«Farmers in the Zuni area of the semiarid American Southwest have successfully cultivated maize and other crops for over three millennia without using ...»
Anthropogenic Influences on Zuni
Jeffrey A. Homburg,1,* Jonathan A. Sandor,2 and Jay B. Norton3
Statistical Research, Inc., 6099 East Speedway Boulevard., Tucson, Arizona 85712
Agronomy Department—Crop Soil, and Environmental Sciences, Iowa State
University, Ames, Iowa 50011-1010
University of California Cooperative Extension, 2 South Green Street, Sonora,
Farmers in the Zuni area of the semiarid American Southwest have successfully cultivated
maize and other crops for over three millennia without using artificial fertilizers. Zuni agricultural fields are among the oldest, more or less continuously cultivated areas in the United States. Traditional Zuni agriculture is based on runoff farming, a system whereby runoff and organic-rich sediment generated in small watersheds are captured and directed onto fields for crop use. We conducted a study to compare soil properties associated with paired and unpaired cultivated, abandoned, and uncultivated fields to evaluate the long-term effects of cultivation on soil quality. Sampling and analytical methods of this research are especially applicable to geoarchaeological studies of anthropogenic effects on soil fertility and agricultural sustainability in ancient and traditional historical farming systems. Results of the Zuni soil study indicate that cultivation has altered some soil properties, including bulk density, organic carbon, total nitrogen, and C:N ratios in paired fields, but there is no indication that agricultural soils are degraded. This assessment supports the perception of Zuni farmers that long-term cultivation has not caused a decline in agricultural productivity. © 2005 Wiley Periodicals, Inc.
INTRODUCTIONMost assessments of cultivation effects on soil productivity rely on observations obtained over brief periods, often less than five years and rarely exceeding 100 years (Fenton et al., 1999). Given such limited time perspective on anthropogenic soil changes, there is a need for geoscientists to study the oldest farming systems of the New World, those of Native Americans (for some exceptions, see Doolittle, 2000; Sullivan, 2000; Glaser and Woods, 2004; Lehmann et al., 2004). To help fill this data gap, we studied soils associated with an American Indian agricultural system in a semiarid region of west-central New Mexico (Figure 1). Zuni fields are among the oldest identifiable agricultural fields in the United States, so this project provided a unique opportunity to document and evaluate soil properties associated with long-term agricultural practices that are very similar to those used prehistorically. This study has important methodological and theoretical *Corresponding author; E-mail: firstname.lastname@example.org.
Geoarchaeology: An International Journal, Vol. 20, No. 7, 661–693 (2005) © 2005 Wiley Periodicals, Inc.
Published online in Wiley Interscience (www.interscience.wiley.com). DOI:10.1002/gea.20076
HOMBURG, SANDOR, AND NORTONFigure 1. Location of the Zuni Reservation and paired (intensive) and unpaired (extensive) fields.
implications for how ancient agricultural soils and anthropogenic effects can be sampled and evaluated in archaeological contexts. The soil-sampling approach and suite of soil tests used to measure soil quality are directly applicable to geoarchaeological studies of ancient agricultural soils.
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ANTHROPOGENIC INFLUENCES ON ZUNI AGRICULTURAL SOILSOvercoming low water availability is usually viewed as the major hurdle to achieving agricultural sustainability in the semiarid Southwest, both today and in the past. This contrasts sharply with humid regions where soil-fertility maintenance is the main limiting factor (Dregne, 1963:219; Sanders, 1992:283). Soil fertility is also an important concern in understanding the agroecology of farming systems in the Southwest, where productivity is not limited by water alone (Ludwig, 1987). Nitrogen deficiency, in fact, is so common in desert soils that its effect in limiting agricultural production is almost as great as water availability (Rommey et al., 1978; Nabhan, 1983, 1984; Sandor and Gersper, 1988). Cultivation of crops with high nutrient requirements, such as maize, heightens this problem by depleting already low nitrogen stores (Stevenson, 1982; Doolittle, 1984; Loomis and Connor, 1992:Figure 12.1).
Research objectives of the Zuni soil study are to: (1) characterize the chemical and physical properties of agricultural soils; (2) identify and assess soil and geomorphic factors important to the functioning of runoff fields; and (3) determine if long-term cultivation has altered the quality of agricultural soils. To measure the effects of cultivation on soil quality, chemical and physical properties of soils from modern Zuni fields were analyzed at two spatial scales: (1) sampling at three paired (intensive) cultivated and uncultivated fields; and (2) sampling at 29 unpaired (extensive) cultivated, abandoned, and uncultivated fields (Figure 1).
