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SS-AGR-246 Application of the Soil Taxonomy Key to the Organic Soils of the Everglades Agricultural Area1 R. W. Rice, R. A. Gilbert and S. H. Daroub2 1. This document is SS-AGR-246, one of a series of the Agronomy Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Reviewed March 2005. This publication is also a part of the Florida Sugarcane Handbook, an electronic publication of the Agronomy Department. For more information you may contact the editor of the Sugarcane Handbook, R. A. Gilbert (firstname.lastname@example.org). Please visit the EDIS Web site at http://edis.ifas.ufl.edu. 2. R.W. Rice, assistant professor; R.A Gilbert, assistant professor, and S.H. Daroub, assistant professor, Everglades Research and Education Center, Belle Glade, Florida Agricultural Experiment Stations, Institute of Food and Agricultural Sciences, University of Florida. The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition. The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service/Institute of Food and Agricultural Sciences/University of Florida/Larry Arrington, Dean. Soil taxonomy is the process of describing and classifying soil types. It is analogous to the scientific classification of plants and animals. The soil taxonomy system helps us to understand the types of soils we have, how they were formed, and how they may be changing. By understanding how soils in the Everglades Agricultural Area (EAA) are classified, we can learn more about their properties and can effectively communicate information regarding soil effects on crop and natural resource management. This document provides an overview of the soil taxonomic system in relation to the organic soils found in the EAA. The discussion also addresses recent revisions to the soil taxonomy key and how these modifications affect the classification of organic soils. The Histosol soils of the EAA were formed over a 4,400-yr period from partially decomposed remains of hydrophytic (water loving) vegetation that accumulated under anaerobic (low oxygen) wetland conditions (McDowell et al., 1969). Consequently, soil organic matter contents are high, ranging between 80 to 90% across roughly 93% of the region (Snyder, 1994; USDA, 1988). Early soil classification schemes in the EAA focused on the botanical origins of the organic soil material. Remnants of this scheme are still evident, with long-term residents occasionally referring to soils bordering Lake Okeechobee as custard apple mucks, and soils in the central and southeast regions of the EAA as elderberry peaty mucks and sawgrass peats, respectively. The term peat was loosely used for soils with notably high fiber composition (and low mineral content) while muck was used to describe the more highly decomposed soils (lower fiber and higher mineral content) in the region. Soils of intermediate fiber and/or mineral content were termed peaty mucks or mucky peats. The soil taxonomy system employs a specific nomenclature that both classifies the soil and confers a distinctive name to the individual soil. Names are constructed from various formative elements (generally originating from Greek or Latin), which are used in specific combinations to provide a highly
Application of the Soil Taxonomy Key to the Organic Soils of the Everglades Agricultural.... 2 descriptive name to a specific soil type. The six categories in soil taxonomy, in order of decreasing rank (level), are the soil order, suborder, great group, subgroup, family, and series. In this classification scheme, soil characteristics and information about the soil become increasingly more specific as one continues from the highest level (order) to the lowest level (soil series). The following discussion presents each of the six classification categories, and summarizes the logic and major principles underlying both the classification and the names assigned to the different organic soils found in the EAA. Soil Order All soils in the world can be classified within 12 different soil orders (Soil Survey Staff, 1999; Fig. 1). The names of soil orders end with the formative element sol (from Latin solum, soil or ground) (Table 1). The Histosol soil order includes most of the worlds organic soils, with the formative element Hist (from Greek histos, tissue) indicating the presence of organically-derived soil material. A portion of this formative element (ist) is consistently used as a suffix within the names of all Histosol soils. This suffix appears in soil names at the suborder, great group, and subgroup levels. Thus, any soil name ending with ist (such as Torrifolist, Sphagnofibrist, Sulfihemist, or Cryosaprist) is an organic Histosol. In general, soils are classified as Histosols when more than half of the upper 80 cm (32 inches) of the soil is highly organic, or in the case of shallow soils, if organic material of any thickness resides above bedrock or within fragmental material containing voids filled with organic materials. Under the latest taxonomic key (Soil Survey Staff, 1998; 1999), organic soils in extremely cold environments are now classified as Histels, a suborder within the new Gelisol soil order (the suffix el in Histel is derived from Gel, indicating that the soil is a Gelisol).The organic soils in the EAA are