Name: ______Date: ______Period:_____ Unit 2: Earth’s Land Resources Section 2: Soil and Soil Degradation Part 1

Essential Questions: What factors influence soil formation?

A. Pedology is the study of soil. What is Soil?

Soil is not just the dirt beneath our feet and it is much more important then what most people think. It is a complex, life-filled, life giving substance. Healthy soil is essential for agriculture, forestry, the cycles of matter, and the flow of energy that keep Earth’s ecosystems running. Soil is a complex plant-supporting system made up of disintegrated rock, remains and wastes of organisms, water, gases, nutrients, and microorganisms.

Soil is considered a renewable resource even though it can take hundreds or thousands of years for just one inch of topsoil to form. The thing about soil that is renewable is the nutrients it contains, which can be replaced over time.

The Importance of Soil 1. The base of life on land. 2. Provides the bulk of the nutrients needed for plant growth. 3. Serves as primary filter of water as it passes through it. 4. Helps decompose and recycle biodegradable wastes. 5. Major component of the earth’s water recycling and water storage processes.

B. Soil Formation

Soil is composed of many different types of matter from solid rocks to gasses. (See “Composition…” to the right.) You might be surprised to find that one teaspoon of soil can contain millions of bacteria and thousands of fungi, algae, and single-celled animals! Soil also provides a habitat for larger animals, including hundreds of thousands of invertebrate species, amphibians, reptiles, and burrowing mammals.

Soil formation begins when the parent material is exposed. The parent material the base geological material in a particular location such as volcanic ash, rock, or sediment deposited by glaciers; sand dunes; sediments deposited by rivers, in lakes, or in the ocean, or the bedrock itself. Bedrock the mass of solid rock that makes up Earth’s crust.

Once the parent material is exposed to air, the processes that form most soils are weathering, deposition, and the decomposition of organic matter.

Factors That Influence Soil Formation 1 Unit 2, Section 2, Page Factors Effects Climate Soil forms faster in warm, wet climates. Heat speeds chemical reactions, weathering, decomposition, and growth of organisms. Moisture is required for many biological processes so it speeds weathering. Organisms Earthworms and other burrowing animals mix and aerate the soil, add organic matter, and speed decomposition. Plants add organic matter and affect a soil’s composition and structure. Landforms Hills and valleys affect exposure to sun, wind, and water. Steeper slopes promote runoff and erosion; they also slow leaching, accumulation of organic matter, and formation of soil layers. Parent Chemical and physical attributes of parent material influence properties of the Material soil formed from it. Time Soil formation takes decades, centuries, or millennia.

1. Weathering The first process in soil formation is often weathering. Weathering is the physical and chemical processes that break down rocks and minerals into smaller particles. There are two types of weathering.

a. Physical Weathering Physical weathering is the natural breakup of rock without a chemical change. Wind and rain are two main causes of physical weathering. Changing temperatures contribute as well by weakening rocks as they expand and contract repeatedly. Low temperatures also cause water trapped in rock to expand and push outward. Finally, tree roots break up rocks as they grow.

b. Chemical Weathering When water and other substances chemically break down parent material and rocks, transforming them into different materials, chemical weathering is occurring. Living and once-living things also cause this type of weathering with chemical products of their life processes and decomposition, such as water and carbon dioxide. Warm, wet conditions increase chemical weathering.

2. Deposition Erosion is often viewed as a destructive process, but it frequently plays a part in soil formation. Erosion may help form soil in one area by depositing material eroded from another. Deposition is the drop-off of eroded material in at a new location.

3. Decomposition As plants, animals, and microorganisms deposit waste or die and decompose, nutrients are incorporated into the soil. Example: When deciduous trees drop their dead leaves

2 which is broken down by decomposers, returning matter to the soil. Partially decomposed organic matter is known as humus. Soils with high humus content hold moisture well and contain many plant nutrients.

C. Soil Horizons As soon as soil begins to form, it starts to resemble distinct layers called soil horizons. A soil profile is a cross-section of all the soil horizons in a specific soil, from surface to bedrock.

