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Soil (soil (composition, 43% mineral matter, 25% air, 25% water, 5% humus,…
Soil
soil
composition, 43% mineral matter, 25% air, 25% water, 5% humus, 2% living organisms
mineral matter
main ingredient, rock particles weathered and eroded, stones, sand, silt and clay, minerals help growth
air
fills spaces between rock particles, contains oxygen and nitrogen, vital for plant growth
water
25%, bind soil together, minerals dissolved in water absorbed into roots
humus
, dark jelly substance, forms from decaying animals / plants,
living organisms break down remains creating humus, binds soil together, provides nutrients that make the soil fertile
Living Organisms
living things, earthworms, bacteria, fungi, insects, burrowing animals
animals break down organic matter to form humus, mix up soil to make it easier for water and air to pass through
Soil Profile
cross-section of different layers of soil, surface down to bedrock, each layer horizon, each horizon varies in organic content, texture and colour
horizon goes downwards, o horizon, a horizon, b horizon, c horizon
Horizons
o horizon
organic matter, leaves / decomposing vegetation called plant litter, plant litter provides humus
a horizon
upper layer of soil called topsoil, most organisms live, high humus content, usually darker than other layers and most fertile
B Horizon
called subsoil, lighter in colour than A horizon, less humus, located closer to bedrock, more stones protected from weathering by A horizon
C horizon
bedrock, parent material, lower layer consists of solid rock, upper layer broken down into rock particles
leaching
rain fall, water passes through soil, washing minerals, humus and nutrients from A to B horizon, called leaching
plant roots, A horizon, leaching can interfere with growth because out of reach
extremely wet conditions, minerals can build up at the bottom of A creating a hardpan, impermeable layer, A horizon become waterlogged
Soil Formation
influenced by factors
interaction of these factors leads to formation of distinctive soil
factors
Time
can take 400 years for 1 cm of soil to form, weathering process slow, longer a rock is exposed the more it is broken down
Vegetation
provides humus, gives soil fertility, ares with deciduous trees more plant litter than coniferous and provide more nutrients
landscape
upland thin, mass movement, badly drained, more rainfall, lowland, deeper well drained and fertile, rich in humus
parent material
bedrock broken down, minerals from bedrock provide nutrients for soil, soils form on limestone fertile
organisms
micro-organisms, bacteria, fungi, plant litter, humus, fertile, earthworms / burrowing animals break up soil, movement, water / air, die add nutrients
climate
weathering, depends, freeze-thaw action cold climates, chemical weathering hot climates, moisture / heat influence veg, animals,
thin layer of material on earths surface, plants have roots, natural resource, heavy dependence, plants need soil, plants as food source
Tropical Red Soils
hot wet climates in tropical / equatorial zones, Amazon Basin, high temperatures and heavy rainfall, chemical weathering leads to deep soil
large amounts of humus rapid vegetation growth, high temperatures lead to rapid breakdown of plant litter by organisms
chemical weathering weathers bedrock, increased by acidity from decaying humus, reddish colour because of iron content
leaching from heavy rainfall
very fertile, lush vegetation, humus supply decreases with deforestation, soil left unprotected and leaching increases, loses fertility
Irish Soil Types
Gley
grey develop where bedrock above impermeable
sticky and waterlogged, difficult to cultivate
Peaty
dark, cold upland areas, high rainfall, lowland areas with bad drainage
often waterlogged, source of fuel in blanket and raised bogs
Brown Earth
most common, lowland in Irish Midlands
developed on boulder clay deposited at end of Ice Age
deciduous forests, plant litter, humus, dark colour, little leaching and fertile
cleared for agriculture, intensive arable / pastoral farming, nutrients to soil, manure and ertilisers
Podzol
floors of coniferous forests, cold / wet areas, little humus, little earthworm activity
high leaching and hardpan
infertile and acidic, poorly drained upland area, Cork / Galway
Natural vegetation and soil
natural vegetation = plants or trees that grow naturally, natural vegetation of a region related to climate conditions
vegetation varies according to soil conditions
influence of soil on vegetation
deep fertile soils, support wide variety of vegetation
shallow infertile soils limited in vegetation, coniferous trees planted here
rhododendrons grow in acidic soil, vegetation limited in acidic areas, farmers spread lime to reduce acidity and increase fertility
clay soils waterlogged easily, difficult to cultivate
sandy-soils free-draining and have ability to support a wide range of vegetation
influence of vegetation on soil
vegetation provides plant litter to humus, brown earths rich in humus and fertile, poszol soils are infertile with less humus
vegetation binds soil and protects from soil erosion and mass movement, cover lost soil vulnerable and erosion occurs
vegetation acts as an umbrella, reduces leaching, leaching occurs in tropical areas, deep roots allow access to nutrients
Human Interference with soil
vital natural resource, many economic activities dependent on it, over-exploitation is harmful, soil erosion worst
soil erosion causes
deforestation
conversion of forest to non-forest land, removal of trees for economic use and clearing of land for other purposes
removal of vegetation removes source of humus and soil loses fertility
removal leaves soil exposed to wind and rain, erodes soil, can lead to flooding in lowland and mass movement in upland
Farming methods
over cropping
crops continuously grown on same land, same nutrients removed, loses fertility and becomes exhausted, replenish nutrients
monoculture practised in many areas, growth of one single crop, cash crop coffee or cotton, soil becomes infertile, crop rotation solves problem
Overgrazing
vegetation exposed intensive grazing long periods of time, roots destroyed and soil left bare and exposed to wind and rain, erosion