classified within the Histosol soil order, based on high organic matter composition and the absence of consistently frigid conditions. Soil Suborder The 12 soil orders collectively represent 64 soil suborders (Soil Survey Staff, 1999). Histosols can be classified into four different suborders, including Folists, Fibrists, Hemists, and Saprists (Fig. 1). The suborder Folist (from Latin folia, leaf) describes a group of organic soils that have formed under non-flooded conditions, composed of leaf litter and decaying wood fragments that have accumulated over bedrock, a scenario found in some forested environments. Organic soils that formed under flooded conditions are represented by the remaining three suborders, which differ based on the extent of organic fiber decomposition. Soils composed of organically-derived material that exhibit the least amount of decay are classified as Fibrists (from Latin fibra, fiber). Fibrists generally contain three-fourths or more (by volume) fibers that are retained on a 100-mesh sieve (0.15 mm openings). Due to the absence of appreciable decomposition, plant cellular structures are still clearly visible within individual fibers. Fibrists will generally have the lowest bulk densities (< 0.10 gm cm-3), lowest ash contents (or greatest organic matter contents), and highest saturated gravimetric water contents (850-3000% on an oven-dry basis) (McCollum et al., 1976). At the other extreme are the Saprists, with soil profiles dominated by soils exhibiting the greatest evidence of decomposition. Fiber contents after rubbing are less than one-sixth (by volume). Saprists are predominately black in color, with bulk densities generally exceeding 0.20 gm cm-3 and saturated gravimetric water contents less than 450% (McCollum et al., 1976). Hemists (from Greek hemi, half; implying an intermediate stage of decomposition) represent those Histosols that exhibit a decomposition stage that is intermediate between the less decomposed Fibrists and more thoroughly decomposed Saprists. Physical characteristics (bulk density, saturated gravimetric water content) are also intermediate in value. The black organic muck soils of the EAA are comprised of highly decomposed organic materials, and are thus Saprists (from Greek saprose, rotten; implying a high degree of decomposition) (Table 1).
Application of the Soil Taxonomy Key to the Organic Soils of the Everglades Agricultural.... 3 Soil Great Group Descriptions at the great group level seek to identify distinctive differences across various soils found within a given soil suborder. This includes the presence or absence of diagnostic soil horizons and may allude to the general soil temperature or moisture regimes that prevail in the region. Former soil taxonomic key Recent changes in the soil taxonomic key (Soil Survey Staff, 1998; 1999) affect the classification of Histosol soils at the great group level. From the inception of the modern soil taxonomic system (Soil Survey Staff, 1975), the organic soils in the EAA were classified as Medisaprists (from Latin media, middle; implying that the soils are located in a temperate climate) (Table 1; Fig. 2). Current soil taxonomic key The latest soil taxonomic key (Soil Survey Staff, 1998; 1999) de-emphasizes the use of temperature regime as a classification criterion for Saprists at the great group level, focusing more on characteristics that are intrinsic to soil properties and horizons present within the soil profile. The Troposaprist, Medisaprist, and Borosaprist classifications have been discontinued. The current soil taxonomy key (Soil Survey Staff, 1998, 1999) includes only four great groups within the Saprist suborder (Table 1). The Haplosaprist (from Greek haplous, simple; implying minimal evidence of true soil horizon development) classification is a new great group category for Saprists. The organic soils of the EAA indeed lack strong evidence of horizon development, and are thus all classified as Haplosaprists (Fig. 1). Soil Subgroup The prior three classification levels (order, suborder, and great group) focused on categorizing soils based on major features or geological/environmental processes that dominated the direction and/or extent of soil development. The subgroup classification seeks to recognize distinctive soil features across different soils within a given soil great group. The subgroup name includes the great group name, modified by one or more descriptive adjectives. These descriptive adjectives fall into three general categories termed typic, intergrade, and extragrade. Typic subgroup The Typic adjective is normally assigned to the soil within a great group that reflects characteristics that are consistent with the diagnostic properties already defined by the order, suborder, and great group to which the soil belongs. A Typic subgroup soil lacks any significant properties that would suggest it is in a transition phase between related great groups or some other soil taxonomic level. Intergrade subgroups Haplosaprists can be classified into four different intergrade subgroups, including Hemic, Fluvaquentic, Halic, and Halic Terric Haplosaprists (Table 2, Fig. 1 Intergrade subgroup soils are those that belong to one soil great group but share various soil properties common to another recognized great