We attempted to hold nonanthropogenic soil-forming factors as constant as possible by focusing soil sampling on similar elevations, landscape positions, and geologic contexts. Soil samples were collected from alluvial fans and a few colluvial footslopes, mainly at elevations of about 2070 m and in watersheds smaller than 150 hectares. Sampling concentrated on map units of the Hosta soil series (Aridic Haplustalf), a widespread soil where many runoff fields are located in the eastern part of the reservation.
Two intensive fields were selected near historic farming villages, one near Lower Nutria and the other near Pescado. Archival records indicate that both areas were used extensively for agriculture from about the turn of the last century to about World War II. The third field is in an area identified by some local farmers as Bear Canyon. We refer to the intensive fields in the Nutria, Pescado, and Bear Canyon study areas as the Laate, Sanchez, and Weekoty fields, respectively, named for the farmers who most recently cultivated them. The 29 extensive fields are roughly evenly divided between the Nutria, Pescado, and Bear Canyon study areas, and between cultivated, abandoned, and uncultivated land. For the purpose of this study, cultivated fields are defined as those that are either currently farmed or left fallow within the last decade, and that have been plowed mechanically since about World War II. Abandoned fields include pre-1940s fields that were tilled using horse-drawn plows and then left fallow. These fields were identified based on archival records and interviews with Zuni farmers. Uncultivated fields are ones lacking archival evidence of farming activity over the last century.
Archaeological traces (e.g., agricultural rock alignments, remnants of masonry field houses and farmsteads, and a granary) of Pueblo II period (A.D. 1050–1150) farming activity were found at many fields we sampled (Homburg, 2000).
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HOMBURG, SANDOR, AND NORTON
BACKGROUND DISCUSSIONThe Zuni and Runoff Farming The Zuni, who now number over 9000 people, are one of the Western Pueblo tribes of the Southwest (Eggan and Pandey, 1979; Woodbury, 1979). The traditional homeland of the Zuni extends over a broad region in west-central New Mexico and east-central Arizona, extending far outside of the modern reservation boundary (Ferguson and Hart, 1985). Zuni and other American Indian groups of the semiarid Southwest have a long tradition of runoff farming. Zuni agricultural fields are among the oldest, more or less continuously cultivated lands in the United States. Macrobotanical remains of maize were radiocarbon-dated to about 2270 70 yr B.P. (Beta-25998) (Rhode, 1990:49) on the Zuni Reservation. Evidence of early agriculture, including irrigation canals dating to 2000–3000 yr B.P. (Late Archaic and Basketmaker II periods), was found during recent archaeological projects (Damp and Kendrick, 2000; Damp et al., 2002) in Y Unit Draw and on the Zuni River floodplain near Black Rock (see Figure 1).
Significantly, even today Zuni farmers do not rely on artificial fertilizers, and that makes the present study especially applicable to many geoarchaeological studies of prehistoric farming systems. Instead of applying artificial fertilizers, Zuni fields are fertilized naturally with organic-rich sediments carried in runoff water (Norton, 1996, 2000;
Homburg, 2000; Homburg et al., 2000; Norton et al., 2003; Sandor et al., in review).
Runoff farming is an agricultural system that involves capturing runoff and sediment from watersheds and directing them onto agricultural fields (see Figure 2a). This type of agricultural system takes advantage of natural erosion in the watershed and field placement in areas of deposition (Lowrance, 1992). Earthen berms, rock alignments, wooden dams, and shallow ditches are commonly built to control erosion and divert runoff across fields for crop use. Frank Cushing was the first to document the effectiveness of Zuni techniques in spreading water and organic-rich sediment across an agricultural field (Cushing, 1979; reprint of writings first published in 1884).
A number of studies of ancient and historical Zuni agriculture were undertaken many decades later (e.g., Bohrer, 1960; Kintigh, 1984, 1985; Ferguson, 1985; Ferguson and Hart, 1985; Graham, 1990; Brandt, 1992, 1995; Prevost et al., 1993; Manolescu, 1994;
Cleveland et al., 1995; Hart, 1995; Havener, 1999; Maxwell, 2000; Damp et al., 2002).
