Soils Rumi’s Seven Advices: “In modesty and humility, be like the soil

Soils Definition Pedogenesis-factors Classification/Taxonomy Texture texture triangle Phi scale Stoniness Structure Color-Munsell color pH phosphates Study of profiles Sampling Grain size distribution

Definition of Soil soil - (i) The unconsolidated mineral or organic material on the immediate surface of the Earth that serves as a natural medium for the growth of land plants. (ii) The unconsolidated mineral or organic matter on the surface of the Earth that has been subjected to and shows effects of genetic and environmental factors of: climate (including water and temperature effects), and macro- and microorganisms, conditioned by relief, acting on parent material over a period of time. A product-soil differs from the material from which it is derived in many physical, chemical, biological, and morphological properties and characteristics. (Soil Science Society of America, Soil Science Glossary) “Soil consists of the horizons near the earth’s surface that, in contrast to the underlying parent material, have been altered by the interactions of climate, relief, and living organisms over time.” (from Soil Taxonomy, USDA) Note: Soil usually must have biological activity

Pedogenesis Soils evolve naturally through a process called pedogenesis. The five main factors the influence soil evolution and development are: Time Parent material Climate Relief and topography (geomorphology) Flora and fauna These factors in combination lead to the characteristics of the many individual soil types we observe in nature Note that the first three are the same that influence geomorphology Soils and landforms are very closely correlated The concepts of soil associations and catenas help describe the relationships between geomorphology and soils

Soil Taxonomy Soil scientists have developed taxonomies to help describe and analyze the variations and similarities among soil types Many classifications Mostly national, but also indigenous ones USDA Classification A hierarchical taxonomy with multiple levels Order, Suborder, Great group, Subgroup, Family, series County soil surveys focus on lower levels FAO—Food and Agriculture Organization of the United Nations Attempt at a world-wide classification

USDA Soil Taxonomy Alfisols — moderately weathered, form under boreal or broadleaf forests, rich in iron and aluminum Andisols — form in volcanic ash and defined as containing high proportions of glass and amorphous colloidal materials, including allophane, imogolite and ferrihydrite Aridisols — (from the Latin aridus, for “dry”) form in an arid or semiarid climate Entisols — do not show any "significant" soil profile development. Minimal soil horizons. Gelisols — soils of very cold climates which are defined as containing permafrost within two meters of the soil surface Histosols — consist primarily of organic materials Inceptisols — form quickly through alteration of parent material Mollisols — form in semiarid to semihumid areas, typically under a grassland cover Oxisols — best known for their occurrence in tropical rain forest Spodosols — typical soils of coniferous or boreal forests Ultisols — commonly known as red clay soils Vertisols — high content of expansive clay

Soil Catena

Soil horizons Soil horizons develop over time as a result of the biological, chemical, and physical changes that affect soils They are not necessarily depositional units They are developmental units the evolve over time There is a pretty standard sequence of major units: A, B, C or sometimes A, E, B, C, R Major units can have subtypes

Soil horizons—Alfisols moderately weathered, form under boreal or broadleaf forests, rich in iron and aluminum

Soil Horizons

Soil Horizons

Basic Master Soil Horizons Subordinate distinctions Basic Master Soil Horizons O A E E/B AC B BC C R a Highly decomposed organic matter b Buried soil horizon c Concretions or nodules e Intermediately decomposed organic matter f Frozen soil g Strong gleying h Illuvial accumulation of organic matter k Accumulation of carbonates m Strong cementation n Accumulation of sodium o Residual accumulation of sesquioxides p Plowing or other disturbance q Accumulation of silica r Weathered or soft bedrock s Illuvial accumulation of sesquioxides t Accumulation of clay v Plinthite w Color or structural B x Frangipan character y Accumulation of gypsum z Accumulation of salts

Figure 2. Peoria loess at study site, showing 39 soil horizons. Wang H et al. Geology 2000;28:771-774 Figure 2. Peoria loess at study site, showing 39 soil horizons. Horizon 1 is modern Bt, and 2 to 39 are buried soil horizons, in which 36 to 39 (inset) are from a trench. Meter labels (white squares) indicate 12 m exposure above ground and 2 m exposure in trench. 14C ages obtained from corresponding soil horizons were used for 14C age-depth model. ©2000 by Geological Society of America

Soil Texture Soil texture can be estimated in the field by observing its physical characteristics. A sandy soil feels gritty and falls apart easily if formed into a ball when moist. A loamy soil feels somewhat gritty, yet is easy to work; it has relatively even amounts of sand, silt, and clay; if formed into a ball when moist, it holds its shape, yet still breaks apart easily when squeezed. A silty soil breaks apart easily and has a floury appearance when dry. When moist, silty soils have a slick feel and form no ribbon when pinched between fingers and thumb. A clayey soil forms large, hard clods and cracks form on the surface. Clayey soils feel sticky and are bendable when moist. A ribbon can be formed when moist by pinching soil between fingers and thumb. A longer ribbon formed before it breaks indicates a higher amount of clay.

Texture: Particle size Wentworth and phi scales

Particle Sorting This is about the statistical size distribution and can be studied mathematically

Rounding-Angularity

Sphericity-platyness (and rounding)

Sphericity

Field test for soil texture (simplified)

Soil Texture triangle

Soil Particle sizes Table 1. The Size of Sand, Silt and Clay Name Particle Diameter Clay below 0.002 millimeters Silt 0.002 to 0.05 millimeters Very fine sand Fine sand Medium sand Coarse sand Very coarse sand 0.05 to 0.10 millimeters 0.10 to 0.25 millimeters 0.25 to 0.5 millimeters 0.5 to 1.0 millimeters 1.0 to 2.0 millimeters Gravel 2.0 to 75.0 millimeters Rock greater than 75.0 millimeters (~2")

Munsell Color system Hue, value, and chroma And the color name Example: 2.5YR 5/4, reddish brown Measure colors of mottles too