Soil - A Layer of Life"
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.
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.
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.
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.
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,
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 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 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.
Studies by the USDA 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
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
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
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 of 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) to 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
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
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
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
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 Agency, 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!