OBJECTIVES:

1. Define what a soil is

2. List and describe the factors interact to produce soil

3. Explain how soil is formed

4. Classify different soil horizons

5. Recognize the four important factors for soil conservation

6. Identify the regions of classification in South Dakota

7. Discuss how soils differ

1. Climate:    

South Dakota is located in nearly the center of the North American continent.  Because of SD’s inland position, the climate varies with extremes of summer heat, winter cold, and rapid fluctuations of temperature.  Annual precipitation ranges from 26 inches in the southeast to less than 14 inches in the northwest. Most precipitation is in spring and early summer. Approximately 75% of the total annual precipitation falls when temperatures are ideal for plant growth. Seasonal snowfall averages about 30 to 50 inches in the lower elevations of the State to over 100 inches in the Black Hills. The average frost penetration depth ranges from 25 inches in southwestern SD to 50 inches in northeastern SD.  Frost depth depends on amount of residue cover, soil moisture content, soil color, and, to a large degree, on amount and timing of snowfalls relative to temperature extremes.

The prevailing wind during cold seasons is from the northwest, and is from the southeast during warm seasons. Annual average surface wind velocity is 10 to 12 miles per hour.

2. Biological organisms: 

Climate controls the distribution of vegetation.  Together climate and biological organisms often are called the "active factors" of soil formation. The native vegetation of SD was originally grassland.  Exceptions include the Black Hills that was forest and the river valleys where trees occurred.  The tall grass prairie ranged from the eastern SD border to the eastern edge of the James River Valley.  The principal vegetative were grasses of big bluestem, sand dropseed, and switchgrass and upland and lowland forbs.

Moving westward across the James River Valley, medium and short grasses assumed dominance throughout central SD.  Important species of this area were needleandthread, green needlegrass, western wheatgrass, slender wheatgrass, blue grama, prairie junegrass, and buffalo grass.

In western SD, shorter grasses largely replaced medium grass species, because of decreased rainfall.  Important grass species in western SD included blue grama, western wheatgrass, needleandthread, prairie junegrass, and little bluestem.

The flora (plant) and fauna (animal) life that occurs in the soil also affects soil formation.  Decayed plant roots from previous years' growth can provide channels for water and air to move through the soil profile.  Earthworms also create channels for water and air movement through soil.  Earthworms literally eat their way through soil and form burrows as they move through the soil.  These burrows also allow water and air to move through the profile.  Earthworms also enhance soil fertility and productivity by altering physical and chemical conditions in soils.  For example, mineral availability to plants is increased when soil is passed through an earthworm’s digestive tract.

Soil microorganisms also affect soil structure.  Microorganisms can break down decayed plant material and add organic compounds to the soil structure.  Other microorganisms can take elemental nitrogen (N) gas from the air and ‘fix’ or change the N into a form that can be used by plants.

3. Parent material: 

Parent material is the inorganic material from which the soil was derived.  In eastern SD, the parent material for most soils resulted from glacier activity that occurred during the Pleistocene Epoch (1.8 million to 11,000 years ago).    The Pleistocene Epoch witnessed a continued cooling, culminating in a series of ice ages.  Glaciers entered SD from the northeast or north and flowed south and west.  The western margin of glaciation was the Missouri River. Today, glacial deposits cover most of SD east of the Missouri River. West of the Missouri River, the soil parent material is primarily sedimentary rock.  Soil west of the Missouri River was derived primarily from sedimentary rock.

Eastern SD contains many productive soils that were derived from glacial deposits.  Glacial deposits are divided physically into main four groups:

1.     Till

2.    Outwash

3.    Glacial lake deposits

4.    Ice contact stratified drift

Till:  Glacial till deposits are a mixture of all sized particles, boulders to clay. Till is thought to have been deposited the flowing ice shield.

Outwash:   Glacial outwash consists mostly of gravel and sand.  Outwash was deposited by glacial melt water as it flowed away from the ice.

