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"Our Soil - A Layer of Life"

Study Guide

"Each soil has had its own history. Like a river, a mountain, a forest, or any natural thing, its present condition is due to the influences of many things and events of the past." --- Charles Kellogg, The Soils That Support Us, 1956

Our soil is a layer of life. Protect your life! Protect our soil, a layer of life! Your local Soil and Water Conservation District (SWCD), together with Minnesota’s other ninety soil and water conservation districts, was formed to help you protect your soil. This educational material is just one way the districts help you protect your soil.

Soil Lives

Healthy soil is a living, dynamic substance! Soil is sand, silt, clay, air, water, minerals and organic matter crawling with earthworms, moles, grubs, centipedes, millipedes, snails, slugs, beetles, ants, fungi, insect larvae, bacteria, mushrooms and many other organisms. An average soil sample is 45% minerals, 25% water, 25% air and 5% organic matter. The soil’s texture comes from the different sizes of the rock and mineral particles. Sandy soils have larger particles. Silt is fine particles, and in clay soils, the particles are too fine to be distinguished with an ordinary microscope.





A mixture of sand, silt and clay makes up most soils. The water and the air are found in a maze of small open spaces called pores. Plant roots and other soil life need the air and the water. Animals burrowing and plant roots growing down into the soil create the pores in the soil for the air and the water.

The organic matter in the soil comes from the decay of dead plants and animals. Earthworms, bacteria and fungi are just a few of the organisms that live in the soil, feed on the organic matter and decay or recycle plant nutrients. All of the organisms that live in the soil are such an important part of the continuous, natural process of decomposing organic materials and preparing the soil for future plant growth, that we cannot talk about soil without including all of the living things.

The “liveliest” soils are the best soils. Moles, shrews, mice, gophers and prairie dogs are some of the larger mammals that spend all or most of their lives in the soil. There are also millions of insects which spend at least part of their life cycles in the soil.

Earthworms, sowbugs, mites, centipedes, millipedes and spiders also live in the soil. In addition, there are many organisms living in the soil that are so small that they cannot be seen without a microscope.

According to S.A. Waksman, a microbiologist, in just ¼ teaspoon of fertile soil you could find:


That’s “lively” soil!

Of all the countless millions of organisms that live in an acre of soil, earthworms are perhaps the most significant group of larger organisms. Earthworms can range in number from a few hundred to more than a million per acre. They digest organic matter, recycle nutrients and can make the surface soil richer.

One earthworm can digest 36 tons of soil in one year! But did you know that earthworms are not native to Minnesota? In fact, the Minnesota DNR has designated earthworms as an invasive species. They speculate that the worms probably got here during the late 1800's and early 1900's when many European settlers imported European plants that likely had earthworms or earthworm cocoons (egg cases) in their soils. More recently, the widespread use of earthworms as fishing bait has spread them to more remote areas of the state.

Earthworms can have positive and negative affects on the soil around them. In agricultural settings earthworms can have harmful effects because their castings (worm excrement) can increase erosion along irrigation ditches. In the urban setting, earthworm burrows can cause lumpy lawns. However, for soils that are compacted due to heavy use by agriculture and urbanization, for example, earthworm tunnels can have a positive impact by creating "macro-pores" to aid the movement of water through the soil. They also help incorporate organic matter into the mineral soil to make more nutrients available to plants.

Soil is much more than just dirt! Healthy, fertile soil is “lively” soil.



Soil Formation

Most of Minnesota’s present landscape was shaped by continental glaciers. The last glacier melted about 12,000 years ago. When these glaciers moved over the land, they ground rocks together, rubbing off tremendous quantities of rock particles of all sizes ranging from house-sized chunks to dust. These rocks are called the parent materials for our soil. The differences in the rocks, limestone deposits to non-lime rock bedrock, produced a wide variety of parent material from which Minnesota soils were formed.

Parent material, topography, time, climate, and living organisms are the five major factors in soil formation. Soil formation is a continuous, natural process that happens very slowly. These natural processes, depending on the conditions, can take from 30 to 100 to 1,000 years to form a single inch of topsoil. Both physical and chemical factors act on the parent material to form soil. Water (rain, rivers, waves, tides, freezing and thawing), wind, sun (heat expansion, cold contraction), and biological activity (roots expanding in crevices, lichens secreting acids, decomposition, animal and human movement) all contribute to soil formation.

More than 600 different soil types have been identified in Minnesota. Each soil type has its own unique character. Soil scientists call it a soil profile. Topsoil, subsoil, and parent material are the three major layers found in most soil profiles. The layers can be as thin as a dime or several feet thick.

The bottom layer is the parent material from which the soil is formed. The middle layer is the subsoil, and plants don’t grow well in it. The top layer is the topsoil. Most life is found in the topsoil, and plants thrive in it. Topsoil is the most fragile layer because it is exposed to wind and water erosion and misuse.