The simplest way to categorize soil horizons is by the A, B, C horizons which correspond to topsoil, subsoil, and weathered parent material respectfully. Some scientists further divide those layers into more complex layers, but not all soils contain all of those layers.

Horizon Description

Topsoil is the loose surface layer of soil and consists mostly of mineral particles and humus. This is a crucial layer for agriculture and ecosystems because it has the most plant nutrients available. Its loose texture, dark color, and ability to A – Topsoil hold water come from its humus content. However, this layer is also the most fragile and human activities such as agriculture can deplete it of its nutrients and erode it.

Subsoil is the horizon below the topsoil and acts as a transition layer between the highly organic A horizon and the rocky parent material in C horizon below. B – Subsoil Generally, as one moves downward through the soil profile, the particle sizes increase and the concentration of organic matter decreases.

C – Weathered This horizon is just above bedrock and includes some of the parent material Parent Material that has broken off in the process of weathering.

When soil becomes moist with water or another liquid, minerals and other components are filtered through the soil. Leaching is the process whereby solid particles suspended or dissolved in liquid are transported to another location, usually downward due to gravity. In some soils, leaching occurs so rapidly that plants do not have the opportunity to take up the nutrients.

D. Soil Characteristics

3 Unit 2, Section 2, Page Soils display great variety. The characteristics of a region’s soil can have as much influence on the region’s ecosystems as do the climate, latitude, and elevation. Scientists classify soils into 12 major groups based largely on what forms them, but they also use properties such as color, texture, structure, and pH.

1. Color – The color of a soil reveals details about its composition and fertility. Dark soils are usually rich in humus and therefore nutrients, whereas pale soils often have less humus and nutrients.

2. Texture – Soil texture is based on particle size. Clay consists of particles less than 0.002 millimeters (mm) in diameter, silt consists of particles between 0.002 and 0.05 mm, and sand consists mostly of particles between 0.05 – 2 mm. Sand particles are large enough to see and do not stick to each other. In contrast, clay particles easily stick together. Most soils are some combination of the three. When soil is a mixture of relatively equal parts clay, silt, and sand, it is called loam.

3. Structure – Soil structure describes the arrangement of soil particles. You can see it in the “clumpiness” of soil. If the soil has clumps, this usually means it has a high amount of humus and therefore is fertile. However, do not confuse clumps with compaction. If soil is densely compacted, it can prevent plant roots from growing. Compaction can occur from repeated traffic (like forest paths), heavy farm equipment, or grazing cattle.

Soil texture influences a soil’s “workability” which is essentially how easy it is to plant in and harvest from. It also indicates how porous a soil is, or the size of the spaces between particles. The smaller the spaces between particles, the harder it is for water and air to get to the roots of plants or to the microorganisms living in the soil.

4. Ph – A soil’s acidity or alkalinity affects its ability to support plant growth. The ph of most soils range from 4.0 to 8.0 with 7.0 being neutral. Different plants require different pH levels and plants die when the soil’s pH falls outside their range. Soil pH varies naturally, but acid precipitation and the subsequent leaching of minerals from the soil can also affect the pH. Few plants can grow at the extremes.

Review Questions

1. List all the contributing pieces of what make up soil. ______

______

2. Soil is made up of ______% mineral, ______% organic matter, and ______% water and air.

3. Describe two reasons why soil is important.

______

4 ______

4. What are the 5 factors that contribute to soil formation?

______

5. What are the three soil horizons and their descriptive names?

______

6. What are the two types of weathering? ______

7. What are the two major causes of physical weathering? ______

8. What two conditions aid chemical weathering? ______

9. Rapid leaching is considered to be a negative quality of soil because ______

______

10. The organic matter in soil includes: (circle one) a. minerals b. living & decomposing organisms c. living organisms only d. bedrock

11. Soil with a large amount of humus (and therefore fertile) is usually a light or dark color? ______

12. Place the following types of soil in order from smallest to largest particle size. sand, clay, silt ______

13. True or False: Acid precipitation and the leaching of minerals and metals affect the pH of soil and the types of plants that can grow in it. ______

14. True or False: It takes one year to produce one inch of topsoil. ______

15. Clumps in soil is usually a sign of a high ______content, but when soil particles are too close together, they are considered ______which is not good for growing plants.

