1. What is Soil?
Thin surface layer of the Earth’s crust consisting of minerals and organic matter that has been modified by natural agents such as weather
Formed from rock (parent material) that is slowly broken down or fragmented into smaller particles by biological, chemical or physical weathering processes.
Takes years to make 1-inch of topsoil.

2. What is Soil Made of? 45% mineral particles
Provides anchorage for rocks, essential nutrients, pore space
25% water
5% organics
Litter, dead animals/plants, dung. Increases water holding capacity of soil
Humus: black or dark brown organic material that remains after decomposition.
Last for ~20 years in soil.
25% air

3. Soil Horizons-See Diagram
O horizon – organic material
A horizon – top soil; high in organics, may be nutrient poor, dark colored
E horizon – heavily leached zone between the A & B horizons
B horizon – subsoil; light colored, typically rich in iron and aluminum & clay.
C horizon – weathered bedrock-inorganic material
Bedrock – parent material
Leaching – when percolating (seeping) water removes dissolved materials from soil. They get carried downward.

4. Soil Classification
Entisols: soils that do not show any profile development other than an A horizon.
Ultisols: highly weathered leached red or reddish-yellow acid soil with a clay-rich B horizon (subsoil), occurring in warm, humid climates.
Vertisols: a clay based soil with little organic matter that occurs in regions having distinct wet and dry seasons.

5. Soil Classification (Cont.)
Andisols: formed in volcanic ash and defined as soils containing high proportions of glass and amorphous colloidal materials, including allophane, imogolite and ferrihydrite.
Histosols: a soil consisting primarily of organic materials. They are defined as having 40 centimetres (16 in) or more of organic soil material in the upper 80 centimetres (31 in).

6. Which Soil am I?
Entisol
Vertisol
Histosol
Andisol
Ultisol

7. Station 3=Color the Map only based on the soil types given on the handout

8. Soil Organisms Microscopic – bacteria, fungi, algae, and protozoa
Macroscopic – plant roots, insects, earthworms, moles, snakes
Worms are very important
Breakdown debris
Put nutrients back into soil via their castings
Aerate the soil

9. Nutrient Cycling
Movement of nutrient materials from soil to organisms and back again

10. What are the Physical Characteristics of Soil
Soil texture
determined by % (by weight) of sand, silt and clay
Size order (Big to small) Sand, Silt, Clay
Loam – ideal for agriculture
40% sand – drain soil, add in air
40% silt – holds organics
20% clay hold nutrients/minerals

11. Sand Silt Clay 0.05–2 mm diameter 0.002–0.05 mm diameter
less than mm
Diameter
Water
Water
Figure 3.25
Natural capital: the size, shape, and degree of clumping of soil particles determine the number and volume of spaces for air and water within a soil. Soils with more pore spaces (left) contain more air and are more permeable to water than soils with fewer pores (right).
High permeability
Low permeability
Fig. 3-25, p. 70

12. Soil Acidity Most fall between pH 4 & 8
Solubility of mineral nutrients vary pH
Optimal pH for plants = 6 to 7

13. Major Soil Groups-See Diagram
Coniferous forest (Pines) – humid, cold climate
Acidic litter and humus
Deciduous forests
A-horizon is low on minerals due to sufficient precipitation
Sufficient fertilization from leaf litter; good O-horizons

14. Major Soil Groups (cont.)
Grassland soil –semi-arid climate
Very fertile
Thick dark A-horizon that is rich in humus
Desert Soil
No leaching (no precipitation)
Low organics; higher mineral content
Pebbles, boulders

15. Major Soils Groups (cont.)
Tropical & subtropical forest
Low nutrients (organic matter decomposed quickly in O layer)
Thick, highly leached B-horizon

16. Soil problems
Soil Erosion – wearing away or removal of soil from land, often by wind and rain.
Mineral Depletion – agricultural system that uses soil nutrient but disrupts nutrient cycling so its not returned to the land (examples – farming techniques, slash & burn)
Salinization -too much salt, plants can’t grow
Overgrazing-occurs when plants are exposed to intensive grazing for extended periods of time, or without sufficient recovery periods. It can be caused by either livestock in poorly managed agricultural applications, or by overpopulations of native or non-native wild animals.
Monoculture- planting the same crops year after year-taking out all the soil nutrients that it needs to grow without replenishing

17. Soil Problems U.S and Worldwide
Over-farming, soil degredation leading to desertification
Erosion (wind and water)
Overgrazing
Monoculture (planting the same crops year after year-taking out all the nutrients that it needs to grow without replenishing)

18. Soil Reclamation Stabilize land to prevent further erosion
Restore land to former fertility
Shelter belts – rows of trees that lessen winds and therefore soil erosion

19. Food Security Act of 1985 (cont.)
Requires farmers to develop and adopt a 5-year conservation plan
Created Conservation Reserve Program (CRP) – voluntary program to pay farmers to stop producing crops on high erodible farmlands.

20. More policies
Federal Agricultural Improvement & Reform Act (Farm Bill) of 1996
Restructured earlier farm bill to have fewer inspections and more lenient inspectors
Grassland Reserve Program – included in 2002 Farm Bill
Pays farmers to protect virgin and improved pastureland for a period of at least 10 years.

21. Fertilizers Two types – Organic and Inorganic Organic Inorganic Manure
Bone meal
Compost (tilled into soil)
Mulch (placed on top)
Inorganic
Nitrogen/phosphorus

22. Fertilizers (cont) Pro Con Organic Fertilizer Last longer, cheaper
Complex/vary in composition
Slow to give off nutrients
Inorganic Fertilizer
Immediately available to plants
Costly, very mobile/easily leached, do not improve water holding capacity, last short amount of time, create air/water pollution

23. The Dust Bowl (1930s)
One of the greatest man-made ecological disasters in US history

24. Soil Conservation
Conservation tillage – residues from previous crops left in soil
Crop rotation – plant series of different crops in same field over a period of years
Typically alternating with legumes that increase soil fertility thru relationships with bacteria that fix atmospheric nitrogen

25. Soil Conversation (cont.)
Contour plowing – plow/plant to natural curves of land (preventing erosion)
Strip cropping – alternative strips of different crops with contouring
Terracing – produce level areas to grow drops and minimize soil erosion.

26. Soil Conservation Policies
Soil Conservation Act of 1935 –
Formed Soil Conservation Service (now Natural Resource Conservation Service)
It gave farmers subsidies to plant native grasses and trees or raise vegetables rather than commercial crops that depleted soil nutrients.