Soil and Land Resources Essential Concepts

Fertile soil is the basis for most food, livestock feed, timber, forage, and natural fiber production; hence needs for fertile soil are increasing. Unfortunately, productivity of the world's soil has declined as soils have eroded and lost fertility. Degradation of soil is occurring in most countries throughout the world, including the United States.

Obj 1 Describe how soil is formed from organic and inorganic materials

Soil is the loose part of the Earth's crust that gives physical support and chemical nutrition to plant life. Soil is created through both geological and biological processes. Inorganic soil particles are created geologically when rocks disintegrate in various processes known as weathering. Organic soil particles are created biologically when dead organisms decay. Soil that can support the growth of healthy plants is called fertile soil.

Obj 2 Evaluate how soil layers and soil composition affect soil's ability to support life

Soils are made of inorganic (mostly mineral) particles (45%-49%), organic matter (1% - 5%), air, and water (50%). The three major types of mineral particles found in soil, which define its structure, are:

  • clay (very small particles, <0.002 mm in diameter). Clay holds soil nutrients, determines the acidity of the soil, and holds moisture well. Soils with too much clay tend to form hard clods that inhibit the growth of plant roots
  • silt (medium sized particles, from 0.002 to 0.05 mm in size). Soils with too much silt tend to separate and erode under heavy rainfall.
  • sand (large particles, 0.10 to 0.25 mm in diameter). Soils with too much sand dry out rapidly and are usually infertile because they don't provide nutrients to growing plants.
  • Soil with about an equal mix of sand and clay is called loam and is good for plant life.

The organic components of soil are derived from plants and animals. Decaying organic matter is called humus. Soils with high content of organic matter have many benefits. These soils will:

  • hold water well
  • allow water to move through the soil,
  • support microorganisms that promote decay of plants and animals, and
  • have the right pH to encourage the release of mineral nutrients.

Composting is one way of ensuring high organic matter in soil.

A typical soil's "profile" consists of

  • topsoil that supports plant life
  • subsoil that is similar in structure to the topsoil, but not as rich in nutrients
  • bedrock that is not as loose and porous as the other two layers.

Obj 3 Identify major soil-related problems and their causes

Problems associated with soil are:

  • erosion -- the process of losing soil from one place as it moves to another, usually by wind or water. In the U.S., about half of the original topsoil has been lost to erosion in the past 200 years. Almost all farming methods increase the rate of soil erosion.
  • nutrient depletion -- vital elements can leach from soil after too much rain, or nutrients can be lost when the same crop is planted year after year,
  • salinization -- irrigation can leave excess salts in the soil as water evaporates and leaves dissolved minerals behind.
  • changes in soil pH -- acid rain and the use of fertilizers and pesticides can alter soil pH and thereby affect the availability of plant nutrients
  • desertification -- the loss of arable land as soil loses its fertility and productivity, as a result of planting crops too frequently, shortening or eliminating fallow periods, and overgrazing.

Obj 4 Describe ways to conserve soil and reduce erosion

Because soil usually erodes downhill, building soil-retaining terraces across a hillside, contour plowing (plowing across the slope instead of up and down), leaving strips of vegetation across the hillside, or leaving hills not suitable for farming as forest or grazing land.

Instead of the traditional plowing the soil after a crop is harvested, no-till farming eliminates the plowing step, reducing soil erosion (but may result in too densely packed soil over time).

Obj 5 Distinguish between urban and rural land

  • Urban land is covered mainly with buildings and roads and accounts for about 6% of land cover type in the United States. Areas are considered urban if they contain more than 2500 people and a governing body.
  • Rural areas contain relatively few people and large areas of open space and accounts for the other 94%. Rural land can be categorized as:
  • cropland (20% of U.S. lands)
  • rangeland and pasture (26%)
  • forest land (28%)
  • parks and preserves (13%)
  • other (7%)

Obj 6 Describe the urban crisis and explain what people are doing to deal with it

The urban crisis describes the problems resulting from too rapid growth of urban areas. A rapidly growing population can overwhelm the infrastructure and lead to traffic jams, substandard housing, and polluted air and water. (Infrastructure is all the things that a society builds for public use, like roads, sewers, schools, etc.)

Urban planning, determining in advance how land will be used, can result in a reduction in problems associated with growth and add to the quality of life in urban areas. Such planning often considers:

  • intelligent design of sewer lines, roads, parks, etc.
  • transportation, particularly mass transit (buses, trains) which save energy, reduce highway congestion, reduce air pollution, and limit the loss of land to roadways and parking lots.
  • open spaces -- land within urban areas set aside for scenic and recreational enjoyment.

Obj 7 Explain how urban sprawl affects the environment

Urban sprawl is the rapid expansion of a city into the countryside around the city. Suburbs are areas with housing and associated commercial buildings on the boundary of a larger town. More Americans live in suburbs than in cities and the countryside combined. Each year suburbs spread over another 2.5 million acres of land in the U.S. (that was often previously used for food production).

Urban sprawl can include marginal lands -- land that is poorly suited for buildings. Buildings on mountain slopes that are prone to mudslides, along the coast where erosion occurs, or in a floodplain, can be difficult or impossible to repair and expensive to insure.

Obj 8 Explain how open spaces provide urban areas with environmental benefits

Open spaces in urban areas, often called greenbelts, include parks, public gardens, and bicycle and hiking trails. The plants in open spaces absorb carbon dioxide, produce oxygen and filter out pollutants from air and water, help keep the city cooler in summer, reduce drainage problems, minimize flooding, and provide exercise and relaxation for urban dweller.

Obj 9 Explain the function of parks and of wilderness areas

Public lands (as opposed to private property) are managed by government agencies. Some public lands, like the 50 national parks in the U.S. (Yellowstone was the world's first) are intensively protected. Other public lands are leased to private companies for logging, mining, and ranching. Some are maintained for hunting and fishing, as wildlife refuges, or to protect endangered species.

Internationally, biosphere reserves have been set up to protect some of the world's most unique areas.

Certain lands are designated, by the U.S. Wilderness Act, as wilderness areas in which the land is protected from all exploitation.