Most of these studies, however, do not focus on soil properties and anthropogenic effects associated with Zuni agroecosystems. Rhode (1990, 1995) modeled productivity and water use for traditional Zuni farming systems, and Pawluk (1995) interviewed Zuni farmers to document their knowledge and concepts of agricultural soils and organic-rich sediment. Pawluk learned of tanayan sowe (“tree soil”; Figure 2b), a Zuni term that shows that farmers clearly recognize the crucial role of organic-rich sediments in nutrient renewal, especially debris from decomposed juniper litter (Pawluk, 1995; Sandor et al., 2002). Norton (1996, 2000) and Norton et al. (1998, 2002, 2003) investigated the hydrology of Zuni fields and demonstrated the importance of small watersheds in supplying water and nutrients to Zuni fields. The importance of small watersheds for runoff farming has been reported by a number of studies in the Southwest (McGee, 1895; Bryan, 1929; Stewart, 1939; Stewart, 1940a, 1940b; Hack, 1942; Nabhan,
Figure 2. (a) Floodwater draining into a field during a runoff event; (b) Organic-rich sediment delivered to alluvial fan by runoff.
GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL
HOMBURG, SANDOR, AND NORTON1979, 1983, 1984, 1986a, 1986b) and other desert settings around the world (Parr, 1943;
Boers and Ben-Asher, 1982; Evenari et al., 1982; Bruins 1986, 1990; Bruins et al., 1987;
Kowsar, 1991; Cohen et al., 1995; Lavee et al., 1997; Niemeijer, 1998). Muenchrath et al.
(2002) found that maize productivity in modern Zuni fields is highly variable but averages 572 (SE 181) kg/ha (see Schroeder [1999, 2001] for comparative data on maize productivity in Native American fields in North America). Sandor et al. (in review) investigated the biogeochemistry and agroecology of traditional Zuni runoff fields placed in valley-margin and canyon settings, and noted that alluvial fans and footslopes are productive settings for agriculture because: (1) runoff water and nutrients are naturally concentrated; (2) the growing season is extended because cold-air drainage effects are decreased relative to valley bottoms; and (3) potential salinization effects are less than on irrigated valley floors.
Previous Soil Studies of American Indian Farming Systems Few soil studies of American Indian farming systems have been conducted, and most of these were based on very small sample sizes or were focused on ancient, abandoned systems lacking continuity to the present. Ancient agricultural soils of the Southwest are well suited for geoarchaeological research because soil-formation processes (e.g., weathering, leaching, and illuviation) proceed much more slowly in deserts than in humid environments, so soil changes caused by cultivation practices tend to persist and remain detectable for long periods, probably on time scales of at least 1000 years (Sandor et al., 1986). A few soil studies in the Southwest have found that ancient farming systems degraded the quality of agricultural soils. For example, long-term cultivation significantly lowered the fertility of terraced fields in the Mimbres area (Sandor, 1983, 1995; Sandor et al., 1986, 1990), and farming practices at prehistoric fields near Flagstaff, Santa Fe, and at Mesa Verde tended to deplete phosphate and other nutrients to levels that made fields unproductive and caused them to be abandoned (Arrhenius, 1963). Other studies in central Arizona, especially studies of rock mulch agriculture, have not found that soils were degraded, and, in fact, soil productivity was often enhanced (Homburg, 1994; Homburg and Sandor, 1997, 2002, 2004). The few soil studies conducted thus far in the Southwest indicate that the consequences of agriculture are highly variable in terms of soil fertility and productivity, due to many interacting environmental and cultural factors (e.g., climate, topography, hydrology, soil type, native vegetation, crop type and variety, agricultural technology, and duration and intensity of cultivation).
Rationale for Tests Used in This Soil Study To document soil properties and assess anthropogenic effects of Zuni agriculture on soils in runoff fields, we measured long-term indicators of soil quality and sustainable land use, focusing on soil morphology, organic matter, and nutrients. A common outcome of long-term agriculture is degradation, whereby anthropogenic changes in soil properties cause a decline in agricultural productivity (Dale and Carter, 1955; Butzer, 1982; Hillel, 1991). Many studies of modern and ancient agri
Table I. Agricultural soil properties analyzed by this study.
Soil Property Criteria for Recognizing Degradation: Typical Causes and Consequences