible explanation is that these birds were fed cultigens and specifically maize fertilized using marine bird guano, as has been documented historically (10) and verified by isotopic studies on plant remains and human populations buried in coastal and desert pre-Columbian cemeteries, including both Pica 8 and Camarones 8 (39,(58)(59)(60).…”

2000 years of agriculture in the Atacama desert lead to changes in the distribution and concentration of iron in maize

“…1 and 2 ). During this period, maize had a low degree of manipulation 7 , 15 . Thus, there is a low amount of macrobotanical maize remains in archaeological sites that do not exceed 3% of the total macrobotanicals recovered in the period’s settlements 16 .…”

“…The reason for this shift in production is not yet fully known, though environmental fluctuation could be related. But despite the environmental challenges, cobs and kernels reached their major size probably due to the prolonged human selection and the use of seabird guano fertilizer 15 .…”