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Salic Horizons in Soils of the USA
Pedosphere 23(5): 600–608, 2013 ISSN 1002-0160/CN 32-1315/P c 2013 Soil Science Society of China Published by Elsevier B.V. and Science Press
Salic Horizons in Soils of the USA J. G. BOCKHEIM∗1 and A. E. HARTEMINK Department of Soil Science, University of Wisconsin, Madison, WI 53706 (USA) (Received December 18, 2012; revised April 26, 2013)
ABSTRACT The taxonomic hierarchy and nationwide distribution of soils with a salic horizon were studied using the USA Natural Resources Conservation Service Soil Survey Geographic (SSURGO) Database to provide a more holistic view of the role of soil-forming factors in pedogenesis than from isolated case studies. Soils with a salic horizon occupied an area of 11 000 km 2 , i.e., 0.1% of land area in the contiguous USA. These soils occur narrowly in three great groups (Aquisalids, Haplosalids and Halaquepts), 11 subgroups, and 97 soil series. Soils with a salic horizon commonly had a mesic (50% of soil series) or thermic (19%) soil-temperature class, an aquic (89%) soil-moisture class, a mixed mineral class (79%), a calcareous (52%) reaction class, a superactive (59%) cation exchange activity class, and a fine (24% of soil series), fine-loamy (24% of soil series), or fine-silty (19% of soil series) particle-size class. Soils with a salic horizon were concentrated in the Basin and Range Province of western USA. The key pedogenic processes leading to the development of salic horizons were salinization, gleization, and calcification, with some evidence for argilluviation and silicification. Key Words:
saline soils, soil classification, solonchak
Citation: Bockheim, J. G. and Hartemink, A. E. 2013. Salic horizons in soils of the USA. Pedosphere. 23(5): 600–608.
INTRODUCTION The definition of the salic horizon in Soil Taxonomy (Soil Survey Staff, 2010) started with taxonomic placement problems from field mapping of soils with a high temporary water table and abundant salts in Nevada in the late 1950s (Blackburn, 2000). In the USA, these soils are unsuitable for agricultural uses unless they are leached of salts, an expensive undertaking, especially if there is no natural outlet for the drainage water. In the USA, most of these soils are used as rangeland, wildlife habitat, or auto racing. However, elsewhere in the world soils with a salic horizon may be drained and used for growing rice, barley, maize, and citrus crops. Saline soils comprise 2.6% of the world land surface, mainly in the Russian Federation, China, Argentina, Iran, India, and Paraguay (Abrol et al., 1988). A key concern with the management of soils with a salic horizon is salinization of soils and groundwater, the cost of which has been estimated worldwide at $12 billion per year (Ghassemi et al., 1995). There is a large body of data on saline soils in Eurasia (Abtahi, 1977; Pfisterer et al., 1996; Schofield ´ et al., 2001; Alvarez Rogel et al., 2001; Khresat and Qudah, 2006; Kotenko and Zubkova, 2008; Lebedeva et al., 2008; Sierra et al., 2009; Chernousenko et al., 2011; Ubugunov and Ubugunova, 2012). However, in ∗1 Corresponding
author. E-mail: [email protected].
the US only a few studies have addressed the distribution, classification, and genesis of soils with a salic horizon (e.g., Reid et al., 1996; Joeckel and Ang Clement, 2005). In Soil Taxonomy (Soil Survey Staff, 2010), the requirements for a salic horizon include a thickness of ≥ 15 cm, an electrical conductivity (EC) in a saturated paste of ≥ 30 dS m−1 , and the product of EC and thickness of ≥ 900. In the World Reference Base for Soil Resources (IUSS Working Group WRB, 2007), the salic horizon must have a thickness of ≥ 15 cm, an EC of ≥ 15 dS m−1 , and the product of EC and thickness of ≥ 450. In other national soil taxonomic systems, these soils are referred to as Solonchaks, halomorphic soils, and saline soils. The objectives of this study were i) to show the distribution of soils with a salic horizon in the USA, ii) to identify the relative importance of the soil-forming factors globally on the development of salic horizons, and iii) to summarize the dominant soil-forming processes of these salt-affected soils. MATERIALS AND METHODS Using the “Soil Classification Database” (Soil Survey Staff, 2013a), we prepared lists of active soil series for all taxa in which salic horizons existed. Soil series
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were examined using the “Official Soil Descriptions” function (Soil Survey Staff, 2013b). We also examined 21 case studies from the international literature to support or refute our findings. Soil characterization data were obtained from Soil Survey Staff (2013c). Thirteen representative pedons were selected to show their analytical properties according to their areal abundance and frequency distribution in various taxonomic groups. A map of soils with a salic horizon was prepared using the July 5, 2006 version of the Digital General Soil Map of the U.S. published by the US Department of Agriculture (USDA)-Natural Resources Conservation Service (NRCS). This dataset consists of general soil association units created by generalizing more detailed soil survey maps. Since the taxonomic nomenclature for a map unit is recorded at the component level and a map unit is typically composed of one or more components, aggregation is needed to reduce a set of component attribute values to a single value that will represent the map unit as a whole. For taxonomic order, suborder and great group distribution maps, data were aggregated to the map-unit level using the “dominant-component-aggregation” approach. This approach returns the attribute value associated with the component with the highest percent composition in the map unit, which may or may not represent the dominant condition throughout the map unit. For taxonomic subgroup distribution maps, data were aggregated to the map-unit level using the “presence method”, that is, if any component attribute matched the taxonomic subgroup of interest, then that map unit would be shown on the map regardless of its map unit composition.
