Isotopic insights into quinoa agriculture at an Andean hillfort town (cal ad 1250–1450)

Quinoa (Chenopodium quinoa) agriculture has been a cornerstone of highland Andean diets for thousands of years, but it has received relatively little attention from archaeologists studying diet through stable isotope analysis. In this study, we present the largest sample published to date (n = 49) of archaeological carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios in quinoa, as well as single samples of cactus (Opuntia spp.), wild bean (Trifolium amabile), and potato (Solanum tuberosum) from a Late Intermediate Period (cal ad 1250–1450) hillfort town in the western Lake Titicaca basin. Quinoa δ¹⁵N averages + 8.83‰±2.17, indicating that agricultural fields at this site were fertilized with camelid manure, but values were significantly higher in samples recovered from high-status compounds than low-status ones. This suggests that high-status groups within the community had larger camelid herds and/or older fields that had been improved with fertilizer for longer periods of time, possibly allowing their plants to be more productive than those of lower-status groups. Mean quinoa δ¹³C was − 23.95‰±0.72, which indicates that plants were not significantly more water-stressed than modern or historic comparative samples grown with similar methods. This concurs with paleoclimate data suggesting that the environment surrounding this settlement was in a period of drought recovery during the occupation. Alternatively, fertilizer may have allowed plants to combat the effects of drought without recycling sub-stomatal CO₂. This study is an important contribution to research on foodways in the ancient Andes and non-cereal grain-dependent societies more broadly.