The geoarchaeology of terraced agriculture in the southern Peruvian Andes: A case study from San Francisco de Sangayaico

William Parashar Nanavati

This study addresses the geoarchaeology of terraced agriculture from a case study near the SAN1 site of San Francisco de Sangayaico, in the Southern Peruvian Andes. The objective of this Master's thesis is to assess soil fertility and evidence for paleosols formed from under agriculture strategies during the periods of documented occupation between the Early Intermediate Period (200 B.C.-A.D. 700) through the Spanish Colonial Period (A.D.1532-1821). To accomplish this objective, an excavation of targeted areas of terrace systems situated under the SAN-1 site was undertaken in order to examine the changes of soil physical and chemical characteristics downprofile and downslope. The results of these excavations and soil fertility analyses are placed within the context of Andean ethnohistory and the archaeological record, to address questions regarding how and why the terraces were built and maintained over time. This study provides the first analyses of their kind done on the agrarian soil systems surrounding Sangayaico. Results presented here demonstrate that the soil system around Sangayaico is characterized by low pH, a consistent electrical conductivity, reasonable-butvariable and phosphorus, and a loamy soil texture containing plate-like micaceous particles as a result of the volcanic tonalite parent material. The use of agricultural terraces mitigates the effects of erosion related to slope cultivation. Such erosion leads to the loss of the mineral and organic-material rich A-horizon, and, in cases where erosion occurs faster than pedogenesis, exposes lower, non-arable soils leached of organic material. Organic material and phosphorous values demonstrate that it is unlikely that the terraces were heavily fertilized, making the stabilizing nutrient-rich topsoil vital. Given the variability of the local soil system, strict adherence to models relying on defined ecotones is ill-advised, and that models based on "overlapping patchwork" framework offer a more holistic explanation of Andean ecology. Given the large variability in organic material and plant macronutrients such as phosphorus in the soil systems around Sangayaico, increased consideration was needed to select the proper crop for each area. This amount of forethought in crop selection would have called for a great deal of knowledge about the behavior of local crops and soils.

The geoarchaeology of terraced agriculture in the southern Peruvian Andes: A case study from San Francisco de Sangayaico

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