RESULTS Characteristics of salic horizons Salic horizons are designated with the symbol z, which refers to the pedogenic accumulation of salts more soluble than gypsum. Since the salic horizon is pedogenic, these symbols are applied to the A, B, and BC horizons. Soils with salic horizons in the USA contained a variety of structures, including granules, subangular blocks, plates, and massive, structureless conditions. Masses of Fe or Mn and redox features were common in the soils. The water table was present at depths of 40 to 100 cm for periods ranging from 1 to 12 months of the year in many of the soils. Fine, tubular pores were common in soils with a salic horizon. From an examination of 97 official soil series descriptions with a reported salic horizon, the average depth to the salic horizon was 5 cm, and the depth ranged from 0 to 53 cm. The average thickness of the salic horizon was 83 cm, with a range of 15 (minimum required) to 203 cm. Silt was the dominant particle-size fraction in salic horizons, averaging 42% of the fine-earth (< 2 mm) fraction (Table I). The mean bulk density was 1.4 g cm−3 . Salic horizons in dominant soil series of the National Soil Survey Laboratory (NSSL) database were strongly alkaline due to the presence of calcium or sodium carbonate. The mean pH of the salic horizon was 8.5, with values ranging from 7.4 to 10.5 (Table I). The mean sodium adsorption ratio (SAR) was 161, and the mean EC of the salic horizon was 40 dS m−1 . In the salic horizon, calcium carbonate and gypsum averaged 120 and 130 g kg−1 , respectively. Cation ex-
TABLE I Selected chemical and physical propertiesa) of soils with a salic horizon, National Soil Survey Laboratory database Horizon
Depth
Clay
cm Az1 Az2 Az3 Az4 Bz1 Bz2 Bz3 A1 A2 Bk Bkq1 Bkq2
Silt %
0–3 3–20 20–41 41–58 58–84 213–272 107–152
20.0 28.8 34.8 32.7 27.6 20.5 29.6
0–8 8–18 18–38 38–74 74–91
21.5 26.7 19.4 13.4 16.1
Db g
cm−3
pH
SOC g
kg−1
CEC cmol(+)
SAR kg−1
EC dS
Carbonate m−1
Pedon No. 40A0962, Saltair series, Tykpic Aquisalids, Davis, California 60.2 ndb) 7.7 27.4 14.4 291 219.0 210 60.2 nd 8.0 14.9 22.6 198 129.0 220 57.3 nd 7.9 16.1 26.6 139 121.0 270 60.6 1.33 8.0 6.4 21.7 133 121.0 280 63.8 1.63 8.1 3.0 16.2 130 97.0 300 63.9 1.56 8.2 2.9 12.0 145 123.0 220 64.1 1.60 8.2 2.8 16.3 136 101.0 nd Pedon No. 83P0867, Wendane series, Aquandic Halaquepts, Lander, Nevada 61.6 nd 8.5 12.8 21.9 457 57.9 80 59.2 1.40 8.6 6.7 27.5 197 21.6 100 65.1 1.14 8.7 4.9 26.4 144 13.0 120 67.8 1.31 8.5 2.2 20.4 98 10.4 100 78.9 nd 8.6 2.4 27.2 53 2.9 120
g
Gypsum kg−1 nd nd nd nd nd nd nd nd nd nd nd nd
(to be continued)
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TABLE I (continued) Horizon
Depth
Clay
C Akqb Bkb
cm 91–104 104–130 130–152
9.0 40.4 18.3
Anz1 Anz2 Bnz1 Bnz2 Bz1 Bz2 C1 C2
0–1 1–7 7–15 15–23 23–30 30–37 37–58 58–95
13.9 18.4 36.9 26.2 23.5 19.4 16.5 5.0
A/B Btkz1 Btkz2 Btkz3 Btkz4 Btkz5 2C
0–5 5–13 13–23 23–53 53–66 66–94 94–132
19.3 21.6 24.0 12.1 14.0 9.8 nd
A1 A2 AC1 AC2 C1 C2
0–10 10–18 18–25 25–43 43–64 64–89
4.1 3.3 2.8 3.6 2.8 3.2
A1 A2 AB Bq 2Bkqm
0–10 10–25 25–69 69–86 86–112
11.2 27.8 28.7 11.6 13.3
A1 A2 Bz1 Bz2 Bz3 Bz4 Bz5 C1 C2
0–3 3–8 8–20 20–46 46–71 71–112 112–130 130–166 166–200
41.5 46.5 51.2 46.1 48.3 46.0 48.9 47.1 46.4
E B1 B2 C1 C2
0–3 3–10 10–20 20–76 76–152
13.8 27.1 27.8 20.3 7.3
0–10 10–18 18–30 30–48 48–76 76–102 102–152
7.0 10.0 15.2 25.7 17.6 7.5 12.1
0–9
76.7
Akn1 Akn2 Abkn Bkn1 Bkn2 Bkn3 C An
Silt %
Db cm−3
pH
SOC kg−1
CEC
SAR kg−1
EC
Carbonate m−1
g g cmol(+) dS nd 8.9 1.9 10.7 17 1.5 110 nd 8.1 2.9 39.5 17 1.0 50 nd 8.2 1.8 23.6 9 1.0 70 Pedon No. 89P0541, Land series, Typic Aquisalids, Clark, Nevada 39.9 nd 7.4 8.2 5.7 378 50.6 50 44.0 1.33 8.0 5.0 9.8 143 28.1 80 51.1 nd 8.2 4.3 16.5 136 27.0 160 56.4 nd 8.3 3.7 15.8 120 23.5 160 73.2 1.28 8.3 4.2 14.1 122 24.7 220 74.4 nd 8.2 5.3 11.0 93 nd 270 76.8 1.38 8.4 3.2 12.5 74 16.0 190 54.9 1.46 8.5 1.5 7.1 42 9.0 160 Pedon No. 40A1162, Ligurta series, Calcic Haplosalids, La Paz, Arizona 48.7 1.56 7.8 0.5 15.0 21 2.8 130 36.0 1.51 7.5 0.9 9.6 20 19.4 100 28.6 nd 7.4 0.9 9.5 17 33.6 120 21.9 1.51 7.4 0.7 6.1 15 34.0 110 10.8 1.46 7.5 1.1 6.1 15 28.2 160 20.4 nd 7.7 0.4 7.2 16 24.6 10 nd nd 7.6 0.5 10.5 nd 17.1 30 Pedon No. 80P0094, Wildhorse series, Typic Haplaquepts, Morrill, Nebraska 6.0 nd 8.5 14.0 5.8 12 1.8 10 5.6 nd 8.9 7.3 4.7 27 3.4 10 5.5 nd 9.1 3.6 3.4 28 3.2 10 4.6 nd 9.1 2.9 3.1 22 2.3 20 1.0 nd 8.4 1.3 1.9 6 0.8 10 0.4 nd nd 0.7 1.8 nd nd 10 Pedon No. 86P0991, Reese series, Aeric Halaquepts, Lake, Oregon 34.3 nd 8.6 17.0 24.1 161 16.7 70 43.0 nd 9.0 6.9 22.3 443 26.3 120 47.1 nd 8.7 5.8 23.0 138 7.1 230 38.8 nd 8.2 3.3 23.6 35 1.8 240 19.7 nd 8.1 2.7 nd 25 1.3 260 Pedon No. 08N0488, Parran series, Typic Aquisalids, Churchill, Nevada 39.1 1.42 8.6 5.4 24.1 153 14.7 30 38.0 nd 8.7 4.5 24.2 533 41.1 30 39.4 1.27 8.4 3.8 24.0 249 42.3 30 45.4 1.29 8.4 3.1 25.4 237 32.7 20 46.6 1.48 8.6 1.4 25.6 240 25.0 10 49.5 1.58 8.8 2.7 25.9 230 16.5 20 46.8 1.53 8.7 2.0 28.1 241 11.2 20 50.3 1.56 8.9 1.7 27.9 303 8.6 10 50.7 1.51 9.1 1.0 26.6 497 6.8 10 Pedon No. 40A2114, Janise series, Typic Halaquepts, Scotts Bluff, Nebraska 47.6 nd 7.7 22.3 15.7 13 1.7 10 33.5 1.41 8.8 8.0 20.0 35 1.9 60 48.2 1.42 9.4 2.6 26.5 124 5.0 130 55.3 1.43 10.1 0.7 26.3 1 158 20.0 130 52.3 nd 10.2 0.4 22.2 288 11.5 30 Pedon No. 87P0031, Umapine series, Typic Halaquepts, Baker, Oregon 62.4 nd 10.3 2.2 nd 824 22.3 20 69.0 nd 10.3 1.1 nd 441 16.9 20 49.3 nd 10.0 1.3 nd 229 8.7 60 53.8 nd 10.0 1.3 nd 278 10.3 100 38.7 nd 9.8 1.5 nd 264 7.6 210 62.5 nd 9.7 0.7 nd 120 5.3 80 66.9 nd 9.7 0.6 nd 164 7.6 0 Pedon No. 88P0952, Wherry series, Typic Aquisalids, Kern, California 16.7 1.43 8.3 2.9 33.5 175 63.7 140 72.1 53.7 65.1
g
Gypsum kg−1 nd nd nd 150 130 30 30 20 50 40 20 nd nd 3 nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd trace 10 20 trace nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd
(to be continued)
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603
TABLE I (continued) Horizon
Depth
Clay
Bky Bnz Cn1 Cn2 Cn3
cm 9–20 20–31 31–69 69–94 94–147
65.9 57.8 60.5 52.1 49.0
A1 E A2 C1 C2 C3 C4
0–10 10–25 25–41 41–58 58–86 86–130 130–165
13.0 18.0 19.7 22.2 24.2 22.2 29.9
Agz Bgz1 Bgz2 Bgz3 BCg1 BCg2
0–8 8–18 18–53 53–94 94–147 147–200
23.8 7.3 20.9 25.4 22.5 9.1
Akzg Bkz1 Bkz2 CBkz Czg Average
0–13 13–25 25–38 38–114 114–140
26.7 40.0 44.5 42.4 48.7 25.4
Silt %
Db cm−3
pH
SOC kg−1
CEC
SAR kg−1
EC
Carbonate m−1
g g cmol(+) dS 18.1 1.54 8.5 2.4 26.6 121 40.3 170 20.7 1.73 8.5 2.0 20.9 95 38.9 180 21.5 1.49 8.7 2.4 23.2 155 24.3 160 23.2 1.60 9.0 1.6 19.0 156 11.5 190 19.6 1.85 9.1 1.5 16.8 89 5.4 180 Pedon No. 81P0694, Yobe series, Aeric Haplaquepts, Lassen, California 60.5 1.44 10.5 8.1 30.4 380 13.6 110 59.8 1.25 9.9 4.0 35.4 120 4.6 100 58.4 1.08 9.6 3.9 37.6 76 3.6 100 58.5 1.29 9.3 3.8 36.2 57 3.1 130 57.3 1.2 8.7 3.8 30.0 21 1.2 300 65.4 1.17 8.1 3.5 33.9 11 0.7 250 55.9 1.20 7.6 1.9 43.6 12 0.7 nd Pedon No. 99P0026, Arrada series, Typic Halaquepts, Kenedy, Texas 13.3 nd 7.9 nd 6.7 74 111.0 trace 7.9 nd 7.9 nd 2.5 65 88.6 nd 10.6 nd 7.5 nd 5.8 86 130.0 nd 12.9 nd 8.5 nd 4.8 92 111.0 140 13.8 nd 8.4 nd 3.6 107 108.0 300 6.2 nd 8.4 nd 3.0 108 101.0 50 Pedon No. 02N0156, Eimarsh series, Aeric Haplaquepts, Box Elder, Utah 58.2 nd 8.0 nd 11.6 25 11.9 280 52.5 nd 8.0 nd 13.6 56 22.5 130 51.1 nd 7.9 nd 14.9 59 25.8 280 48.1 nd 8.0 nd 14.9 74 32.1 280 48.8 nd 8.2 nd 17.1 85 30.9 260 42.4 1.4 8.5 5.0 17.1 161 40.2 123
g
Gypsum kg−1 nd nd nd nd nd nd nd nd nd nd nd nd 250 540 310 20 10 nd nd nd nd nd nd 132
a) D = bulk density; SOC = soil organic C; CEC = cation exchange capacity; SAR = sodium adsorption ratio; EC = electrical b conductivity; b) nd = not detected.
