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Soil Studies

Erosion Control

The lesson objectives are to:

  • research the importance of soil to agriculture
  • develop an understanding of the relationship between climate, vegetation, and agricultural practices
  • identify different farming practices designed to sustain crops in soil
  • realize soil as a resource we need to sustain

Focusing Questions

  • What is soil erosion and how can it be prevented?
  • What is a nutrient cycle?
  • How has agriculture changed the soil in our region?
  • What impact do different farming practices have on the sustainability of the soil?

Students should be able to:

  • compare and contrast different agricultural practices and discuss their impact on soil
  • discuss how differences in agricultural patterns are created by diverse water, nutrient, organic matter, and climatic conditions, and how they relate to soil
  • identify and discuss the soil types in their region, recognizing localized differences
  • describe the economic, social, and environmental advantages and disadvantages soil provides to agriculture in their region

Introductory Activities

  • Create compost as an in-class project using vermicomposter and scrap foods from lunches.
  • Compare different soil types. Ask students to bring soil from their farm, back yard, cottage, etc. in an air tight container. Also bring in a small supply of peat moss, sand, some commercial potting soils, and compost. Compare:
    • the texture, (rub a soil sample in your fingers)
    • particle size, (using various grades of screens)
    • organisms found in each. (use microscope)
    • organic matter,
    • density (mass by volume),
    • water content, (weigh sample and allow to dry, weigh again)
    • and water retention abilities. (pour a fixed amount of water through a soil sample in a cylinder and time how long it takes to percolate to bottom)
    • Test each for pH levels. Check with school science department for additional soil test equipment and supplies.
    • Ask students to describe attributes of each sample.

    Developmental Activity

    Divide class into groups and have them research one of the following:

    1. What are the soil classifications. Research the predominant soil types in your region. (One source is the Canada Land Inventory, see resource guide) Have this group prepare a report on findings, including their findings on the type of agriculture most common in the region. Ask students to identify which farming approaches are used in their region. If they have better alternatives, present with reasons why it is better for their region.
    2. Identify agricultural practices in the region. Have this group talk to federal and provincial (or State) departments of Agriculture, to representatives of organizations like the Prairie Farm Rehabilitation Administration, grower groups, and individual farmers in their region. Urban students could include green houses and nurseries in this list. Develop a list of questions with students to ask farmers and government officials. Include questions which explore such issues as:
      1. rebuilding/retention of organic matter
        extent of topsoil depletion since farming started
        impact of wind and water erosion and the effectiveness of shelter belts and other forms of erosion control
    3. the impact of irrigation, where it's used and its long term effects
    4. wetlands and their role in the health of agriculture in the region
    5. energy use and efficiency
    6. effects on wildlife
    7. effects on society
    8. Have group report on their findings.

    Agricultural economics which have influenced farming practices.

    1. Have students discuss how economic factors have affected the quality of the soils in their region. Ask them to suggest how to promote a healthy environment and farm economy. Have group report on their findings.
    2. What is the diversity of agriculture in the region the students live? Ask students to explore how agricultural practices in their region affect human health and well-being. Have students consider how the type of soil in their region might determine the nature of the agricultural practices and how these in turn affect human activity.
    3. Depending on the region, this group could explore diversity in agriculture such as market gardening, ranching, grain farming, fruit-growing, or row-crop farming. Ask group to investigate links between the health of the soil, agricultural use of the soil, and the well-being of the economy and society. Have group report on their findings.
      Using this information, challenge your class to identify how agricultural practices in their region might affect other regions.


    Concluding Activity

    Based on the research above, have students describe the best use of soil resources in their region. Can these resources be described without considering water and climatic resources? Ask them to build a description which includes a consideration of economic, environmental, and the health and well-being for the region.

    The Nutrient Cycle

    Plants need a balanced diet to be healthy. To grow, plants use nutrients and water from the soil, carbon dioxide from the air, and sunlight. Some basic nutrients in the soil are readily available to plants. Others are made available by organisms in the soil. For example, nitrogen, the most important soil borne nutrient, is made usable by nitrogen fixing bacteria in the roots of leguminous crops, such as peas, beans, lentils, alfalfa and clover, and by decomposing organic matter. Other nutrients needed by plants include phosphate, potassium, and trace elements such as iron, copper, boron, and zinc.

