1. Chapter 14 Soil Resources

2. CHAPTER TOPICS Rock cycle Soil formation Soil composition
Physical and chemical properties of soil
Main soil types
Erosion and other soil problems
Soil conservation

3. Rock groups: igneous, sedimentary, metamorphic
Igneous – from melted rock that has cooled/solidified (Ex. granite)
Rarely has fossils, crystals
Sedimentary – formed on surface (land/water) from layered sediment broken from rock (Ex. limestone, shale)
Most rock, fossils, visible layers
Metamorphic – other rock that changes due to heat/pressure (ex. slate and marble)
Rarely has fossils, may have layered crystals

4. THE ROCK CYCLE !

5. EXAMPLES OF METAMORPHIC ROCK

6. Soil Holds nutrients and water
IT TAKES A YEAR TO MAKE 1 mm TOPSOIL
Holds nutrients and water
Cleanses and filters water as it flows through soil
Affects the amount of water that returns to atmosphere
Named for physical and chemical properties
EX: texture, pH

7. Soil Formation
Formed from weathering, takes TIME (rocks broken into smaller and smaller bits)
Physical weathering – alternate freezing and thawing, wind/water erosion, ocean waves
Chemical weathering – carbonic acid in soil (from CO2 and H2O)
Biological weathering – lichen produce acid
several factors influence the soil formed:
Parent material – rock/mineral it came from
Living organisms – decompose litter and recycle nutrients (Ex. Rhizobium, fungi, insects, worms, snails)

8. PERCENTS ARE FOR A TYPICAL/HEALTHY SOIL
Soil Composition
1. Mineral Particles (45%)
Weathered rock
Provides essential nutrients for plants
2. Organic Material (5%)
Litter, animal dung, dead remains of plants and animals
Increase water-holding capacity
Humus – decomposed org. matter, binds nutrients/water
3. Water (25%)
4. Air (25%)
PERCENTS ARE FOR A TYPICAL/HEALTHY SOIL

10. Soil Composition Pore space air- good for aeration (O2, CO2, N2)
water- provides water to roots

11. Soil Horizons O-horizon A-horizon E B-horizon C-horizon
Rich in plant litter/organic matter
A-horizon
Topsoil (organic matter and humus), plant growth, leached E
B-horizon
Lighter colored subsoil, illuviation, high inorganic
C-horizon
Somewhat weathered parent material, groundwater, no organic
Bedrock - unweathered

12. Soil Organisms
There are millions of microorganisms in 1 tsp of fertile agricultural soil

13. Soil Organisms Soil organisms provide ecosystem services Examples
Decaying and cycling organic material
Breaking down toxic materials
Cleansing water
Soil aeration (especially done by earthworms)

14. Nutrient Cycling
Nutrients are cycled between plants, organisms and soil
Example
Bacteria and fungi decompose plant and animal wastes
They are transformed into CO2, soil nutrients and water

15. Soil Properties - physical
Soil Texture
Relative proportion of sand, silt and clay
Sand: 2mm-0.05mm (large)
Silt: 0.05mm-0.002mm (medium)
Clay: less than 0.002mm (small)

17. Soil Properties - physical
Soil texture affects soil properties
Coarse textured soil (sandy)
Will not hold water well- flows through easily
Fine textured soil (high in clay)
Due to negatively charged surface, able to hold onto important plant nutrients (K+, Ca2+)
Poor drainage
Low oxygen levels in soil

19. Soil Properties - physical

20. Soil Properties - physical
Loam
Combo all textures – 20% clay, 40% sand and silt
Ideal for agriculture
Sand holds air/water
Clay holds nutrients

21. Soil Properties - chemical
Nutrients: Nitrogen, potassium (potash), phosphorus
Soil Acidity
Measured using pH scale
0-7 = acidic ; 7 = neutral ; 7-14 = basic
pH of most soils range from 4-8
Affects solubility of certain plant nutrients
Affects leaching of nutrient minerals
Ex: acidic soil doesn’t bind positive ions as well
Optimum soil pH is 6-7
plant nutrients are most available to plants
Soil amendments (ex: lime) can be used to achieve this pH

22. Re-group Physical and chemical properties of soil
Soil vocab: clay, silt, sand, loam, humus, topsoil

23. Soil examples coniferous forests O-horizon composed of needles
Not good farmland- too acidic

24. Soil examples Temperate Deciduous Forests
Precipitation high enough to leach most organics and nutrients out of O-, A- and B-horizons
Soil fertility maintained by leaf litter

25. Soil examples temperate, semi-arid grassland Very fertile soil
Soluble nutrients stay in A-horizon due to low leaching