change capacity (CEC) of the salic horizon was moderate, reflecting the abundance of clay (mean = 25%) and organic C (mean = 5 g kg−1 ). The base saturation (data not shown) is 100% for all pedons, with Ca and Na dominating the exchange sites. Mineralogy of soils with salic horizons are reported for the < 2 μm clay fraction (7 soil series), the 50–20 μm coarse-silt fraction (3 soil series), and the 100–50 μm very-fine-sand fraction (1 soil series). The clay fraction contained primarily illite group minerals, kaolinite, smectite, and quartz; glass and sponge spicules were common in the coarse-silt fraction; and a variety of minerals were present in the very-fine-sand fraction (Table II). These data were corroborated by the fact that the mineral class is commonly mixed. The dominant salts were halite (NaCl) and trona (NaHCO3 + Na2 CO3 ·2H2 O), with carbonate flecks and gypsum fibers also being common. Classification of soils with a salic horizon Soils with a salic horizon occurred in two orders, two suborders, three great groups, 11 subgroups, and 97 soil series (Table III). Soil series with a salic horizon were most abundant in the Inceptisols (62), followed
by the Aridisols (35). Soils with a salic horizon are recognized in the Alfisols (Salidic Natrustalfs), Gelisols (Salic subgroups of Anhyorthels, Aquorthels, and Anhyturbels), Inceptisols (Salidic Sulfaquepts), Mollisols (Salidic subgroups of Calciustolls and Haplustolls), and Vertisols (the great groups of Salaquerts, Salitorrerts, and Salusterts), but no soil series have been officially recognized in these orders. However, it is likely that soil series included in these order contain a salic horizon but that the horizon is secondary in the classification of the series. Of the 97 soil series with a salic horizon 50% had a mesic and 19% had a thermic soil-temperature class, 89% had an aquic soil-moisture class, 79% had a mixed mineralogy class, 52% had a calcareous reaction class, 59% had a superactive cation exchange activity class, and 24%, 24%, and 19% had a fine, fine-loamy, or finesilty particle-size class, respectively. Soils with a salic horizon predominantly contained an ochric epipedon (98% of pedon descriptions); subsurface horizons present in soils with a salic horizon included the calcic (24% of pedons), cambic (18%), gypsic (11%), and duric (7%), argillic (4%), and natric (2% of pedons).
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Distribution of soils with a salic horizon
TABLE II
Soil mapping units with a salic horizon comprised 11 000 km2 , accounting for 0.1% of the total soil area of the conterminous USA (Fig. 1). Soils with a salic horizon occurred primarily in the Basin and Range province of the western USA (Nevada, California, western Texas, and Utah) and the Columbia Plateau (eastern Oregon).
Mineralogy of soils with salic horizons
DISCUSSION Comparison of salic horizon properties in USA with other areas There are only scattered pedons with salic horizons reported in the literature, with the exception of Spain (Table IV). The depth to the salic horizon ranges from 0 cm in Iran and Israel to 26 cm in Somalia, as compared to a value of 5 cm for the USA. The thickness of the salic horizon ranged from 75 to > 170 cm and averaged 83 cm for soils with salic horizons in the USA. Clay concentrations ranged from 7.2% to 42.0% and averaged 25.4% in the USA. The low clay values in the Negev desert of Israel can be attributed to the sandy eolian and fluvial materials. Silt concentrations range from 20.0% in Israel to 72.0% in Hungary and averaged 42.4% in the USA. The abundant clay and silt in soils with salic horizons is due to the fact that these soils often form in playas. The mean bulk density of salic horizons in USA soils was 1.4 g cm−3 , which is lower than the 1.58 to 1.60 g cm−3 values reported in salic soils of Israel and Hungary, reflecting the maintenance of ped structure. The mean pH of soils with salic horizons generally varied from 7.3 to 8.9 and was 8.5 for USA soils (Table IV). The low value (5.0) for soils with a salic horizon in Ghana can be attributed to the existence of pyrites in the sediments. The high values (10.0) in Russia are related to the sodicity of the soils. Soil organic C values range from 1.1 to 10 g kg−1 , as compared to a mean value of 5.2 g kg−1 for salic horizons in the USA. The CEC ranges from 15.8 to 48.3 cmol(+) kg−1 , with values for salic horizons in the USA toward the low end of the range at 17.1 cmol(+) kg−1 . The SAR of soils with a salic horizon ranges from 38 to 132, as compared to
Mineral Biotite Chlorite Halloysite Hydrous mica Kaolinite Palygorskite Smectite Vermiculite Apatite Beryl Calcite Chert Cristobalite Feldspars Garnet Gibbsite Glass Goethite Gypsum Hornblende Opal Opaque minerals Plagioclase Pyrophyllite Pyroxene Quartz Sponge spicules Tourmaline Zeolites Zircon
Clay (< 2 μm) 3 1 5 5 1 4 1
2 1 2
Coarse-silt (50–20 μm)
Very-fine sand (100–50 μm)
1a) 1
1
1
1 1 1 1
1
1 1
1
2 1
1
1 1 1 1
1
1
1
1 1
1 4
1 1 2 1 1 1
1
a) Relative X-ray diffraction peak size: 1 = very small; 2 = small; 3 = medium; 4 = large; 5 = very large.
a mean value of 161 for USA salic soils. The EC ranges from 5.1 to 53.9 dS m−1 , with a mean value of 40.2 for salic soils in the USA. Calcium carbonate ranges from 115 (Hungary) to 400 g kg−1 (Iran); CaCO3 was toward the low end of the range in salic soils of the USA, averaging 123 g kg−1 . There were minimal data for gypsum concentrations; however, salic soils in the USA had higher values (132 g kg−1 ) than salic soils in Spain and Iran. In general, salic horizons in the USA were comparable with those of Hungary. Factors influencing the formation of salic horizons In the USA soils with salic horizons occurred in
TABLE III Classification of soils with a salic horizon in Soil Taxonomy Order
Suborder
Great group
Subgroups (No. of soil series)
Sum of soil series
Aridisols
Salids
Inceptisols Total
Aquepts
Aquisalids Haplosalids Halaquepts
Calcic (4), Gypsic (4), Typic (18) Calcic (1), Gypsic (2), Typic (6) Aeric (24), Aquandic (2), Duric (7), Typic (28), Vertic (1)
26 9 62 97
SALIC HORIZONS IN SOILS
Fig. 1
605
Distribution of soils with a salic horizon in the USA.
TABLE IV A global comparison of the properties of soils with salic horizons Propertya)
USAb)
Iranc)
Somaliad)
Ghanae)
Jordanf)
Israelg)
Spainh)
Hungaryi)
Russiaj)
No. of pedons Depth to salic horizon (cm) Thickness of salic horizon (cm) Clay (%) Silt (%) Bulk density (g cm−3 ) pH Soil organic C (g kg−1 ) CEC (cmol(+) kg−1 ) SAR EC (dS m−1 ) CaCO3 (g kg−1 ) Gypsum (g kg−1 ) Salt class
13 5 83 25.4 42.4 1.4 8.5 5.2 17.1 161 40.2 123 132 sal, sal-sodl)
2 0 > 140 42.0 41.0 nd 8.9 3.5 48.3 38 22.8 400 < 52 sal-sod
3 26 > 67 nd nd nd 7.3 nd nd nd 8.3 612 nd sal
3 ndk) nd 54.1 42.5 nd 5.0 8.2 33.2 nd 5.1 nd nd sal
2 21 75 nd nd nd 8.1 2.8 22.7 nd 40.2 nd 6.5 sal
6 0 > 158 7.2 20.0 1.6 8.8 1.1 nd nd nd 135 nd sal
23 nd nd 17.8 49.8 nd 8.4 10 nd 67.5 53.9 331 89 sal
3 nd nd 36.0 62.0 1.58 8.8 5.3 15.8 132 7.4 115 nd sal-sod
2 5 > 170 nd nd nd 10 8.3 nd 1.5 nd 119 nd sal-sod
a) CEC
= cation exchange capacity; SAR = sodium adsorption ratio; EC = electrical conductivity; b) This study; c) Abtahi, 1977; ´ 1995; e) Allotey et al., 2008; f) Khresat and Qudah, 2006; g) Pfisterer et al., 1996; h) Alvarez oth and Rogel et al., 2001; i) T´ j) k) l) Jozefaciuk, 2002; Bronnikova et al., 2011; nd = not detected; sal = saline; sal-sod = saline sodic.