group, suborder, or order. For example, a Haplosaprist soil containing appreciably more fibric material than the norm (Typic Haplosaprist) would be classified within the Hemic Haplosaprist subgroup, since the higher fiber content reflects a dominant characteristic of the Hemist suborder of the Histosol soil order. Extragrade subgroups Haplosaprists can be classified into three different extragrade subgroups, including Terric, Limnic, and Lithic Haplosaprists (Table 2, Fig. 1). Extragrade subgroup soils reflect specific properties that are otherwise anomalous to the main concept of the great group. These anomalous properties are also not common diagnostic features dominating the classification of other known soils and thus do not reflect an evolutionary transition phase between one soil type and another. For this reason, adjectives describing extragrade subgroup soils are not derived from the formative elements used in the
Application of the Soil Taxonomy Key to the Organic Soils of the Everglades Agricultural.... 4 nomenclature underlying the names of soil great groups, suborders, and orders. Halosaprist subgroup soils in the EAA With respect to the organic soils in the EAA, the Torry, Terra Ceia, and Okeechobee soil series have the deepest soil profiles, composed of organic material exceeding 130 cm (51 inches) over limestone (Table 3). Both the Torry and Terra Ceia are classified as Typic Haplosaprists (Fig. 1), which recognizes the deep soil profiles dominated by well decomposed saprist material. The Okeechobee soil is the only intergrade soil subgroup in the EAA. Although fairly similar to the Terra Ceia soil, the Okeechobee soil contains a significant presence of less-decomposed hemic materials within the subsurface soil profile (Soil Survey Division, 2001), and is thus classified as a Hemic Haplosaprist (Fig. 1). The remaining four EAA soil series are classified as extragrade soil subgroups. Soil profiles are less than 130 cm (51 inches) in depth (Table 3). The Pahokee, Lauderhill, and Dania are classified as Lithic Haplosaprists (Fig. 1) due to the presence of a lithic (in this case, limestone) contact within 51 inches (130 cm) of the soil surface (Soil Survey Division, 2001; Table 3). Because the Okeelanta soil series is underlain by sandy material (rather than limestone bedrock) and/or has a significant accumulation of sandy materials within an otherwise organic soil profile (Soil Survey Division, 2001; Table 3), it is classified as a Terric Haplosaprist (Fig. 1). Soil Family The soil family category subdivides soils within a given soil subgroup, based on physical and/or chemical characteristics deemed important to soil management, plant growth, and/or engineering uses. Soil family names are composed of any number of appropriate descriptive terms that identify specific classes of soil characteristics. In order of their chronological appearance within a family name, the soil family classes relevant to Histosols include particle size, particle mineralogy, soil reaction (pH), soil temperature regime, and soil depth. With respect to reaction class, all EAA soils are classified as euic (whereby soil pH in 0.01 M CaCl2 > 4.5) due to the consistently elevated soil pH levels found throughout the region. The hyperthermic temperature regime applies to all EAA soils [whereby mean annual soil temperatures are 22oC (72oF) or greater, and average soil temperatures fluctuate more than 6oC (roughly 11oF) between summer and winter]. The soil depth class applies only to the Dania soil series, classified at the family level as shallow [whereby a root-limiting layer (limestone bedrock) is found within 18 to 50 cm (roughly 7 to 20 inches) of the soil surface]. The particle size and particle mineralogy classes apply only to the single Terric Haplosaprist found in the EAA, the Okeelanta soil series. The term sandy or sandy-skeletal recognizes that the particle sizes within the Okeelanta mineral layer are sands or loamy sands in texture, with less than 50% (by weight) very fine sands. The term silicious recognizes that these mineral materials are dominated by 90% or more (by weight) silica materials and other durable minerals resistant to weathering (Soil Survey Staff, 1999; Fig. 1). Soil Series Soil series within a family group represent closely related soil units that have narrow but readily observable differences. For example, both the Torry and Terra Ceia are classified as euic, hyperthermic, Typic Haplosaprists, but the appreciably higher mineral content of the Torry is a distinguishing feature not shared by the Terra Ceia (Table 3). Likewise, both the Pahokee and Lauderhill are euic, hyperthermic Lithic Haplosaprists, but the Pahokee soil profile is considerably thicker than the Lauderhill (Soil Survey Division, 2001; Table 3). The soil series name carries none of the descriptive information inferred by the taxonomic nomenclature used to formulate soil names at the higher (order, suborder, great group, and subgroup) taxonomic soil categories. In general, soil series carry names that are highly recognizable within the local area where the soil series was first officially recognized. Names of towns, lakes, counties, and local physical or geographic features are commonly used as soil series names. The complete taxonomic
