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The ancient agroecology of Perry Mesa: integrating runoff, nutrients, and climate

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Understanding agricultural land use requires the integration of natural factors, such as climate and nutrients, as well as human factors, such as agricultural intensification. Employing an agroecological framework, I use

Understanding agricultural land use requires the integration of natural factors, such as climate and nutrients, as well as human factors, such as agricultural intensification. Employing an agroecological framework, I use the Perry Mesa landscape, located in central Arizona, as a case study to explore the intersection of these factors to investigate prehistoric agriculture from A.D. 1275-1450. Ancient Perry Mesa farmers used a runoff agricultural strategy and constructed extensive alignments, or terraces, on gentle hillslopes to slow and capture nutrient rich surface runoff generated from intense rainfall. I investigate how the construction of agricultural terraces altered key parameters (water and nutrients) necessary for successful agriculture in this arid region. Building upon past work focused on agricultural terraces in general, I gathered empirical data pertaining to nutrient renewal and water retention from one ancient runoff field. I developed a long-term model of maize growth and soil nutrient dynamics parameterized using nutrient analyses of runoff collected from the sample prehistoric field. This model resulted in an estimate of ideal field use and fallow periods for maintaining long-term soil fertility under different climatic regimes. The results of the model were integrated with estimates of prehistoric population distribution and geographical characterizations of the arable lands to evaluate the places and periods when sufficient arable land was available for the type of cropping and fallowing systems suggested by the model (given the known climatic trends and land use requirements). Results indicate that not only do dry climatic periods put stress on crops due to reduced precipitation but that a reduction in expected runoff events results in a reduction in the amount of nutrient renewal due to fewer runoff events. This reduction lengthens estimated fallow cycles, and probably would have increased the amount of land necessary to maintain sustainable agricultural production. While the overall Perry Mesa area was not limited in terms of arable land, this analysis demonstrates the likely presence of arable land pressures in the immediate vicinity of some communities. Anthropological understandings of agricultural land use combined with ecological tools for investigating nutrient dynamics provides a comprehensive understanding of ancient land use in arid regions.

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Date Created
  • 2013

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Eolian deposition and soil fertility in a prehistoric agricultural complex in central Arizona

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Prehistoric farmers in the semi-arid American Southwest were challenged by marked spatial and temporal variation in, and overall low levels of, precipitation with which to grow their crops. One strategy

Prehistoric farmers in the semi-arid American Southwest were challenged by marked spatial and temporal variation in, and overall low levels of, precipitation with which to grow their crops. One strategy they employed was to modify their landscape with rock alignments in order to concentrate surface water flow on their fields. A second challenge that has been less focused on by archaeologists is the need to maintain soil fertility by replenishing nutrients removed from the soil by agricultural crops. Numerous studies have shown that rock alignments can result in long-lasting impacts on soil properties and fertility. However, the direction and magnitude of change is highly variable. While previous work has emphasized the importance of overland flow in replenishing soil nutrient pools, none have investigated the influence of eolian deposition as a contributor of mineral-derived nutrients. This thesis explores the effects of the construction of rock alignments, agricultural harvest, and eolian deposition on soil properties and fertility on Perry Mesa within the Agua Fria National Monument. This site experienced dramatic population increase in the late 1200s and marked depopulation in the early 1400s. Since that time, although agriculture ceased, the rock alignments have remains, continuing to influence runoff and sediment deposition. In the summer of 2009, I investigated deep soil properties and mineral-derived nutrients on fields near Pueblo La Plata, one of the largest pueblos on Perry Mesa. To examine the effects of rock alignments and agricultural harvest independent of one another, I sampled soils from replicated plots behind alignments paired with nearby plots that are not bordered by an alignment in both areas of high and low prehistoric agricultural intensity. I investigated soil provenance and the influence of deposition on mineral-derived nutrients through analysis of the chemical composition of the soil, bedrock and dust. Agricultural rock alignments were significantly associated with differences in soil texture, but neither rock alignments nor agricultural history were associated with significant differences in mineral-derived nutrients. Instead, eolian deposition may explain why nutrient pools are similar across agricultural history and rock alignment presence. Eolian deposition homogenized the surface soil, reducing the spatial heterogeneity of soils. Dust is important both as a parent material to the soils on Perry Mesa, and also a source of mineral-derived nutrients. This investigation suggests that prehistoric agriculture on Perry Mesa was not likely limited by long term soil fertility, but instead could have been sustained by eolian inputs.

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Date Created
  • 2012

Adding a Soil Fertility Dimension to Locust and Grasshopper Management, a Case Study in West Africa

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In Senegal, West Africa, soils are a vital resource for livelihoods and food security in smallholder farming communities. Low nitrogen (N) soils pose obvious challenges for crop production but may

In Senegal, West Africa, soils are a vital resource for livelihoods and food security in smallholder farming communities. Low nitrogen (N) soils pose obvious challenges for crop production but may also, counterintuitively, promote the abundance of agricultural pests like the Senegalese locust, Oedaleus senegalensis. In this study I investigated how the abundance of locusts and grasshoppers are impacted by soil fertility through plant nutrients and how these variables change across land use types. We worked in two rural farming villages in the Kaffrine region of Senegal. Overall, there was little variation in soil properties and an agricultural landscape low in soil organic matter (SOM) and inorganic soil nitrogen. I corroborated that SOM is a significant driver of soil inorganic N, which had a positive relationship to plant N content. Of the management practices we surveyed, fallowing fields was important for soil nutrient restoration and years spent fallow was significantly correlated to inorganic soil N and SOM. O. senegalensis was least abundant in groundnut areas where plant N was highest. Additionally, I found a significant negative correlation between O. senegalensis abundance and plant N, suggesting that plant nutrients are an important driver of their populations. Grasshoppers, excluding O. senegalensis, were more numerous in grazing areas and fallow areas, perhaps due to a higher diversity of ecological niches and host plants. These results connect land use, soil, and vegetation to herbivores and suggest that improving soil fertility could be used as an alternative to pesticides to keep locusts at bay and improve crop yields.

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Date Created
  • 2018-04-10