d) Alaily,
variety of climates. The soil-temperature class was dominantly mesic, but soils with thermic and frigid soil-temperature regimes were common. The mean annual precipitation averaged 300 mm year−1 , but ranged
widely between 100 and 1 015 mm year−1 (data not shown). The mean annual air temperature averaged 12 ◦ C, but ranged from 6 to 24 ◦ C (data not shown). The western USA is divided into four desert regions based
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on rainfall distribution and amount, elevation, and other factors: the Chihuahuan (southeastern Arizona, southwestern Texas), the Sonoran (southern California and southwestern Arizona), the Mojave (southeastern California), and the Great Basin (Nevada, Utah, Oregon, and portions of adjoining states). The salt-affected areas of these deserts contain the following shrubs: black greasewood (Sarcobatus vermiculatus), creosote bush (Larrea tridentata), saltbush (Atriplex spp.), and the following shortgrasses: alkali sacaton (Sporobolus airoides), inland saltgrass (Distichlis spicata), wild rye (Elymus glaucus), western wheatgrass (Pascopyrum smithii), and alkali bluegrass (Poa secunda). Soils with salic horizons occur on gentle slopes, averaging between 0% and 3%. Although 59% of the soils are derived from alluvium, other common parent materials include lacustrine (32%) and marine deposits (6%). In the literature, topography is viewed as a very important factor leading to the development of the salic horizon, including groundwater level and salinity, slope position, proximity to the edge of playas, the presence of depressions, and the influence of flooding (Table V). Of the soil series in the USA containing salic horizons, 38% were somewhat poorly drained and 38% were poorly drained. Parent material is important, particularly where evaporites exist and in areas
where dust is deposited. The case studies reported in Table V all occur in semiarid to hyperarid regions. Humans have played an important role on modifying salic horizons through irrigation and cropping. Few studies have addressed the time required to form a salic horizon. Harris (1990) observed salic horizons forming on deltas in the Yukon Territory, Canada in as little as 100 years. In the Negev Desert, Israel, salts began accumulating in the last 1 million years due to an increasingly aridic climate (Amit et al., 2011). Genesis of salic horizons The dominant processes leading to the development of saline soils were salinization, gleization, and calcification, with silicification and argilluviation occurring in some soils. The salts in soils with salic horizons in the USA originated from evaporites, groundwater seeps, and dust deposition. In the USA, soils containing salts more soluble than gypsum are classified into three broad classes, sodic, saline, and saline-sodic, based on pH, EC, and exchangeable sodium percentage (United States Salinity Laboratory Staff, 1954). Soils of the latter two classes may contain a salic horizon. In that 89% of the soil series with salic horizons in the USA contain an aquic soil-moisture class, gleization was an important soil-forming process. This was further evidenced by the masses of Fe or Mn and redox
TABLE V Relation of soil-forming factors to the development of salic horizons Area
Soil taxa
World
Salt-affected soils
Aral Sea
Solonchaks
Iran; Hungary
Solonchaks
Mongolia Astrakhan, Russia
Solonchaks
Solonetz on sideslopes & solonchaks on footslopes
Abtahi, 1977; Schofield et al., 2001; T´ oth et al., 2001 Ubugunov and Ubugunova, 2012 Karpachevskii et al., 2008; Boroda et al., 2011
Israel Kulunda, Russia Sulak, Dagestan Israel
Solonchaks Solonchaks Solonchaks
Solonchaks develop on edges of playas Solonchaks form in depressions Flooding an important source of salts
Lebedeva et al., 2008 Kotenko and Zubkova, 2008 Pfisterer et al., 1996
Solonchaks Salic reg; solonchaks
Parent materials Salts originate from evaporites Salts and minerals contributed by dustfall
Hungary; Spain Israel; South Africa
Role of soil-forming factor Humans Irrigation and cropping induces salinization Drying of seabed enables formation of salic horizon Relief Groundwater level important
Tunisia; Jordan Yukon, Canada Israel
Solonchaks Salic reg
Time Saline soils develop in < 100 year Salts accumulated in last 1 million year due to increasingly aridic climate
Reference(s)
Abrol et al., 1988 Stulino and Sektimenko, 2004
Schofield et al., 2001; Sierra et al., 2009 Yaalon, 1964; Singer et al., 1995; Drake, 1997; Khresat and Qudah, 2006; Amit et al., 2011 Harris, 1990 Amit et al., 2011
SALIC HORIZONS IN SOILS
features commonly described in salic soils of the USA. Calcification was evidenced by the abundance of CaCO3 (mean = 120 g kg−1 ) and gypsum (CaSO4 + 2H2 O) or anhydrite (CaSO4 ) (mean = 130 g kg−1 ) in the 13 pedons (Table I). In addition, five of these pedons had Bkz horizons, 11% of the soils with salic horizons occurred in calcic or gypsic subgroups (Table III), and 23% of the 97 soil series contained a calcic horizon. Three of the 13 pedons for which laboratory data were provided (Table I) contained either an argillic horizon or had duric properties; therefore, argilluviation and silicification were processes that only infrequently accompany salic horizon formation in the USA. CONCLUSIONS The salic horizon tended to occur at a shallow depth, commonly 0–5 cm; it was thick, commonly ranging from 75 cm to greater than 170 cm. The salic horizon contained abundant silt and clay (62%–93%) because of a common playa origin. The pH of the salic horizon generally was slightly to strongly alkaline (7.3–8.9). The salic horizon contains abundant soil organic C (3.5–100 g kg−1 ), a moderate cation exchange capacity that ranged between 16 and 48 cmol(+) kg−1 , an electrical conductivity in excess of 5 dS m−1 , abundant exchangeable Ca and Na, abundant CaCO3 (120– 400 g kg−1 ) and moderate quantities of gypsum (< 10–130 g kg−1 ). In the NRCS database, soils with a salic horizon occurred in two orders, two suborders, three great groups, 11 subgroups, and 97 soil series. Soil mapping units with a salic horizon comprise 11 000 km2 in the USA, primarily in the Basin and Range province of western USA. Topography and parent material were key soil-forming factors contributed to the formation of salic horizons. However, humans have played a major role in their transformation and development in many parts of the world. The predominant pedogenic processes leading to the development of the salic horizon included salinization, gleization and calcification, with silicification and argilluviation occurring in some soils. ACKNOWLEDGEMENTS The authors are grateful to the professional soil surveyors and scientists of Natural Resources Conservation Service, United States Department of Agriculture, the laboratory technicians, and information technologists that have made the data used in this study generously available to the public. The authors appreciate three anonymous reviews of an earlier draft of this manuscript.
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REFERENCES Abrol, I. P., Yadav, J. S. P. and Massoud, F. I. 1988. Saltaffected soils and their management. FAO Soils Bulletin 39, Rome. Abtahi, A. 1977. Effect of a saline and alkaline ground water on soil genesis in semiarid southern Iran. Soil Sci. Soc. Am. J. 41: 583–588. Alaily, F. 1995. Soil properties of Quaternary deposits in the arid part of northeastern Somalia. Arid Soil Res. Rehab. 9: 39–50. Allotey, D. F. K., Asiamah, R. D., Dedzoe, C. D. and Nyamekye, A. L. 2008. Physico-chemical properties of three salt-affected soils in the lower Volta basin and management strategies for their sustainable utilization. West Afr. J. Appl. Ecol. 12: 163–182. ´ Alvarez Rogel, J., Ortiz Silla, R., Vela de Oro, N. and Alcarez Ariza, F. 2001. The application of the FAO and US soil taxonomy systems to saline soils in relation to halophytic vegetation in SE Spain. Catena. 45: 73–84. Amit, R., Simhai, O., Ayalon, A., Enzel, Y., Matmon, A., Crouvi, O., Porat, N. and McDonald, E. 2011. Transition from arid to hyper-arid environment in the southern Levant deserts as recorded by early Pleistocene cummulic Aridisols. Quat. Sci. Rev. 30: 312–323. Blackburn, P. W. 2000. A history of soil survey in Nevada: A Compilation of Short Stories Commemorating the 100th Anniversary of the Soil Survey Program. Natural Resources Conservation Service, United States Department of Agriculture. Available online at ftp://ftp-fc.sc.egov.usda.gov/NV/ web/Nevada Soil Survey/History Soil Survey Nevada Part1. pdf (verified on June 4, 2013). Boroda, R., Amit, R., Matmon, A., Team, A. S. T. E. R., Finkel, R., Porat, N., Enzel, Y. and Eyal, Y. 2011. Quaternaryscale evolution of sequences of talus flatirons in the hyperarid Negev. Geomorphology. 