Glacial lake deposits:  When the ice front movement slowed to almost a standstill, there was no ready escape for water and ponding occurred.  Soil deposits formed in lake deposits are called lacustrine.  The lacustrine deposits that occurred from these lakes range from sand deposits near old shorelines to deposits of clay and silt materials from the deeper more still waters in the center of the lake.  The deposits in the Red River Valley along the North Dakota and Minnesota state borders were formed from material settling out of Glacial Lake Agassiz.  The deposits in most of Brown and part of Spink counties in SD were formed in sediments from Glacial Lake Dakota.  These deposits usually produce soils with high fertility and somewhat poor drainage.

Ice contact stratified drift:  Undifferentiated sediments deposited by glaciers is called drift.  Ice contact stratified drift was formed when a glacier was melting.  These deposits occur as knobs or small hills often in rough terrain.  These deposits are called kames which are short, steep sided hills and eskers which are serpentine-shaped ridges.

Soils may form from actions other than glaciers as well.  Factors that can carry and deposit soil from one place to another include the wind, waterways and gravity.  Loess is a deposit of wind blown silt. Sandy and clay materials may also be carried and deposited by the wind, eolian sand and eolian clay, respectively. They also are important SD soil parent materials.

Alluvium is a deposit that occurs when gravel, sand, silt, and/or clay, settle out of flowing water. Generally, alluvial deposits west of the Missouri River have a clayey texture while deposits east of the Missouri River are have a loam texture. Local alluvium is a water-laid deposit along upland swales and depressions. It is usually finer textured than surrounding soils.

Colluvium is a deposit of rock fragments and unconsolidated earth materials accumulated at the base of slopes as a result of gravity and runoff. The deposit is usually unsorted because gravity can move all sizes. The soils can have textures ranging from sands to extremely bouldery clay.

A variety of factors created the landscape that occurs in SD today.  Up-lifting and warping in the west created the Black Hills and wind and water erosion created the badlands and buttes.  Glacier movement formed coteaus (low hills or divides) and plains in the east.   The rocks and soils that make up these regions provide a wealth of resources upon which life in the state is based.

4. Topography and Time:

Topography refers to the lay-of-the-land. The land may be level, undulating, rolling, hilly, rough broken, or mountainous. It may be smooth with a network of small streams, or it may be choppy with many closed basins dotting the landscape. Topography determines what drainage a soil will have. Steep slopes have excessively drained, thin soils; flat or depressed topographic areas usually have poorly drained, thick soils.  The factor of time (the age of soil stability) can be illustrated by comparing a soil on a flood plain that receives annual deposits of alluvium with a soil on a stable upland ridge. The floodplain soil has few developed horizons, while the soil on the stable upland ridge has a well-developed soil profile with many horizons. For additional information on geology in South Dakota, this website may be helpful: http://www.sdgs.usd.edu/. 

Soils develop through a series of changes. The starting point is freshly accumulated parent material. Weathering processes release simple compounds that serve as food for bacteria, fungi, and other soil organisms. Dead soil organisms decay in the parent material causing organic matter (humus) to accumulate. Gradually, the developing soil is able to support higher forms of plant and animal life. The present level of humus in our soils is due principally to the activity of higher forms of plant life. Upper layers of the loose parent material at the Earth's surface accumulate humus from dead plant material. The soil pH becomes reduced and leaching takes place. Leaching is the removal of materials in solution from the soil by percolating waters. These changes form distinctive soil layers called horizons.

There are four types of processes involved in horizon development. A soil horizon is a layer of soil parallel to the soil surface that had distinct properties from the adjacent layers. Additions to the soil come from precipitation, organic matter, and solar energy. Losses are processes that often are destructive, such as erosion, leaching of nutrients, night radiation of energy, nitrogen losses by microbial activity, and water loss through plant transpiration. Movement of materials within the soil occurs through nutrient cycling by plants and soil mixing by organisms. Lastly, new compounds are formed within soil from weathered rocks and minerals and organic material.

