INNOVATIVE
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SOIL
Soil is a mixture of minerals, organic matter, gases, liquids, and countless organisms that together support life on Earth. Soil is a natural body called the pedosphere which has four important functions: it is a medium for plant growth; it is a means of water storage, supply and purification; it is a modifier of Earth's atmosphere; it is a habitat for organisms; all of which, in turn, modify the soil.
Soil is a mixture of minerals, organic matter, gases, liquids, and countless organisms that together support life on Earth. Soil is a natural body called the pedosphere which has four important functions: it is a medium for plant growth; it is a means of water storage, supply and purification; it is a modifier of Earth's atmosphere; it is a habitat for organisms; all of which, in turn, modify the soil.
Soil is called the Skin of the Earth and interfaces with the lithosphere, the hydrosphere, the atmosphere, and the biosphere.[2] The term pedolith, used commonly to refer to the soil, literally translates ground stone. Soil consists of a solid phase of minerals (the soil matrix) and organic matter, as well as a porous phase that holds gases (the soil atmosphere) and water (the soil solution). Accordingly, soils are often treated as a three-state system of solids, liquids, and gases.
Soil is a product of the influence of climate, relief (elevation, orientation, and slope of terrain), organisms, and its parent materials (original minerals) interacting over time. Soil continually undergoes development by way of numerous physical, chemical and biological processes, which include weathering with associated erosion. Given its complexity and strong internal connectedness soil has been considered as an ecosystem by soil ecologists.
There are 5 different soil types that gardeners and growers usually work with. All five is a combination of just three types of weathered rock particles that make up the soil: sand, silt, and clay. How these three particles are combined defines your soil’s type—how it feels to the touch, how it holds water, and how it’s managed, among other things.
How soils form
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.
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.
Most soils exhibit 3 main horizons:
- 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:
- alluvial (water transported)
- colluvial (gravity transported)
- aeolian (wind transported) soils.
Time
Soil properties may vary depending on how long the soil has been weathered.
Minerals from rocks are further weathered to form materials such as clays and oxides of iron and aluminium.
Queensland (and Australia) is a very old weathered landscape with many ancient soils.
Type of Soil
Sandy
Sandy soil has the largest particles among the different soil types.
It’s dry and gritty to the touch, and because the particles have huge spaces
between them, it can’t hold on to water.
Water drains rapidly, straight through to places where the roots, particularly
those of seedlings, cannot reach. Plants don’t have a chance of using the
nutrients in sandy soil more efficiently as they’re swiftly carried away by the
runoff.
The upside to sandy soil is that it’s light to work with and warms much
more quickly in the spring.
Testing what type of soil you’re working with involves moistening the
soil and rolling it into a ball to check the predominating soil particle. When
you roll the slightly wet sandy soil in your palms, no ball should be formed
and it crumbles through your fingers easily.
Silty
Silty soil has much smaller particles than sandy soil so it’s smooth to
the touch. When moistened, it’s soapy slick. When you roll it between your
fingers, dirt is left on your skin. Silty soil retains water longer, but it
can’t hold on to as much nutrients as you’d want it to though it’s fairly
fertile. Due to its moisture-retentive quality, silty soil is cold and drains
poorly. Silty soil can also easily compact, so avoid trampling on it when
working your garden. It can become poorly aerated, too.
Clay
Clay soil has the smallest
particles among the three so it has good water storage qualities. It’s sticky
to the touch when wet, but smooth when dry. Due to the tiny size of its
particles and its tendency to settle together, little air passes through its
spaces. Because it’s also slower to drain, it has a tighter hold on plant
nutrients. Clay soil is thus rich in plant food for better growth. Clay soil is
cold and in the spring, takes time to warm since the water within also has to
warm up. The downside is that clay soil could be very heavy to work with when
it gets dry. Especially during the summer months, it could turn hard and
compact, making it difficult to turn. (When clay soil is worked while it’s too
wet though, it’s prone to damage). If moistened soil feels sticky, rolls up
easily, and forms into a ball or sausage-like shape, then you’ve got yourself
clay.
Peaty
Peaty soil is
dark brown or black in color, soft, easily compressed due to its high water content,
and rich in organic matter. Peat soil started forming over 9,000 years ago,
with the rapid melting of glaciers. This rapid melt drowned plants quickly and
died in the process. Their decay was so slow underwater that it led to the
accumulation of organic area in a concentrated spot. Although peat soil tends
to be heavily saturated with water, once drained, it turns into a good growing
medium. In the summer though, peat could be very dry and become a fire hazard.
(I kid you not—peat is the precursor of coal.) The most desirable quality of
peat soil, however, is in its ability to hold water in during the dry months
and its capacity to protect the roots from damage during very wet months.Peat
contains acidic water, but growers use it to regulate soil chemistry or pH
levels as well as an agent of disease control for the soil.
When wet peat soil is rolled, you
won’t form a ball. It’s spongy to the touch and when squeezed, water could be
forced out.
Saline Soil
The soil in extremely dry regions is usually brackish
because of its high salt content. Known as saline soil, it can cause damage to
and stall plant growth, impede germination, and cause difficulties in
irrigation.
It’s easy enough to test if you have saline soil. You’ll
probably see a white layer coating the surface of the soil, your plants are
growing poorly, and they’re suffering from leaf tip burn, especially on young
leaves.
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