Stable carbon isotope signatures of ancient Maize agriculture at El Kinel, Guatemala

Abstract Stable C isotope studies of the soil organic matter (SOM) have delineated areas with histories of vegetation change from C3 forest to C4 maize (Zea mays L.) agriculture and back to the contemporary C3 forest. The objectives of this study were to: (1) determine if land around El Kinel, Guatemala possessed a vegetative history of shifts from C3 forest to C4 maize agriculture in the past, (2) determine if 10 years of contemporary maize production is sufficient time to deposit an isotopic signature of C4 plants in the root zone (top 40 cm), and (3) to examine the extractable phosphorus concentrations and δ13C in soils of important archaeological features that included a midden, a burial, and two ancient reservoirs (aguadas). The lack of a shift in δ13C greater than 3.5‰ in the top 40 cm of the contemporary maize field suggested that continual maize cultivation of more than ten years is required to create an isotopic signature for maize agriculture. Carbon isotopic evidence was found in soil profiles to confirm that long-term agriculture was practiced by ancient Maya farmers at El Kinel. The man-made aguadas did not show isotopic shifts greater than 2.3‰ in any part of the profile, indicating they were used for other purposes not associated with C4 plant growth. The relatively low P (−1) was found in soil at the same depth but at a distance of 30 cm from an ancient burial. The high P concentration (127 mg kg−1) found within millimeters of the bones implied that the P enrichment came from the remains but P remained fixed in the soil and did not migrate