Soils vary in the types and number of horizons present. Very young soils may have only one or two soil horizons present. The soils in SD are relatively young. Soil horizons are identified or described by standard symbols (i.e. 'A', 'B', 'k', 'w', 't', and many others). Each symbol shows how the material has been altered when compared to the original parent material. Most master soil horizons have only one capital letter (i.e. 'A', 'B', 'C', 'E', 'O', and 'R') but some require two (i.e. 'AB', 'EB', 'AC', 'BC', 'EB', and others) if the layer is mixed or composed of two major horizons or is a transitional layer. Two different soil profiles with the different horizons identified are shown in Figure 1. Figure 1. The soil type shown left is HOUDEK which is the State Soil of SD. Horizons present: 1. 'A' horizon (0 - 7 inches); 2. 'Bt' horizon (7 - 15 inches); 3. 'Bk' horizon (15 - 36 inches); 4. 'C' horizon(36+).

An 'O' horizon is a layer dominated by organic materials (i.e. leaves, needles, twigs, moss, and other un-decomposed or partially decomposed plant litter). 'O' horizons are common in forest derived and saturated, wetland soils. Organic matter content in 'O' horizons commonly exceeds 35 %.

An 'A' horizon is a mineral horizon that is high in humus (1-10 %) or shows the influence of cultivation, grazing, or similar agricultural disturbance. Usually, the 'A' horizon is called "topsoil". 'A' horizons are usually found at the soil surface but can be found below an 'O' horizon. An 'A' horizon that is cultivated is called an 'Ap' horizon.

A 'B' horizon is a mineral layer that forms beneath an 'A', 'E', or 'O' horizon.

'B' horizons are sometimes referred to as the "subsoil". It represents a layer where there has been either a significant gain of clay ('Bt'), humus ('Bb'), salts ('Bk', 'By', or 'Bz') or iron/aluminum oxides or change in soil color and structure ('Bw').

A 'C' horizon is a mineral horizon that is usually found beneath 'O', 'A', 'B', or 'E' horizons. 'C' horizons are soil layers that are little changed.

'Cr' horizons are composed of soft bedrock that can be dug with a spade (i.e. shale, siltstone, weathered sandstone).

The 'C' horizon is often called the "parent material".

The 'E' horizon is a mineral horizon where significant loss of clay, humus and/or iron/aluminum oxides has resulted in a lighter colored and coarser textured layer than the layers above or below. 'E' horizons occur above 'B' horizons and are found at or near the soil surface. 'E' horizons are most commonly found in forest derived, sodium affected, or depression soils.

The 'R' horizon is hard bedrock that cannot be dug with a spade. Examples of hard bedrock present in SD include granite, limestone, and sandstone. This horizon does not exhibit evidence of soil genesis or weathering. Lower case letters (e.g. b, g, t, w, and many others) are used to further define the properties of the layer. If a layer needs to be subdivided, then numbers are used. Discussion of further soil naming can be found in the soil survey manual: USDA - Soil Survey Division Staff, 1993.

Soil horizons are identified by collecting and analyzing soil cores from different areas in fields. The soil cores that are collected are usually deeper than what can be collected with a hand probe. Therefore a soil probe mounted on a tractor or truck is usually used to collect the sample (Figure 2). The soil properties (for example, color, reaction to weak acid, etc) in the core are analyzed to determine the depths of the different horizons (Figure 3).

Protecting soil quality is critical to the welfare of our people and our economy. There are four major concerns in soil conservation: loss of moisture; loss of organic matter and nitrogen; loss of mineral nutrients; and loss of topsoil through erosion.

Moisture loss occurs through evaporation, transpiration, leaching, and runoff. Evaporation and runoff are particularly serious when water does not quickly soak into the soil. Water will move more quickly through sandy soils as compared to clay soil. Additions of organic matter to the soil assist with water uptake and storage.  Other solutions include leaving stubble in the fields through minimum till or no-till practices.  Moisture loss through weed transpiration can also be significant. Weed reduction can be accomplished through applying herbicides, cultivation and crop rotations.

