Soil

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Soil has six functions within an ecosystem. First, soil supports plant life by providing a medium for plant roots and nutrients plants need to live. Second, soil properties determine water functions such as water loss, utilization, contamination, and purification. Third, dead organic matter is broken down and incorporated into the soil to be used by the next generation of life. Fourth, soil provides habitat for animals. Fifth, soil influences the composition and physical condition of the atmosphere by taking up and releasing large quantities of carbon dioxide, oxygen, methane, and other gases as well as reflecting heat energy back into the air. The six function of soil within an ecosystem is providing an engineering medium to humans both as a building material and as a foundation (Brady and Weil (2008) p. 2-3).


Soil is made up of organic matter, and inorganic material (minerals), air, and water. Different combinations of the four components cause the differences in soil type. Loam surface soil which is good for plant growth, approximately consists of 45% minerals, 5% organic matter, 20-30% water, and 20-30% air. The inorganic part of soil consists of three different particles sizes excluding gravel and stones. The particles sizes, from largest to smallest, are sand, slit, and clay. The combination of the different particle sizes determine the type of soil and how much space there is for water and air in the soil which affects what organisms can live there (Brady and Weil (2008) p. 17-19).

Brady, N. C. and Weil, R. R. (2008). The nature and properties of soils. 14th edition. Upper Saddle River, New JErsry. Pearson Education, Inc.


Alternative Conceptions: Children's Ideas About Soil


Below are common ideas children in grades K-6 have about this topic, compiled from research on children's ideas about science (see the Session 1 Children's Ideas Bibliography). Consider what evidence might refute this idea, and why a child would be likely to believe this? Once you've entered all your answers you can click "printable page" at the bottom of this form to be taken to a page with all your answers formatted for printing. You can also click "see possible response" for any question to see one possible response from the series content advisors.


1. Soil is ‘just dirt’ or ‘any stuff’ in the ground.

Possible response: Soil is a complex combination of organic and inorganic materials, as well as air and water; it forms from the interaction of environmental factors.Children often interchange the words "soil" and "dirt" and use them as synonyms.


2. Soil is unchanging.

Possible response: Soil is dynamic. It continuously undergoes changes caused by biological, chemical and physical processes. Soil can be repeatedly eroded, polluted, or rejuvenated. Children’s everyday experiences with soil, which are brief in terms of soil development, confirm their idea that soils do not visibly change.

 

3. Some children think that soil is quite young and has been formed in a few years; others think that soil is as old as the Earth.

Possible response: With few exceptions, soils take hundreds to thousands of years to form.. Children do not generally understand that soils have different ages. Their ability to perceive time and the passage of time is limited. Also, many children think soil comes from plants, which contributes to the common misconception that soil is “just a few years" old. Some children perceive soil as an inseparable part of the Earth, formed when the Earth was formed.


4. Soil is brown and homogeneous. Twigs, leaf mold, and small stones are found in soil, and not an integral part of it.

Possible response: There are many types of soils, each with differences in appearance and composition. Soil color ranges from yellows, browns, and reds to grays and blacks. Soil is a mixture of many diverse components, including live and decaying plants and animals and rocks at varying stages of weathering. Children's experiences with soil — often garden soil — foster the idea that it is a single substance. Most children assume that all soil is the same as the soil with which they are familiar.


5. Soil does not contain air.

Possible response: 25% of soil is comprised of air. Air, as well as water, fills the spaces between soil particles, and is an integral part of soil that performs important functions. Air is gaseous and transparent, and its presence as a component within a solid, visible substance is not readily comprehended by children.


6. Many children think that they are living on land that is mostly soil, within which can be found masses of rock.

Possible response: Childhood experiences may indicate that soil is the predominant material into which rocks are scattered. Under the relatively thin layer of soil, however, lies a solid unweathered layer of rock called bedrock.


7. Soil depth is anywhere from six inches to ten miles.

Possible response: Soil depths vary from a few inches to over fifty feet. Children's common experiences with soils, such as planting a garden or playing with mud, are limited to the soil surface. It is challenging for children to know about or visualize what they haven’t seen.


There are 3 classifications of particles that are used to determine the texture of soil, sand, silt, and clay. Soil texture is the percent of sand, silt, and clay that is present in a sample. The texture of soil is important because it helps influence the rate at which air and water are able to move through the soil medium, texture also affects the ease of tillage as well as stability against wind and water erosion.


Sand is the largest particle, too much sand in a soil creates a problem because sand does not retain water well and it leads to a lot of leakage. Silt is the medium size particle and clay is the smallest. Too much clay in a soil can cause problems because water is slow to infiltrate the soil and once it has causes the problem of bad drainage. 

CROPT: an acronym that can help you remember things that affect soils!

Climate

Relief 

Organic matter

Parent Material

Time

Climate: Climate has more of an effect on older soils than younger soils. A warm and moist environment creates soil quickly because it is able to more quickly break down organic matter. 

Relief: The topography of a landscape will have an effect on the soil because it will help to determine the amount of sunlight and the rainfall distribution of an area. The type of vegetation that can be supported will also be influenced. 

