The lithosphere and the soil as power equipment and hazard 7. Soil formation

1. Influences of soil formation Parent material Climate Topography Organisms Time Soil formation, or pedogenesis, is the combined effect of physical, chemical, biological and anthropogenic processes on soil parent material.

Parent material Active geological influences Volcanism Tectonics Ground waters Surface waters Andesite as soil forming rock Shallow side of aa meandering river Alluvial plain

A földtani tényezők Passive geological influences Soil forming rocks Minerals of soil forming rocks Stucture of soil forming rocks Rendzina – chaarcteristic soil on limestone Shallow soil on hard rocks Thick soil on loess

Climate Climate is the dominant factor in soil formation, and soils show the distinctive characteristics of the climate zones in which they form. Mineral precipitation and temperature are the primary climatic influences on soil formation. Climate directly affects the rate of weathering and leaching. Soil is said to be formed when detectable layers of clays, organic colloids, carbonates, or soluble salts have been moved downward. Wind moves sand and smaller particles, especially in arid regions where there is little plant cover. The type and amount of precipitation influence soil formation by affecting the movement of ions and particles through the soil, and aid in the development of different soil profiles. Soil profiles are more distinct in wet and cool climates, where organic materials may accumulate, than in wet and warm climates, where organic materials are rapidly consumed. The effectiveness of water in weathering parent rock material depends on seasonal and daily temperature fluctuations. Cycles of freezing and thawing constitute an effective mechanism which breaks up rocks and other consolidated materials. Climate also indirectly influences soil formation through the effects of vegetation cover and biological activity, which modify the rates of chemical reactions in the soil.

Topography The topography, or relief, characterised by the inclination of the surface, determines the rate of precipitation runoff and rate of formation or erosion of the surface soil profiles. Steep slopes allow rapid runoff and erosion of the top soil profiles and little mineral deposition in lower profiles. Organisms Plants, animals, fungi, bacteria and humans affect soil formation (see soil biomantle and stonelayer). Animals, soil mesofauna and micro-organisms mix soils as they form burrows and pores, allowing moisture and gases to move about. In the same way, plant roots open channels in soils. Plants with deep taproots can penetrate many metres through the different soil layers to bring up nutrients from deeper in the profile.

Time Time is a factor in the interactions of all the above. Over time, soils evolve features that are dependent on the interplay of other soil forming factors. Soil is always changing. It takes about 800 to 1000 years for a 2.5 cm (0.98 in) thick layer of fertile soil to be formed in nature. For example, recently deposited material from a flood exhibits no soil development because there has not been enough time for the material to form a structure that further defines soil. The original soil surface is buried, and the formation process must begin anew for this deposit. Over a period of between hundreds and thousands of years, the soil will develop a profile that depends on the intensities of biota and climate. While soil can achieve relative stability of its properties for extended periods, the soil life cycle ultimately ends in soil conditions that leave it vulnerable to erosion. Despite the inevitability of soil retrogression and degradation, most soil cycles are long.

Human activity Human activities have had pronounced impacts on soil properties. Conifer afforestation in the uplands has caused significant decreases in soil pH and in the quality and turnover of organic matter. Human trampling, while highly localised, affects sensitive mountain soils in popular areas, leading to loss of surface organic horizons, and therefore, carbon storage. Step-working on a hill Ploughed soil

2. Processes of pedogenesis Physical weathering Physical weathering is the class of processes that causes the disintegration of rocks without chemical change. Physical weathering on dolomite

1. Thermal stress 2. Frost weathering 3. Pressure release 4. Hydraulic action Thermal weathering Physical weathering because of the roots

Chemical weathering Chemical weathering changes the composition of rocks, often transforming them when water interacts with minerals to create various chemical reactions. Chemical weathering is a gradual and ongoing process as the mineralogy of the rock adjusts to the near surface environment. dissolution and carbonation - rainfall is acidic because atmospheric carbon dioxide dissolves in the rainwater producing weak carbonic acid. hydrolysis - in such reactions, pure water ionizes slightly and reacts with silicate minerals oxidation - within the weathering environment chemical oxidation of a variety of metals occurs. The most commonly observed is the oxidation of Fe2+ (iron) and combination with oxygen and water to form Fe3+ hydroxides and oxides such as goethite, limonite, and hematite.

Biological weathering A number of plants and animals may create chemical weathering through release of acidic compounds, i.e. moss on roofs is classed as weathering. Mineral weathering can also be initiated and/or accelerated by soil microorganisms. Humification The process of "humification" can occur naturally in soil, or in the production of compost. The importance of chemically stable humus is thought by some to be the fertility it provides to soils in both a physical and chemical sense. It helps the soil retain moisture by increasing microporosity, and encourages the formation of good soil structure. Traces of earthworm in soil

Leaching Leaching is the movement of contaminants, such as water-soluble pesticides or fertilizers, carried by water downward through permeable soils. Lime leaching in soil

Argillization Lessivage Argillization is used to reduce filtration capacity of fissured, rocky cavernous strata and of gravelly soils. In this method a clay suspension, with a small amount of a coagulant added, is inserted under high pressure into the fissures of the stratum . Lessivage Lessivage is a kind of leaching from clay particles being carried down in suspension. The process can lead to the breakdown of peds (the particles that give the soil its characteristic structure).

Podzolization Solodization Gleization Podzolization occurs in cool and moist climates under pine forests. They are typical of the colder portions of the humid continental and subarctic climates. The E horizon is heavily leached and basically composed a of light colored layer of sand. Solodization Most Solonetzic soils have a neutral to acidic A horizon indicating that some solodization has occurred. The horizons of salt and lime accumulation move downward from the B to the C horizon. Gleization Gleization occurs in regions of high rainfall and low-lying areas that may be naturally waterlogged. Gleization in bog soil

Forming of argillic sand laminae It is a type of concentration in soils. In this case small argillic sand laminae arise in the ‘B’ horizon during accumulation clay minerals and fine grained sand. Salinization Salinization occurs in warm and dry locations where soluble salts precipitate from water and accumulate in the soil. Saline soils are common in desert and steppe climates. Salt may also accumulate in soils from sea spray. Bog formation Bog formation is a soil-forming process that results in excessive wetting of soil. Bog formation starts with a change in the water and aeration budgets, an accumulation of moisture, and the development of anaerobic conditions in the soil.

3. Functions of soil Soils perform five key functions in the global ecosystem: Medium for plant growth Regulator of Water Supplies Recycler of raw materials Habitat for soil organisms Landscaping and engineering medium

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