Organic matter and nitrogen loss from soils can seriously reduce crop yields and make soils more susceptible to erosion. South Dakota soils have lost about 30 to 50% of their original organic matter and organic nitrogen as a result many years of tillage.  Nitrogen can be returned to the soil through application of natural waste products, commercial organic and inorganic fertilizers, or through the planting of nitrogen-fixing plants, such as alfalfa or clover.  No-till or minimum tillage methods allow for organic matter to build up more quickly as compared to conventional till methods like moldboard or chisel plow.

Mineral nutrient losses due to erosion varies from one nutrient to another. Nutrients such as potassium, calcium, and magnesium are usually present in adequate amounts in South Dakota soils. Phosphorus content, however, is low in most soils of the state, and is highest in topsoil, which is lost in erosion. Phosphorus can be returned to the soil by adding waste products and commercial fertilizers.

Soil loss from erosion can be caused by the action of wind and/or water. Soil texture, soil structure, slope of the land, and the amount of plant cover affect the amount of soil erosion that can occur.  Soil blowing can be reduced through conservation tillage that keeps a growing crop or plant residues on the land throughout the year. No-till or minimum till are a conservation tillage strategies where the soil is disturbed only in the immediate area of the planted seed row.  Another method to reduce wind erosion is to plant shelterbelts.  Retaining soil also increases the water and nutrient storage and increase microbial activity. Water erosion from runoff can be reduced through residue management, terracing, contour tillage and contour strip cropping, all of which lessen the impact of land slope.  Further information about the USDA Soil Survey can be obtained at: http://www.statlab.iastate.edu/soils/index.html/.

Soil forming processes interact to produce soils in different environments with unique characteristics and management requirements. Large areas of variation in the physical relief or topography are called physiographic regions. Such large areas are described by terms such as hills, plateaus, or plains. Often these large areas are subdivided into smaller areas.

South Dakota is divided into 3 major physiographic regions: The Central Lowlands of eastern South Dakota; the Great Plains of central and western South Dakota; and the Black Hills. These 3 regions are subdivided into a total of 12 distinguishable areas called physical divisions. These are listed below:

1. The Minnesota River-Red River Lowlands (Division 1, Fig. 2) is a broad, gently undulating, valley-like area. Elevations range from 900 to 1,100 feet.

2. The Coteau des Prairies (Division 2) is a highland area between the Minnesota-Red River Lowland and the James River Lowland to the west. Elevations range from 1,600 to 2,000 feet.

3. The James River Lowland (Division 3) is a gently undulating plain lying considerably lower than the Coteau des Prairies on the east and the Coteau du Missouri on the west. Elevations range from 1,300 to 1,400 feet.

4.The Lake Dakota Plain (Division 4) is the nearly level surface formed by deposition of sediment when Glacial Lake Dakota was filled with water. The area is sandy at the northern end with silty clay loam and silty clay textures elsewhere. Elevation is about 1,310 feet.

5. The James River Highlands (Division 5) consist of a group three ridges located at the southern end of the James River Lowland. These highlands are glacial drift deposits over bedrock. These ridges are up to 300 feet higher than the surrounding country.

6. The Coteau du Missouri (Division 6) is part of the Missouri Plateau of the Great Plains Province, separated from the main body of the Missouri Plateau by the Missouri River. Elevations is about 1400 to 1800 feet.

7. The Missouri River Trench (Division 7) averages a little over a mile in width. Rapid erosion apparently was in progress before the advent of agriculture. Cultivation in the tributary regions has added significantly to the sediment load in the river. The dams have slowed the flow of the river and siltation is now a problem. Elevations range from 1200 to 1600 feet.

