Option 7 Soils and Biome Soils Notice of

Option 7: Soils and Biome Soils

Notice of Use Restrictions v Certain materials in this presentation are included under the Fair Use exemption of the U. S. Copyright Law and/or under the Fair Dealing exemption of the Ireland Copyright and Related Rights Act, 2000 v Materials are included in accordance with the [U. S. ] multimedia fair use guidelines; and v Materials are restricted from further use. v © EDMAN YOST, J. (1999), Copyright Chaos - An Educator's Guide to Copyright Law and “Fair Use”, Intel Teach to the Future CD

Soil Forming Factors • • • Parent material Climate Topography Living organisms time

Parent Material

Parent Material • Mineral matter from which soils develop • May develop from local rock broken down by physical and chemical weathering • Or from material transported and deposited by fluvial, coastal, glacial and aeolian (wind) action

Parent Material • Parent material influences soil in two ways: – Since loose deposits are already partly weathered, soil formation is more rapid than when parent material is solid bedrock – Soils retain some of the features of parent material, producing differences in mineral content and texture • Soils that develop from sandstone are sandy and free draining • Soils from shale have a high clay content and tend to b badly drained • Soils from limestone are alkaline and have high p. H

Climate • Temperature and precipitation • Affects : Type and rate of weathering • Rate of growth an decay of organic material • As well as the rate of leaching

Climate • Bacteria thrive in hot climates, vegetation rapidly decomposed into humus • Chemical weathering dominates in hot climates, great depths of soil • Heavy precipitation is associated with leaching • Drought results in upward moving of water by capillary action causing salinisation and calcification

Topography

Topography • Relief, altitude and aspect – Soils tend to accumulate on flat or gently-sloping lands, increased risk of waterlogging – Where slops are steeper soils tend to be thin and prone to erosion, however, steep slopes encourage run off and so are well drained – With altitude comes precipitation, cloud cover and wind, decrease in temperature and growing season – Different soils may form on north or south facing slopes

Soil Organisms

Soil Organisms • Plant roots help bind loose soil particles ad prise open compacted soil. Vegetation cover also protects against soil erosion • Plants take up nutrients from the soil and return them when they die • Burrowing animals aerate the soil and mix topsoil with subsoil • Darwin estimated that earthworms bring 20 tons of soil particles per hectare to the surface per year • Insects, fungi and bacteria help break don material into humus

Time • Time does not allow soil to change but it allows for various processes to operate • Soils can take up to 400 years per centimetre of depth to form • Time needed for soil formation varies with parent material, sandstone develops soil much faster than granite or basalt • Most Irish upland soils must be less than 10000 years old because glacial erosion has removed any earlier soil cover

Soil Forming Process

Soil Forming Processes • • • Weathering Erosion Humification Leaching Salinisation Calcification

Weathering • Helps break down exposed surfaces of parent rock – Physical weathering: freeze-thaw and exfoliation, des not alter the characteristics of the original parent material – Freeze-thaw in upland areas where temps move above and below freezing point – Exfoliation (onion weathering) in desert areas where day and night temps vary greatly Exfoliation is the process in which rocks weather by peeling off in sheets rather than eroding grain by grain

Weathering • Chemical weathering: causes rocks and minerals to decompose by various processes – Carbonation: rainwater reacts with calcium carbonate in limestone dissolving it to a solution – Hydrolysis: breaks down granite when it causes feldspar in the rock to change to kaolin clay – Oxidisation: when rocks are exposed to oxygen in the air (like iron-oxide), it causes rocks o crumble much easier

Erosion • Much of parent material is not derived from local bedrock alone • Erosion, transportation and deposition bring rock to different locations – Alluvial soils are formed when rivers erode rock into fine particles and transport an deposit them elsewhere (middle and lower stages of a river, floodplains and deltas)

Erosion – Glaciers erode existing soil cover before blanketing it with more glacial deposits (boulder clay) Fluvio-glacial deposits like sands and gravel are deposited by meltwater – Wind erosion can move topsoil not covered by vegetation mainly silt and fine sand soils

Humification The process by which organic mater is broken down and decomposes to form humus

Humification • Organic matter consists of plant litter and the remains and waste products of the many animals living in it • As it decomposes it releases nutrients including nitrogen into the soil • Humification sped up by the presence of oxygen in the soil…why? ?