A Typical Soil Profile

Each soil’s profile determines how that soil will respond to our use of it. Soils used according to the capabilities and limitations defined by their characteristics will provide food, water, recreation, wildlife and timber for future generations.

Soils that are not used according to their capabilities and limitations will wash away, blow away or become depleted of their life giving nutrients.

Healthy, Living Soil Supports Our Life

This fragile layer of topsoil, together with air and water, supports our life. This layer of life grows our food and fiber. Our soil supports the roads we drive on, the buildings we live in and the recreation areas we enjoy. Our soil cleanses and holds our water, and it absorbs the sun and radiates heat.

Our soil has played an important role in our history and our prosperity. In construction, agriculture, recreation and the many other ways that we use our soil, we often have not treated our soil with the care needed to make sure our soil remains healthy and productive.

As a young nation, people pushed westward after having depleted the soil in the east. Little effort to conserve topsoil was made on the rich, prairie soil. Consequently, tremendous amounts of soil were (and still are being) lost to erosion.

Generally, people still think of soil as a natural resource that will always be available to produce our crops. However, through the process of wind and water erosion, soil becomes an exhaustible resource. The fertile topsoil cannot be replaced as fast as it is being lost. As these lands erode, we lose our ability to produce crops. Without soil, plants cannot grow, and without plants, we would have little to eat!

Our soil is so important to our lives that the Minnesota Association of Professional Soil Scientists (MAPSS) decided in 1987 to promote a state soil. MAPSS chose the Lester soil series to nominate for the Minnesota state soil because, like the people of Minnesota, it was formed from many different backgrounds. MAPSS states,

“A state soil is a symbol to increase the public’s understanding and appreciation of Minnesota’s rich soil resources… the loon, the showy lady slipper, the agate, the red pine and the walleye are all well known symbols of Minnesota’s resources. One important unheralded resource central to Minnesota’s wealth and heritage is its soil resource. Two of those symbols, the showy lady slipper and the red pine, owe their existence to and have their roots in this important resource. Then, too, the livelihood of the loon and the walleye is related to both the quality of and management of the soil resources.”

Soil Erosion

Soil erosion has been occurring since the first drop of water fell from the sky and the first wind blew across the land. It is a natural, geologic process of wearing away and displacing soil by means of gravity, wind, ice and water. While erosion is a natural process necessary to form soil, it has been greatly accelerated by human action.

Wind Erosion

Wind erosion causes soils to move from one location to another. Most wind erosion occurs in areas of high prevailing wind speeds and with light soils composed of particles that are easily moved by the wind. Soil from a large open field, where winds can get a good sweep, is more likely to blow than soil from a field protected by trees, grass strips and residue or from a smaller field.

Damage from wind erosion often spreads to other areas. Windblown soil may fill drainage ditches and pile up along fence rows and on roads. Blowing soil may even create highway driving hazards by limiting vision. The most dramatic example of the effects of wind erosion occurred during the 1930s, the Dust Bowl Era.

Water Erosion

Studies by the U.S.D.A Natural Resources Conservation Service show that from 1 to 100 tons of soil per acre may be splashed into the air during one rain. Small clods and granules are broken down by the impact of the falling drops of water. This splashed up soil consists of single particles that have been dislodged from the soil mass. They are easily transported by any water movement on the surface, no matter how slight, regardless of slope.

It is usually easy to find evidence of soil erosion that is caused by moving water. Soil scientists have identified three types: sheet, rill and gully erosion.

Sheet erosion is the most difficult to see. It is the gradual wearing away of a thin, uniform layer (or sheet) of soil. There are no channels formed by the slow moving water. Sheet erosion occurs where there is not enough vegetation covering the soil to stop erosion completely, yet there is enough cover to prevent rill erosion.

Rill erosion occurs on slopes where the runoff water accumulates into small channels. Rill erosion can be seen as many small channels a few inches deep. Yet the channels are not large enough to interfere with the movement of farm or yard equipment. Rill erosion occurs on slopes that are gentle or have little protective vegetation.

Gully erosion is the most dramatic form of soil erosion. Gullies form when the runoff water accumulates into channels. The rapidly moving water causes the channel to grow wider and deeper. Gullies may become too deep for farm or yard equipment to cross. Gully erosion occurs on steeper slopes which have little or no vegetation.

Although gully erosion is the most dramatic form of soil erosion, sheet and rill erosion are a greater national concern. It is estimated that we have lost one-third of the topsoil from United States cropland.

According to the Natural Resources Conservation Service (1997), the statewide estimated annual sheet and rill erosion rate on cultivated cropland is estimated at 2.1 tons per acre per year. Although 2.1 is well below the generally accepted tolerable rate of five tons per acre per year, the most severe erosion is well above five tons per acre per year and occurs on significant acreages, especially in southeastern and northwestern Minnesota. Forty-five percent of cultivated cropland in Minnesota is eroding above the tolerable level. The 42 percent of the cultivated cropland acres that have the potential for wind erosion above the tolerable level account for a startling 82 percent of the total wind erosion.

