We will begin by looking at the 5 factors of soil formation that cause great differences in the development of soil profiles on Maui.
For a more detailed presentation of soil formation, click on the United States Department of Agriculture link below. Parent material affects soil fertility in many ways. First, the type of parent material determines which minerals link to mineralogy will predominate in the soil. Secondly, as parent material weathers, nutrients are released into soil solution, which subsequently can be taken up by plants and other organisms or leached from the soil.
Parent material is the starting point for most soil development. The type of parent material and how the soil is formed will greatly influence the properties of the soil. There are two general rules that we may state about the influence of parent material on soil formation:.
There are various types of parent rock material. The major two types of rocks on Earth are granite and basalt. While granite is prevalent on most of the continental United States, the primary parent rock material on Maui is basalt Table 2. On Maui, basalt rock formed from the slow-moving lava flows of the East and West Maui shield volcanoes. Basalt rock is finely textured and comprised of small crystals which cooled rapidly along the surface of the earth.
As a result, the soils which were weathered from basalt tend to be finely textured, as well as fertile when not highly weathered. In contrast to basalt, granite is coarse-textured rock that generally weathers into coarsely-textured soils. Granite is the parent material of most soils in the continental United States. Figure 9. A depiction of basalt rock.
The primary parent rock material in Maui is basic igneous basic rock. Since basalt consists of small crystals, soils that weather from basalt tend to become finely-textured soils. Figure Cliffs on Maui which consist of basalt rock columns. Basalt rock outcrops in Maui pastures. Volcanic ash has a non-crystalline, or amorphous, structure due to its rapid cooling.
The soils that developed from volcanic ash contain mostly amorphous materials and minerals, such as allophane, imogolite, and ferrihydride. Coral is a carbonaceous material that develops along coastal areas. In nutrient management, coral can serve as a valuable source of liming material to raise soil pH.
In uplands of Maui, some soils have formed from the deposition and accumulation of plant residues, and other organic materials. Often these soils are called peat or muck.
In Maui, organic soils are not widely used in agriculture. Organic soils of the world can be very important and productive agricultural soils. Climate: Temperature and moisture influence the speed of chemical reactions, which in turn help control how fast rocks weather and dead organisms decompose.
Soils develop faster in warm, moist climates and slowest in cold or arid ones. Rainfall is one of the most important climate factors in soil formation. Organisms: Plants root, animals burrow, and bacteria eat — these and other organisms speed up the breakdown of large soil particles into smaller ones.
For instance, roots produce carbon dioxide that mixes with water and forms an acid that wears away rock. Learn more on our Soil Biology page! Termites can generate mounds in the soil that are three stories tall!!! Relief landscape : The shape of the land and the direction it faces make a difference in how much sunlight the soils gets and how much water it keeps.
Deeper soils form at the bottom of a hill because gravity and water move soil particles down the slope. Soils are different depending on the location in the slope that they are located. For example, soils that form from limestone are rich in calcium and soils that form from materials at the bottom of lakes are high in clay. Every soil formed from parent material deposited at the Earth's surface. A soil profile may have soil horizons that are easy or difficult to distinguish.
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.
Soil forms continuously, but slowly, from the gradual breakdown of rocks through weathering. Weathering can be a physical, chemical or biological process:. 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:. 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.
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. When well developed, caliche cements the surrounding material together to form a layer that has the consistency of concrete.
Like all geological materials, soil is subject to erosion, although under natural conditions on gentle slopes, the rate of soil formation either balances or exceeds the rate of erosion. Human practices related to forestry and agriculture have significantly upset this balance. Soils are held in place by vegetation.
When vegetation is removed, either through cutting trees or routinely harvesting crops and tilling the soil, that protection is either temporarily or permanently lost.
The primary agents of the erosion of unprotected soil are water and wind. Water erosion is accentuated on sloped surfaces because fast-flowing water obviously has greater eroding power than still water Figure 5.
Raindrops can disaggregate exposed soil particles, putting the finer material e. Sheetwash , unchannelled flow across a surface carries suspended material away, and channels erode right through the soil layer, removing both fine and coarse material. Wind erosion is exacerbated by the removal of trees that act as wind breaks and by agricultural practices that leave bare soil exposed Figure 5.
Tillage is also a factor in soil erosion, especially on slopes, because each time the soil is lifted by a cultivator, it is moved a few centimetres down the slope.
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