16. Soil has a natural pH range of ______to ______.

17. What two factors can change a soil’s pH drastically? ______

and ______.

5 Unit 2, Section 2, Page Section 2 Vocabulary bedrock – the mass of solid rock that makes up Earth’s crust. clay – soil particles that are less that 0.002 mm in diameter. deposition – the drop-off of eroded material to a new location. humus – partially decomposed organic matter in soil. leaching – the process whereby solid particles suspended or dissolved in liquid are transported to another location, usually downward. loam – soil that is approximately equal parts clay, silt, and sand. parent material – the base geological material in a particular location. sand – soil particles that are 0.05 to 2 mm in diameter. silt – soil particles that are 0.002 to 0.05 mm in diameter. soil – a complex plant-supporting system made up of disintegrated rock, remains and wastes of organisms, water, gases, nutrients, and microorganisms. soil horizon – a division between distinct layers of soil. soil profile – a cross-section of all the soil horizons in a specific soil. subsoil – the horizon below the topsoil and acts as a transition layer between the highly organic A-horizon and the rocky parent material in C-horizon below. topsoil – loose surface layer of soil. weathering – the physical and chemical processes that break down rocks and minerals into smaller particles.

Name: ______Date: ______Period:_____ Unit 2: Earth’s Land Resources Section 2: Soil and Soil Degradation Part 2

6 Essential Question: Describe the mechanisms that contribute to the depletion of soil characteristics.

Humans have been farming for thousands of years and we learned very early on that the most productive soil is loam with neutral pH that is workable, contains nutrients, and hold water. The deterioration of the soil characteristics needed for plant growth or other ecosystem services is called soil degradation. Certain farming, ranching, and forestry practices can erode soil, but other practices can protect it.

A. Erosion

Remember that erosion and deposition are natural processes that, in the long run, can help create soil. Erosion is the removal of soil by water, wind, ice, or gravity. Flowing water can deposit sediment eroded from other areas into river valleys and deltas producing rich and productive soils. But erosion is a problem for farmers because they cannot move with the eroded soil to more fertile lands. Plus, erosion usually happens faster than the soil can be formed. Occasional natural flooding is actually good for soil because it can replace many of the sediments and nutrients that was lost from erosion.

Today, human activities cause more erosion than natural events. More than 47 billion acres of the world’s croplands now suffer from erosion and other forms of soil degradation resulting from human activities. People make fertile soils vulnerable to erosion in several ways, including leaving soil bare after harvests; overgrazing rangelands; and clearing forests on steep slopes or with large clear-cuts.

1. Farming Practices

Plant communities, including crops, protect soil from erosion. Plants slow wind and water, and their roots hold soil in place and absorb water. After fields are harvested, and there is no plant cover protecting the soil, wind and water can erode soil, especially if the land is sloped. The type of farming technique you use mostly depends on the terrain. Terrain refers to an area of land, including its characteristics such as shape and height. See insert in notes to learn more about soil conservation techniques.

2. Ranching Practices

The raising and grazing of livestock also affects soils and ecosystems. When sheep, goats, cattle, or other livestock graze on open rangelands, they feed primarily on grasses. Grazing can be sustainable if the livestock do not eat the grasses faster than they can grow back. However, when too many animals eat too much of the plant cover, impeding regrowth, the result is overgrazing. In addition to erosion, overgrazing also results in the compaction of soil, a decrease in pores for water absorption, and the removal of nutrients from the local environment.

7 Unit 2, Section 2, Page How overgrazing results in soil degradation: 1. Livestock removes too much plant cover, soil is exposed and erodes. 2. Soil erosion makes it difficult for vegetation to regrow, allowing yet more erosion. 3. Non-native weedy plants may invade exposed soil. 4. Livestock often avoid tough non-native plants. 5. The non-native species reproduce and outcompete the native plants further decreasing useful grazing land.

