Anthropogenic Soil Change in Ancient Irrigated Agricultural Terraces, Atacama Desert, Jonathan Sandor (Iowa State University), Gary Huckleberry (University of Arizona), and Frances Hayashida (University of New Mexico)

Introduction Anthropogenic Soil Change In this hyperarid climate, agriculture is only possible with irrigation, so natural soils on the same geomorphic surface adjacent to irrigated soils provide baseline data Agriculture has profoundly altered soils world-wide over thousands of years, both for assessing anthropogenic soil change. Initial data from 16 soil profiles and surface soil sample transects (including four pairs of agricultural/natural soil sample through deliberate management, and unintentionally. Ancient agricultural soils are areas) indicate intentional soil change through terracing, removal of soil rock fragments, and probable fertilization. The agricultural soils studied have anthropogenic long-term sources of data on anthropogenic soil change and processes. upper horizons ranging from 16-54 cm thick, with smaller rock fragment volume and size compared with natural soils. Changes in organic carbon, nitrogen, and phosphorus in the fine-earth fraction are most evident expressed on a volume rather than mass basis, because of deliberate removal of larger rock fragments from Ancient terraced agricultural soils are being investigated as part of an the anthropogenic soil horizons. Bulk densities (oven-dry, fine-earth basis) mostly range from 1.1 to 1.7 g cm-3, and are not different between natural and agricultural archaeological study of the high-altitude (~ 3200 m) area of the hyperarid Atacama soils. Most agricultural soils have higher phosphorus levels, suggesting enrichment from fertilization. Changes in organic carbon and nitrogen are also evident in Desert in northern Chile. The agricultural system mostly dates from the Late agricultural soils. Unintentional anthropogenic soil change resulted from CaCO input through long-term irrigation with calcareous spring water. Intermediate Period (ca. 950–1450 AD) through the Inka period, with some use 3 historically to the present. Water sources for canal irrigation were primarily springs, Intentional Anthropogenic Soil Change through Management possibly supplemented by snowmelt from nearby Andean volcanoes. One research objective is to evaluate long-term soil change from agriculture by comparing the terraced irrigated soils with adjacent natural soils.

Objective: To present data about ancient terraced and irrigated soils in the Atacama Desert, as an example of the valuable information about long-term anthropogenic soil change and processes that can be gained from research on ancient agricultural soils.

Soil – Geomorphic Setting The agricultural terraces and soils occur mainly on -age alluvial fan terraces and colluvial hillslopes underlain by volcanic bedrock. Much of the Pleistocene alluvium is cemented by silica. Photos of these profiles lower left.

Natural soils used for agriculture are mainly Haplocambids, Haplargids, Haplodurids, Argidurids, and possibly some Andisols or soils with andic properties. Example of texture depth function in a natural (control) soil at left (Typic Example of rock fragment removal from Example of total phosphorus accumulation They are more weathered and have different pedogenic development than has Argidurid) and nearby paired terraced agricultural soil at right. The terraced soil anthropogenic horizons of agricultural in anthropogenic horizons of agricultural been documented at lower elevations in the Atacama Desert, where gypsum and has 32 cm thick anthropogenic horizons overlying the natural argillic horizon. soils. soils. more soluble salts accumulate. Textures are predominantly sandy, and particle-size 80 SD = 32 0.7 0.9 10 60 NO3-N

Terraced Ag. Soil CarbonOrganicm (kg classes are sandy, coarse-loamy, and fine-loamy. 200 70 SD 0.6 0.8 NH4-N

= 0.3 Available P m (g

Control Soil ) 8 )

50 2 2 - 0.7

- 60 SD = 11 0.5

) 2 0.6 - 150 40 50 6

0.4 N (g m (g N

- 0.5 40 SD 4 30 100 = 0.1 0.3 0.4 4

Total N (g m (g N Total 30

N, NH N,

- -

0.3 2

20 m (g P Total 3

0.2 ) -

20 2 ) 0.2 50 2 10 0.1 NO 10 0.1 Rock Fragments (Volume %) Fragments (Volume Rock 0 0.0 0 0 0 0.0 Ag.Terrace Control High Atacama flow – Paired Terraced Agric. and Natural (Control) Soils Ag. Terrace Control Ag. Terrace Control world’s ~ largest Study, Chile Quaternary silicic Comparison of organic carbon, and total and available nitrogen and phosphorus between natural (control) soils and 3 Removal of rock fragments from Paniri body (26 km ) anthropogenic horizons of agricultural soils (0-15 cm depth shown here). Data are means (error bars are standard Topaín anthropogenic horizons of agricultural White areas in Topaín and Paniri soils shown in comparison with natural deviations [SD]), with all four paired transects combined (N=48). Agricultural soils have more organic carbon, total reflect CaCO3 in springs and canals. (control) soils to same depths. Data from nitrogen, total phosphorus, and nitrate-N than control soils (p < 0.01). Available P (Olsen test) is not higher in all four paired soil profiles. agricultural soils probably due to their higher pH from irrigation with calcareous water (see pH data below). Conclusions Unintentional Anthropogenic Soil Change Resulting from Irrigation • Soils in the high-altitude area of the Atacama Desert have been Agricultural Setting Unintentional anthropogenic soil change resulted from CaCO input through long-term 3 significantly altered by ancient and traditional agriculture, both Two study areas of terrace agriculture are at Topaín and Paniri, shown above. irrigation with calcareous spring water. Consequently, agricultural soils have higher pH than intentionally and unintentionally. Fields cover an estimated 50+ ha. Terraced fields were carefully compartmentalized natural soils. However, salinity (EC) and sodium (SAR) are mostly low. to distribute limited irrigation water in this hyperarid environment. • Intentional soil change through management includes creation of anthropogenic soil horizons by terracing, rock fragment removal, and probable fertilization. Unintentional soil change has resulted

