The 12 Soil Orders

A field guide to all twelve USDA soil orders

USDA Soil Taxonomy groups soils by diagnostic properties of their profiles. An order describes formation and broad features; it is different from a texture class such as sandy loam. A routine nutrient panel cannot determine the order by itself. Use a mapped survey or a described soil profile for classification, then use your laboratory report to plan nutrients and amendments.

Ranking by approximate global ice-free land area

The figures below use the NRCS-derived dataset already used by this page's chart. They are rounded estimates from a specific historical global classification, not current measurements of your property. Other editions and mapping methods differ. The twelve values do not add to 100% because other land categories are outside these order totals. This ranking describes extent, not soil quality.

Entisols

These soils show little development of diagnostic subsurface horizons. New deposits, erosion, or resistant parent materials can limit profile formation. They occur in river deposits, dunes, and steep terrain, among other settings. Their growing potential varies widely: a deep alluvial soil and a shallow rocky soil can both be Entisols. Check depth, flooding, drainage, and texture rather than assuming all young soils are fertile.

Aridisols

Aridisols form in dry environments where moisture limits growth for much of the year. Carbonates, salts, gypsum, or clay can accumulate below the surface because rainfall does not regularly wash them away. Irrigation can support crops in suitable settings, but water quality and drainage matter. Monitor salinity and avoid interpreting a nutrient test without considering the amount of usable water.

Inceptisols

Inceptisols have begun to develop recognizable horizons but lack the stronger diagnostic features of several other orders. They are common on landscapes where weathering, deposition, or erosion limits further development. Properties vary with climate and parent material. For a growing plan, examine effective rooting depth, slope, and drainage before deciding whether the mapped order tells you much about crop performance.

Alfisols

Alfisols commonly have a subsurface accumulation of clay and a relatively high base saturation compared with Ultisols. Many developed under forest or mixed vegetation. They can support productive agriculture, but surface structure, erosion, and nutrient balance still need attention. A clay-rich subsoil can influence drainage and rooting even when the surface looks loose. Use local survey information and laboratory results together.

Gelisols

Gelisols are associated with permafrost near the surface and may show mixing caused by freezing and thawing. Frozen conditions strongly affect drainage, rooting, and decomposition. These soils occur mainly in cold regions and store important amounts of organic carbon. Their behavior can change when the frozen ground thaws. An ordinary garden nutrient recommendation does not describe these landscape and temperature constraints.

Ultisols

Ultisols are strongly weathered soils with subsurface clay accumulation and low base saturation. They often occur on older surfaces in humid regions. Many are acidic and need careful nutrient and pH management for demanding crops. A red or yellow color can be a clue to iron compounds, but color alone does not establish the order. Base amendment decisions on crop needs and measured soil chemistry.

Oxisols

Oxisols are deeply weathered soils with an oxic horizon dominated by low-activity minerals and iron or aluminum oxides. They occur largely in tropical landscapes. Strong phosphorus retention and limited nutrient reserves can affect management. Terms such as oxidic or ferrallitic describe related weathering or mineral features in different classification contexts; they are not exact substitutes for a USDA order. Confirm the classification system before comparing names.

Mollisols

Mollisols typically have a dark, organic-rich surface horizon with substantial base saturation. Many formed under grasslands and support major crop-growing regions. Their productive reputation does not remove the need to protect the surface from erosion or maintain organic inputs. Tillage history, compaction, drainage, and nutrient removal can change the condition of an individual field even within the same mapped soil order.

Spodosols

Spodosols have a diagnostic accumulation of organic matter with aluminum, and sometimes iron, beneath the surface. A pale leached layer may appear above the darker accumulation. Many occur under forest vegetation in moist settings and have acidic conditions. Texture and drainage vary, so inspect the actual profile. Growing decisions may require pH management and careful nutrient planning rather than relying on the appearance of the surface.

Vertisols

Vertisols contain abundant expanding clay and show strong shrinking and swelling. Dry-season cracks and internal soil movement help shape their profiles. They can retain nutrients well, yet their physical behavior complicates tillage, drainage, and building foundations. Work the soil only when moisture conditions are suitable. Adding a small amount of sand does not remove shrink and swell behavior or turn the whole profile into loam.

Histosols

Histosols are dominated by organic soil materials rather than mineral particles. Many develop where wet conditions slow decomposition, though not all are permanently saturated. Drainage can accelerate organic matter loss and cause the surface to subside. Their carbon storage and water relationships make them distinct from mineral garden soils. Management should account for depth, water levels, and the consequences of disturbing accumulated organic material.

Andisols

Andisols have distinctive properties associated with volcanic materials and their weathering products. They often have low bulk density, substantial water retention, and strong phosphorus retention. These features can support productive soils while creating special testing and fertilizer challenges. A dark surface is not enough to identify an Andisol. Use the local soil survey and methods appropriate to volcanic soils when interpreting laboratory results.

Explore your area with the SSURGO Soil Map, then compare mapped properties with field observations. Read the USDA NRCS introduction to the twelve soil orders for classification background. For nutrient planning, choose a soil test that answers your growing question.