Anthropogenic Effects on Soil Quality of the Las Capas Irrigation System

Summary

A soil quality study was conducted at the Las Capas site to document and evaluate the soil productivity and hydraulic soil properties of this ancient agricultural irrigation complex. This site presents an unprecedented opportunity to study the complete configuration and evolution of the oldest irrigation system documented in the Southwest to date. Mechanical stripping permitted earthen berms around small field grids to be identified so that soil samples could be collected in relation to nearby uncultivated control samples. Long-term indicators of agricultural soil quality, such as organic carbon, nutrient content, and hydraulic soil water properties, indicate that anthropogenic changes were favorable for agricultural production and that the Las Capas irrigation system was sustainable. Canals regularly supplied water to the fields, but they also supplied nutrient-rich sediments that continually renewed soil fertility, enough to counter nutrient losses resulting from crop uptake, volatilization, leaching, and oxidation. Fields have significantly elevated organic carbon, nitrogen and available phosphorus levels relative to the borders, and levels that are slightly below but comparable to the control soils. Sodium and sodium adsorption ratios, though elevated in the Las Capas fields, are far below levels that could have had a serious detrimental effect on crop production.

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This Resource is Part of the Following Collections

• Society for American Archaeology 80th Annual Meeting, San Francisco, CA (2015)   •
• Multidisciplinary Studies of Anthropogenic Change, Subsistence, Social Organization, Regional Interaction, and Technology at the Las Capas Site, BC 1200-400, Southern Arizona

Keywords

Spatial Coverage