Soils Flashcards
4 Components of Soil
- Mineral Matter
- Organic Matter
- Air
- Water
Mineral Matter
consists of weathered parent material (rock) that has been deposited by running water, wind, or glacial ice
Organic Matter
The remains of plants and animals living on, or in, the soil. Forms a distinct layer on the soil surface or be mixed with mineral matter. Lies on surface of soil where it accumulates
Air
Provides oxygen used in the decay of organic matter and the growth of plants. Also dissolves soluble chemical compounds needed for plant growth
Water
Transports mineral particles and soluble chemical compounds through the soil
Properties of soil
Texture
Structure
Matter
Colour
Peds
The tendancy of individual grains of the soil to group together to form larger units. Increases soil porosity making space for air and water in the soil
Soil Colour
Humid/Tropical Regions: Red to reddish brown. Reason: Bedrock has a high iron content
Temperate Grasslands: Black to dark brown. Reason: Organic matter and humus
Coniferous Forests: Grey in upper levels and brown to yellow at lower levels
Arid: White in colour. Reason: Concentrations of calcium carbonate
Rate of organic decay
Changes with temperature, the amount of water, volume of air in the soil, and the activity of soil bacteria
Humus
Partly composed organic matter within a soil. Large quantities equals bronw/black colour. Humus decay releases soluble plant nutrients (nitrogen, potassium, phosphorus)
Air and Water
The proportion of air in soils is controlled by soil texture and structure. The coarser the texture = greater porosity = greater activity of soil bacteria. The amounts are complementary to each other, high of one then lower of the other. Where soil pores are saturated = less growth
Soil Chemistry
Fertility is closely related to clay and humus content.
- Higher the pH value, the more alkaline the soil (higher the concentration of calcium and salts)
Soil Horizons
- Soils have distinct horizontal layers called “horizons” Each layer has distinct textures, colours and chemical compositions and structures
- They are created by the movement of water upwards and downwards through the soil, transporting soluble compounds and fine clay particles
Leaching in soil
The process by which water removes materials in solution from one horizon to another. Greater amount of water = greater amount of leeching. Greater acidity = greater leaching effect.
Leaching in Tropical Climates
Leaching occurs all year round and removes many minerals from the soil
Leaching cooler climates
Winter freeze-up stops leaching action
Leaching in arid/semi-arid regions
High evaporation rates lead to formation of a layer of calcium carbonate near the surface of the soil
Caliche
A hard layer of calcium carbonate deposits develops in the soil
Factors affecting soil formations
Climate Organisms and Plants Relief Parent material Time Soil as a system
Climate Factors
Humidity, evaportation, precipitation and the duration of sunshine
Evapotranspiration
Combined processes of evaporation of water to the atmosphere and the transpiration of water by plants. (affects the amount of water available for soil formation)
Temperature
Higher temps break down organic and inorganic materials. Tropical climates have more weathering than polar regions
Organisms and Plants
Living organisms affecting soil development are bacteria and fungi, along with earthworms and burrowing insects and animals. Bacteria and fungi cause initial breakdown of plant and animal tissues.
Plant influence on soil development
Roots open up soil, allowing water and air to penetrate the below surface. Plant tissues act as storage reservoirs for soluble nutrients that would otherwise be leached from the soil in humid areas. When plants die, nutrients are released into soil for new plants to take up
Relief
Configuration of land surface affects soil formation
Steep slopes = erosion = lack of development of deep soil profiles. Level areas suffer from drainage problems
Parent Material
Parent material is the weathered mineral matter from which soils originally develope
Size fragments determines soil texture, which influences the speed with which soil-forming processes operate
Also influences pH, acidic rocks have a low pH, but if the parent material forms over limestone will have a high pH
Time
Soils require time to form
Young soils reflect nature of parent materials
As time passes, vegetation, climate and slope become dominant
Soil as a system
Soil formation is an open system in which soil results from additions such as solar energy and water, and losses of such things as water, nutrients and soil particles through drainage, leaching and erosion
