Order (12) Suborder (~ 65) Family (~ 8,000) Great Group (~ 250) Subgroup (~ 1,500) Series (~ 20,000) (in U.S)

Soil Orders (a) few, in any, genetic horizons 1. Entisols (c) lack development ( (d) productivity - variable (e) location - any climate (b) highly variable properties sands alluvium

The central concept of Entisols is that of soils that have little or no evidence of development of pedogenic horizons. Many Entisols have an ochric epipedon and a few have an anthropic epipedon. Many are sandy or very shallow.

2. Inceptisols (b) quickly formed horizons like cambic more developed than entisols less than others no clay movement or eluviation (c) productivity - variable (d) location - any location or climate (a) inceptum (L.), beginning

The central concept of Inceptisols is that of soils of humid and subhumid regions that have altered horizons that have lost bases or iron and aluminum but retain some weatherable minerals. They do not have an illuvial horizon enriched with either silicate clay or with an amorphous mixture of aluminum and organic carbon. The Inceptisols may have many kinds of diagnostic horizons, but argillic, natric kandic, spodic and oxic horizons are excluded.

3. Aridisols (a) aridus (L.) - dry (b) horizons dry for major part of year unless, ground water or irrigation  not extensively leached  often contain lime, gypsum and/or salt in upper profile  calcic, gypsic or duripans (d) may have argillic or natric (c) ochric epipedon (f) if irrigated - often productive

The central concept of Aridisols is that of soils that are too dry for mesophytic plants to grow. They have either: (1) an aridic moisture regime and an ochric or anthropic epipedon and one or more of the following with an upper boundry within 100 cm of the soil surface: a calcic, cambic, gypsic, natric, petrocalcic petrogypsic, or a salic horizon or a duripan or an argillic horizon, or (2)A salic horizon and saturation with water within 100 cm of the soil surface for one month or more in normal years.

4. Mollisols (a) mollis (L.) - soft (b) mollic epipedon results in a mollisol (c) structure - granular (soft) (d) may have argillic, albic, natric, cambic (e) high bases and O.M. - productive, rich (f) usually, prairie (grassland) vegetation some forest (h) some of the worlds most productive soils

The central concept of Mollisols is that of soils that have a dark colored surface horizon and are base rich. Nearly all have a mollic epipedon. Many also have an argillic or natric horizon or a calcic horizon. A few have an albic horizon. Some also have a duripan or a petrocalic horizon.

5. Alfisols (a) gray to brown surface - ochric (b) have an argillic with medium to high base saturation (BSP (c) no mollic, oxic nor spodic (d) more weathered than Inceptisols (have an argillic) less weathered than Spodosols (no spodic) or Ultisols (more (e) humid regions - deciduous forest and grass (f) quite productive soils

The central concept of Alfisols is that of soils that have an argillic, a kandic, or a natric horizon and a base saturation of 35% or greater. They typically have an ochric epipedon, but may have an umbric epipedon. They may also have a petrocalcic horizon, a fragipan or a duripan.

6. Spodosols (a) Spodos (Gr.) - wood ash (b) cool to cold and humid climate (c) coniferous forest vegetation (d) Genesis: slow decomposition of litter layer + acidic conditions leaching through organic matter layer solubilize Fe and Al (acid + soluble organics) eluviated SiO layer (Fe and Al eluviated) illuviated spodic horizon (Fe, Al, O.M.) (e) must have spodic horizon (f) often have albic horizon (Si oxide) (g) highly leached and acid soils (h) limited productivity - acid, low CEC, highly leached

The central concept of Spodosols is that of soils in which amorphous mixtures of organic matter and aluminum, with or without iron, have accumulated. In undisturbed soils there is normally an overlying eluvial horizon, generally gray to light gray in color, that has the color of more or less uncoated quartz.

7. Ultisols (a) Ultimus (L.) - last (b) warm to tropical climates (c) older land forms (d) have argillic or kandic with low base saturation (BSP) w low activity clays (1:1 and hydrous oxides) e) more weathered than alfisols (lower base saturation) less weathered than spodosols (no spodic) or oxisols (no oxic) (f) color is commonly red-yellow (g) have some weatherable minerals - kaolinite

The central concept of Ultisols is that of soils that have a horizon that contains an appreciable amount of translocated silicate clay (an argillic or kandic horizon) and few bases (base saturation less than 35 percent). Base saturation in most Ultisols decreases with depth.

8. Oxisols (a) have oxic horizons (b) intense weathering - hot, humid climate (c) "tropical" soil (d) very high clay content (e) termed Latosols or Laterites (very old surfaces) (f) large areas and population in the tropics (g) high rainfall = leaching of bases (h) high P fixation (i) low CEC and high pH-dependant charge (+ and -)

The central concept of Oxisols is that of soils of the tropical and subtropical regions. They have gentle slopes on surfaces of great age. They are mixtures of quartz, kaolin, free oxides, and organic matter. For the most part they are nearly featureless soils without clearly marked horizons. Differences in properties with depth are so gradual that horizon boundaries are generally arbitrary.

9. Vertisols (a) high content (> 30 %) swelling-type clays (b) verto (L.) - to turn (self-mixing) (c) large shrink-swell = cracks (d) old term - Grumusols (e) very unstable - difficult to work (f) wet - stickey and plastic (g) very "heavy" soils (i) productivity - very difficult to manage

The central concept of Vertisols is that of soils that have a high content of expending clay and that have at some time of the year deep wide cracks. They shrink when drying and swell when they become wetter.

10. Histosols (b) organic soils (a) histos (Gr.) - tissue (c) excessive water (saturation) = slow organic residue decomposition (d) any climate (e) if low clay - > 12 % C is required (f) low Db and high water-holding capacity (on weight basis) (g) can be very productive

The central concept of Histosols is that of soils that are dominantly organic. They are mostly soils that are commonly called bogs, moors, or peats and mucks. A soil is classified as Histosols if it does not have permafrost and is dominated by organic soil materials.

11. Andisols (a) developed in volcanic ash & pumice (b) ando (dark soil) - can have melanic epipedon (c) not highly weathered (d) amorphous Si minerals (allophane, imogolite (e) previously, inceptisols (f) can be productive

The central concept of Andisols is that of soils dominated by short- range-order minerals. They include weakly weathered soils with much volcanic glass as well as more strongly weathered soils. Hence the content of volcanic glass is one of the characteristics used in defining andic soil properties.

12. Gelisols (e) large areas in northern climates (Alaska) (a) permafrost layer (c) little profile development

The central concept of Gelisols is that of soils that have permafrost within 100 cm of the soil surface and/or have gelic materials within 100 cm of the soil surface and have permafrost within 200 cm. Gelic materials are mineral or organic soil materials that have evidence of cryoturbation (frost churning) and/or ice segeration in the active layer (seasonal thaw layer) and/or the upper part of the permafrost.

Santa, coarse silty, mixed, frigid Ochreptic Fragixeralfs Santa, | coarse silty, mixed, frigid | Ochreptic | Fragi | xer | alfs A gentle hand may lead even an elephant by a hair

مواد آلی خاک بخش فعال و مهم خاك است مواى ألي بر روي خصوصيات فيؤيكي و شيميايي و بيولوؤيكي خاك تاثير رى بخش فعال و مهم خاك است