1. Characterizing Soil
Ag 1 Unit 1: Soil Science

2. Objectives Outline the processes involved in soil formation
Describe a mature soil profile
Discuss the eight land capability classes
Define soil series and explain how those differ from land capability classes

3. What Is Soil? Defining soil is not as simple as it seems.
How do you define soil?
We will consider soil to be the layer of organic material on earth’s surface containing both organic and inorganic matter that is capable of supporting plant life.

4. What Is Soil?
Supports our buildings, catches and stores our water and provides us with food, fiber and forest products.
So durable it can last as long as our species survives.
So fragile it can be destroyed over night
Complex. Once destroyed it can’t be replaced.

5. Soil Components Inorganic material- 45- 48% Organic matter- 2-5%
Water- 25%
Air-25%

6. Ideal Soil
½ air, ½ water
½ organic, ½ inorganic

7. Soil Formation
Slow
Results from natural forces acting on the mineral and rock portions of the earth’s surface

8. Parent Material Materials that soil is formed from
Five general categories
Minerals and rocks
Glacial deposits
Loess deposits
Alluvial and marine deposits
Organic deposits

9. Minerals Solid Inorganic Chemically uniform
Common minerals that soils form from:
Feldspars, micas, silica, iron oxides, calcium carbonates
Mica

10. Rocks Not chemically uniform Made up of minerals
Classified into three groups
Igneous
Sedimentary
Almost ¾ of the earths surface
Metamorphic

11. Glacial Deposits
During the Ice Ages, glaciers moved taking surface material with them.
Much of Midwestern US is covered by glacial deposits

12. Loess Deposits Generally thought of as wind blown silt
Much of the soil in the eastern Mississippi Valley are loess soils

13. South Dakota- 1934

14. Alluvial & Marine Deposits
Alluvial deposits-left by fresh water
Occur when water fans out after traveling down hill and then slowing down on more level areas
Often in the form of floodplains and deltas
Marine deposits- formed on an ancient ocean floors

15. Organic Deposits
Occur in marshy or swampy areas where plant life is lush
When plants die they fall in the water and decay slowly
Eventually builds up and forms muck or peat soil

16. Peat & Muck Soils
Peat soils are made up of recognizable plant materials
Muck soils are more completely decayed so that plant parts are no longer recognizable
In the case of lakes the deposits may become thick

17. Weathering Major types Temperature change Water action Plant roots
Ice expansion
Mechanical grinding

18. Soil Organic Matter Two basic
Original tissue: that portion of the organic matter that remains recognizable
Humus: organic matter that is decomposed to the point that it is not longer recognizable

19. Soil Organic Matter Functions
Acts as a cementing agent for soil particles
Returns plant nutrients to the soil, most notably phosphorous, sulfur and nitrogen
Helps store soil moisture
Makes soil more tillable
Provides food for soil microorganisms, which make the soil capable of plant production

20. Soil Profile

21. Soil Profile Horizons- visibly distinct layers in the soil
A Horizon: Top and surface soil
B Horizon: Subsoil
C Horizon: parent material

22. Soil Profile

23. C Horizon
Except for peat and muck soils consists of weathered rock and minerals
Looks like the rock it came from
May be soft enough to dig in or to crumble.
Very few plant roots

24. B Horizon More thoroughly weathered Often a different color
Contains little organic matter
May be much finer and harder
packed
Plant roots begin to appear

25. A Horizon Surface High organic matter content
May be grayish, brownish or blackish in color as a result of humus content
Most productive
Most plant nutrients are available here

26. Physical Properties

27. Slope
Single most important factor in determining the productive potential of the soil
Affects productive potential in many ways
Runoff rates
Relates to the danger of soil erosion
Affects the use of farm machinery
Size and shapes of fields

28. Texture The proportions of sand, silt and clay
Course soils have more sand
Fine soils have more clay.

29. Soil Drainage How well water flows through the soil naturally
Well drained soils-excess water moves out quickly
Poorly drained soils- hold excess water

30. Flood Hazard How likely a field will receive flood damage
Frequent flood plains do not have good productive potential
Example: James River Bottom

31. Erosion Refers to the degree that the soil has already been damaged.
May range from none to severe

32. Top Soil & Subsoil Thickness
Refers to the depth of each layer that is available for plant root growth.
Very thin top and subsoil’s limit crop production

33. Land Capability Classes

34. Land Capability Classes
Categorize the productive potential of the soil
System begins with class 1 (most useful) to class 8 (least useful)

35. Class 1 Very good, productive land Nearly level Well drained
Medium textured
Not subject to erosion or flooding
Easily cultivated
Very little land is class 1; even in the most productive farming areas!

36. Class 2 Good for all types of farming Has some limitations
Gentle slope
Suffers from the effects of past erosion
Less than ideal soil depth
May also have drainage problems that can be corrected with the use of drainage systems
Requires careful soil management to prevent erosion damage

37. Class 3 Moderately good land
May be cultivated and farmed regularly but it has some important limitations
Moderate slope; making it high susceptible to erosion damage
May already have severe erosion damage
Drainage problems
Shallow rooting zone
Some shallow wetlands are Class 3 if they can be improved with drainage systems
Should be farmed with care to prevent erosion damage

38. Class 4 Severe limitations
Can be cultivated with careful soil management practices
May have strong slope and be subject to severe erosion
May be very shallow
May be very dry or very wet
If wet even drainage systems may still allow occasional water logging

39. Class 5
Nearly level
Little erosion hazard but may be in a frequent floodplain
May be very wet, very dry or very rocky
Swampy areas are generally class 5
Quite suitable for pasture, wildlife habitat or forest production

40. Class 6 Serious limitations
May have very rocky or very shallow unusable surface soil.
Can be used for tree production, permanent pasture or wildlife habitat

41. Class 7 Severely limiting properties May be very steep
May be severely eroded with deep gullies
Very strong slope with course soils may cause land to be rated at a class 7
May be impractical for establishing pasture but native grasses may be utilized with controlled grazing
Land may be used for forest production, wildlife and recreation

42. Class 8 Has one or more extreme limitations Examples of Class 8 land
Sand dunes
River washes
Stream beds
Lake bottoms
Other nearly barren
areas

43. Soil Classification NRCS and USDA use a soil taxonomy
They are broken down into:
Order
Suborder
Great Group
Subgroup
Family
Series

44. South Dakota’s State Soil

45. Houdek Deep, well drained, loamy soil,
Represents many soils formed in South Dakota under the influence of prairie grass
The dark color of the surface layer is a result of decayed
plants and other materials that have been deposited over
thousands of years.
Of major economic importance to SD because it is used as crop or rangeland.

46. South Dakotas State Soil
Designated as the State Soil in 1990
Has been mapped on about 600,000 acres.
Total Land Area of SD is 75,885 sq mi. or 48,566,400 acres
Average annual precipitation is 22 inches,
Average annual air temperature is about 48 F.

47. South Dakota’s State Soil

48. Houdek Soil Profile Houdek Soil Profile
Surface layer: dark grayish brown loam
Subsoil - upper: dark grayish brown clay loam
Subsoil - middle: grayish brown clay loam
Subsoil - lower: light olive brown clay loam
Substratum: light yellowish brown clay loam