The Application of Pedology, Stable Carbon Isotope Analyses and Geographic Information Systems to Ancient Soil Resource Investigations at Piedras Negras, Guatemala
The ancient inhabitants of the Maya Lowlands enjoyed a long and fruitful period of growth which climaxed at around AD 800. At that time, millions of people successfully subsisted in a challenging environment that today only supports a population a fraction of that size. These facts, and the subsequent "Maya Collapse", are the impetus of many recent studies that utilize environmental data, in addition to conventional archaeology, to investigate this Maya mystery. Pedological studies and stable carbon isotope analysis of soil organic matter, combined with Geographic Information Systems (GIS) are three tools that can be used to answer crucial questions as to how the Maya managed their soil resources. GIS maps that indicated areas of best agricultural potential based on slope and soil type were used as a guide to opportunistically sample soils in an area south of Piedras Negras Guatemala – an area that was densely vegetated and unexplored. Soils that represented the different soil resources of the area were sampled with a bucket auger at 15 cm intervals. The samples were then tested in a laboratory for physical and chemical characteristics and δ-13C values were determined for soil organic matter. Soil taxonomical descriptions indicated that overall the soil resources of the area were very good as almost all the soils were classified as Mollisols - the most fertile of all the soil orders. The suite of great groups found was Haprendolls, Argiudolls, Argiaquolls and Udorthents. The characteristics which distinguish these great groups were used to further investigate relative agricultural productivity from an ancient soil resources point of view. Haprendolls were better drained and probably made for good agricultural soils given soil depth and rainfall were adequate. The Argiudolls and especially the Argiaquolls were probably less favored because of very high clay contents that made them more difficult to work with and poor drainage. Stable carbon isotope analyses revealed strong evidence for maize agriculture in some environments of the study area. δ-13C values as high as -16.6‰ (76% C4—Carbon) were observed in areas of significant soil accumulation in well drained and moderately drained soils. Minimal evidence of maize agriculture was found in more marginal environments such as those with little soil accumulation or poorly drained areas. Also, the pattern of the graph of δ-13C values versus depth indicated that ancient agriculture occurred continuously in some areas, but in other areas as distinguishable events. Finally, when the strength of the C4 signal was represented graphically and overlaid with a modified GIS agricultural potential map, a visual representation of the extent and degree of ancient agriculture was achieved. Our findings suggest that upland agriculture was favored by the ancient Maya of Piedras Negras and that the region between Piedras Negras and Yaxchilan was an agriculturally important breadbasket. The methods and results of this study provide foundational information for the investigation of ancient Maya agriculture. In future studies, it may be possible to more systematically map ancient agricultural fields and estimate the carrying capacity of a region based on its soil resources.
Ancient agriculture, Soil taxonomy, Stable carbon isotopes, Geographic Information Systems, Piedras Negras, Animal Sciences
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