Effects of Soil Erosion

Soil washed from a field is not necessarily lost forever, but it is lost for a very long time. The soil that is at the bottom of a lake, for example, is still soil, but is useless for agriculture. Soil that is piled deeply at the lower edge of a field covers over other soil, making it useless. Soil that is carried to the sea may lie there, turn to rock, and later become raised from the ocean floor by geologic action to be broken down again into soil.

Topsoil is a vital part of the earth’s life support system, and its loss or displacement has profound effects. Many experiments have shown that in general, the deeper the original topsoil, the higher the yield of crops. So not only the farmer suffers from a loss of soil, but also all people suffer since they depend on the farmer to grow their food.

A decrease in the depth of topsoil, through wind and water erosion, decreases the area favorable to root growth, thus lowering productivity. Removal of organic matter through runoff is another reason for lower productivity in eroded soils. This depletion reduces the soil’s nutrient values and water holding capacity and also affects the nutritional values and growth of plants in that soil.

Soil erosion, while affecting topsoil, also affects our water. Sediment washes from farmland, construction sites and streambanks. Reservoirs, ditches, culverts, stream channels and rivers all fill with sediment. Harbors and river channels must be dredged when filled with sediment. Clearing these pathways takes money – affecting both the farmer and the city dweller.

Besides being expensive, sedimentation is a dangerous threat to water quality. Water that does not evaporate or soak into soil is runoff or excess water that is discharged and runs across land carrying topsoil and other materials. This water finally drains into ditches, streams, lakes, etc. This land area from which the water drains to a given point is a watershed.

Unlike point source pollution where one identifiable source of contamination is located, sedimentation carries with it numerous harmful chemicals from many unidentified sources. This nonpoint source pollution occurs in both urban and rural areas in the forms of wastes from construction sites, cars, road salts, livestock feedlots, human and animal litter, fertilizers and pesticides carried by sediments. Nonpoint source pollution increases the level of infectious agents, nutrients and pesticides in streams, lakes and rivers, affecting water quality.

Though some soil erosion and sedimentation are the results of natural occurrences, for the most part, nonpoint source pollution is the result of human activities.

Conserving Our Soil

Today, many homeowners, builders, farmers, government and business leaders, school teachers and students understand the importance of using soil conservation practices. Minnesota’s 91 Soil and Water Conservation Districts work closely with these people to conserve and protect our soil. Soil and Water Conservation Districts were formed in the 1930s as a result of the soil erosion caused during the Dust Bowl Era. They are the only local unit of government with a major role in conserving and protecting our soil.

The SWCD Idea – Born in the Dust Bowl

“The morning of Sunday, April 14, 1935, dawned clear and dry across the Great Plains. Families went to church, planning to enjoy picnics and visits to friends during the pleasant afternoon hours ahead. Then, in mid-afternoon the air turned suddenly cooler. Birds began fluttering nervously. All at once, a rolling black cloud of dust darkened the northern horizon. Everyone hurried home trying desperately to beat the overwhelming “black blizzard” before it struck. Within minutes, the sky overhead was dark, streetlights flickered in the gloom, and drivers switched on headlights as the swirling dust storm blotted out the sun.” Peter Roop, Living in the Dust Bowl.

photo courtesy of USDA NRCS

In the 1930s, the United States was in the middle of two great crises: The Great Depression and the Dust Bowl. Because the skies were frequently black with a blizzard of dirt, this decade is frequently called the “Dirty Thirties.” In the midst of blowing fertile topsoil, severe drought, crop failures and bankruptcy, thousands of farmers and ranchers just packed up and headed west in search of a new beginning.

Throughout this natural disaster, Hugh Hammond Bennett, a soil scientist, was one of the leaders who hammered on the point of what was happening to the American land. He realized we needed something to help Americans conserve and protect this valuable natural resource, our soil. His idea – conservation districts all across the United States.

On April 2, 1935, Mr. Bennett used the drama of a dirt storm that hit Washington, DC while he was testifying before the Senate to prove to the Senators that the United States needed Soil and Water Conservation Districts (SWCDs). The Senators tasted the dirt in the air that darkened Washington, DC that day, and Congress quickly passed the soil conservation act, which enabled states to set up conservation districts.

In 1937, Minnesota’s legislature passed the law allowing SWCDs and their state agency, now named the Board of Water and Soil Resources (BWSR), to be established in the state. In 1938, Minnesota’s first SWCD, the Burns-Homer-Pleasant District (now part of the Winona SWCD), was organized. World War II delayed the organization of districts, and many of Minnesota’s SWCDs were established right after the war. By 1973, Minnesota had 100% coverage by its 91 SWCDs, creating the patchwork quilt protecting the state’s soil and water resources.

