soil characteristics

characteristics of soil

Soil is a complex mixture of different materials. About half of most soils are inorganic materials, such as the products of weathered rock, including pebbles, sand, silt, and clay particles. About half of all soils are organic materials, formed from the partial breakdown and decomposition of plants and animals. The organic materials are necessary for a soil to be fertile. The organic portion provides the nutrients, such as nitrogen, needed for strong plant growth. In between the solid pieces, there are tiny spaces filled with air and water. Within the soil layer, important reactions between solid rock, liquid water, air, and living things take place. In some soils, the organic portion could be missing, as in desert sand. Or a soil could be completely organic, such as the materials that make up peat in a bog or swamp (Figure 1.1).

soil texture

The inorganic portion of soil is made of many different size particles, and these different size particles are present in different proportions. The combination of these two factors determines some of the properties of the soil. A permeable soil allows water to flow through it easily because the spaces between the inorganic particles are large and well connected. Sandy or silty soils are considered "light" soils because they are permeable, water-draining types of soils. Soils that have lots of very small spaces are water-holding soils. For example, when clay is present in a soil, the soil is heavier, holds together more tightly, and holds water. When a soil contains a mixture of grain sizes, the soil is called a loam (Figure 1.2). A loam field.



soil the ecosystem

Soil is an ecosystem unto itself. In the spaces of soil, there are thousands or even millions of living organisms. Those organisms could include earthworms, ants, bacteria, or fungi (Figure 1.4).



When soil scientists want to precisely determine soil type, they measure the percentage of sand, silt, and clay. They plot this information on a triangular diagram, with each size particle at one corner (Figure 1.3). The soil type can then be determined from the location on the diagram. At the top, a soil would be clay; at the left corner, it would be sand; at the right corner, it would be silt. Soils in the lower middle with less than 50% clay are loams. Soil types by particle size.


instructional diagrams

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which of these are inorganic materials?

-->  a) pebbles

b) plants

c) animals

d) none of the above

about half of the soil is made of organic material.

-->  a) true

b) false

a material with interconnecting holes so that water can move through it.

a) loam

b) soil

c) inorganic

-->  d) permeable

which of these organisms can help change rock into soil?

a) earthworms

b) bacteria

c) fungi

-->  d) all of the above

millions of organisms live within the soil.

-->  a) true

b) false

soil is classified by its proportions of sand, silt and loam.

a) true

-->  b) false

soil that is so rich in organic matter it can be burned is called

-->  a) peat

b) loam

c) pedocal

d) laterite

if a soil holds together and holds water it is high in

a) loam

b) silt

-->  c) clay

d) sand

diagram questions

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