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‘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 (δ15N) from around ad 1000. Maize was most affected, with δ15N values as high as +30‰, and human bone collagen following a similar trend; moreover, their carbon isotope values (δ13C) indicate a considerable increase in the consumption of maize at the same time. We attribute the shift to extremely high δ15N values—the highest in the world for archaeological plants—to the use of seabird guano to fertilize crops. Guano—‘white gold’ as it came to be called—thus sustained agricultural intensification, supporting a substantial population in an otherwise extreme environment.

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Fig. 1
Fig. 2: Stable isotope results for carbon and nitrogen (calibrated in relation to the international standards VPDB and AIR) in archaeological crops and wild plants.
Fig. 3: Modern, historical and archaeological images associated with seabird guano and crops.
Fig. 4: Boxplots showing variation in the isotope composition of carbon and nitrogen (calibrated in relation to the international standards VPDB and AIR) in different tissues from archaeological human samples from coastal, inland and Precordillera sites dating to the Formative, Middle, Late Intermediate and Late Periods.

Data availability

The authors declare that all data generated or analysed during this study are included in this published article (and its Supplementary Information files).

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Acknowledgements

We thank the National Geographic Society for Early Career grant nos. EC-53250R-18, FONDECYT 3180317, 1181829 and 1191452 and the Becas Chile-PhD Scholarship for funding support. C.H. is supported by Nucleo Milenio INVASAL funded by Chile’s government programme, Iniciativa Científica Milenio from the Ministerio de Ministerio de Ciencia, Tecnología, Conocimiento e Innovación. C.L. acknowledges support from grant no. ANID PIA CCTE AFB170008 and Nucleo Milenio UPWELL. We are grateful to P. Ditchfield, T. Higham, D. Chival, J. Cameron and F. Docmac for their help in the laboratory. We thank S. Santana-Sagredo for helping and improving the figures of this article. We are also grateful to the institutions that allowed us sampling their archaeological collections. All samples were analysed at the University of Oxford under Chilean government permit (no. 42.649, CVE 1757327, Diario Oficial de la República de Chile).

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F.S.-S., R.J.S. and J.L.-T. came up with the original idea and research design. F.S.-S., P.M.-Q., A.V.-E., M.U., R.L. and A.M.-F. conducted and participated in the fieldwork. F.S.-S., A.V.-E. and A.M.-F. carried out sampling in universities and museum collections. A.V.-E., V.B.M., V.M. and F.P.D. undertook taxonomic analysis of crops and wild fruits. F.S.-S. and A.M.-F. conducted sample processing and laboratory work. F.S.-S and P.M.-Q collected information and worked on the human isotope and radiocarbon dates databases. F.S.-S., R.J.S. and C.H. undertook the statistical analysis. R.L. designed the map. F.S.-S., J.L.-T., R.J.S. and C.H. interpreted the results. C.L. and C.M.S. contributed to interpreting the data based on the local ecology and archaeology. F.S.-S. wrote the paper with the help of R.J.S. and J.L.-T. All the authors commented on the paper.

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Correspondence to Francisca Santana-Sagredo.

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Peer review information Nature Plants thanks Jonathan Sandor and the other, anonymous, reviewers for their contribution to the peer review of this work.

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Santana-Sagredo, F., Schulting, R.J., Méndez-Quiros, P. et al. ‘White gold’ guano fertilizer drove agricultural intensification in the Atacama Desert from ad 1000. Nat. Plants 7, 152–158 (2021). https://doi.org/10.1038/s41477-020-00835-4

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