Soil Science

This is a

1. Soils
Ag Science

2. Soil
I.Soil is a layer on the earth’s crust that
provides a combination of resources.
Allow for the growth of plants and
animals.
A.Oxygen – needed for adequate root growth
B.Temperature – soil absorbs heat from the
sun. Used for plant growth and seed
germination

3. C. Water – used for plant growth
D. Carbon – utilized in the form of organic matter
E. Nutrients – provided as minerals. Broken
down as nitrogen and recycled through
decaying material.

4. II. Soil is composed of 4
different components.
A.Solid Portion (50%)
1.Mineral Matter – 45% of the soil. Partially
decomposed rock, ie. sand, silt, clay
2.Organic Matter - ~5% of the soil. Partially
decomposed plant & animal material. Gives
soil its color

5. B. Pore spaces (50% of the soil)
1. Air – accounts for 25% of the soil. When
soils are wet, less air. When soils are dry,
more air.
2. Water – accounts for 25% of the soil.
When it rains, water either enters the soil or
runs off.

6. Water cont.
Infiltration – process of water soaking into
the soil.
Once water is in the soil, the movement
downward is called percolation.
A soil that allows for both is called
permeable

7. •Water in the soil my be one of three types
–Gravitational water – water that drains
through the pore spaces (leaching occurs)
–Capillary water – water that is held between
particles of soil against forces of gravity; may
move upward or sideways
–Hygroscopic water – water that forms a thin
film around individual soil particles; unavailable
to plants.

8. III. Abundant life can be found in
soil.
A.Forms of life in the soil include:
1.Earthworms
2.Insects
3.Bacteria
4.Fungi
5.Other organisms
B.Bacteria & fungi have an important role in
the soil. They breakdown o.m. and
release nutrients

9. C. Earworms, ants, crawfish, moles, and
other organisms improve the tilth, or ease
at which soil can be worked.
These organisms create openings in the
soil as they tunnel. This helps drainage and
improves gas exchange.

10. IV. Plants depend on soil to
provide 4 basic needs.
A. Anchorage – soil acts to provide a firm
support as roots grow throughout the soil.
B. Water – soil provides nearly all of the
water used by plants. Water is absorbed
through the plants’ roots.
C. Oxygen – nearly all organisms need
oxygen. Roots don’t have ample supplies,
so they need good soil aeration to allow
gas exchange.

11. D. Nutrients – of the 16 nutrients considered
to be essential for plant growth, 13 are
obtained from the soil. Root hairs absorb
the nutrients dissolved in soil water.

12. V. Ag depends on soil to grow
food, fiber, and other plants.
A.Cropland – land on which soil is worked
B.Grazing land – land used for grazing
cattle and sheep; perennial forage.
C.Forests – land used for growing trees,
which is later harvested
D.Water structures – ponds and other
reservoirs are constructed out of soil.

13. Non-ag uses of soil
A.Recreation – playgrounds, sports fields,
jogging paths, golf courses, parks, camp
grounds,etc.
B.Foundations – buildings depend on a
solid soil base upon which a building is to
be built and remain sound.
C.Waste disposal – used for the treatment
of human sanitary wastes.
D.Building materials – build underground,
into hillsides, adobe

14. Five factors that affect soil
formation
A. Parent Material – type of rock that soil is
made from.
Igneous
sedimentarymetamorphic

15. B. Climate – temperature & moisture
C. Living organisms – organisms (bugs &
worms) and plants in the soil.
D. Topography – hills and valleys
E. Time or weathering – age of the soil and
climate

16. THE MAIN KINDS OF SOIL
PARENT MATERIALS
Parent material is formed
by the disintegration and
decomposition of rock

17. A. Most soils in Illinois were formed by
glaciers.

18. Newer and more
productive
Older and less
productive

19. B. About 64% of the soil is formed from
loess. Loess occurred from the
blowing of the soil after the
glaciers.

20. C. About 7% of the state soil is due to recent
stream deposits. This is referred to as
alluvium.
D. Bedrock – most of the shale, sandstone,
or limestone bedrock in Illinois is buried by
loess. Except in extreme NW and Southern
Illinois.

21. •Organic soils – less than 1% of the soils in
Illinois are classified as organic. Occur
where formerly shallow ponds or supported
swamp vegetation. Wet conditions slow
decay of organic materials.
–Two types: muck and peat

22. Topography is the slope characteristics of
land.

23. How do living organisms affect
the soil?
Organisms living in the soil, like plants,
insects and microbes actively affect soil
formation.

