The USDA Soil Taxanomy Classified Soil: Halplorthox/ Haplustox - Coursework Example

Halplorthox/ Haplustox Dominant features of Haplorthox Haplustox: Haplorthox is considered as a group of Andosols which are strong acid soils and have low levels of organic matter content and low levels of cation exchange capacity. They contain cation exchange capacity ranging from 7.5 to 9.5 cmol+ kg-. Kaolinite and sesqui oxide minerals are dominant minerals in these soils (Geonadi and Tan, 1991). The base saturation of soil profile is very low resulting in drastic leaching due to humid nature (Geonadi and Tan, 1989). The volcanic ash resulted from volcanic eruptions led to the formation of two major soil groups i.e. andosols and latosols. At 600m above sea level, andosols were formed and below 600 sea level, latosols were formed (Dudal and Supraptohardjo, 1961, 1975). However, some andosols were formed in altidues lower than 600 m sea level (Tan, 1960, 1984) These latosols were later classified as ultisols and oxisols under American classification (USDA classification) (Tan and Goenadi, 1994). According to the modern classifications including USDA classification, the haplorthox group of soils have been categorized under haplustox. Hence both these terms can be considered as synonymous with each other. Haplustox is a great group of the suborder Ustox and the order Oxisols, so to define the features of this great group of soils the features of Oxisols and Ustox must be laid down first as they are shared by all Haplustox soils. Oxisols can be defined as highly weathered soils that are found primarily in the inter tropical parts of the world and they contain few weatherable minerals and abundant in sesqui oxides like Fe and Al oxide minerals (Beinroth, 1996). It is estimated that they occupy about 7-8% of the global ice-free land area. They pose threat to soil fertility due to their extremely low native fertility resulting from very low nutrient reserves, low cation exchange capacity and high phosphorus retention by oxide minerals. However, they become productive upon addition of reasonable quantity of inputs of lime and fertilizers. Oxisols can be categorized into 5 suborders: Aquox, Torrox, Ustox, Perox, and Udox. Aquox – It denotes the oxisols with a water table at or near the surface for much of the year Torrox – It represents oxisols of arid climates Ustox – It denotes oxisols of semiarid and subhumid climates Perox – It comprises of oxisols of continuously humid climates, where precipitation exceeds evapotranspiration in all months Udox – It represents oxisols of humid climates Let us examine the basic properties of Ustox sub order. Ustox Properties: Ustox can be defined as oxisols that have an ustic SMR with from 90 to 270 consecutive days of plant available moisture in the normal years. One or two crop growing seasons are possible each year. They represent 53% of all oxisols (S.W. Buol, 2006). Ustox suborder contains the following great groups: a. Sombiperox: It represnts sombric horizon with in 1.5 m (Boul et al., 1989) b. Acroperox: It contains effective cation exchange capacity less than 1.5 meq/100g clay with in 2 m. c. Eutroperox: It contains more than 35 % base saturated (NH4OAc) to 1.25m. d. Kandiustox: It represents greater than 40 % clay in surface 18 cm and an 8 % clay content increase with in a 15 cm thickness between 18 cm and 1.5m e. Haplustox: It represents all other characteristics of Ustox suborder other than the ones mentioned above. Let us concentrate much on Haplustox now. USDA soil taxonomy defines haplustox as the ustox that do not contain sombric horizon within 150 cm of the mineral soil surface but that have, in all subhorizons of an oxic horizon within 150 cm of the mineral soil surface. I will have an effective cation exchange capacity of 1.50 or more cmol(+) per kg clay or a pH value (1N KCl) of less than 5.0. They possess a base saturation (by NH4OAc) of less than 35 % in some horizon within 125 cm of the mineral soil surface and at the same time do not contain a kandic horizon that has its upper boundary within 150 cm of the mineral soil surface. The subsoil exhibits a granular structure, and the epipedons appear as either dark or light colored. Haplustox in general are dark red to yellow in color in the subsoil and they are found in vast areas in central South America and Africa" (USDA soil taxonomy, 1999). Genesis of the soil: Oxisols have an oxic horizon i.e. a mineral subsurface horizon of sandy loam or finer texture with low CEC and few weatherable minerals (Luken, et al., 1983). The genetic concept of the oxic horizon involves extreme weathering and long-term soil formation under a hot, humid climate. Intense weathering and leaching are evident on many fronts. Processes that concentrate aluminum and deplete silicon facilitate the formation of oxis soil material. Low Si/Al ratios may have their origin in the magma of the earths crust and persist when exposed to the soil environment. Silicon loss is to be expected in the surface of almost all soils as rainwater infiltrates and moves through the surface layer. The amount of silicon removed depends upon the type of silicate mineral and residence time of water around the silicate mineral. Net silicon loss results in destruction of 2:1 lattice clays and favors kaolinite, halloysite, and gibbsite enrichment. Almost all of the iron in oxisols is present as iron oxides. Iron oxides impart many red, red-yellow and yellow hues to soil. Red hues are indicative of hematite, while the yellow colors indicate goethite. Mixtures of these minerals have intermediate colors. If soil material is subjected to reducing conditions, all iron oxides are chemically reduced to soluble ferrous ions and removed, thereby leaving only the gray color of the clays and sand (S.W. Buol, 2006). The study conducted on polygenetic oxisols from Minas Gerais, Brazil using micromorphology and electron microscope, revealed the relation between mineralogical aspects and polygenesis (Muggier et al., 2007). The oxisols under study exhibited strong extent of weathering and weathered grains of ilmenite and quartz. The soils also contained two phases of kaolinite formation and of accumulation of iron compounds. The diagram of