Anthropogenic Effects On Soil Quality in Ancient Terraced Agricultural Fields of Chihuahua, Mexico.

Agricultural soil quality was investigated in ancient field systems near Casas Grandes (also known as Paquimé), one of the largest and most complex prehistoric settlements in the North American Southwest. This research was completed as part of an interdisciplinary study of the anthropogenic ecology of the Casas Grandes area during the Medio period (~A.D. 1200-1450). Dramatic human population rise at Paquimé during the Medio period must have increased pressure on subsistence resources such as agricultural land for food production and wild animal and vegetation resources. Soil quality of agricultural terraces was evaluated by measuring chemical and physical soil properties (pH, organic C, N, total and available P, SAR, CEC, bulk density, particle-size distribution, and unsaturated hydraulic conductivity) for four agricultural fields compared to similar soils and landforms that were uncultivated. Comparisons were made between fields in high versus low population valleys and between two fields thought to have been owned by chiefs based on their proximity to special administrative sites. Although a number of statistical differences were identified, there is no indication that agriculture reduced soil quality. Consequently, soil degradation does not explain the ultimate decline of the Casas Grandes cultural system. Soil differences were greatest between fields, likely due to geologic differences in the parent material. The chief’s fields have a lower fertility than other fields, but their placement in better watered landscape positions accounts for their larger size.