127: 41–52. Bronnikova, M. A., Turova, I. V., Kuznetsova, E. P., Kozlov, D. N. and Khokhlova, O. S. 2011. Soils of cryogenic subarid steppe landscapes in the Terekhol Intermontane Depression of the Sangilen Upland. Eurasian Soil Sci. 44: 589–603. Chernousenko, G. I., Kalinina, N. V., Khitrov, N. B., Pankova, E. I., Rukhovich, D. I., Yamnova, I. A. and Novikova, A. F. 2011. Quantification of the areas of saline and solonetzic soils in the Ural Federal Region of the Russian Federation. Eurasian Soil Sci. 44: 367–379. Drake, N. A. 1997. Recent Aeolian origin of surficial gypsum crusts in southern Tunisia: Geomorphological, archaeological and remote sensing evidence. Earth Surf. Proc. Land. 22: 641–656. Ghassemi, F., Jakeman, A. J. and Nix, H. A. 1995. Salinisation of land and water resources: Human Causes, Extent, Management and Case Studies. CAB International, Wallingford, UK. Harris, S. A. 1990. Dynamics and origin of saline soils on the Slims River Delta, Kluane National Park, Yukon Territory. Arctic. 43: 159–175. IUSS Working Group WRB. 2007. World Reference Base for Soil Resources 2006: A Framework for International Classification, Correlation and Communication. World Soil Resources Reports No. 103. Food and Agriculture Organization of the United Nations (FAO), Rome. Joeckel, R. M. and Ang Clement, B. J. 2005. Soils, surficial geology, and geomicrobiology of saline-sodic wetlands, North Platte River Valley, Nebraska, USA. Catena. 61: 63–101. Karpachevskii, L. O., Yakovleva, L. V., Bednev, A. V. and Fedotova, A. V. 2008. Distribution of exchangeable cations in
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Soil Survey Staff. 2013a. Soil Series Classification Database (SC). Natural Resources Conservation Service, United States Department of Agriculture. Available online at http://soils.usda.gov/technical/classification/scfile/index.html (verified on June 4, 2013). Soil Survey Staff. 2013b. Official Soil Series Descriptions (OSDs). Natural Resources Conservation Service, United States Department of Agriculture. Available online at http://soils.usda.gov/technical/classification/osd/index.html (verified on June 4, 2013). Soil Survey Staff. 2013c. Soil Lab Data Mart (Soil Characterization). Natural Resources Conservation Service, United States Department of Agriculture. Available online at http://ncsslabdatamart.sc.egov.usda.gov. (verified on June 4, 2013). Stulino, G. and Sektimenko, V. 2004. The change in soil cover on the exposed bed of the Aral Sea. J. Marine Syst. 47: 121–125. T´ oth, T. and Jozefaciuk, G. 2002. Physicochemical properties of a solonetzic toposequence. Geoderma. 106: 137–159. T´ oth, T., Kuti, K., Kabos, L. and P´ asztor, L. 2001. Use of digitalized hydrogeological maps for evaluation of salt-affected soils of large areas. Arid Land Res. Manag. 15: 329–346. Ubugunov, L. L. and Ubugunova, V. I. 2012. Soils of floodplains in arid regions of inner Asia (the Zavkhan River, Mongolia). Eurasian Soil Sci. 45: 237–245. United States Salinity Laboratory Staff. 1954. Diagnosis and Improvement of Saline and Alkali soils. Agricultural Handbook No. 60. US Department of Agriculture. US Government Printing Office, Washington, DC. Yaalon, D. H. 1964. Airborne salts as an active agent in pedogenic processes. Trans. 8th Congress Int. Soil Sci. Soc. 5: 997–1000.
Salic Horizons in Soils of the USA J. G. BOCKHEIM∗1 and A. E. HARTEMINK Department of Soil Science, University of Wisconsin, Madison, WI 53706 (USA) (Received December 18, 2012; revised April 26, 2013)
ABSTRACT The taxonomic hierarchy and nationwide distribution of soils with a salic horizon were studied using the USA Natural Resources Conservation Service Soil Survey Geographic (SSURGO) Database to provide a more holistic view of the role of soil-forming factors in pedogenesis than from isolated case studies. Soils with a salic horizon occupied an area of 11 000 km 2 , i.e., 0.1% of land area in the contiguous USA. These soils occur narrowly in three great groups (Aquisalids, Haplosalids and Halaquepts), 11 subgroups, and 97 soil series. Soils with a salic horizon commonly had a mesic (50% of soil series) or thermic (19%) soil-temperature class, an aquic (89%) soil-moisture class, a mixed mineral class (79%), a calcareous (52%) reaction class, a superactive (59%) cation exchange activity class, and a fine (24% of soil series), fine-loamy (24% of soil series), or fine-silty (19% of soil series) particle-size class. Soils with a salic horizon were concentrated in the Basin and Range Province of western USA. The key pedogenic processes leading to the development of salic horizons were salinization, gleization, and calcification, with some evidence for argilluviation and silicification. Key Words:
saline soils, soil classification, solonchak
Citation: Bockheim, J. G. and Hartemink, A. E. 2013. Salic horizons in soils of the USA. Pedosphere. 23(5): 600–608.
INTRODUCTION The definition of the salic horizon in Soil Taxonomy (Soil Survey Staff, 2010) started with taxonomic placement problems from field mapping of soils with a high temporary water table and abundant salts in Nevada in the late 1950s (Blackburn, 2000). In the USA, these soils are unsuitable for agricultural uses unless they are leached of salts, an expensive undertaking, especially if there is no natural outlet for the drainage water. In the USA, most of these soils are used as rangeland, wildlife habitat, or auto racing. However, elsewhere in the world soils with a salic horizon may be drained and used for growing rice, barley, maize, and citrus crops. Saline soils comprise 2.6% of the world land surface, mainly in the Russian Federation, China, Argentina, Iran, India, and Paraguay (Abrol et al., 1988). A key concern with the management of soils with a salic horizon is salinization of soils and groundwater, the cost of which has been estimated worldwide at $12 billion per year (Ghassemi et al., 1995). There is a large body of data on saline soils in Eurasia (Abtahi, 1977; Pfisterer et al., 1996; Schofield ´ et al., 2001; Alvarez Rogel et al., 2001; Khresat and Qudah, 2006; Kotenko and Zubkova, 2008; Lebedeva et al., 2008; Sierra et al., 2009; Chernousenko et al., 2011; Ubugunov and Ubugunova, 2012). However, in ∗1 Corresponding
author. E-mail: [email protected].
the US only a few studies have addressed the distribution, classification, and genesis of soils with a salic horizon (e.g., Reid et al., 1996; Joeckel and Ang Clement, 2005). In Soil Taxonomy (Soil Survey Staff, 2010), the requirements for a salic horizon include a thickness of ≥ 15 cm, an electrical conductivity (EC) in a saturated paste of ≥ 30 dS m−1 , and the product of EC and thickness of ≥ 900. In the World Reference Base for Soil Resources (IUSS Working Group WRB, 2007), the salic horizon must have a thickness of ≥ 15 cm, an EC of ≥ 15 dS m−1 , and the product of EC and thickness of ≥ 450. In other national soil taxonomic systems, these soils are referred to as Solonchaks, halomorphic soils, and saline soils. The objectives of this study were i) to show the distribution of soils with a salic horizon in the USA, ii) to identify the relative importance of the soil-forming factors globally on the development of salic horizons, and iii) to summarize the dominant soil-forming processes of these salt-affected soils. MATERIALS AND METHODS Using the “Soil Classification Database” (Soil Survey Staff, 2013a), we prepared lists of active soil series for all taxa in which salic horizons existed. Soil series
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601
were examined using the “Official Soil Descriptions” function (Soil Survey Staff, 2013b). We also examined 21 case studies from the international literature to support or refute our findings. Soil characterization data were obtained from Soil Survey Staff (2013c). Thirteen representative pedons were selected to show their analytical properties according to their areal abundance and frequency distribution in various taxonomic groups. A map of soils with a salic horizon was prepared using the July 5, 2006 version of the Digital General Soil Map of the U.S. published by the US Department of Agriculture (USDA)-Natural Resources Conservation Service (NRCS). This dataset consists of general soil association units created by generalizing more detailed soil survey maps. Since the taxonomic nomenclature for a map unit is recorded at the component level and a map unit is typically composed of one or more components, aggregation is needed to reduce a set of component attribute values to a single value that will represent the map unit as a whole. For taxonomic order, suborder and great group distribution maps, data were aggregated to the map-unit level using the “dominant-component-aggregation” approach. This approach returns the attribute value associated with the component with the highest percent composition in the map unit, which may or may not represent the dominant condition throughout the map unit. For taxonomic subgroup distribution maps, data were aggregated to the map-unit level using the “presence method”, that is, if any component attribute matched the taxonomic subgroup of interest, then that map unit would be shown on the map regardless of its map unit composition.