8. The Northern Plateaus (Division 8) is a series of plateaus and isolated buttes. Elevations are 2000 to 3000 feet.

9. The Pierre Hills (Division 9) consist of a series of smooth hills and ridges with rounded tops. Elevations are 1,800 to 2,800 feet.

10. The Black Hills (Division 10) is a mountainous area. Elevations range from 3,200 to 7200 feet above sea level.

11. The Southern Plateaus (Division 11) are divided into two regions. The large area in the southwestern part of the state consists of a series of benches and buttes. The Badlands comprise the northern part of the southwestern region. Elevations are 2,800 to 3,600 feet. The second region of the Southern Plateaus is located in southeast SD primarily in Lincoln and Union Counties. This area is a stream dissected highland underlain by a thick mantle of loess. Elevations range from 1,200 to 1,500 feet.

12. The Sand Hills (Division 12) is an example of the Sand Hills region of Nebraska. It consists of a series of rounded hills interspersed with low, swampy areas. Elevations range from 3,000 to 3,600 feet.

Soils have many different physical characteristics and properties.  These characteristics are used to distinguish between different soil types.  Some soil characteristics are listed below:

1.Aeration:  Aeration is the exchange of air in the soil with air from the atmosphere.  Well-drained (aerated) soils contain air that is similar in composition to that in the atmosphere.  Air in poorly-drained (poor aerated) soils tends to have high carbon dioxide and low oxygen levels.  Soils that have large spaces between the soil particles like sand tend to be well aerated whereas soils that have small spaces between the soil particles like clay tend to be less well aerated.

2.  Organic Matter and Nitrogen:  Native grassland vegetation, which was greatly influenced by climate, has influenced soil organic matter content and distribution.  In general, eastern SD is more humid and this climate supported a tall grass prairie ecosystem.  This tall grass prairie left large amounts of organic matter (humus) in the soils.  Moving westward, the grass type changed to mid- and finally to short grasses in response to the drier climate.  This change is reflected in the lower contents of soil organic matter in these regions. Temperature has also influenced soil organic matter content.  In the cooler northern regions, more soil organic matter and total nitrogen (N) are present when compared to southern regions under comparable precipitation.  This is due to slower biological activity under cooler temperatures. Organic matter and total N content of most cultivated soils in SD today are substantially lower than when original prairie sod was first tilled. These losses are generally about one-third to one-half of the original total and apply equally over the state. Therefore, present contents of organic matter and total N in cultivated soils reflect the original amounts but are one-third to one-half less.

3.  Nitrogen Release:  Research in SD has shown that nitrogen release from the soil to plants is a function of temperature rather than precipitation.  Thus, southern and western soils release nitrogen faster than northern and eastern soils.

4.  Permeability:  Soils differ in their ability to transmit fluids (permeability).  Factors such as texture, structure, and amount of organic matter influence a soil's permeability.  For example, water flows quickly through sandy soils while soils with high clay content will barely let water pass through.

5.  pH Level:  The pH scale is a numerical measure of acidity or alkalinity ranging from 0 (very acid) to 14 (very alkaline).  A soil pH of 7 is considered neutral while one at pH 4.5 or lower would be very strongly acid.  Soils with a pH of 9.1 or higher are very strongly alkaline.

6.  Salinity: Soils differ in amount of dissolved salts present.  Some soils have dissolved salt content so high that plant growth is impaired.  These soils are referred to as a saline.

7.  Sodium Content: Some salt-affected soils have sodium levels that are so high that the soil's physical and chemical properties are changed.  The soil's ability to support plant growth is also adversely affected. These soils are called sodic.

8.  Soil Colors: Soil color correlates well with total amounts of organic matter, organic nitrogen and drainage present. Differences are apparent in when surface soil color is compared across various regions.  Soil colors can be determined scientifically by comparing the soil color with specially prepared color charts. The darkest soils are found in northeast SD where the climate is cool and moist or where soils are poorly drained.  These dark soils have the highest organic matter and total organic nitrogen supplies in the state.  In contrast, soils from warm and dry southwestern SD have the lightest color and have less organic matter and total organic N.