Leaching • When soluble minerals and organic matter are carried downward through the soil by rainfall • Nutrients are moved down through the A horizon often too far for plants to reach • Occurs where precipitation is higher than evaporation and mostly in upland areas and on steep slopes

Podzolisation • An advanced form of leaching • If surface vegetation is moorland or coniferous forest, rain percolating through it becomes acidic (p. H 4. 5 or lower) • Acidified rainwater is capable of dissolving almost all the constituents of soil including clay particles • Podzol soil often very infertile • A horizon is ash-grey colour, B horizon reddish, hardpan may develop

Laterisation • Extreme leaching process • Widespread in tropical and equatorial regions • Heavy rainfall washes nutrients deep into the soil • Due to rapid decay of vegetation soil has very little acid • Large concentrations of iron remain in the soil, close to the surface • Reddish colour, may harden on exposure to atmosphere causing a hardpan

Salinisation • Accumulation of soluble mineral salts near the surface of the soil • Where precipitation is low or irregular • Where evaporation is greater than precipitation • Much groundwater is naturally saline • Drawn upwards through capillary action • Water evaporates before reaches hot surface and salts are left behind • Hard toxic crust • A problem in irrigated areas

Calcification • Occurs mainly in regions with low rainfall, interior of continents • Evaporation generally higher than precipitation • Water drawn to surface by capillary action • Calcium builds up close to surface • Very fertile environment • Exp. Prairies in USA, roots draw up calcium from lower layers, grass dies and decomposes, calcium returned to surface

Global Pattern of Soils • Zonal soils • Azonal soils • Intrazonal soils

Zonal Soils • Each occupies a large zone or region of the earth’s surface • Where landscape and climate have been stable for a long time • Climate most important soil forming factor • Influences weathering, water content and vegetation • Climactic regions

Zonal Soils • Develop over long periods of time • Mature soils with distinctive soil profiles, very well-developed horizons • Zonal soil found in regions with cooltemperate climate is brown earth • Aridisols found in desert and semidesert regions including N. America

Intrazonal Soils • Where some local soil-forming factor has a stronger influence than climate and vegetation • A different soil types develops within (intra) the zonal soil • Local influences include parent material, coastal location (impact salt), poor drainage (waterlogging) • Soil profile will show local influences exp. Peaty soils of Ireland’s upland areas

Azonal Soil • Of recent origin, immature due to soil forming processes not having time to operate • Do not have well developed soil profile • Young soils, show no distinct characteristics of parent material • Where material has been deposited by wind (loess, sand dunes), sea (salt marsh) or rivers (alluvial) • Also found where volcanic ash is deposited

Examples • Zonal soils: – Latosols (tropical/equatorial) rainforest – Aridisols (desert) – Terra Rossa (warm temperate maritime) – Brown Earths (cool temperate maritime) – Podzols (Cold temperate boreal) – Tundra soils (tundra)

Examples • Intrazonal Soils: – Gley (Impeded drainage, waterlogging) – Peat (extreme waterlogging) • Azonal Soils: – Regosols (Recent deposits of materials by river and wind) – Lithosols (Mass movement and erosion too rapid to allow for soil development)

Brown Earths

Brown Earths • Between 30 degrees and 55 degrees north of equator • Associated with lowland regions with a cool temperate maritime climate • Most common soil type in Ireland

Brown Earths • Characteristics: – Well-developed crumb structure – A medium texture – A p. H slightly acidic – Well developed dark brown coloured soil profile – Natural fertility

Brown Earths • Deciduous forests and thick undergrowth • Heavy leaf fall and other plant litter for the soil • Warm temperatures allowed for presence of numerous earthworms and micro-organisms • As a result rich dark humus (brown colour and crumb structure) • Considerable recycling…why? • Loamy mineral particles, good drainage • Loosely packed crumb structure (aeration)

Brown Earths • • Slight leaching, so slight acidity (5 -7) Due to limited leaching, no hardpan Free draining No distinct A and B boundary due to leaching and burrowing organisms Natural fertility and easy to work with Deciduous woodlands have be cut down to use soil for agriculture Support both pasture and tillage Manure, fertiliser and ground lime added