24. •Native Vegetation has
the greatest affect on
the development of
soil – plants that once
grew in it.
•Two primary types
–Tall grass prairie
–Deciduous hard wood
forest

25. A.Prairie soils have a dark and deep
surface layer. The roots of the prairie
grass filled the top of the soil.

26. B. Timber soils tend to have a thin,
moderately dark layer. Due to organic
matter accumulating on the surface and
decaying quickly.

27. Weathering
1.Physical weathering
1.The affects of climatic factors such as
temperature, water, and wind. Freezing and
thawing are a major contributor.

28. Weathing (cont.)
2. Chemical weathering
a. changes the chemical makeup of rock
and breaks it down. Rainwater can dissolve
minerals.
b. Some minerals react with oxygen.
Oxidation further decomposes rock.

29. Weathering (cont.)
B. Weathering causes soil to:
1. Develop
2. Mature
3. Age

30. Climate
Refers to rainfall, freezing, thawing, wind,
and sunlight.

31. Climate (cont)
B. The climate in Illinois is said to be of the
continental type.
Hot Summers, Cold Winter

32. Climate (cont.)
C. Rainfall and Wind wear the rock away a
little at a time.

33. Physical Features of soil
Soils have many features that are used to
recognize the difference between them.
They include:
A. Texture – coarseness of fineness of soil
particles
B. Structure – the way in which soil
particles are held together
C. Depth of horizons – depth of each soil
D. Color – darkness or lightness of soil
color

34. Colors
A.Very Dark - ~5% O.M.
B.Dark - ~ 3.5% O.M.
C.Moderately Dark - ~ 2.5% O.M.
D.Light - ~2% O.M.
E.Very Light - ~1.5% O.M.

35. Soil Texture
A.Soil Texture is the fineness or coarseness
of a soil.
1.Sand – largest particle
2.Silt – medium sized particle
3.Clay – small particle
Sand
Silt
Clay

37. Texture (cont.)
B. Texture is important because it affects:
1. Water holding capacity – the ability of a soil
to retain water for use.
2. Permeability – ease with which air & water
my pass through the soil.
3. Soil Workability – the ease with which soil
may be tilled and amount of time after rain.
4. Ability for plants to grow, ie carrots

38. Texture (cont.)
A.Soil texture may be determined in 2 ways
1. Using a textural triangle. This is found be
using the percentage of each type of soil
particle.

39. Textural Triangle

40. Ribbon Method
a.Fine textured
b.Moderately fine textured
c.Medium textured
d.Moderately coarse
e.Coarse

41. Ribbon testing
Ball of clay made in fist Starting to form a ribbon Clay Ribbon (>2")
Starting to make a ribbon from sand
Ribbons are hard to form with sand (<1")

42. Soil Structures
A.Granular
B.Crumb
C.Platy
D.Prismatic or Columnar
E.Blocky
F.Structureless
1.Single grain
2.Massive

43. Soil Structure

44. Soil Structure

45. Soil Structure

46. Soil Structure

47. Soil Structure

48. Soil Structure

49. Soil Structure

51. Soil Profile
I.A soil profile is a vertical cross section of
soil.
A.Each layer may be different
B.A soil profile is usually studied to a depth of
3 to 5 feet.

52. Soil Profile

53. Changes in soil
II. Soils change over time in response to their
environment.
A. The causes can be classified as:
1. Additions
2. Losses
3. Translocation
4. Transformation

54. Soil Degradation
I.Soil Degradation is lowering the quality
of soil or loss of productivity. Occurs
because people don’t understand the
soil and consequences of its uses.
Results from:
A.Construction
B.Contamination
C.Erosion

55. Construction
A.Construction is altering land by building:
1.Roads
2.Houses
3.Offices
4.Factories
5.Other Structures

57. Contamination
A.Results when chemicals, oil, and other
substances leak into the land.

58. D. Soil may be contaminated by Ag
practices:
1. Too much fertilizer
2. Excess chemicals
3. Irrigation water contains salt

59. Soil Erosion
IV. Soil erosion is the process by which soil is
moved.
A. Natural causes (natural erosion)
1. Round off mountains, fills in valleys
Ex. Mississippi Delta
B. Human actions
1. Human activity, such as construction
& plowing may cause accelerated erosion
a. removes topsoil at an excessive rate

60. Natural Erosion

61. Human actions accelerating

62. Soil Erosion

63. V. Other Sources
A.Improper irrigation practices
1.Salinization – accumulation of salts
2.Alkalinzation – accumulation of sodium
3.Waterlogging – supersaturation
B.Not replacing plant nutrients
C.Pollution
D.Overgrazing, deforestation, desertification
E.Compaction

65. Summary
Soil can be very fragile
Care must be taken to produce crops
Takes many, many years, to make new soil
through weathering (1” > 1000 years)