Organic matter: Organic matter is able to help contribute nutrients to a soil as well as a plant’s ability to use the nutrients of the organic matter. One way is by increasing the Cation Exchange Capacity (CEC) of a soil. Cation exchange is important because it allows plant roots and soil to exchange nutrients with one another. Clay particles naturally have a high CEC however sand particles do not so adding organic matter to sandy soils can make it possible for plants to get the nutrients they need. 

Organic matter can also help with pH buffering, bringing the pH of a soil closer to 7. Too high or low a soil pH can cause problems because the pH of a soil is what regulates the availability of nutrients to plants. A nutrient can become unavailable to a plant OR available to the point of being toxic to the plant! Also toxic nutrients can become available for the plant to take up! Most garden vegetable plants prefer a pH of around 6.2-7.5 however optimal pH for plants does vary. pH can be affected by irrigation water and can be modified with soil amendments if needed. 

Some types of organic matter, like shells are hard and break down over time which is great for soil because it provides a steady supply of nutrients. Additionally organic matter is high in protein and can improve the amount of Nitrogen in soil because every protein contains Nitrogen, an essential element for plant growth. The Nitrogen in organic matter is also released into the soil as the organic matter decomposes.

The arrangement of soil particles, soil structure, can also be improved with organic matter, but must be replaced with the organic matter dries out. Organic matter can bind to clay particles to make them larger which helps to create larger pores in the clay soil which helps with aeration and drainage.

Parent material: Parent material is what is broken down into the sand, silt and clay particles and will ultimately affect the soil texture and the type of minerals that are present in the soil and the rate at which they decompose. (Rocks can turn into small soil particles but soil particles can also be compressed back into rocks!!!)

Time: It takes time for parent material to break down and combine with organic matter and settle into a place where it will be affected by where it lands and what the climactic conditions of that place are! Under optimal conditions it will take about 500 years to create a new top inch of soil! 

Brady, N. C. and Weil, R. R. (2008). Elements of the nature and properties of soils. 14th edition. Upper Saddle River, New Jersey. Pearson Education, Inc.


IslandWood Soils

IslandWood’s soil is heavily influenced by past glacial activity.  Below the humus layer, mineral particles derive from glacial moraines, glacial lakes and glacial outwash.  Primary soils are as follows:

1. Gravelly ashy loam (loam with relatively more gravel sand and ash);

2. Silt loam;

3. Gravelly ashy sandy loam;

4. and Gravelly loam

Two unusual soils found at IslandWood are the Mukilteo Peat [33] which underlies Charlie’s Bog and the Shalcar Muck [50] found in the wetland to the north of Mac’s Pond.  Both are mostly organic matter and have a high water-holding capacity.

Indianola-Kitsap complex [21] is found around Mac's Pond and on slopes of the ravine that drains southeast from Mac’s Pond toward the harbor.  It is a mixture of loamy sand (Indianola) that drains water rapidly and silt loam (Kitsap) that drains water slowly.  The complex is prone to sliding.  Also found on some slopes of the ravine is Dystric Xerorthents [10], another kind of gravelly, sandy loam soil that is slide-prone.

A soil map of the IslandWood vicinity can be generated using the National Resource Conservation Service soil mapping application. 

Soil Map of IW.jpg

Below is a table that shows the soils found on campus.  Numbers in the left column refer to the number in the image above.

Map Unit Symbol

Map Unit Name

Acres in Area

Percent of Area

6

Bellingham silty clay loam

0.5

0.1%

7

Cathcart silt loam, 2 to 8 percent slopes

16.3

2.5%

8

Cathcart silt loam, 8 to 15 percent slopes

31.2

4.7%

9

Cathcart silt loam, 15 to 30 percent slopes

73.3

11.0%

10

Dystric Xerorthents, 45 to 70 percent slopes

53.4

8.1%

14

Harstine gravelly ashy sandy loam, 0 to 6 percent slopes

7.1

1.1%

15

Harstine gravelly ashy sandy loam, 6 to 15 percent slopes

19.8

3.0%

16

Harstine gravelly ashy sandy loam, 15 to 30 percent slopes

42.6

6.4%

17

Harstine gravelly ashy sandy loam, 30 to 45 percent slopes

12.7

1.9%

21

Indianola-Kitsap complex, 45 to 70 percent slopes

29.5

4.4%

22

Kapowsin gravelly ashy loam, 0 to 6 percent slopes

226.1

34.1%

23

Kapowsin gravelly ashy loam, 6 to 15 percent slopes

37.6

5.7%

29

Kitsap silt loam, 8 to 15 percent slopes

39.8

6.0%

32

McKenna gravelly loam

44.2

6.7%

33

Mukilteo peat

4.0

0.6%

50

Shalcar muck

2.2

0.3%

62

Tacoma silt loam

3.6

0.5%

64

Water

12.6

1.9%

Totals for Area of Interest

663.5

100.0%

Soil Mapping Website: http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm