Soil is the thin layer of material covering the earth’s surface and is formed from the weathering of rocks. It is made up mainly of mineral particles, organic materials, air, water and living organisms—all of which interact slowly yet constantly.
Most plants get their nutrients from the soil and they are the main source of food for humans, animals and birds. Therefore, most living things on land depend on soil for their existence.
Soil is a valuable resource that needs to be carefully managed as it is easily damaged, washed or blown away. If we understand soil and manage it properly, we will avoid destroying one of the essential building blocks of our environment and our food security.
The soil profile
As soils develop over time, layers (or horizons) form a soil profile.
Most soil profiles cover the earth as 2 main layers—topsoil andsubsoil.
Soil horizons are the layers in the soil as you move down the soil profile. A soil profile may have soil horizons that are easy or difficult to distinguish.
A horizon—humus-rich topsoil where nutrient, organic matter and biological activity are highest (i.e. most plant roots, earthworms, insects and micro-organisms are active). The A horizon is usually darker than other horizons because of the organic materials.
B horizon—clay-rich subsoil. This horizon is often less fertile than the topsoil but holds more moisture. It generally has a lighter colour and less biological activity than the A horizon. Texture may be heavier than the A horizon too.
C horizon—underlying weathered rock (from which the A and B horizons form).
Some soils also have an O horizon mainly consisting of plant litter which has accumulated on the soil surface.
The properties of horizons are used to distinguish between soils and determine land-use potential.
Factors affecting soil formation
Soil forms continuously, but slowly, from the gradual breakdown of rocks through weathering. Weathering can be a physical, chemical or biological process:
physical weathering—breakdown of rocks from the result of a mechanical action. Temperature changes, abrasion (when rocks collide with each other) or frost can all cause rocks to break down.
chemical weathering—breakdown of rocks through a change in their chemical makeup. This can happen when the minerals within rocks react with water, air or other chemicals.
biological weathering—the breakdown of rocks by living things. Burrowing animals help water and air get into rock, and plant roots can grow into cracks in the rock, making it split.
The accumulation of material through the action of water, wind and gravity also contributes to soil formation. These processes can be very slow, taking many tens of thousands of years. Five main interacting factors affect the formation of soil:
parent material—minerals forming the basis of soil
living organisms—influencing soil formation
climate—affecting the rate of weathering and organic decomposition
topography—grade of slope affecting drainage, erosion and deposition
time—influencing soil properties.
Interactions between these factors produce an infinite variety of soils across the earth’s surface.
Parent materials
Soil minerals form the basis of soil. They are produced from rocks (parent material) through the processes of weathering and natural erosion. Water, wind, temperature change, gravity, chemical interaction, living organisms and pressure differences all help break down parent material.
The types of parent materials and the conditions under which they break down will influence the properties of the soil formed. For example, soils formed from granite are often sandy and infertile whereas basalt under moist conditions breaks down to form fertile, clay soils.
Organisms
Soil formation is influenced by organisms (such as plants), micro-organisms (such as bacteria or fungi), burrowing insects, animals and humans.
As soil forms, plants begin to grow in it. The plants mature, die and new ones take their place. Their leaves and roots are added to the soil. Animals eat plants and their wastes and eventually their bodies are added to the soil.
This begins to change the soil. Bacteria, fungi, worms and other burrowers break down plant litter and animal wastes and remains, to eventually become organic matter. This may take the form of peat, humus or charcoal.
Climate
Temperature affects the rate of weathering and organic decomposition. With a colder and drier climate, these processes can be slow but, with heat and moisture, they are relatively rapid.
Rainfall dissolves some of the soil materials and holds others in suspension. The water carries or leaches these materials down through the soil. Over time this process can change the soil, making it less fertile.
Topography
The shape, length and grade of a slope affects drainage. The aspect of a slope determines the type of vegetation and indicates the amount of rainfall received. These factors change the way soils form.
