Michelle Trogdon
12/04/07
Soils Geography
Final Draft
Ancient Agriculture and Soil Quality
In Oaxaca, Mexico the timing of changing agricultural techniques is poorly understood.
The best evidence available suggests that agricultural terracing began in the Formative Period, but only a few sites have been excavated with both house and terrace contexts (Balkansky et. al.
2000:384; Kowalewski et. al. 2006:199; Joyce and Mueller 1997:84; Perez-Rodriguez 2006:5).
One problem in the Nochixtlan Valley in particular is erosion. Oaxaca in general has been identified as a high risk for major landscape degradation by natural and anthropogenic erosion.
Many early archaeological sites have been either overprinted by later occupation or sites have been completely buried by erosion after abandonment without continued maintenance and mitigation.
The purpose of this research is to chemically analyze one soil profile from the Nochixtlan
Valley. I will measure the nitrite/nitrate, phosphorous, ammonia, and pH concentrations of 17 soil samples associated with two archaeological features in the lower Nochixtlan Valley.
Chemical analysis of soils follows the LaMotte Soil Handbook and protocol. Nitrogen and phosphorous are important nutrients that reflect soil fertility and limit agricultural productivity.
Both are naturally occurring in soils and can be added through various agricultural techniques. I expect buried paleosols to reflect fertility from early agricultural use.
Soil quality is ameliorated with the application of terraces in the Mixteca Alta. Terraces not only retain soil and nutrients, they improve soil moisture in arid environments by trapping water and slowly filtering it to lower terraces (Perez-Rodriguez 2006; Ross et. al. 1999). This decreases run-off, erosion, and flooding in the valley (Homburg et. al. 2005; Perez-Rodriguez
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2006). Terraces also create a flat area on otherwise sloping hillsides where farming is easily accomplished and houses can be constructed near agricultural fields. Certain characteristics of terrace construction have also been associated with political and social organization in the
Mixteca and other parts of Mesoamerica (Kowalewski et. al. 2006; Kunen 2001; Morrison 1994;
Perez-Rodiriguez 2006; Spores 1969). House construction features and ethnographic evidence from the modern town of Teposcolula indicate that commoners were responsible for agricultural production and maintenance of retention terraces (Perez-Rodriguez 2006:17). However, experimental archaeology in Chihuahua suggests building terraces from start to finish is labor intensive and would require community-wide support (Hard et. al. 1999). More recently, the modern town of Ixcatlan in the Mixteca Alta sponsored a community-wide terrace building event
(Personal communication 2007).
During the Formative period in the Mixteca settlement was evenly distributed in small hilltown sites. Many Formative sites identified through extensive field surveys of the Central
Mixteca Alta Settlement Pattern Project (CMASPP) were located along low piedmont
(Balkansky et. al. 2000). By the end of the Formative, populations had aggregated to larger hilltop cities (Kowalewski et. al. 2006:201; Stiver 2001). It is conceivable that many Formative piedmont sites have been buried perhaps as a result of increased erosion with the adoption of agricultural production. Terracing may have been introduced to mitigate erosion and loss of soil as settlement expanded on hillsides. However, current descriptions of Formative terraces are inadequate and the timing of this practice relative to the adaption of agriculture is poorly understood. Archaeological features previously buried and currently in eroding contexts may provide insight into early origins of agricultural adaptation.
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Dating soils is an extremely important factor in determining the age and function of features in eroding contexts. The feature associated with the soil samples analyzed in this study is described as a hearth and dates 600 – 8520 BC by association. It is the smallest feature in the study and lacks association with artifacts. Nitrite/Nitrate and ammonia concentrations of the soil samples did not reveal results to distinguish use or soil fertility variation in the profile. Nitrogen is a limiting nutrient for plant growth, but is quickly used by microorganisms and the turn over is high.
