1. Chapter 15 Soil Resources

2. Overview of Chapter 15 What is soil? Soil Properties Major Soil Orders
Soil Problems
Soil Conservation
Soil Reclamation

3. Soil
Uppermost layer of earth’s crust that supports plants, animals and microbes
Soil Forming Factors
Parent Material
Time
Climate
Organisms
Topography

4. Soil Composition Mineral Particles (45%) Organic Material (5%)
Weathered rock
Provides essential nutrients for plants
Organic Material (5%)
Litter, animal dung, dead remains of plants and animals, humus (picture)
Water (25%)
Air (25%)

5. Soil Composition Pore space 50% of soil Soil air- good for aeration
Soil water- provides water to roots

6. Soil Horizons O-horizon A-horizon B-horizon C-horizon
Rich in organic material
A-horizon
Topsoil
B-horizon
Lighter colored subsoil
C-horizon
Weathered parent material

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

8. Soil Organisms Soil organisms provide ecosystem services Examples
Def: Important environmental benefits that ecosystems provide
Examples
Decaying and cycling organic material
Breaking down toxic materials
Cleansing water
Soil aeration (especially done by earthworms)

9. 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

10. Soil Properties Soil Texture
Relative proportion of sand, silt and clay
Sand: 2mm-0.05mm
Silt: 0.05mm-0.002mm
Clay: >0.002mm

11. Soil Properties Soil texture affects soil properties
Coarse textured soil (sandy)
Will not hold water well- flows through easily
Fine textured soil (high in clay)
Poor drainage
Low oxygen levels in soil
Due to negatively charged surface, able to hold onto important plant nutrients (K+, Ca2+, NO2-)

13. Soil Properties

14. Soil Properties 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
Optimum soil pH is 6-7
This is the pH where plant nutrients are most available to plants
Soil amendments (ex: lime) can be used to achieve this pH

15. Major Soil Groups
Variations in soil forming factors cause variation in soils around globe
Soil Taxonomy
Separates soils into 12 orders
Subdivided into more than 19,000 soil series that vary by locality
Five common soil orders
Spodosols, alfisols, mollisols, aridosols, oxisols

16. Major Soil Groups Spodosols Form under coniferous forests
O-horizon composed of needles
E-horizon is ash-gray under A-horizon
Not good farmland- too acidic

17. Major Soil Groups Alfisols Brown to gray-brown A-horizon
Precipitation high enough to leach most organics and nutrients out of O-, A- and B-horizons
Soil fertility maintained by leaf litter

18. Major Soil Groups Mollisols Found in temperate, semi-arid grassland
Very fertile soil
Thick, dark brown/ black A-horizon
Soluble nutrients stay in A-horizon due to low leaching

19. Major Soil Groups Aridosols Found in arid regions of all continents
Low precipitation preclude leaching and growth of lush vegetation
Development of salic horizon possible

20. Major Soil Groups Oxisols
Found in tropical and subtropical areas with high precipitation
Very little organic material accumulation due to fast decay rate
B-horizon is highly leached and nutrient poor

21. Soil Problems Soil Erosion Why a problem?
Def: wearing away or removal of soil from the land
Caused primarily by water and wind
Why a problem?
Causes a loss in soil fertility as organic material and nutrients are eroded
More fertilizers must be used to replace nutrients lost to erosion
Accelerated by poor soil management practices

22. 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

23. Soil Problems
Nutrient Mineral Depletion

24. Soil Problems Soil Salinization Often in arid and semi-arid areas
Def: gradual accumulation of salt in the soil, usually due to improper irrigation techniques
Often in arid and semi-arid areas
The little precipitation that falls is quickly evaporated
Leaves behind salts
Salt concentrations get to levels toxic to plants

25. Soil Problems Desertification Typically a human-induced condition
Def: degradation of once-fertile rangeland, agricultural land, or tropical dry forest into nonproductive desert
Typically a human-induced condition
Change in vegetation changes climate, further decreasing precipitation levels

26. Soil Conservation Conservation Tillage Crop Rotation
Residues from previous year’s crops are left in place to prevent soil erosion
Includes no tillage
Crop Rotation
Planting a series of different crops in the same field over a period of years
Lessens pest and insect disease

27. Soil Conservation Contour Plowing Strip Cropping Terracing
Plowing around hill instead of up-down
Decreases soil erosion
Strip Cropping
Alternating strips of different crops along natural contours
Terracing
Creating terraces on steep slopes to prevent erosion
Terracing

28. Preserving Soil Fertility
Organic fertilizers
Animal manure, crop residue, bone meal and compost
Nutrient available to plants only as material decomposes
Slow acting and long lasting
Inorganic fertilizers
Manufactured from chemical compounds
Soluble
Fast acting, short lasting
Environmentally sound to limit use
Mobile- easily leach and pollute groundwater

29. Soil Reclamation Two steps Best way to do this is shelterbelts
Stabilize land to prevent further erosion
Restoring soil to former fertility
Best way to do this is shelterbelts
Row of trees planted to reduce wind erosion of soil

30. Soil Conservation Policies in US
Soil Conservation Act 1935
Authorized formation of Soil Conservation Service, now called Natural Resource Conservation Service (NRCS)
Assess soil damage and develop policies to improve soil
Food Security Act (Farm Bill) 1985
Required farmers with highly erodible soil had to change their farming practices
Instituted Conservation Reserve Program
Pays farmers to stop farming highly erodible land