Research Article: Soil analysis in discussions of agricultural feasibility for ancient civilizations: A critical review and reanalysis of the data and debate from Chaco Canyon, New Mexico

Date Published: June 14, 2018

Publisher: Public Library of Science

Author(s): Jon-Paul P. McCool, Samantha G. Fladd, Vernon L. Scarborough, Stephen Plog, Nicholas P. Dunning, Lewis A. Owen, Adam S. Watson, Katelyn J. Bishop, Brooke E. Crowley, Elizabeth A. Haussner, Kenneth B. Tankersley, David Lentz, Christopher Carr, Jessica L. Thress, John P. Hart.

http://doi.org/10.1371/journal.pone.0198290

Abstract

Questions about how archaeological populations obtained basic food supplies are often difficult to answer. The application of specialist techniques from non-archaeological fields typically expands our knowledge base, but can be detrimental to cultural interpretations if employed incorrectly, resulting in problematic datasets and erroneous conclusions not easily caught by the recipient archaeological community. One area where this problem has failed to find resolution is Chaco Canyon, New Mexico, the center of one of the New World’s most vibrant ancient civilizations. Discussions of agricultural feasibility and its impact on local population levels at Chaco Canyon have been heavily influenced by studies of soil salinity. A number of researchers have argued that salinized soils severely limited local agricultural production, instead suggesting food was imported from distant sources, specifically the Chuska Mountains. A careful reassessment of existing salinity data as measured by electrical conductivity reveals critical errors in data conversion and presentation that have misrepresented the character of the area’s soil and its potential impact on crops. We combine all available electrical conductivity data, including our own, and apply multiple established conversion methods in order to estimate soil salinity values and evaluate their relationship to agricultural productivity potential. Our results show that Chacoan soils display the same salinity ranges and spatial variability as soils in other documented, productive fields in semi-arid areas. Additionally, the proposed large-scale importation of food from the Chuska Mountains region has serious social implications that have not been thoroughly explored. We consider these factors and conclude that the high cost and extreme inflexibility of such a system, in combination with material evidence for local agriculture within Chaco Canyon, make this scenario highly unlikely. Both the soil salinity and archaeological data suggest that there is no justification for precluding the practice of local agriculture within Chaco Canyon.

Partial Text

Whether it has been through the investigation of individual remains (e.g. [1]) or entire landscapes (e.g. [2]), growth in interdisciplinary studies within archaeology has unequivocally increased our knowledge of past cultures across the globe. By opening up the range of approaches to understanding past peoples, existing research questions can be answered in new ways and new questions can be incorporated into archaeological discussions. However, this opportunity can also be perilous as errors in analyses can result in misleading conclusions that become part of the canon for particular regions. An archaeologist working with the implications of these results may not have the requisite training to assess the highly specialized methods employed by the initial study, while scientists trained in the utilized methodology may not be exposed to the results presented in the archaeological literature or aware of critical contextual information. In this environment, it becomes increasingly important for archaeological scientists and interdisciplinary teams to critically evaluate existing work, particularly when this work challenges archaeological expectations. We review and assess the application of a common and relatively simple method for assessing soil salinity from archaeological contexts in Chaco Culture National Historical Park, located in northwestern New Mexico. While archaeologists have long debated the implications of these studies, the results have largely remained unchallenged, as most archaeologists working in the region did not have the soil science background necessary to assess the data. Ultimately, a thorough reassessment of the original data, as well as the addition of data collected by a recent project, does not substantiate the original interpretations, instead suggesting agriculture was feasible for Chaco residents. This case study at a World Heritage Site, one of the most important archaeological regions in North America [3], highlights both the benefits and the dangers of interdisciplinary studies in archaeological research.

The amount of salt in a soil can prevent plants from taking up water, even if water is in physical contact with their roots. As such, soil salinity is an important component of agricultural success. To give non-specialists an introduction to the topic, we present a brief overview of the nature of chemical salts and the formation of a salt solution, the physics of water uptake from such a solution, and the common methodologies used to assess the salinity, or salt concentration, in a solution.

To evaluate existing studies of Chaco Canyon soils and their implications for agricultural productivity, we must first review the methods employed to determine soil salinity assessments. We particularly focus on those who have worked in the area of ‘downtown’ Chaco (the concentration of great houses in the area now encompassing the Chaco Culture National Historical Park), but also include work conducted ~30 km farther upstream at Pueblo Pintado as this analysis also falls within the Chaco Wash watershed and examines soils in the floodplain of the Wash. Research done in adjacent watersheds, such as at Kin Klizhin or the Escavada Wash, is not included as the emphasis here is the salinity of soils directly impacted by the Chaco Wash drainage regime.

Studies of potential past agricultural productivity are built on a number of assumptions and often rely on assessments of modern agricultural conditions to estimate past potential. These practices are certainly necessary and useful, but applications of modern quality standards must be treated carefully when applied to archaeological contexts. Care must also be taken when using modern geochemical signatures as a gauge for those of the past, especially when analyzing a characteristic such as soil salinity, which can be rapidly altered by changing environmental conditions. For example, Benson ([47] p96) states that “agricultural productivity and field-life calculations should be considered only in an illustrative sense, given their assumptions.” Caution seems particularly justified when results of agricultural productivity studies suggest extreme limitations that defy reasonable expectations.

 

Source:

http://doi.org/10.1371/journal.pone.0198290

 

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