    Plants store energy from one season to the next in a number of ways. Some make tubers in the ground, like potatoes, others create bulbs, like onions or garlic. Many plants drop leaves and then absorb the nutrients from the decomposing leaves in the following seasons. The flow of nutrients from growth to decay and back to growth again is called the nutrient cycle. When a tree drops its leaves; or a plant dies; or an animal's remains are left after it has died; or it has been devoured by a pack of wolves, digested and excreted, the processes of decay return these nutrients to the soil. Plants cannot eat a dead moose or a fallen log until it has been broken down into usable forms. Fungus and bacteria eat organic matter and excrete nutrients back to the soil. Plants feed on these nutrients and in turn, these plants are consumed by animals, who eventually die, perhaps from being devoured by wolves again.

    Crop Nutrition

    When soil is low in the required nutrients, there will be a low crop yield with possible poor nutritional content, unless this deficiency is corrected. Fertilizers can be used to correct the shortfalls. They work by introducing nutrients directly into the soil.

    Chemical fertilizers are mineral based compounds containing nutrients necessary for plant growth. Chemical fertilizers are readily available in a wide variety of formulations and are easily applied with the right equipment. They have been designed for many different applications and can be formulated to match existing soil conditions.

    However, these chemical fertilizers do not significantly renew organic matter in the soil, so the prolonged use of chemical fertilizers alone may result in a decrease of both organic material and biological activity in the soil. Over time, this can result in a reduced capacity to produce crops. Therefore farmers must use other methods to maintain organic matter in their soil, such as summer fallow, crop rotation, or using additional inputs.

    The high solubility of synthetic fertilizers can result in nutrient imbalances in the soil and run off absorbed into the ground water. They also require the use of non-renewable resources, and considerable amounts of energy, for their extraction, production and transportation.

    Fertilizers from naturally occurring sources contain nutrients in more stable forms which are less prone to run off and often have considerable active microbial populations. However, run off of either synthetic or natural fertilizers can pollute ground water and cause eutrophication. We have to take care with the storage and application of both.

    Natural fertilizers come from a variety of sources. These include:

    • plough-down crops
    • the recycling of wastes such as manure, wastes from slaughterhouses and packing plants
    • composted plant materials and microbial cultures of beneficial species.

    Proper agriculture requires better soil care than simply the replacement of used minerals with fertilizers. Crop rotation can also provide a cost effective way to grow fertilizer. This can enhance soil microbial activity, and replace consumed organic matter and nutrients. Taking land out of production, called fallow, allows it time to regain lost nutrients. Green fallow employs a cover crop to protect the soil from erosion and increase the organic matter. It is preferred to black fallow which leaves the soil uncovered and prone to erosion and damage from the sun.

    Different plants draw different nutrients from the soil. Planting the same crop in the same field, year after year (monocrop agriculture), depletes the nutrients that plant requires and results in less productivity. The planned changing of crops on a given field is called a crop rotation. This varies the draw of nutrients from season to season and so allows for nutrients to be replenished naturally. Rotation and use of leguminous plants such as beans, lentils, and alfalfa allows farmers to create their own nitrogen in the soil, while producing a marketable crop.


    Soil degradation is the depletion of the productive capability of Canada's precious soils and is a costly problem.
    • It is estimated that erosion of 2.54 cm (one inch) of soil can reduce wheat yields by 100 to 233 kilograms per hectare (1.5 to 3.4 bushels per acre).
    • In Southwestern Ontario, the erosion problem has caused a loss in corn yields of some 30 to 40 percent.
    • lands affected by salinization in the Prairies, crop yields have been reduced by 10 to 75 per cent.
    • It is estimated, at 1982 prices, that it would cost the farmers $239 million in fertilizer to fully recover the present loss of grain production from wind and water erosion.
    • More difficult to put a dollar figure on, but equally as serious, is the permanent loss of rich agricultural land to urban use. Between 1961 and 1976, Canada lost more than 1.4 million hectares (3.5 million acres) of farmland - the equivalent of the size of Prince Edward Island.
    Soil at Risk, Canada's Eroding Future, A Report on Soil Conservation by the Standing Committee on Agriculture, Fisheries, and Forestry, to the Senate of Canada, 1984, Ottawa pp3-4. Note: Values originally in Imperial, converted to Metric.

    Soil erosion can occur when wind or water sweep away the topsoil.

    The dust bowl of the "dirty thirties" was a result of sustained drought with poor agricultural practices. Huge clouds of blowing topsoil turned the sky dark, clogged the water systems, and made the air unbreathable.

    There are a variety of methods farmers use to combat erosion. Some plant tree wind rows to reduce the effect of wind on the fields, and others leave stubble on a field after the crop is harvested, to bind the soil together. The practice of zero-tillage reduces soil erosion by eliminating ploughing and any other tillage. Planting crops in the direction opposite the natural water run-off pattern decreases water erosion.