RESULTS Characteristics of salic horizons Salic horizons are designated with the symbol z, which refers to the pedogenic accumulation of salts more soluble than gypsum. Since the salic horizon is pedogenic, these symbols are applied to the A, B, and BC horizons. Soils with salic horizons in the USA contained a variety of structures, including granules, subangular blocks, plates, and massive, structureless conditions. Masses of Fe or Mn and redox features were common in the soils. The water table was present at depths of 40 to 100 cm for periods ranging from 1 to 12 months of the year in many of the soils. Fine, tubular pores were common in soils with a salic horizon. From an examination of 97 official soil series descriptions with a reported salic horizon, the average depth to the salic horizon was 5 cm, and the depth ranged from 0 to 53 cm. The average thickness of the salic horizon was 83 cm, with a range of 15 (minimum required) to 203 cm. Silt was the dominant particle-size fraction in salic horizons, averaging 42% of the fine-earth (< 2 mm) fraction (Table I). The mean bulk density was 1.4 g cm−3 . Salic horizons in dominant soil series of the National Soil Survey Laboratory (NSSL) database were strongly alkaline due to the presence of calcium or sodium carbonate. The mean pH of the salic horizon was 8.5, with values ranging from 7.4 to 10.5 (Table I). The mean sodium adsorption ratio (SAR) was 161, and the mean EC of the salic horizon was 40 dS m−1 . In the salic horizon, calcium carbonate and gypsum averaged 120 and 130 g kg−1 , respectively. Cation ex-
TABLE I Selected chemical and physical propertiesa) of soils with a salic horizon, National Soil Survey Laboratory database Horizon
Depth
Clay
cm Az1 Az2 Az3 Az4 Bz1 Bz2 Bz3 A1 A2 Bk Bkq1 Bkq2
Silt %
0–3 3–20 20–41 41–58 58–84 213–272 107–152
20.0 28.8 34.8 32.7 27.6 20.5 29.6
0–8 8–18 18–38 38–74 74–91
21.5 26.7 19.4 13.4 16.1
Db g
cm−3
pH
SOC g
kg−1
CEC cmol(+)
SAR kg−1
EC dS
Carbonate m−1
Pedon No. 40A0962, Saltair series, Tykpic Aquisalids, Davis, California 60.2 ndb) 7.7 27.4 14.4 291 219.0 210 60.2 nd 8.0 14.9 22.6 198 129.0 220 57.3 nd 7.9 16.1 26.6 139 121.0 270 60.6 1.33 8.0 6.4 21.7 133 121.0 280 63.8 1.63 8.1 3.0 16.2 130 97.0 300 63.9 1.56 8.2 2.9 12.0 145 123.0 220 64.1 1.60 8.2 2.8 16.3 136 101.0 nd Pedon No. 83P0867, Wendane series, Aquandic Halaquepts, Lander, Nevada 61.6 nd 8.5 12.8 21.9 457 57.9 80 59.2 1.40 8.6 6.7 27.5 197 21.6 100 65.1 1.14 8.7 4.9 26.4 144 13.0 120 67.8 1.31 8.5 2.2 20.4 98 10.4 100 78.9 nd 8.6 2.4 27.2 53 2.9 120
g
Gypsum kg−1 nd nd nd nd nd nd nd nd nd nd nd nd
(to be continued)
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J. G. BOCKHEIM AND A. E. HARTEMINK
TABLE I (continued) Horizon
Depth
Clay
C Akqb Bkb
cm 91–104 104–130 130–152
9.0 40.4 18.3
Anz1 Anz2 Bnz1 Bnz2 Bz1 Bz2 C1 C2
0–1 1–7 7–15 15–23 23–30 30–37 37–58 58–95
13.9 18.4 36.9 26.2 23.5 19.4 16.5 5.0
A/B Btkz1 Btkz2 Btkz3 Btkz4 Btkz5 2C
0–5 5–13 13–23 23–53 53–66 66–94 94–132
19.3 21.6 24.0 12.1 14.0 9.8 nd
A1 A2 AC1 AC2 C1 C2
0–10 10–18 18–25 25–43 43–64 64–89
4.1 3.3 2.8 3.6 2.8 3.2
A1 A2 AB Bq 2Bkqm
0–10 10–25 25–69 69–86 86–112
11.2 27.8 28.7 11.6 13.3
A1 A2 Bz1 Bz2 Bz3 Bz4 Bz5 C1 C2
0–3 3–8 8–20 20–46 46–71 71–112 112–130 130–166 166–200
41.5 46.5 51.2 46.1 48.3 46.0 48.9 47.1 46.4
E B1 B2 C1 C2
0–3 3–10 10–20 20–76 76–152
13.8 27.1 27.8 20.3 7.3
0–10 10–18 18–30 30–48 48–76 76–102 102–152
7.0 10.0 15.2 25.7 17.6 7.5 12.1
0–9
76.7
Akn1 Akn2 Abkn Bkn1 Bkn2 Bkn3 C An
Silt %
Db cm−3
pH
SOC kg−1
CEC
SAR kg−1
EC
Carbonate m−1
g g cmol(+) dS nd 8.9 1.9 10.7 17 1.5 110 nd 8.1 2.9 39.5 17 1.0 50 nd 8.2 1.8 23.6 9 1.0 70 Pedon No. 89P0541, Land series, Typic Aquisalids, Clark, Nevada 39.9 nd 7.4 8.2 5.7 378 50.6 50 44.0 1.33 8.0 5.0 9.8 143 28.1 80 51.1 nd 8.2 4.3 16.5 136 27.0 160 56.4 nd 8.3 3.7 15.8 120 23.5 160 73.2 1.28 8.3 4.2 14.1 122 24.7 220 74.4 nd 8.2 5.3 11.0 93 nd 270 76.8 1.38 8.4 3.2 12.5 74 16.0 190 54.9 1.46 8.5 1.5 7.1 42 9.0 160 Pedon No. 40A1162, Ligurta series, Calcic Haplosalids, La Paz, Arizona 48.7 1.56 7.8 0.5 15.0 21 2.8 130 36.0 1.51 7.5 0.9 9.6 20 19.4 100 28.6 nd 7.4 0.9 9.5 17 33.6 120 21.9 1.51 7.4 0.7 6.1 15 34.0 110 10.8 1.46 7.5 1.1 6.1 15 28.2 160 20.4 nd 7.7 0.4 7.2 16 24.6 10 nd nd 7.6 0.5 10.5 nd 17.1 30 Pedon No. 80P0094, Wildhorse series, Typic Haplaquepts, Morrill, Nebraska 6.0 nd 8.5 14.0 5.8 12 1.8 10 5.6 nd 8.9 7.3 4.7 27 3.4 10 5.5 nd 9.1 3.6 3.4 28 3.2 10 4.6 nd 9.1 2.9 3.1 22 2.3 20 1.0 nd 8.4 1.3 1.9 6 0.8 10 0.4 nd nd 0.7 1.8 nd nd 10 Pedon No. 86P0991, Reese series, Aeric Halaquepts, Lake, Oregon 34.3 nd 8.6 17.0 24.1 161 16.7 70 43.0 nd 9.0 6.9 22.3 443 26.3 120 47.1 nd 8.7 5.8 23.0 138 7.1 230 38.8 nd 8.2 3.3 23.6 35 1.8 240 19.7 nd 8.1 2.7 nd 25 1.3 260 Pedon No. 08N0488, Parran series, Typic Aquisalids, Churchill, Nevada 39.1 1.42 8.6 5.4 24.1 153 14.7 30 38.0 nd 8.7 4.5 24.2 533 41.1 30 39.4 1.27 8.4 3.8 24.0 249 42.3 30 45.4 1.29 8.4 3.1 25.4 237 32.7 20 46.6 1.48 8.6 1.4 25.6 240 25.0 10 49.5 1.58 8.8 2.7 25.9 230 16.5 20 46.8 1.53 8.7 2.0 28.1 241 11.2 20 50.3 1.56 8.9 1.7 27.9 303 8.6 10 50.7 1.51 9.1 1.0 26.6 497 6.8 10 Pedon No. 40A2114, Janise series, Typic Halaquepts, Scotts Bluff, Nebraska 47.6 nd 7.7 22.3 15.7 13 1.7 10 33.5 1.41 8.8 8.0 20.0 35 1.9 60 48.2 1.42 9.4 2.6 26.5 124 5.0 130 55.3 1.43 10.1 0.7 26.3 1 158 20.0 130 52.3 nd 10.2 0.4 22.2 288 11.5 30 Pedon No. 87P0031, Umapine series, Typic Halaquepts, Baker, Oregon 62.4 nd 10.3 2.2 nd 824 22.3 20 69.0 nd 10.3 1.1 nd 441 16.9 20 49.3 nd 10.0 1.3 nd 229 8.7 60 53.8 nd 10.0 1.3 nd 278 10.3 100 38.7 nd 9.8 1.5 nd 264 7.6 210 62.5 nd 9.7 0.7 nd 120 5.3 80 66.9 nd 9.7 0.6 nd 164 7.6 0 Pedon No. 88P0952, Wherry series, Typic Aquisalids, Kern, California 16.7 1.43 8.3 2.9 33.5 175 63.7 140 72.1 53.7 65.1
g
Gypsum kg−1 nd nd nd 150 130 30 30 20 50 40 20 nd nd 3 nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd trace 10 20 trace nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd
(to be continued)
SALIC HORIZONS IN SOILS
603
TABLE I (continued) Horizon
Depth
Clay
Bky Bnz Cn1 Cn2 Cn3
cm 9–20 20–31 31–69 69–94 94–147
65.9 57.8 60.5 52.1 49.0
A1 E A2 C1 C2 C3 C4
0–10 10–25 25–41 41–58 58–86 86–130 130–165
13.0 18.0 19.7 22.2 24.2 22.2 29.9
Agz Bgz1 Bgz2 Bgz3 BCg1 BCg2
0–8 8–18 18–53 53–94 94–147 147–200
23.8 7.3 20.9 25.4 22.5 9.1
Akzg Bkz1 Bkz2 CBkz Czg Average
0–13 13–25 25–38 38–114 114–140
26.7 40.0 44.5 42.4 48.7 25.4
Silt %
Db cm−3
pH
SOC kg−1
CEC
SAR kg−1
EC
Carbonate m−1
