Soil Flashcards
Without soil
Without soil, we would not be able to grow crops and plants.
Therefore, there would be no food for animals or for people.
It is therefore a very important natural resource.
What is soil made from?
Soil is made of five main ingredients.
Mineral matter Air Water Living organisms Humus
Percentage of the main ingredients of soil
Mineral matter (43%) Air (25%) Water (25%) Living organisms (2%) Humus (5%)
Soil definition
The layer of loose material on the Earth’s surface.
Mineral matter
This is the biggest ingredient in soil. It is made o of small pieces of rocks (sand, silt, clay) broken down by weathering and erosion.
Air
Air fills the spaces between the soil particles. It contains oxygen and nitrogen which are essential for plants and organisms living in the soil.
Water
Water contains dissolved minerals. Plants absorb these minerals through their roots, helping them to grow. Therefore, these minerals are called nutrients.
Living organisms
Earthworms, slugs, woodlice and insect and millions of micro-organisms. They break down dead plants and help to create humus.
Humus
This is dark, decaying matter. It is the remains of dead creatures, plants, leaves, and grass. Humus provides nutrients to the soil.
How soils are formed
Climate Parent material Vegetation Living organisms Landscape Time
Climate
Temperature and rainfall influence rate at which parent rock is broken down by weathering.
Hot climates experience chemical weathering while cold climates experience freeze-thaw.
Parent material
Thpe of rock affects soil formation
Granite is slow to break down by weathering while sandstone breaks down easily and forms soil quickly
Soils that develop from limestone are more fertile than soils that develop from granite and sandstone.
Vegetation
When vegetation dies it is broken down and decays to add humus and nutrients to the soil.
Deciduous vegetation provides more lead fall than coniferous.
Living organisms
Micro-organisms such as bacteria and fungi help to break down the dead plant and animal life in the soil, turning it to humus.
As animals such as earthworms dig through the soil, they break it up and mix it, allowing more water and air to enter the soil.
When these creatures die their remains add nutrients to the soil.
Landscape
Upland areas are cold and wet, so soils are often waterlogged. There is little pant and animal life, so there is less humus.
Lowland soils are generally deeper and well drained. They have more humus so there is plentiful plant and animal life.
Time
Time is one of the most important factors in soil formation
The longer the rock is exposed to the forces of weathering the more it is broken down
It may take up to 400 years for 1cm of soil to form.
Soil profile
There are a number of different layers of soil. Each layer is called a horizon.
There are three horizons, called the A, B, and C horizons. These three layers make up the soil profile.
A horizon
Upper layer of soil
Darker in colour bc lots of humus
Most organisms live here
B horizon
Beneath topsoil
Called subsoil
Lighter in colour bc less humus
Contains more rocks than A horizon
C horizon
Parent rocj
Made from bedrock + pieces of rock
Leaching
Occurs when heavy rainfall washes minerals, nutrients, humus down into B horizon
Means A horizon loses fertility as roots of plants cannot reach nutrients in B horizon
Hardpan
With severe leaching, minerals can accumulate at bottom of A horizo
They are cemented together into hard impermeable crust called hard
Can cause water logging in soil above
Brown soils
Formed on areas covered by deciduous forest which provide large amounts of plant litter. Litter decays to form humus.
Rainfall is limited so leaching and hardpan do not develop
Very fertile and suitable for farming
Brown in colour
Found in the dried lowlands of the south, midlands, and east
irish soils
brown soils
podzol soils
peaty soils
gley soils
Podzol soils
Formed on areas covered by coniferous trees, Pine needles provide limited plant litter, Plant litter decays slowly providing limited amount of humus.
Greater rainfall causes leaching, Hardpan may develop and A horizon becomes grey colour.
Podzol soils infertile, slightly acidic
Found in wetter upland areas of Cork, Galway, Wexford
Tropical Red Soils
Found in regions with tropical climates with hot, wet climates
Hot, wet conditions mean chemical weathering decomposes bedrock quickly, creating deep soil cover.
Normally fertile but can become leached due to heavy rainfall, esp as result of deforestation.
Continuous leaf fall in forest which gives thick layer of plant litter, This is rapidly broken down partly by organisms and partly due to humid conditions.
Acids from decaying humus speed up the weathering of the bedrock. High temps encourage chemical actions, again causing bedrock to break down.
Weathering breaks down iron in soil into iron oxide (rust), giving soil reddish colour,
Soil is heavily leached due to very heavy rainfall.
Soil influence on vegetation
Ability to retain water: Sandy soils are free-draining and support wide range of vegetation. Clay soils become waterlogged easily and are only able to support limited range of vegetation.
Fertile soils have many nutrients including nitrogen and calcium, They support wide range of vegetation, incl coniferous forests.
Acid soils lack lime: limit range of vegetation that they can support, although plants such as rhododendrons flourish.
Deep soils support vegetation with long roots such as ash. Coniferous trees, incl pine and spruce have roofs that spread outwards, so they can survive in shallow soils.
Vegetation influence on soil
Provides plant litter to form humus: deciduous trees provide plentiful supply of humus, leading to brown earth soils. Coniferous trees provide limited supply of needles, leading to podzol soils.
Reduces effect of leaching: plentiful supply of plant litter ensures supply if humus, If sone leaching occurs, deep roots can bring leached materials back to surface.
Vegetation cover slows down or prevents soil erosion, Reduces impact of heavy rain on soil. Roots help bind soil particles together. When soil cover is lost, soil erosion occurs.
Human interference with soil
Soil - vital natural resource
Many economic activities dependent on soil
Biggest threat - soil erosion
Main causes:
deforestation
intensive farming methods
Deforestation
Conversion from forest to non-forest land
Two major effects
- Removes source of humus, loses fertility
- Leaves soil exposed to soil erosion
Solution:
forest management - controlled felling and replacing trees
Farming methods
Over cropping
Overgrazing
Over cropping
Crops continuously grown on land Nutrients removed from soil Soil becomes exhausted Needs time to replenish Monoculture - growth of single cash crop Solution: crop rotation
Overgrazing
Vegetation exposed to intensive grazing Over long periods of time Too many animals grazing an area of land Roots destroyed Soil left bare and exposed to soil erosion Happened in many upland areas of Ireland