3. Forestry Practices

Forestry practices have been altered over the years to try to minimize the damage to soils, as you may recall from our previous section. Nevertheless, some current methods, such as clear-cutting, can lead to severe erosion, particularly on steep slopes. Selective logging methods tend to lead to less erosion because they keep some root systems intact.

B. Desertification

Desertification is the loss of more than 10 percent in the productivity of soil due to erosion, deforestation, overgrazing, drought, or other factors. Desertification reduces the productivity of arid (mostly dry) lands, which are more susceptible to the process. Severe desertification can enlarge existing deserts and create new ones in once-fertile regions.

This process has occurred in areas of the Middle East that have been inhabited, farmed, and grazed for thousands of years – including the Fertile Crescent region, where agriculture began more than 10,000 years ago. The Fertile Crescent is not so fertile anymore.

Arid and semiarid lands are prone to desertification because they get too little precipitation to meet growing human demands for water. Declines in soil quality have endangered the food supply of more than 1 billion people living in the affected areas.

1. Global Desertification

By some estimates, desertification affects one third of Earth’s land area, costing people tens of billions of dollars in lost crop income. In western China, for example, deserts are expanding and combining due to overgrazing. In Kenya, overgrazing and deforestation has left 80% of their usable land exposed to desertification. It is an ever-intensifying cycle forcing ranchers to use less-productive land and farmers to continue to grow in poor soil.

In 2007, the United Nations released a report that predicted desertification, worsened by climate change, could displace 50 million people in 10 years. The report suggested that industrialized nations fund reforestation projects in dryland areas of the developing world. But why would nations like the United States pay for reforestation elsewhere? This is mostly because the effects of desertification knows no national boundaries. In recent 8 years, gigantic dust storms have blown across the Pacific Ocean from China to North America and dust storms from Africa’s Sahara Desert have blown across the Atlantic Ocean to the Caribbean Sea!

2. The Dust Bowl

Prior to large-scale farming on North America’s Great Plains, the native prairie grasses there held the soil in place. In the late 1800’s and early 1900’s, many settlers arrived in the central area of the country and began farming the land on a massive scale. The farmed area of the Great Plains during this time increased by 700%! Unfortunately, the careless agricultural practices and the overgrazing of livestock removed the native grasses and made the land susceptible to widespread soil erosion.

In the early 1930’s, a drought occurred, aggravating the erosion. The region’s strong winds began to erode millions of tons of topsoil, which would blow around in huge dust clouds. Some dust clouds traveled over a thousand miles and would blacken rain and snow in places as far away as New York. The most-affected region (the southern plains) became known as the Dust Bowl, which eventually became the name for the event itself. The Dust Bowl forced thousands of farmers off their lands.

C. Soil Conservation Policies 1. U.S. Policies

In response to the devastation of the Dust Bowl, the U.S. government, along with state and local governments, increased support for soil conservation. In 1935, the U.S. Congress passed the Soil Conservation Act, establishing the Soil Conservation Service (SCS). This group began to work with farmers to develop conservation plans for their farms. In 1995, the SCS was renamed the Natural Resources Conservation Service and its responsibilities were expanded to include water quality protection and pollution control.

In order to continue its policies, Congress passes farm bills about every 5-6 years, which mostly deal with paying farmers subsidies as an incentive to adopt soil conservation plans. The Conservation Reserve Program (CRP) pays farmers to stop cultivating cropland that erodes easily and to instead harvest in conservation reserves planted with grasses and trees. Besides reducing erosion, the CRP generates income for farmers, improves water quality, and provides habitat for wildlife.

2. International Programs

Internationally, the United Nations promotes soil conservation and sustainable agriculture through its Food and Agriculture Organization (FAO). The FAO’s Farmer-Centered Agricultural Resource Management Program (FARM) supports creative approaches to resource management challenges in many developing nations. Rather than relying on government control, FARM encourages local leaders to educate and encourage local 9 Unit 2, Section 2, Page farmers.

D. Soil Pollution Erosion is not the only threat to the health of soils. Irrigation and pesticide use can improve soil productivity in the short term, but can pollute soil in the long term.