g g cmol(+) dS 18.1 1.54 8.5 2.4 26.6 121 40.3 170 20.7 1.73 8.5 2.0 20.9 95 38.9 180 21.5 1.49 8.7 2.4 23.2 155 24.3 160 23.2 1.60 9.0 1.6 19.0 156 11.5 190 19.6 1.85 9.1 1.5 16.8 89 5.4 180 Pedon No. 81P0694, Yobe series, Aeric Haplaquepts, Lassen, California 60.5 1.44 10.5 8.1 30.4 380 13.6 110 59.8 1.25 9.9 4.0 35.4 120 4.6 100 58.4 1.08 9.6 3.9 37.6 76 3.6 100 58.5 1.29 9.3 3.8 36.2 57 3.1 130 57.3 1.2 8.7 3.8 30.0 21 1.2 300 65.4 1.17 8.1 3.5 33.9 11 0.7 250 55.9 1.20 7.6 1.9 43.6 12 0.7 nd Pedon No. 99P0026, Arrada series, Typic Halaquepts, Kenedy, Texas 13.3 nd 7.9 nd 6.7 74 111.0 trace 7.9 nd 7.9 nd 2.5 65 88.6 nd 10.6 nd 7.5 nd 5.8 86 130.0 nd 12.9 nd 8.5 nd 4.8 92 111.0 140 13.8 nd 8.4 nd 3.6 107 108.0 300 6.2 nd 8.4 nd 3.0 108 101.0 50 Pedon No. 02N0156, Eimarsh series, Aeric Haplaquepts, Box Elder, Utah 58.2 nd 8.0 nd 11.6 25 11.9 280 52.5 nd 8.0 nd 13.6 56 22.5 130 51.1 nd 7.9 nd 14.9 59 25.8 280 48.1 nd 8.0 nd 14.9 74 32.1 280 48.8 nd 8.2 nd 17.1 85 30.9 260 42.4 1.4 8.5 5.0 17.1 161 40.2 123
g
Gypsum kg−1 nd nd nd nd nd nd nd nd nd nd nd nd 250 540 310 20 10 nd nd nd nd nd nd 132
a) D = bulk density; SOC = soil organic C; CEC = cation exchange capacity; SAR = sodium adsorption ratio; EC = electrical b conductivity; b) nd = not detected.
change capacity (CEC) of the salic horizon was moderate, reflecting the abundance of clay (mean = 25%) and organic C (mean = 5 g kg−1 ). The base saturation (data not shown) is 100% for all pedons, with Ca and Na dominating the exchange sites. Mineralogy of soils with salic horizons are reported for the < 2 μm clay fraction (7 soil series), the 50–20 μm coarse-silt fraction (3 soil series), and the 100–50 μm very-fine-sand fraction (1 soil series). The clay fraction contained primarily illite group minerals, kaolinite, smectite, and quartz; glass and sponge spicules were common in the coarse-silt fraction; and a variety of minerals were present in the very-fine-sand fraction (Table II). These data were corroborated by the fact that the mineral class is commonly mixed. The dominant salts were halite (NaCl) and trona (NaHCO3 + Na2 CO3 ·2H2 O), with carbonate flecks and gypsum fibers also being common. Classification of soils with a salic horizon Soils with a salic horizon occurred in two orders, two suborders, three great groups, 11 subgroups, and 97 soil series (Table III). Soil series with a salic horizon were most abundant in the Inceptisols (62), followed
by the Aridisols (35). Soils with a salic horizon are recognized in the Alfisols (Salidic Natrustalfs), Gelisols (Salic subgroups of Anhyorthels, Aquorthels, and Anhyturbels), Inceptisols (Salidic Sulfaquepts), Mollisols (Salidic subgroups of Calciustolls and Haplustolls), and Vertisols (the great groups of Salaquerts, Salitorrerts, and Salusterts), but no soil series have been officially recognized in these orders. However, it is likely that soil series included in these order contain a salic horizon but that the horizon is secondary in the classification of the series. Of the 97 soil series with a salic horizon 50% had a mesic and 19% had a thermic soil-temperature class, 89% had an aquic soil-moisture class, 79% had a mixed mineralogy class, 52% had a calcareous reaction class, 59% had a superactive cation exchange activity class, and 24%, 24%, and 19% had a fine, fine-loamy, or finesilty particle-size class, respectively. Soils with a salic horizon predominantly contained an ochric epipedon (98% of pedon descriptions); subsurface horizons present in soils with a salic horizon included the calcic (24% of pedons), cambic (18%), gypsic (11%), and duric (7%), argillic (4%), and natric (2% of pedons).
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Distribution of soils with a salic horizon
TABLE II
Soil mapping units with a salic horizon comprised 11 000 km2 , accounting for 0.1% of the total soil area of the conterminous USA (Fig. 1). Soils with a salic horizon occurred primarily in the Basin and Range province of the western USA (Nevada, California, western Texas, and Utah) and the Columbia Plateau (eastern Oregon).
Mineralogy of soils with salic horizons
DISCUSSION Comparison of salic horizon properties in USA with other areas There are only scattered pedons with salic horizons reported in the literature, with the exception of Spain (Table IV). The depth to the salic horizon ranges from 0 cm in Iran and Israel to 26 cm in Somalia, as compared to a value of 5 cm for the USA. The thickness of the salic horizon ranged from 75 to > 170 cm and averaged 83 cm for soils with salic horizons in the USA. Clay concentrations ranged from 7.2% to 42.0% and averaged 25.4% in the USA. The low clay values in the Negev desert of Israel can be attributed to the sandy eolian and fluvial materials. Silt concentrations range from 20.0% in Israel to 72.0% in Hungary and averaged 42.4% in the USA. The abundant clay and silt in soils with salic horizons is due to the fact that these soils often form in playas. The mean bulk density of salic horizons in USA soils was 1.4 g cm−3 , which is lower than the 1.58 to 1.60 g cm−3 values reported in salic soils of Israel and Hungary, reflecting the maintenance of ped structure. The mean pH of soils with salic horizons generally varied from 7.3 to 8.9 and was 8.5 for USA soils (Table IV). The low value (5.0) for soils with a salic horizon in Ghana can be attributed to the existence of pyrites in the sediments. The high values (10.0) in Russia are related to the sodicity of the soils. Soil organic C values range from 1.1 to 10 g kg−1 , as compared to a mean value of 5.2 g kg−1 for salic horizons in the USA. The CEC ranges from 15.8 to 48.3 cmol(+) kg−1 , with values for salic horizons in the USA toward the low end of the range at 17.1 cmol(+) kg−1 . The SAR of soils with a salic horizon ranges from 38 to 132, as compared to
Mineral Biotite Chlorite Halloysite Hydrous mica Kaolinite Palygorskite Smectite Vermiculite Apatite Beryl Calcite Chert Cristobalite Feldspars Garnet Gibbsite Glass Goethite Gypsum Hornblende Opal Opaque minerals Plagioclase Pyrophyllite Pyroxene Quartz Sponge spicules Tourmaline Zeolites Zircon
Clay (< 2 μm) 3 1 5 5 1 4 1
2 1 2
Coarse-silt (50–20 μm)
Very-fine sand (100–50 μm)
1a) 1
1
1
1 1 1 1
1
1 1
1
2 1
1
1 1 1 1
1
1
1
1 1
1 4
1 1 2 1 1 1
1
a) Relative X-ray diffraction peak size: 1 = very small; 2 = small; 3 = medium; 4 = large; 5 = very large.
a mean value of 161 for USA salic soils. The EC ranges from 5.1 to 53.9 dS m−1 , with a mean value of 40.2 for salic soils in the USA. Calcium carbonate ranges from 115 (Hungary) to 400 g kg−1 (Iran); CaCO3 was toward the low end of the range in salic soils of the USA, averaging 123 g kg−1 . There were minimal data for gypsum concentrations; however, salic soils in the USA had higher values (132 g kg−1 ) than salic soils in Spain and Iran. In general, salic horizons in the USA were comparable with those of Hungary. Factors influencing the formation of salic horizons In the USA soils with salic horizons occurred in
TABLE III Classification of soils with a salic horizon in Soil Taxonomy Order
Suborder
Great group
Subgroups (No. of soil series)
Sum of soil series
Aridisols
Salids
Inceptisols Total
Aquepts
Aquisalids Haplosalids Halaquepts
Calcic (4), Gypsic (4), Typic (18) Calcic (1), Gypsic (2), Typic (6) Aeric (24), Aquandic (2), Duric (7), Typic (28), Vertic (1)
26 9 62 97
SALIC HORIZONS IN SOILS
Fig. 1
605
Distribution of soils with a salic horizon in the USA.
