Soil processes

Soil Processes

Soil processes are specific changes to a soil influencing the relationship between soil and its ecosystem, landscape, flora, and fauna (Krzic M.). One key component to soil processes is the formation of soil. The formation of soil can be condensed into four major components as outlined in the Jenny Equation: Climate (temperature, moisture), biological factors (organisms), Topography (relief/slope), parent material (origin of soil particles), and Time. Based off the formation processes and the different horizons of soil layers, a soil sample may be classified into 12 soil orders according to a Soil taxonomy (Natural Resources Conservation Service).

Image 1: 12 soil groups: (Natural Resources Conservation Service.” The Twelve Orders of Soil Taxonomy )

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Soil Processes can be characterized into four groups:

Image 2: Four groups of soil processes (Fairman, Patrick)

1: Additions: Adding material to the soil helps build soil horizons. Materials can be made up of detritus (organic material), atmospheric dust, or soluble salts from groundwater (Krzic M.). 2: Translocations: Transportation of materials (organic or inorganic) between soil horizon layers either up or down. Primararly water driven however on a small scale, fauna have great influence.

pedoturbationis the term for mixing of soils.

Fauna translocators examples: Earthworms, Ants, moles, rodents.

Flora translocators occur when blowdown trees uproot. The root ball exposes new soil horizons to the surface and provide opportunity for seeds to germinate. Eventually this blown down tree will create pit and mound features in a forest (Krzic M.)

Algillic pedoturbation occurs with the mixing of clays through churning processes called sink-swell cycles. These cycles are dominated by moisture and when dry, clays will crack allowing for lower horizons to be exposed to new materials (K-State Research and Extension.)

3: Transformations: Transferring soil constituents from one form to another. Ex: Mineral weathering and organic matter breakdown.

Humification: This is the process in which dead organic material or soil additions (leaves, detritus, woody matter) are converted to humus by decomposers such as bacteria and fungi. Humus is a dark black gel like substance. Dark soils (brown/black) are usually high in humus concentration. Humus affects the crumb structure of soil particles which affects the amount of pore space. Hunus also affects the amount of water held in soil within the pore spaces. Humification tends to keep a neutral soil pH that is suitable for most microorganisms (Natural Processes and Soil).

Weathering: This is the breakdown of rocks or minerals into smaller pieces through chemical or physical processes. Physical weathering includes mechanisms such as freezing and thawing, wind erosion, and water erosion. These processes influence the soil's pH, water content, texture, and structure. Physical weathering creates smaller particles which provide mineral content to a soil. Chemical weathering through oxidation, carbonation, and hydrolysis either create or destroy minerals thus altering the soils mineral composition. Oxidation yields different soil colors such as a orange/ red soil from the oxidation of iron within the soil. Carbonation is a reaction with carbonic acid which breaks down or dissolves rocks and minerals. hydrolysis is a reaction with water helping minerals and rocks become less resistant to weathering (Soil Genesis and Development).

4: Losses: This final group includes the loss of material from either leaching processes via groundwater or surface erosion (wind, water, anthropogenic actions) (Krzic M.).