1. Irrigation

The providing of water other than precipitation to crops is called irrigation. Some crops, such as rice and cotton, require large amounts of water, whereas others, such as beans and wheat, require relatively little. By irrigating crops, people have managed to turn previously dry and unproductive regions into fertile farmland.

Irrigation is not without its consequences. A frequent problem is salinization, which is the buildup of salts in upper soil horizons. In dry areas where precipitation is minimal and evaporation happens quickly, water evaporating from A-horizon may pull water up from lower horizons by capillary action. As the water rises through the soil, it pulls up with it - dissolved salts. The salt does not evaporate with the water once it reaches the surface and instead forms a white crust on the soil, making growing plants very difficult.

Salinization is easier to prevent than to correct. First, farmers should not plant crops that require a large amount of water in dry climates. Second, water with a low salt content should be used to irrigate crops. And third, only supply plants with as much water as they need and do so as close to the roots as possible. Drip irrigation systems work on this last principle, delivering water slowly and near the roots of the plants.

2. Pesticides

Pesticides are chemicals that kill organisms that attack or compete with plants we value. Pesticides may kill animal, fungal, bacterial, or viral pests. (Chemicals that kill other plants are usually called herbicides.) Some pesticides are toxic to humans and the chemicals they break down into may remain in soil for long periods of time, basically poisoning it. They may filter through the soil and eventually reach groundwater or evaporate into the air.

Pesticides may increase the yield of a crop in the short term, but can be hazardous to humans and other animals in the long term as they build up over time. The biggest problem is that pesticides sometimes can kill helpful insects or bacteria that live in the soil. We will learn more about pesticides in the next section.

Review Questions

1. True/False: Today, human activities cause as much erosion as natural events. ______

10 2. Erosion is the removal of soil from a location by ______, ______,

______, or ______.

3. What two things can natural flooding replace in the soil?

______and ______

4. One chooses what type of farming technique to use based on the area’s ______.

5. Describe one farming practice that can erode soil. ______

______

6. Describe one farming practice that can conserve soil. ______

______

7. Crop rotation does all of the following EXCEPT a. minimize erosion c. let fields lie fallow b. return nutrients to soil d. break cycles of disease

8. Grazing is only sustainable if ______

______.

9. Name three things that result from the overgrazing of livestock.

a. ______

b. ______

c. ______

10. The area that is considered to be where humans first began agriculture is called the

______. 11. List five possible causes of desertification. ______

______

12. Arid and semiarid lands are prone to desertification because a. the Sahara is expanding. b. gigantic dust storms blow sand from China into North America. c. the precipitation cannot meet the growing human demand for water. 11 Unit 2, Section 2, Page d. 10% of productivity is lost to erosion.

13. What two actions by farmers removed the native grasses from the southern Great Plains resulting in erosion? ______

______

14. What natural event in the early 1930’s sent the Dust Bowl in motion? ______

15. In order to receive aid from the U.S. government, farmers must have a working ______plan in place.

16. The United Nations FARM program focuses on ______leaders rather than government control to ______and ______local farmers.

17. Why is it important for countries that have soil conservation programs to worry about countries that are experiencing widespread erosion?

______

______

18. What two crops require a large amount of water? ______

19. What two crops require relatively little water? ______

20. What are the 3 ways of controlling salinization of soils?

a. ______

b.______

c. ______

21. ______irrigation is a form of irrigation where plants are watered slowly and close to the roots to prevent water loss. 22. Chemicals that kill other plants are usually called ______.

23. Besides the effect pesticides have on the water and air, what is the negative effect it has on the soil itself? ______

______

12 Section 2 Vocabulary desertification – a loss of more than 10 percent in the productivity of soil due to erosion, deforestation, overgrazing, drought, or other factors. erosion – the removal of soil by water, wind, ice, or gravity. irrigation – the providing of water other than precipitation to crops. overgrazing – when too many animals eat too much of the plant cover, impeding regrowth. pesticides – chemicals that kill organisms that attack or compete with plants we value. salinization – the buildup of salts in upper soil horizons. soil degradation – the deterioration of the soil characteristics needed for plant growth or other ecosystem services terrain – An area of land, including its characteristics such as shape and height.

13 Unit 2, Section 2, Page