Soil Chapter 6 Soil Formation & Morphology Pages 159 – 192

Soil formation... Parent materials and topography determine the amount and types of soil formation

Parent materials... Unconsolidated materials Sediments of erosion and weathering Can vary in mixture and particle size – rocky, sandy, clayey

CROPT... Acronym for soil forming factors... climate relief organisms parent materials time

Climate and soil formation... And climate is? average patterns and conditions of weather (rain, wind, relative humidity, fog, average high and low temperatures, etc.) at a given location over a period of years

Climate and soil formation... vs. weather? current state of the atmosphere with respect to rain, wind, relative humidity, fog, high and low temperatures, etc.

Climate and soil formation... Formation of soils is faster in regions with higher precipitation and higher temperatures... And is slower in more arid regions

Relief and soil formation... How do you spell relief? T-O-P-O-G-R-A-P-H-Y And topography is? the difference between the high and low areas in a landscape – the natural landscape that is....

Relief and soil formation... Soils develop more quickly and more deeply on terrain with a shallow slope Rainfall tends to runoff on steep terrain slowing soil development Rainfall tends to infiltrate on terrain with less slope

Organisms and soil formation... Plants, animals and their residue found in soil also referred to as biota Where they exist in large numbers, burrowing animals turn and incorporate materials speeding soil formation

Organisms and soil formation... Microorganisms aid soil development through the decomposition of organic matter Areas with abundant vegetation contribute humus to the soil

Parent materials and soil formation... Weathering and chemical erosion of parent materials can form secondary minerals or clays Source of A and B soil horizons

Parent materials and soil formation... Unconsolidated materials Sediments of erosion and weathering Can vary in mixture and particle size – rocky, sandy, clayey Weathering and chemical erosion of parent materials can form secondary minerals or clays

Time and soil formation... Time as related to climate, relief, organisms and parent materials Soils can begin to form quickly – years to decades – as results of river deposits on floodplains

Time and soil formation... Glacial sediments may be several thousand years old Soil formation can occur rapidly in warm, humid, forested regions

Bajadas Merging and blending of a series of alluvial fans Formed as alluvium descends downhill Large bajadas can take on the form of gravely plains

Alluvium Eroded soil sediments deposited on land by streams Larger particles drop out sooner

Alluvium As particles move further downslope, particle sizes decrease leaving larger particles behind

Alluvium pH and salinity often increase moving downslope Carbonates and bicarbonates (of Ca, Mg) levels increase

Santa Ana River Deposits deep alluvial sands and gravels in Orange County as a result of being watershed of San Bernardino and Riverside Counties

Weathering... Chemical action of air and rainwater Biological action of animals, plants, fungi, etc. Carbonic acid (H 2 CO 3 ) formed from the combination of air and water

Weathering... Rocks and minerals decompose and disintegrate and change characteristics Clays are formed by weathered or chemically broken-down soils Basalts are an example of a clay producing mineral

Erosion... Wearing away of land surfaces by wind, water, ice, and other geologic forces Physically eroded soils produce sands and silts

Serpentine soils... Derived from ultramafic rock Low in silica High in magnesium and iron Low calcium to magnesium ratio

Serpentine soils... Low in essential nutrients – nitrogen, phosphorus and potassium Plants characteristic to serpentine soils are called serpentine

Organic matter... Rich in humus Holds cations Holds nutrients Reduces pH Increases water-holding capacities Increases soil porosity Changes structure

Department of repetitive redundancy department... In flatter areas with warmer, wetter weather, soils form faster In colder, dryer areas with more slope soils form more slowly

Soil horizons...

O-Horizon... Organic horizon Surface layer inc. leaves, moss and other plant materials Rich in organic matter in various stages of decomposition

O-Horizon... The O-Horizon can be further divided into two layers... Oi – where organic mater is still identifiable Oa – where organic matter is becoming highly decomposed

A- Horizon... ‘Topsoil’ layer Often darker in color and contain more organic matter than deeper layers May contain less clay and sesquioxides (metal oxides) Most biological activity occurs Closely associated with plant root growth

A- Horizon... May be rich in soil organisms: worms, nematodes, fungi and bacteria The term “biomantle” can only be used if biological activity does not extend deeper into subsequent horizon layers ‘Eluvial’ layer – layer in which materials leach (migrate) from

E-Horizon... Leached by water Organic matter and clays may be removed by leaching ‘Eluviated’ layer (migrated out from)

E-Horizon... Often pale containing mostly silicates Only present in older, well-developed soils Generally occurs between the A- and B- horizons

B-Horizon... ‘Subsoil’ layer ‘Illuviated’ layer (migrated into) Leached minerals may accumulate – clay minerals like iron or aluminum

B-Horizon... Organic materials may accumulate May have more intense colors or a stronger chroma than the a-horizon

C-Horizon... Follows the A- and B- Horizons Mostly unweathered materials Contains mostly parent materials

D-Horizon... May be recognized by contrasting pedologic organization between it and overlying layers Found below layers referred to as ‘solum’ (O-, A-, E-, and B-horizons)

R-Horizon... Partially weathered bedrock at the base of the soil profile

Degradation of Soils... Soils with various accumulations of different minerals

Soils with accumulated salts Calcic – accumulated carbonates Gypsic - accumulated gypsum Salic – accumulated soluble salts

Soils with accumulated clays Argillic – accumulated clay Kandic – accumulated low-activity clay Natric – accumulated clay with sodium

Soils with accumulated humus Orstein – cemented soils; high in humus and aluminum Sombric – acidic; high in humus without aluminum Spodic – acidic; high in humus and aluminum

Soils with hardpans Duripan – silica cemented soils Fragipan – brittle soils Petrocalcic – soils cemented by carbonates Petrogypsum – soils cemented by gypsum Placic – soils cemented by iron

Soils showing losses of materials Albic – leached and light colored Glossic – leached, degraded clay layer

Other conditions Agric – caused by tillage Cambic – showing little development Oxic – excessively weathered Pesticides Other toxic materials