Phosphorous and pH levels did however, have a rough correlation and phosphorous is in high concentrations in a few samples. Phosphorous is a necessary nutrient for plant growth and although it is typically in high concentrations, much of it is chemically bound in clays or calcium compounds and remains unavailable to plants. High pH or more alkaline soils have more calcium available to bond with phosphates. Phosphorous peaks in the upper levels of paleosol 3 and 4. In both these paleosols the soil is described as having a prismatic and blocky structure.
The blocky structure and high concentration of bound phosphorous are indicative of drier climate. It is possible that agricultural terracing associated with alkaline soils demonstrating high levels of phosphorous functioned to reduce runoff erosion and retain water, soil moisture, and nutrients under arid conditions where soil quality is ordinarily limited. More humid conditions would leach calcium making it less available to bind with phosphates and hence, lowering phosphorous and pH levels. With the available information regarding some previously documented features in eroding contexts, only one feature, Yucuita F1, is likely to be a retention wall. However, distinctions between domestic and agricultural use cannot be made without more information about the feature and the associated soil profile.
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My future work will involve a more detailed analysis of soil structure and soil quality.
Some research has been done regarding erosion in Oaxaca (Goman et. al. 2005; Joyce and
Mueller 1997; Spores 1969). More detailed research should focus on associated soils throughout the Nochixtlan Valley. Also, more excavation of terraces on both hillslopes and on valley floors is necessary to determine if agricultural practices varied due to topography or if practices were standardized throughout the valley. Chronological continuity should also be established by comparing agricultural practices through time. This will strengthen the use of ethnographic analogy and support the conclusion that erosion events were caused by abandonment of agricultural terraces due to changes in settlement patterns.
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References
Balkansky, A. K., Kowalewski, S. A., Perez Rodriguez, V., Pluckhahn, T. J., Smith, C., and A., S., L. R., Beliaev, D., Chamblee, J. F., Heredia Espinoza, V. Y., and Santos
Perez, R., 2000, Archaeological survey in the Mixteca Alta of Oaxaca, Mexico. Journal of Field Archaeology , v. 27, p. 365-389.
Gomen, M. Joyce, A. A., and Mueller, R. G., 2005. Stratigraphic evidence for anthropogenically induced coastal environmental change from Oaxaca, Mexico. Quaternary Research , v.
63, pp. 250-260
Homburg, J. A., Sandor, J. A., and Norton, J. B., 2005. Anthropogenic influences on Zuni agricultural soils. Geoarchaeology: An International Journal , v. 20 (7), pp. 661-693.
Joyce, A. A., Mueller, R. G., 1997. Prehistoric human ecology of the Rio Verde drainage basin,
Mexico. World Archaeology , v. 29 (1), pp. 75-94.
Kowalewski, S. A., Feinman, G. M., Nicholas, L. M., and Heredia, V. Y., 2006. Hilltowns and valley fields: Great transformations. Labor, and long-term history in ancient Oaxaca. In
Labor in Cross-Cultural Perspective, eds. E. Paul Durrenberger and Judith E. Marti, pp.
197-215. Altamira Press, Lanham, MD.
Kunen, J. L. 2001. Ancient Maya agricultural installations and development of intensive agriculture in NW Belize . Journal of Field Archaeology, v. 28, pp. 325-346.
Morrison, K. D., 1994. The intensification of production: Archaeological approaches. Journal of
Archaeological Method and Theory , v. 1., pp. 111-159.
Perez-Rodriguez, V., 2006. States and households: The social organization of terrace agriculture in Postclassic Mixteca Alta, Oaxaca, Mexico. Latin American Antiquity , v. 17 (1), pp. 3-
22.
Ross, D. J., Tate, K. R., Scott, N. A., and Feltham, C. W., 1999. Land-use change: Effects on soil carbon, nitrogen, and phosphorous pools and fluxes in three adjacent ecosystems. Soil
Biology and Biochemistry , v. 31, pp. 803-813.
Spores, R., 1969, Settlement, farming technology, and environment in the Nochixtlan
Valley. Science , v. 166, p. 557-569.
Stiver, L. R., 2001, Prehispanic Mixtec settlement and state in the Teposcolula Valley of
Oaxaca, Mexico, Vanderbilt University 377 p.
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