The cornerstone of each SWCD is locally-led conservation. Because the landscape of every SWCD is different and unique, taking care of the soil and water resources is best done by people who live and work in that district. Most SWCDs follow county boundaries. SWCDs are a local unit of government governed by a board of five supervisors elected within the county who develop policy, long range plans and budgets. Local boards have monthly business meetings which are open to the public. SWCD professional staff members use local, state and federal technical, financial and educational resource programs to carry out the local program of conservation, land use and development of soil and water resources.

In rural areas, SWCDs together with the USDA. Natural Resources Conservation Service (NRCS) help landowners control erosion.

Planting methods can control much erosion in agriculture. Crop rotation is a planting method whereby farmers alternate crops instead of planting the same crop every year in a given field. Important nutrients are replenished, close-grown crops prevent erosion and plant diseases are controlled through rotation of crops.

Contour planting (planting crop rows across a slope rather than up and down), stripcropping (planting row crops and close-growing crops in alternating bands) and contour-stripcropping (combining the two practices described above) are all planting methods that reduce erosion by slowing the speed of water as it moves down a hillside.

Cover crops, a close-growing crop that temporarily protects the soil, is grown primarily between periods of regular crop production.

Filter strips (strips of grass, trees or shrubs planted next to a stream or lake), grassed waterways (planting grass in a natural drainageway to prevent gullies from forming) and a field border (a strip of grass at the edge of a field) are some of the permanent plantings that help reduce soil erosion.

Besides planting methods, terraces (constructing stair-like earthen embankments along a contour) and other structures such as farm ponds reduce soil erosion by slowing the speed of water.

Another important soil conservation practice in agriculture is crop residue management. Crop residue management is using last year’s crop residue to protect and improve the soil. The residue protects the soil from wind and water erosion by providing a cover for the topsoil. Crop residue management includes: ridge-till (planting a crop on ridges), mulch-till (using a chisel plow or disk to till the entire field) and no-till (leaving the soil and crop residue undisturbed except the row where the seed is planted).

Crop residue management is a key conservation practice for reducing sediment. Planting methods and crop residue management not only control water erosion but also control wind erosion. Windbreaks (rows of trees or shrubs planted at a perpendicular angle to the prevailing winds) also reduce wind erosion and provide wildlife habitat.

In urban areas, SWCDs together with USDA NRCS help primarily with controlling erosion and runoff from construction sites. However, soil conservation practices also apply to roads and building sites in rural areas.

Mulching (securing a layer of straw, burlap or other material on bare soil until plants begin to grow) can reduce both wind and water erosion. Cover crops of vegetation, usually grasses and other close-growing crops, hold soil at the construction site in place and reduce erosion. The banks of ditches or streams can be lined with riprap, irregularly shaped and sized rock material or they can be stabilized with biological engineering techniques. Contractors can also build a small pond to trap sediment that water washes from construction sites. These sediment basins reduce soil and pollutants from entering wetlands, rivers, lakes and streams.

In hilly areas, building streets and houses along the contour reduces the potential for erosion and runoff problems. This type of development uses the same principles that contour planting and terracing do in agricultural fields.

Conserving Soil in Your Yard

You can help conserve the soil in your own yard. Look for areas where no plants are growing, gullies are forming in sloping areas, or there is exposed soil around your house and downspouts. Once you’ve found the problem areas, you can seed grasses or groundcovers, build small terraces made of logs or rocks on steeper slopes, put splash guards on downspouts, plant trees or shrubs to reduce wind erosion and provide wildlife habitat.

If you have a garden, you can rotate your crops, mulch your plants with grass clippings or compost, and if your garden is on a slope, you can plant along the contour.

You can enrich the soil in your garden by making a compost pile. Construct a small bin beside your garden and fill it with alternating layers of organic material (grass clippings, leaves, kitchen waste, etc.) and garden soil. Keep it moist and turn the compost pile regularly.

Whether we are using our soil in a rural area, an urban area or in our own yard, long-range conservation of our soil is both essential and practical for our well-being. As citizens, we are all responsible for our use and treatment of our soil – our layer of life. We all have a responsibility to support policies which promote the wise use of our soil and for electing officials who will work for this objective.

Your local Soil and Water Conservation District is working together with state and federal agencies such as the Minnesota Board of Water and Soil Resources, the Minnesota Department of Natural Resources, the Minnesota Pollution Control Service, the University of Minnesota Extension Service, the USDA Natural Resources Conservation Service and others to conserve and protect Minnesota’s soil.

Aggressive efforts must be made to promote

the benefits of soil conservation practices for

Our Soil – A Layer of Life

Protect your life!

Protect our soil a layer of life!