9.  Soil Texture and Particle Size:  Soils also differ in texture.  Texture is determined by the relative amounts of sand, silt, and clay in the soil.  Soils with high clay contents have very fine particles, can have a powdery consistence when dry, and become very sticky or slippery when wet.  A soil composed of high silt content feels smooth and silky, like wet talcum powder or flour. Sandy soils have large, granular particles, a gritty texture, and are not slippery when wet. A loam soil is a mixture of sand, silt and clay that exhibits the properties of those separates in about equal proportions (Brady and Weil, 1999).  A loam soil has a medium texture, the highest plant-available water holding capacity, and is usually quite productive. Loam soils often contain a good amount of organic matter.

10.  Soil Layers: Anyone who has looked closely at a recently dug hole or at a roadside cut has noticed that soils contain layers that differ in their appearance. These layers, or horizons, occur in a vertical sequence through the soil. The type and depth of these horizons create the soil profile. Soils vary in the types and number of horizons present.

11.  Productivity: Not all soils are equally well-suited for plant growth. A soil's ability to sustain plants is referred to as its productivity level.  Soil productivity depends on many factors including soil texture, soil pH, amount of organic matter and nitrogen, aeration and permeability as well as other factors not discussed in the scope of this article.

QUESTIONS

Download and print questions here

1. What is soil?

2. How many types of soil can be found in South Dakota?

3. List the factors influencing soil productivity.

4. What is the annual precipitation in South Dakota?

5. What is the annual average wind velocity in South Dakota?

6. What are the "active factors" of soil formation?

7. Explain how worms and other biological organisms help the soil.

8. Briefly describe the different types of soil deposits

9. Why is topography important?

10. Go to http://www.sdgs.usd.edu, briefly describe a current project or collaborative study currently in progress by the Department of Environmental and Natural Resources.

11. Explain the process for how soil is formed.

12. Discuss the additions, losses, movement, and new compounds that impact soil horizons.

13. What is the state soil of South Dakota?

14. Compare and Contrast the O, 'A', A'B', A'C', 'E', and 'R' horizons.

15. List and describe the factors in soil conservation.

16. How many soil regions exist in South Dakota? Which region is similar to where you live? What are its characteristics?

17. Summarize how soils differ.

18. Go to the USGS website for state information. Click on your home state. What kind of information is available here? How can it be useful?

19. Why is it important to know what kind of soil exists in a field?

20. How can soil information help interpret the information from a GIS map?

MAP SECTION

1. Go to the tutorial 8 map section.

2. The map will come up with a red box like this showing in the upper left corner

3. To remove the red box, use your mouse cursor and click on it. The following map should appear.

4. Zoom in on the green marked areas in the lower right.

5. Use the tool to select parts of the green colored field.

QUESTIONS

1. What color in the legend represents the highest yields?

2. What color in the legend represents the lowest yields?

3. Switch from the yield map to the SID map. What two distinct features are in the SID map of the field?

4. Now look at the IKONOS map. What areas of the field appear to be discolored?

5. Now switch to the yield map, what is the yield in the areas of discoloration in the IKONOS map?

6. The IKONOS and SID maps show an area of erosion or drainage going down the middle of the field and out the west side of the field. How does the yields along this area compare to the yields of the rest of the field?

7. Using figure 4. above, what region is Brookings county in and what are the soil characteristics of this region?

8. To the nearest degree, what is the longitude of the field?

9. To the nearest degree, what is the latitude of the field?

10. What advantages does the IKONOS map have over the SID map and yield map?

EMAIL Questions (Message board not yet available)

1. Find out what the soil characteristics are of a farmers land. (i.e. soil type, depth, deposits, and any other information.)

2. Find out what town they are from, locate it on a map, and determine which of the 12 regions they are located in.

3. Come up with a third question as a small group or class.