Stable carbon isotope signature of ancient maize agriculture in the soils of Motul de San José, Guatemala

Abstract Soil profiles collected from a 2.5‐km transect radiating from the Maya center of Motul de San José were analyzed for the stable carbon‐isotope composition of their soil organic matter. The residues of maize ( Zea mays ), the only C 4 plant known to have been cultivated in this area by the ancient Maya, impart a carbon‐isotope signature to the underlying soil organic matter reservoir that is distinct from that produced by the native C 3 forest vegetation. The varying turnover rates of the humic acid and humin fractions of the soil organic matter allowed us to distinguish between the presence of modern and ancient maize residues in these soils, and to delineate the lateral extent of maize cultivation at this ancient Maya site. The strongest isotopic evidence of maize residues is preserved in the soils surrounding the peripheral settlement of Chäkokot and at one locality within the urban center of Motul de San José. © 2007 Wiley Periodicals, Inc.