26. Soil examples arid regions
Low precipitation = no leaching, no vegetation = not much org. matter

27. Soil examples tropical and subtropical areas with high precipitation
Very little organic material accumulation due to fast decay rate
B-horizon is highly leached, acidic, and nutrient poor
Nutrient minerals in plants, not soil

28. Soil Problems Soil Erosion Why a problem?
Def: wearing away of soil from the land
Caused primarily by water and wind
Why a problem?
less soil  grow less plants
Decrease amount of nutrients  need more fertilizers
Sediment into surface water that decreases quality of fish habitat

29. Soil Problems Erosion causes:
natural, but anthropogenic activities make it worse:
Poor agricultural practices
Removing natural plant communities when building roads (plant cover holds soil)
overgrazing

30. Case in Point: American Dust Bowl
Great Plains have low precipitation and subject to drought
severe drought
No natural vegetation roots to hold soil in place
Replaced by annual crops
Winds blew soil as far east as NYC and DC.
Farmers went bankrupt

32. Soil Problems
Nutrient Mineral Depletion

33. Soil Problems Soil Salinization Often in arid and semi-arid areas
Def: gradual accumulation of salt in the soil
Often in arid and semi-arid areas
The little precipitation that falls is quickly evaporated
Leaves behind salts
most plants die
Soil remediation
Dilution, bioremediation/phytoremediation

34. Soil Problems Desertification Typically a human-induced condition
Def: degradation of once-fertile land into nonproductive desert
Typically a human-induced condition
Ex: African Sahel; possible solution: Agroforestry to plant crops and Acacia trees (nitrogen-fixing + decomposing leaves)

35. Soil Conservation Conservation Tillage Crop Rotation (polyculture)
Residues from previous year’s crops are left in place to prevent soil erosion
Includes no tillage
Con: weeds
Crop Rotation (polyculture)
Planting a series of different crops in the same field over a period of years
Lessens pest and insect disease
Replenish nitrogen
Ex: corn  soybeans  oats  alfalfa (soy and alfalfa = legumes)

36. Contour Plowing Strip Cropping Terracing
Soil Conservation – farming on SLOPES – need to slow water run-off to prevent erosion.
Strip Cropping
Contour Plowing
Plowing around hill instead of up-down
Rows catch water
Strip Cropping
Alternating strips of different crops on steep slopes ; prevents erosion by naturally damming water
Terracing
Creating terraces on steep slopes to prevent erosion
Terracing

37. Preserving Soil Fertility
Organic fertilizers
Animal manure, crop residue, worm castings, and compost (individual and municipal)
Nutrients available only as material decomposes
Slow acting and long lasting
Could contain disease-causing pathogens if not properly composted.
Inorganic fertilizers
Made from chemical compounds
Soluble
Fast acting, short lasting
Bad for environment
leach and pollute groundwater and surface run-off
Produced using lots of fossil fuels

39. SOIL SUSTAINABILITY
Use soil without depleting fertility and amount so it’s productive enough for future generations

40. Soil Conservation Policies in US
Food Security Act (Farm Bill) 1985
Required farmers with highly erodible soil to incorporate erosion-control practices or are at risk of losing subsidies

41. What physical test could you do to soil?
What chemical test could you perform on soil?
What are the layers of soil horizons, but top down?
What is the ideal pH for most plants?

42. Having a pH lower than 7 makes a substance a ____.
What is loam?
Why does clay bind readily to some ions?
What inorganic soil particle is the largest?
What inorganic soil particle is the smallest?

43. What happens to the quantity of organic material as you move down the horizons?
Which soil horizon is the illuviation zone?
Which soil horizon is where the topsoil is located?
What does leaching mean?

44. Does rain affect leaching?
Other than organic matter and inorganic particles, what else constitutes soil?
What does anthropogenic mean?
What does sustainable mean?

45. In typical soil, is there more organic matter or inorganic particles?
Why is air space important for soil?
What is humus?
What part of soil increases its water holding capacity?
Where do the inorganic particles of soil come from?

46. Name the 3 types of rock
Which rock is from cooled lava?
Which rock forms from layer upon layer of other rock particles and dead organisms?
What rock forms when either of the other 2 are exposed to high heat and pressure enough to change them?

47. Granite is an example of what type of rock?
Marble is an example of what type of rock?
Limestone and sandstone are examples of what type of rock?
Why is soil important?
What are the 3 types of weathering processes?
What role do earthworms play in forming soil?

48. How does carbonic acid form?
What does it do to rock?
Give an example of physical weathering.
Give an example of biological weathering.
Where is bedrock located?

49. What are the consequences of erosion?
What are causes of erosion?
What is desertification?
What is soil salinization?
How do you remedy it?
What causes it?