predicted genesis of haplustox shows that the soil profile consists of different horizons from Oi to R (fig.1). The formation of ustox sub order soils is mainly in dry regions (fig.2) where as pedox and udox suborders is mainly found in wet regions. Oi = Organic layer (slightly decomposed) Oe= Organic layer (moderately decomposed) Oa= Organic layer highly decomposed) A= A horizon, mineral mixed with humus E= Horixon of maximum eluviation of iron and aluminum oxides Bh= Ustic horizon with humus deposition Bs= Ustic horizon with iron accumulation C=Zone of least weathering R= Bed rock Fig 1: Diagram of predicted genesis of Haplustox (Climatic) Dry Wet AA Wet T = Torrox US= Ustox UD = Udox P = Perox Lower portion of triangle represents “Aquox” suborder Fig 2: Diagram showing the relationship of sub orders of oxisols with the climatic Conditions Haplustox in another classification: World Reference Base for soil resources classification: In 1950’s, the latosols were translated as ferraltic soils in French and Portugeese literature (Aubert, 1958 and Botelho da Costa, 1954). In the World Reference Base for soil classification WRB, Oxisols are translated to Ferralsols; they are the same soils occurring in tropical areas of central South America and Africa (WRB, 2006). Even the FAO-UNESCO classification translated the oxisols to haplic ferralsols (FAO-UNESCO, 1971, Thomas and Raussen, 2002 and Fookes, 1997). These ferralsols are further classified in to humic ferralsol, rhodic ferralsol and hypereutric ferralsols (Esayas, 2005). Features of Ferralsols: The features of ferralsols are laid down in the World reference base for soil classification book as: "Ferralsols represent the classical, deeply weathered, red or yellow soils of the humid tropics. These soils have diffuse horizon boundaries, a clay assemblage dominated by low-activity clays (mainly kaolinite) and a high content of sesquioxides. Local names usually refer to the color of the soil. Many Ferralsols are known as: Oxisols (United States of America)" (WRB, 2006). Although most ferralsols are oxisols, there are differences between them. Differences between oxisols and ferralsols: Most Ferralsols are oxisols, but some have a kandic horizon but less than 40% clay in the surface 18 cm and classify as Ultisols or Aflisols (S.W. Buol, 2003). Haplustox in WRB classifications are closest to "Haplic Ferralsols" Comparison of two classifications Objective of World Reference Base for soil resources: "The world reference base for soil resources is designed as an easy means of communication amongst scientists to identify, characterize and name major types of soils. It is not meant to replace national soil classification systems but will serve as a common denominator through which national systems can be compared and correlated. WRB also serves as a common ground between people with an interest in land- and natural resources. The system draws extensively on the legend of the FAO/ UNESCO soil map of the world. WRB is not a new international classification system, but a basis for better correlation between national systems". (J.A Deckers; F. Nachtergaele; O.C. Spaargaren 1998) Objective of USDA soil taxonomy: "The primary objective of soil taxonomy is to establish hierarchies of classes that permit us to understand, as fully as possible, the relationship among soils and between soils and the factors responsible for their character. A second objective is to provide a means of communication for the discipline of soil science. Soil taxonomy was originally developed to serve the purposes of soil survey. During the last few decades, it has evolved into a means of communication in soil science". (USDA soil taxonomy, 1999) Advantages and disadvantages of each: The classification of World Reference Base for soil resources serves as a common ground for all other classifications, it tries to account for all soils of the world. It consists of 32 different soil groups (WRB, 2006). While this makes it good to use for any kind of soil as it accounts for almost all of them, it is also a disadvantage since there are too many groups which makes it harder to use. The USDA soil classification has many great groups and subgroups, but they are classified in different suborders and orders, which makes it easier to use (Soil survey staff, 1975). The USDA soil classification has a disadvantage of changing often, something that makes it hard for its users to keep up; the classification cancels many groups and sometimes introduces new ones. Another disadvantage of the USDA soil classification system is that it was designed to account only for the soils within the United States of America, and in spite of trying to account for other soils, it does not account for all the soils of the world. Conclusion Haplorthox suborder contains high acidity in soil reaction, but low in organic matter content and cation exchange capacity. They were grouped under andosols in initial classification. Later the latosols have been reclassified as oxisols and the name of haplorthox has become synonymous with haplustox suborder. World reference base for soil resources and USDA system of soil classification have both advantages and disadvantages as far as the classification and genesis of haplustox suborder are concerned. Depending upon the need of the study, one of these two systems can be utilized. References Aubert, G 1958, ‘Classification des sols. Comte rendu, reunion sous comite’, Congo, Brazzaville. Beinroth, FH 1996, ‘Properties, classification, and management of Oxisols, Guy D. Smith Memorial Slide Collection’. USDA-NRCS. Botelho da Costa, JV 1954, ‘Sure quelques questions denomenclature des sols des regions tropicales’. Comte rendu Conf. Int. Sols Africains, Leopoldville, Congo, 2: 1099-1103. Buol, SW 2006, Encyclopedia of Soil Science, R. Lal (eds.), P: 1233. Buol. 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Thomas and Raussen, SD 2002, ‘The agronomic and economic potential of tree fallows on scoured terrace benches in the humid highlands of Southwestern Uganda’ Soil Biology and Biochemistry. 34(4): 477-485. USDA 1999, Keys to USDA soil taxonomy. 2nd Edition, Page 15, 688 http://grunwald.ifas.ufl.edu/Nat_resources/soil_orders/oxisols.htm Read More