Application of the Soil Taxonomy Key to the Organic Soils of the Everglades Agricultural.... 5 names for the seven organic soil series recognized in the EAA are presented in Table 3. Post-script The organic soils of the EAA are continuously undergoing transitional processes, largely due to the aerobic mineralization of organic matter. Expansive areas that once supported the high-fiber sawgrass peats in the early-1900s have since decomposed into low-fiber mucks. Over time, soil mineralization and subsequent soil subsidence (decline in soil thickness) have resulted in a declining percentage of Torry, Terra Ceia, and Okeechobee soils, as they transition into the more shallow Pahokee and Lauderhill soils (Table 3). Should soil subsidence continue unabated, it is likely that the highly decomposed organic materials constituting the various Haplosaprists of the EAA will eventually transition into new soil types that would be classified as mineral. References McCollum, S.H., V.W. Carlisle, and B.G. Volk. 1976. Historical and current classification of organic soils in the Florida Everglades. Soil Crop Sci. Soc. Fla. Proc. 35:173-182. McDowell, L.L., J.C. Stephens, and E.M. Stewart. 1969. Radiocarbon chronology of the Florida Everglades peat. Soil Sci. Soc. Am. Proc. 33:743-745. Soil Survey Staff. 1975. Soil Taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys. USDA Soil Conservation Service Agriculture Handbook # 436, U.S. Government Printing Office, Washington DC. Soil Survey Staff. 1978. Soil survey of Palm Beach County, Florida. USDA Soil Conservation Service, U.S. Government Printing Office, Washington DC. Soil Survey Staff. 1996. Keys to Soil Taxonomy, 7th edition. USDA Natural Resource Conservation Service, U.S. Government Printing Office, Washington DC. Soil Survey Staff. 1998. Keys to Soil Taxonomy, 8th edition. USDA Natural Resource Conservation Service, U.S. Government Printing Office, Washington DC. Soil Survey Staff. 1999. Soil Taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys. USDA Natural Resource Conservation Service Agriculture Handbook # 436, U.S. Government Printing Office, Washington DC. Soil Survey Division. 2001. USDA Natural Resource Conservation Service Official Soil Series Descriptions [online URL: http://www.statlab.iastate.edu/soils/osd/ ] (accessed 23 Mar 2001). Snyder, G.H. 1994. Soils of the EAA. In Everglades Agricultural Area (EAA): Water, Soil, Crop, and Environmental Management, A.B. Bottcher and F.T. Izuno (eds), ch. 3, 27-41. University Press of Florida, Gainesville, Fl. USDA. 1988. Subsidence study of the Everglades Agricultural Area. Soil Conservation Service Greenacres Field Office, Greenacres, Fl.
Application of the Soil Taxonomy Key to the Organic Soils of the Everglades Agricultural.... 6 Figure 1. The current (Soil Survey Staff, 1998, 1999) soil taxonomic classification for EAA organic soils, highlighting the Pahokee muck.
Application of the Soil Taxonomy Key to the Organic Soils of the Everglades Agricultural.... 7 Figure 2. The former (Soil Survey Staff, 1996) soil taxonomic classification for EAA organic soils, highlighting the Pahokee muck.
Application of the Soil Taxonomy Key to the Organic Soils of the Everglades Agricultural.... 8 Table 1. Description of formative elements used in the order, suborder, and great group names of organic soil. Taxonomic level Formative element Derivation Connotation Order Histosols Hist Greek histos (tissue) Presence of organic materials. Sol Latin solum (soil) Soil Suborder Fibrists Fibr Latin fibra (fiber) Least decomposed stage (notable presence of plant fibers) Saprists Sapr Greek sapros (rotten) Most decomposed stage (notable lack of plant fibers) Hemists Hem Greek hemi (half) Intermediate stage of decomposition (some plant fibers). Folists Fol Latin folia (leaf) Mass of leaves, leaf litter Great group Cryosaprists Cry Greek kryos (icy cold) Cold climates Haplosaprists Hapl Greek haplous (simple) Minimum horizon development Sulfosaprists Sulf Latin sulfur (sulfur) Presence of sulfides (or their oxidation products) Sulfisaprists Sulf Latin sulfur (sulfur) Presence of sulfides (or their oxidation products) Troposaprists Trop Greek tropikos (turning) Continually warm climates (lack of cold temperatures, humid, tropical) Medisaprists Med Latin media (middle) Temperate climates Borosaprists Bor Greek boreas (northern) Cool climates Haplosaprists is a new great group classification introduced in the current soil taxonomic key (Soil Survey Staff, 1998; 1999; Fig. 1). The organic soils of the EAA used to be Medisaprists (Soil Survey Staff, 1975; 1996; Fig. 2) but are now classified as Haplosaprists. For Histosol great group names, the Sulfo prefix refers to soils containing a well-defined sulfuric horizon present within 50 cm of the soil surface while the Sulfi prefix refers to soils that lack the well-defined sulfuric horizon but still contain sulfidic materials (which may form sulfuric acid and declining soil pH if and when the soil is aerated) within 100 cm of the soil surface. The Troposaprist, Medisaprist, and Borosaprist great group designations were part of the former soil taxonomic keys (Soil Survey Staff, 1975; 1996; Fig. 2). They have since been discontinued and are not part of the current soil taxonomic key (Soil Survey Staff, 1998; 1999; Fig. 1).