from inputs of CaCO3 from irrigation. natural slope • Initial studies suggest that agriculture here was sustainable in agricultural terraces the sense of conserving soils over centuries through terracing, irrigation, nutrient inputs, and other management. Evidence includes thickened anthropogenic surface horizons with fewer rock fragments, higher levels of organic carbon, N, and P, and Natural (control) soils are nearly non-calcareous (example from Paniri at left), whereas agricultural similar bulk density (no compaction), relative to natural soils. soils have CaCO3 from irrigation water inputs (Paniri example with visible carbonate at right). References/Reading (examples) Casanova, M., O. Salazar, O. Seguel and W. Parcero-Oubiña, C., P. Fábrega-Álvarez, D. Luzio. 2013. The soils of Chile. Springer Salazar, A. Troncoso, F. Hayashida, M. Pino,, C. Netherlands. Borie, and E. Echenique. 2017. Ground to air and back again: archaeological prospection to Cesta, J.M. and D.J. Ward. 2016. Timing and characterize prehispanic agricultural practices in nature of alluvial fan development along the the high-altitude Atacama (Chile). Quaternary Chajnantor Plateau, northern Chile. International 435: 98-113. Cerro Topaín study area Geomorphology 273: 412-427. Sandor, J.A. 2006. Ancient agricultural terraces Above: ancient agricultural terraces Finstad, K., M. Pfeiffer and R. Amundson. 2014. and soils. p. 505-534. In: B. Warkentin (ed.) Hyperarid soils and the Soil Taxonomy. Soil Sci. Footprints in the soil: people and ideas in soil downslope and natural area upslope Soc. Am. J. 78: 1845-1851. history. Elsevier, Amsterdam. from highest irrigation canal. Same Houston, J. 2007 Recharge to groundwater in the Sandor, J.A., and J.A. Homburg. 2017. cactus in both photos marks position Turi Basin, northern Chile: an evaluation based on Anthropogenic soil change in ancient and of highest canal. tritium and chloride mass balance techniques. J. of traditional agricultural fields in arid to semiarid Hydrology 334:534-544. regions of the Americas. J. of Ethnobiology 37: 196-217. Left: natural and terraced soil profiles Keeley, H.C.M. 1988. Soils of pre-Hispanic field systems in the Rio Salado basin, northern Chile - Sandor, J., G. Huckleberry, and F. Hayashida. at Cerro Topaín. Horizons and depth Example of CaCO accumulation & increased pH in anthropogenic horizons of agricultural soils. a preliminary report. p.183-206. In: W. Groenman- 2015. Soils in ancient irrigated agricultural terraces functions for these profiles are 3 van Waateringe and M. Robinson (ed.) Man-made in the high-altitude Atacama Desert, Chile. School Terraced soil: prob. Argidurid, 9 soils. British Archaeological Reports, Oxford, UK. for Advanced Research Group Seminar Natural soil: Loamy-skeletal, shown in the graphs. Scale divisions SD = 1.8 “Agriculture and Empire in the High-Altitude

but with anthropogenic )

2 2.0 mixed, mesic Typic Argidurid horizons 0-32 cm.. of each red and white band 10 cm. - Atacama.” Santa Fe, New Mexico.

1.5 8 Acknowledgments Sponsors: Comisión Nacional de Investigación Científica y Tecnológica de Chile (CONICYT-USA 2013- 0012), National Science Foundation (Catalyzing International Collaborations Grant, award OISE- 1.0 1265816), Spanish Ministry of Culture (Actuaciones Arqueológicas en el Exterior).

Left: examples of m (kg Equivalent pH (1:1) pH

3 7 Project Co-Directors and Colleagues: Diego Salazar, Andrés Troncoso, César Parcero-Oubiña, Cruz ancient agricultural 0.5 Ferro-Vázquez, Jack Johnson, Virginia McRostie, Viviana Manriquez, Mariela Pino, and others.

terraces at Paniri. CaCO SD = 0.2 0.0 People of Turi Basin, Chile for their perspectives on agriculture and environment in this remarkable Ag. Terrace Control 6 region, and Eric Berna and Orlando Cruz for their help in studying soils. Ag. Terrace Control Laboratory Analyses by the University of Kansas Pedology Lab (Dan Hirmas, Aaron Koop, and others), CaCO3 enrichment and increased pH of agricultural soils due to irrigation with calcareous Colorado State University Soil, Water, and Plant Testing Lab (James Self and others), NRCS National spring water (0-15 cm depth shown here). All four paired transects combined (N=48). Soil Survey Center-Kellogg Soil Survey Laboratory (Doug Wysocki and others), New Mexico Bureau of Means and standard deviations (SD) shown; mean differences significant at p < 0.0001. Geology and Mineral Resources (Virgil Lueth and others).