Soil materials are progressively moved within the natural landscape by the action of water, gravity and wind (for example, heavy rains erode soils from the hills to lower areas, forming deep soils). The soils left on steep hills are usually shallower. Transported soils include:
Soil minerals form the basis of soil. They are produced from rocks (parent material
parent material
In soil formation, the parent rock (or parent material) normally has a large influence on the nature of the resulting soil; for example, clay soil is derived from mudstone while sandy soil comes from the weathering of sandstones. Parent rock can be sedimentary, igneous or metamorphic.
) through the processes of weathering and natural erosion. Water, wind, temperature change, gravity, chemical interaction, living organisms and pressure differences all help break down parent material.
Four basic processes occur in soils— additions, losses, transformations (changes), and translocation (movement). A PowerPoint presentation provides some examples. Experiments demonstrate these soil processes.
In some places, soil forms directly on top of bedrock. In other places, soil forms on a thick layer of loose rock and mineral material. This material, called sediment, has been carried from distant areas by rivers or glaciers. What determines the type of soil that forms?
In optimum conditions and a mild climate, it takes between 200-400 years to form 1cm of new soil, and that's if you don't try to grow anything in it. In wet, tropical areas soil formation is faster; here you can create 1cm in a mere 200 years.
Soil is formed from rocks through weathering. By the action of wind, moisture and rain, rocks break down into smaller peices. These smaller pieces are further erroded by rain water. Slowly the particles become smaller and smaller and form soil.
Grass clippings, fallen leaves, mulch, and compost all count as organic matter. The more you add the faster you will have “dirt” that is easy to garden in. The short answer to how to fix soil is quite easy: the best compost is the solution!
Dirt is made up of sand, silt, and clay, and it may be rocky. It has none of the minerals, nutrients, or living organisms found in soil. It is not an organized ecosystem. There is no topsoil or humus, no worms or fungi.
In the last few decades, soil degradation has been sped up by intensive farming practices like deforestation, overgrazing, intensive cultivation, forest fires and construction work. These actions disturb soil and leave it vulnerable to wind and water erosion, which damages the complex systems underneath.
Soil is not dirt because dirt is a subset of soil. Soil has dirt in it but contains additional components that are teeming with life and that make it possible for plants to thrive. Can plants grow in dirt? Plants cannot grow in dirt.
Therefore, the chronosequence consists of three groups of soil ages. The youngest sites include soils from 6 to 14 years old, the intermediate group comprises of soils developed between 1930 and 1950, and the oldest group includes soils that started to evolve during 1870–1897.
Temperature affects the rate of weathering and organic decomposition. With a colder and drier climate, these processes can be slow but, with heat and moisture, they are relatively rapid. Rainfall dissolves some of the soil materials and holds others in suspension.
Once you get it to the surface, mechanical processes like frost wedging and plant roots, and chemical processes, like leaching and hydration, break the constituent minerals down. Soil becomes rocks, then rocks become soil again ... this is called 'rock cycle. '
Soil that has very little capacity to hold water is sandy soil. Sandy soils have low moisture storage. High evaporation and low capacity limit the availability of rainwater for plant use.
What is the breaking down of rocks into soil particles by the natural process called? Weathering is the process where rock is dissolved, worn away or broken down into smaller and smaller pieces. There are mechanical, chemical and organic weathering processes.
Soils are all around us all of the time, growing our food, filtering our water, supporting our buildings and roads, and stabilizing our trees. Soils can be very different from one another. Some are very shallow and rocky, while others are deep and soft, or clayey and hard.
Given that soil is found nearly everywhere on the surface of the continents (with the exception of very rocky areas), it is unlikely that we would ever lose all the soil on Earth. However, what we are at risk of losing is our arable soil, the soil that is deep enough and rich enough to support agriculture.
Most live in the first 5 cm of soil, hunting bacteria, fungi, and organic matter. Yet despite their prevalence, and aside from their use as bait, these animals are not well known. We know even less about the deeper soils. "Often-neglected deep soils…
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