Biogeochemical studies of a Native American runoff agroecosystem

Peter  Stahl

Biogeochemical studies of a Native American runoff agroecosystem

2007, Geoarchaeology

Abstract

Research on soil fertility is presented in the context of runoff agriculture, a venerable farming system that has been used for millennia in arid to semiarid regions, where water is a major limiting resource for crop production. The agroecology of runoff farming was studied with the Zuni to evaluate nutrient and hydrologic processes, management, maize productivity, and soil quality in some of the oldest recognized fields in the United States. This ancient Southwest agriculture has functioned without conventional irrigation or fertilization by tapping into biogeochemical processes in natural watersheds connected to fields. Carefully placed fields are managed on alluvial fans and other valley margin landforms to intercept runoff and associated sediment and organic debris transported from adjoining forested uplands. We report on research to evaluate and link nitrogen and phosphorus, two key nutrients for crop production, in watershed, soil, and crop components of this agroecosystem. Nutrient data have been collected by observational and experimental methods for each component and the transport of nutrients from watershed to field to maize. The condition of Zuni agricultural soils suggests that their knowledge and management of soils contributed to effective conservation. This study and others indicate the need for further long-term monitoring and experimental research on watersheds, runoff processes, field soils, and crops across a range of arid to semiarid ecosystems.

Soil studies of prehistoric to contemporary American Indian agriculture across the Southwest indicate varied, dynamic responses to land use. Soil change is inferred from comparisons of agricultural fields to reference uncultivated areas (space-for-time substitution). Soil response pathways vary by initial ecosystem conditions, diverse agricultural methods, and environmental sensitivity to alteration (varying resistance and resilience). Terrain change detection is complicated by post-farming geoecological processes and land use. Soil change ranges from degradation (e.g., organic matter/nutrient decline, compaction, salt/sodium accumulation), to minimal net change, to enhanced soil quality. Ancient agricultural soils provide long-term perspectives on human-environmental relationships and land use sustainability. Soil forms the base of agriculture, and therefore has been subject to change from this land use in the approximately four millennia since farming began in the American Southwest. Soil change from agriculture is complex and wide-ranging in kind, magnitude, and scales of space and time, encompassing many processes and outcomes (Johnson and Lewis 1995; Sandor et al. 2005). The archaeological record provides a critical long-term perspective on humans and soil change (Holliday 2004; Sandor and Eash 1991). The Southwest contains such a record of anthropogenic soil and landscape alteration, with cases of success and failure in maintaining productivity and conserving land resources. Although complex, soil change can be interpreted on a gradient from enhancement of soil quality to soil degradation, with neutral, mixed, or uncertain outcomes in between. Several themes concerning soil change, and related landscape and ecosystem change, are explored here. Diversity is closely linked to how soils, ecosystems, and human societies change and respond to disturbance. Diversity is a hallmark of Southwest American Indian agriculture, and is also an indicator of soil, ecosystem, and agricultural integrity and viability. Agricultural diversification, such as coupled irrigation and dryland systems, has been a key component of risk management strategies. Likewise, diversity contributes to the stability and resilience of soil resources and ecosystems. Soil degradation commonly involves lowered diversity at several scales. Much of diversity loss, such as through decreased organic matter and structural degradation, is an inadvertent consequence of agriculture. However, some agricultural management, especially in modern industrialized systems, deliberately promotes uniformity in physical soil properties and especially nutrient levels through land leveling, fertilization, and other practices to maximize large-scale crop production. Indigenous peoples of the Southwest and other regions have encountered problems in environmental resource conservation, as have modern societies. Resource depletion and degradation may be partly reflected in population movement and land abandonment, which occurred repeatedly in Southwest prehistory locally and regionally (Cordell 1997). However, it is also true that values of conservation and reverence toward the earth are basic tenets of the religious beliefs and lifeways of many traditional cultures. That peoples such as the Hopi, Zuni, and others have lived and farmed in the same place for many generations indicates the development of sustainable land use strategies.

We propose to investigate factors that support sustainability in sugar beet production on farms in the Big Horn Basin, Northwestern Wyoming. Increasing costs, changing markets, and off-site environmental concerns interact to create a need for better understanding of production efficiency and ecological impacts of irrigated sugar beet systems. The project will provide data that is lacking for these systems, including soil organic matter (SOM) dynamics, nitrogen (N) cycling, greenhouse gas (GHG) emissions, and tradeoffs between economic performance and soil sustainability. This data will provide decision support in the short term and will leverage funding for future, more in-depth research and extension in the mid to long term. This interdisciplinary project would build upon past AES-CGP-funded work by analyzing how rotation systems for pathogen control affect soil quality and productivity under different soil and water conditions. Our primary objectives are to describe ecological and economic sustainability and to make results available to growers. The 16 scenarios include four on-farm crop rotations in place for 10 or more years on clayey and sandy soils and under furrow-and sprinkler-applied irrigation. Each production scenario will be replicated three times and will include an unfertilized pair. The four rotations will be defined by a project advisory team of producers and agricultural advisers. The primary pitfall of this study design is the variability of production practices from farm to farm. We plan to minimize variability through the field selection process and by carefully recording practices within each of the 16 scenarios. The project addresses the first and second priorities of the 2008 RFP by: 1) assessing economic viability and maintenance of the resource base; and 2) evaluating long-term impacts of farming systems on the resource base as on-farm soil quality and off-site contributions to air and water quality. The project addresses the discovery and dissemination focus areas defined in the University of Wyoming College of Agriculture mission. Working closely with a project advisory team of Big Horn Basin producers and ag advisers, along with inclusion of University of Wyoming Cooperative Extension Service (CES) Area Agricultural Educators on the research team, will ensure both the relevance of research questions and the dissemination of results. The instruction mission of the College is also addressed because both graduate students and College faculty with teaching appointments in three departments will participate in the project. Though this proposed work is broad in scope, it's coincidence with complementary projects managed by the Project Director will facilitate field and laboratory work and sharing of human resources and equipment. It parallels a similar on-farm project funded by the USDA-NRI Soil Processes Program that will investigate soil processes and economic factors in dryland cropping systems of Southeastern Wyoming. A PhD student paid through this proposed project and the dryland wheat NRI project will combine investigations of soil quality and economics.

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