TABLE IV A global comparison of the properties of soils with salic horizons Propertya)
USAb)
Iranc)
Somaliad)
Ghanae)
Jordanf)
Israelg)
Spainh)
Hungaryi)
Russiaj)
No. of pedons Depth to salic horizon (cm) Thickness of salic horizon (cm) Clay (%) Silt (%) Bulk density (g cm−3 ) pH Soil organic C (g kg−1 ) CEC (cmol(+) kg−1 ) SAR EC (dS m−1 ) CaCO3 (g kg−1 ) Gypsum (g kg−1 ) Salt class
13 5 83 25.4 42.4 1.4 8.5 5.2 17.1 161 40.2 123 132 sal, sal-sodl)
2 0 > 140 42.0 41.0 nd 8.9 3.5 48.3 38 22.8 400 < 52 sal-sod
3 26 > 67 nd nd nd 7.3 nd nd nd 8.3 612 nd sal
3 ndk) nd 54.1 42.5 nd 5.0 8.2 33.2 nd 5.1 nd nd sal
2 21 75 nd nd nd 8.1 2.8 22.7 nd 40.2 nd 6.5 sal
6 0 > 158 7.2 20.0 1.6 8.8 1.1 nd nd nd 135 nd sal
23 nd nd 17.8 49.8 nd 8.4 10 nd 67.5 53.9 331 89 sal
3 nd nd 36.0 62.0 1.58 8.8 5.3 15.8 132 7.4 115 nd sal-sod
2 5 > 170 nd nd nd 10 8.3 nd 1.5 nd 119 nd sal-sod
a) CEC
= cation exchange capacity; SAR = sodium adsorption ratio; EC = electrical conductivity; b) This study; c) Abtahi, 1977; ´ 1995; e) Allotey et al., 2008; f) Khresat and Qudah, 2006; g) Pfisterer et al., 1996; h) Alvarez oth and Rogel et al., 2001; i) T´ j) k) l) Jozefaciuk, 2002; Bronnikova et al., 2011; nd = not detected; sal = saline; sal-sod = saline sodic.
d) Alaily,
variety of climates. The soil-temperature class was dominantly mesic, but soils with thermic and frigid soil-temperature regimes were common. The mean annual precipitation averaged 300 mm year−1 , but ranged
widely between 100 and 1 015 mm year−1 (data not shown). The mean annual air temperature averaged 12 ◦ C, but ranged from 6 to 24 ◦ C (data not shown). The western USA is divided into four desert regions based
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J. G. BOCKHEIM AND A. E. HARTEMINK
on rainfall distribution and amount, elevation, and other factors: the Chihuahuan (southeastern Arizona, southwestern Texas), the Sonoran (southern California and southwestern Arizona), the Mojave (southeastern California), and the Great Basin (Nevada, Utah, Oregon, and portions of adjoining states). The salt-affected areas of these deserts contain the following shrubs: black greasewood (Sarcobatus vermiculatus), creosote bush (Larrea tridentata), saltbush (Atriplex spp.), and the following shortgrasses: alkali sacaton (Sporobolus airoides), inland saltgrass (Distichlis spicata), wild rye (Elymus glaucus), western wheatgrass (Pascopyrum smithii), and alkali bluegrass (Poa secunda). Soils with salic horizons occur on gentle slopes, averaging between 0% and 3%. Although 59% of the soils are derived from alluvium, other common parent materials include lacustrine (32%) and marine deposits (6%). In the literature, topography is viewed as a very important factor leading to the development of the salic horizon, including groundwater level and salinity, slope position, proximity to the edge of playas, the presence of depressions, and the influence of flooding (Table V). Of the soil series in the USA containing salic horizons, 38% were somewhat poorly drained and 38% were poorly drained. Parent material is important, particularly where evaporites exist and in areas
where dust is deposited. The case studies reported in Table V all occur in semiarid to hyperarid regions. Humans have played an important role on modifying salic horizons through irrigation and cropping. Few studies have addressed the time required to form a salic horizon. Harris (1990) observed salic horizons forming on deltas in the Yukon Territory, Canada in as little as 100 years. In the Negev Desert, Israel, salts began accumulating in the last 1 million years due to an increasingly aridic climate (Amit et al., 2011). Genesis of salic horizons The dominant processes leading to the development of saline soils were salinization, gleization, and calcification, with silicification and argilluviation occurring in some soils. The salts in soils with salic horizons in the USA originated from evaporites, groundwater seeps, and dust deposition. In the USA, soils containing salts more soluble than gypsum are classified into three broad classes, sodic, saline, and saline-sodic, based on pH, EC, and exchangeable sodium percentage (United States Salinity Laboratory Staff, 1954). Soils of the latter two classes may contain a salic horizon. In that 89% of the soil series with salic horizons in the USA contain an aquic soil-moisture class, gleization was an important soil-forming process. This was further evidenced by the masses of Fe or Mn and redox
TABLE V Relation of soil-forming factors to the development of salic horizons Area
Soil taxa
World
Salt-affected soils
Aral Sea
Solonchaks
Iran; Hungary
Solonchaks
Mongolia Astrakhan, Russia
Solonchaks
Solonetz on sideslopes & solonchaks on footslopes
Abtahi, 1977; Schofield et al., 2001; T´ oth et al., 2001 Ubugunov and Ubugunova, 2012 Karpachevskii et al., 2008; Boroda et al., 2011
Israel Kulunda, Russia Sulak, Dagestan Israel
Solonchaks Solonchaks Solonchaks
Solonchaks develop on edges of playas Solonchaks form in depressions Flooding an important source of salts
Lebedeva et al., 2008 Kotenko and Zubkova, 2008 Pfisterer et al., 1996
Solonchaks Salic reg; solonchaks
Parent materials Salts originate from evaporites Salts and minerals contributed by dustfall
Hungary; Spain Israel; South Africa
Role of soil-forming factor Humans Irrigation and cropping induces salinization Drying of seabed enables formation of salic horizon Relief Groundwater level important
Tunisia; Jordan Yukon, Canada Israel
Solonchaks Salic reg
Time Saline soils develop in < 100 year Salts accumulated in last 1 million year due to increasingly aridic climate
Reference(s)
Abrol et al., 1988 Stulino and Sektimenko, 2004
Schofield et al., 2001; Sierra et al., 2009 Yaalon, 1964; Singer et al., 1995; Drake, 1997; Khresat and Qudah, 2006; Amit et al., 2011 Harris, 1990 Amit et al., 2011
SALIC HORIZONS IN SOILS
features commonly described in salic soils of the USA. Calcification was evidenced by the abundance of CaCO3 (mean = 120 g kg−1 ) and gypsum (CaSO4 + 2H2 O) or anhydrite (CaSO4 ) (mean = 130 g kg−1 ) in the 13 pedons (Table I). In addition, five of these pedons had Bkz horizons, 11% of the soils with salic horizons occurred in calcic or gypsic subgroups (Table III), and 23% of the 97 soil series contained a calcic horizon. Three of the 13 pedons for which laboratory data were provided (Table I) contained either an argillic horizon or had duric properties; therefore, argilluviation and silicification were processes that only infrequently accompany salic horizon formation in the USA. CONCLUSIONS The salic horizon tended to occur at a shallow depth, commonly 0–5 cm; it was thick, commonly ranging from 75 cm to greater than 170 cm. The salic horizon contained abundant silt and clay (62%–93%) because of a common playa origin. The pH of the salic horizon generally was slightly to strongly alkaline (7.3–8.9). The salic horizon contains abundant soil organic C (3.5–100 g kg−1 ), a moderate cation exchange capacity that ranged between 16 and 48 cmol(+) kg−1 , an electrical conductivity in excess of 5 dS m−1 , abundant exchangeable Ca and Na, abundant CaCO3 (120– 400 g kg−1 ) and moderate quantities of gypsum (< 10–130 g kg−1 ). In the NRCS database, soils with a salic horizon occurred in two orders, two suborders, three great groups, 11 subgroups, and 97 soil series. Soil mapping units with a salic horizon comprise 11 000 km2 in the USA, primarily in the Basin and Range province of western USA. Topography and parent material were key soil-forming factors contributed to the formation of salic horizons. However, humans have played a major role in their transformation and development in many parts of the world. The predominant pedogenic processes leading to the development of the salic horizon included salinization, gleization and calcification, with silicification and argilluviation occurring in some soils. ACKNOWLEDGEMENTS The authors are grateful to the professional soil surveyors and scientists of Natural Resources Conservation Service, United States Department of Agriculture, the laboratory technicians, and information technologists that have made the data used in this study generously available to the public. The authors appreciate three anonymous reviews of an earlier draft of this manuscript.
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