Application of the Soil Taxonomy Key to the Organic Soils of the Everglades Agricultural.... 9 Table 2. Description of adjectives used to identify the different subgroup soils within the Haplosaprist great group. The seven officially recognized organic soil series found in the EAA are all classified as Haplosaprists. Descriptive adjective Formative element Derivation Connotation Subgroup (typic) Typic --Latin typicos (typical) Used to identify the subgroup soil that typifies the great group. Suggests that there are no other unusual or aberrant properties that need to be specifically recognized with specific adjectives. Subgroup (intergrade) Hemic Hem Greek hemi (half) Intermediate stage of decomposition (some plant fibers). Halic Hal Greek hals (salt) Salty. Fluvaquentic Fluv Latin fluvius (river) Flood plains, recent sediment deposition. Aqu Latin aqua (water) Aquic moisture regime. Subgroup (extragrade) Terric --Latin terra (earth) Containing a mineral substratum. Lithic --Greek lithos (stone) Near stone (presence of a shallow lithic or bedrock contact). Limnic --Greek limn (lake) Presence of a limnic layer (deposits resulting from aquatic organism activities occurring during the open-water stage of bog development). In soil taxonomy, adjectives such as typic, terric, lithic, and limnic are used to distinguish between soils only at the subgroup level. When used alone, these adjectives refer to an extragrade subgroup. Intergrade subgroups are identified with adjectives constructed from the formative elements used to name soil great groups, suborders, and orders. An example is the formative element "Hem", used to name the Hemist suborder as well as the Hemic Haplosaprist subgroup. The current soil taxonomic key (Soil Survey Staff, 1998; 1999; Fig. 1) introduces the new adjective Halic to distinguish among Haplosaprists. Former soil taxonomic keys (Soil Survey Staff, 1975; 1996; Fig. 2) included the intergrade subgroups Fibric and Fibric Terric to distinguish among Medisaprist subgroup soils, but these classifications have been discontinued with the current soil taxonomic scheme. Table 3. Histosol soil series found in the Everglades Agricultural Area. Soil series Soil name Mineral content Thickness of organic material Underlying material Percentage of EAA organic soils 1978 1988 % cm (inches) % % Torry euic, hyperthermic Typic Haplosaprist >35 >130 (>51) limestone 7.0 7.1
Application of the Soil Taxonomy Key to the Organic Soils of the Everglades Agricultural.... 10 Table 3. Histosol soil series found in the Everglades Agricultural Area. Terra Ceia euic, hyperthermic Typic Haplosaprist <35 >130 (>51) limestone 37.9 9.5 Okeechobee euic, hyperthermic Hemic Haplosaprist <35 >130 (>51) limestone 2.6 2.6 Pahokee euic, hyperthermic Lithic Haplosaprist <35 91-130 (36-51) limestone 43.9 27.4 Lauderhill euic, hyperthermic Lithic Haplosaprist <35 51-91 (20-36) limestone 4.7 39.6 Dania euic, hyperthermic, shallow Lithic Haplosaprist <35 <51 (<20) limestone 0.2 10.2 Okeelanta sandy or sandy-skeletal, silicious, euic, hyperthermic Terric Haplosaprist <35 41-127 (16-50) sand 3.6 3.6 Soil depth ranges from Soil Survey Division (2001). Estimated from Soil Survey Staff (1978). USDA (1988).