Soil Formation and Morphology Basics

Processes Additions Losses Translocations Transformations

Pedogenesis: The process of soil formation as the result of the combination of soil forming factors leading to addition, loss, transformation and translocation of materials

Soil Forming Factors

Soil Forming Factors Climate Organisms Relief Parent Material Time

Climate involves both local (microclimatic) and global (macroclimatic) considerations. The key components of climate in soil formation are moisture and temperature. In general, higher temperatures and rainfall lead to greater soil development. So, we tend to find the most well developed soils in warm, moist environments and the least developed in cool, dry climates. Look at the U.S. Temperature speeds reactions Water promotes translocation

Organisms   The soil and the organisms living on and in it comprise an ecosystem. The active components of the soil ecosystem are the vegetation, fauna, including microorganisms, and man.

Organisms: Vegetation Grassland Forest Pineland Vegetation: The primary succession of plants that colonize a weathering rock culminates in the development of a climax community, the species composition of which depends on the climate and parent material, but which, in turn, has a profound influence on the soil that is formed. For example in the Mid-West of the U.S. deciduous forest seems to accelerate soil formation compared to grassland on the same parent material under similar climatic conditions. Differences in the chemical composition of leaf leachates can partly account for a divergent pattern of soil formation. For example acid litter of pines or heather favors the development of acid soils with poor soil structure, whereas litter of decidious trees favors the development of well structured soils.

Organisms: Meso-/Macrofauna Earthworms Termites Ants Beetles Arthropods Rabbits Moles

Organisms: microorganisms Bacteria Virus Algae Fungi Actinomycetes protozoa Microorganisms: The organic matter of the soil is colonized by a variety of soil organisms, most importantly the microorganisms, which derive energy for growth from the oxidative decomposition of complex organic molecules. During decomposition, essential elements are converted form organic combination to simple inorganic forms (mineralization). Most of the microorganisms are concentrated in the top 15 - 25 cm of the soil because C substrates are more plentiful there. Estimates of microbial biomass C range from 500 to 2,000 kg /ha to 15-cm depth (White, 1987). Types of microorganisms comprise bacteria, actinomycetes, fungi, algae, protozoa, and soil enzymes

Relief/Topography Altitude elevation climate, vegetation type, potential energy slope gradient overland and subsurface flow, velocity and runoff rate aspect slope direction solar radiation Relief has also an important influence on the local climate and the vegetation. Changes in elevation affect the temperature (a decrease of approximately 0.5 degree C per 100 m increase in height), the amount and form of the precipitation and the intensity of storm events., thus affecting soil moisture relations. These factors interact to influence the type of vegetation. Translocation, organic matter, clays, erosion, see above

in situ weathering of consolidated rock Parent Material in situ weathering of consolidated rock superficial deposits, which may have been transported by ice, water, wind or gravity The nature of the parent material has a decisive effect on the properties of soils. Properties of the parent material that exert a profound influence on soil development include texture, mineralogical composition, and degree of stratification. Soil may form directly by the weathering of consolidated rock in situ (a residual soil), saprolite (weathered rock), or it may develop on superficial deposits, which may have been transported by ice, water, wind or gravity. These deposits originated ultimately from the denudation and geologic erosion of consolidated rock. Consolidated material is not strictly parent material, but serves as a source of parent material after some physical and /or chemical weathering has taken place. Soils may form also on organic sediments (peat, muck) or salts (evaporites). The chemical and mineralogical compositions of parent material determine the effectiveness of the weathering forces. During the early stages of soil formation, rock disintegration may limit the rate and depth of soil development. The downward movement of water is controlled largely by the texture of the parent material. Furthermore, parent material has a marked influence on the type of clay minerals in the soil profile. Leaching Organic matter content Clay translocation Mineral weathering Horizon differentiation Solum thickness organic sediments

Time The value of a soil forming factor may change Time acts on soil formation in two ways:   The value of a soil forming factor may change with time (e.g. climatic change, new parent material). The extent of a pedogenetic reaction depends on the time for which it has operated.

Soil as a Natural Body Differentiation Bedrock Additions Losses Parent Material Bedrock Additions Losses Translocations Parent material is the substrate from which the soil is formed. Over time the soil forming factors (climate, time, relief, organisms, parent material) act in concert to affect a differentiation of the original material into what we describe as soil. Transformations Bedrock

Soil Horizons Roughly parallel layers in the soil with varying composition and properties

The Essentials of Soils Soil Profile – 2D representation of a vertical section of soil from the surface to its deepest layers or horizons. Soil Profile

Soil Horizons

Soil Horizons Roughly parallel layers in the soil with varying composition and properties

Definitions: Eluviation: the loss of materials including clays, organic matter, oxides of Fe and Al. Illuviation: accumulation of materials resulting from eluvial horizons.

Master Horizons [ A horizon

The A Horizon topsoil/plow layer. A horizon Accumulates organic material Often darker than soil below. high in plant roots, biotic activity Zone of gas and water exchange A horizon A horizon

Master Horizons A horizon E horizon

The E horizon - Zone of Eluviation Elluviation = exit A horizon Elluviation = exit Illuviation = into E horizon (Elluvial) Organic matter Clay Carbonates Fe, Al oxides color (Illuvial)

Master Horizons A horizon E horizon [ B horizon

The B Horizon Accumulates material lost from above, or forms in place. (translocation, transformation) Zone of Illuviation (translocation). - Maximum expression of soil development. clays, O.M., Fe/Al soil structure Strong color development Potentially high reactivity B horizon

Master Horizons A horizon E horizon B horizon [ C horizon

The C horizon -Weakly altered by soil forming processes. -Closely resembles parent material C horizon

Master Horizons Florida? A horizon E horizon B horizon C horizon

The R Horizon limestone R horizon

O Horizon

The O Horizon Surface Horizon Organic horizon Very high in organic matter Usually dark-colored Often called peat, muck Some are very fertile, valuable In some countries, O horizon used as fuel.

Master Horizons