1. Soil
This section is in addition to Chapter 3

2. Soil
Produced slowly ( years typically) by weathering of rock, deposition of sediments, and decomposition of organic matter
Soil horizons – separate zones within soil
Soil profile – cross-section view of soil

3. Horizons O horizon – surface litter
A horizon – top soil, made up of inorganic particles (clay, silt, sand) and humus (organic particles from decomposed organisms)
Dark topsoil is richer in nutrients
Releases water and nutrients slowly
Provides aeration to roots
Healthy soil contains many nematodes and bacteria, fungi, etc.

4. Immature soil Young soil Mature soil
Oak tree
Lords and
ladies
Word
sorrel
Dog violet
Earthworm
Organic debris
Builds up
Grasses and
small shrubs
Millipede
Rock
fragments
Mole
Moss and
lichen
Fern
Honey
fungus
O horizon
Leaf litter
A horizon
Topsoil
Bedrock
B horizon
Subsoil
Immature soil
Regolith
Young soil
Pseudoscorpion
C horizon
Parent
material
Mite
Nematode
Actinomycetes
Root system
Red earth
mite
Fungus
Springtail
Mature soil
Bacteria
Fig , p. 220

5. Poor topsoil
Grey, yellow and red are not the colors of healthy topsoil
Generally means that soil is lacking nutrients
Best soil is called loam with equal parts sand, silt, clay and humus
Leaching – dissolving and carrying nutrients (or pollutants) through soil into lower layers

6. B – horizon and C - horizon
B – Subsoil mostly broken down rock with little organic matter
C- parent material broken down rock on top of the bedrock

7. Soils
Texture – relative amount of different sized particles present (sand, silt, clay)
Porosity – volume of pore space in the soil
Permeability – the ability of water to flow through the soil

8. Water
Water
High permeability
Low permeability
Sandy soil
Clay soil

9. Soils Clay – high porosity, low permeability
Sand – high permeability, low porosity
Acidity is another factor
Where rain is low, calcium and other alkaline compounds may build up (sulfur can be added – turns to sulfuric acid by bacteria)

10. Tropical Rain Forest Soil (humid, tropical climate)
Forest litter
leaf mold
Acid litter
and humus
Acidic
light-
colored
humus
Humus-mineral
mixture
Light-colored
and acidic
Light, grayish-
brown, silt loam
Iron and
aluminum
compounds
mixed with
clay
Dark brown
Firm clay
Humus and
iron and
aluminum
compounds
Tropical Rain Forest Soil
(humid, tropical climate)
Deciduous Forest Soil
(humid, mild climate)
Coniferous Forest Soil
(humid, cold climate)
Fig b, p. 223

11. Desert Soil (hot, dry climate) Grassland Soil (semiarid climate)
Mosaic
of closely
packed
pebbles,
boulders
Alkaline,
dark,
and rich
in humus
Weak humus-
mineral mixture
Dry, brown to
reddish-brown
with variable
accumulations
of clay, calcium
carbonate, and
soluble salts
Clay,
calcium
compounds
Desert Soil
(hot, dry climate)
Grassland Soil
(semiarid climate)
Fig a, p. 223

12. Soil erosion Causes – mainly water and wind
Human induced causes – farming, logging, mining, construction, overgrazing by livestock, off-road vehicles, burning, and more (go us!)

13. Soil erosion Types Sheet Rill Gully
Uniform loss of soil, usually when water crosses a flat field
Rill
Fast flowing water cuts small rivulets in soil
Gully
Rivulets join to become larger, channel becomes wider and deeper, usually on steeper slopes or where water moves fast

14. Global soil loss This is a major problem world wide
Have lost about 15% of land for agriculture to soil erosion
Overgrazing
Deforestation
Unsustainable farming
Also 40% of ag land is seriously degraded due to soil erosion, salinization, water logging and compaction

15. Desertification of arid and semiarid lands
Moderate
Severe
Very Severe
Fig , p. 228
Desertification of arid and semiarid lands

16. Areas of serious concern Stable or nonvegetative areas
Areas of some concern
Stable or nonvegetative areas
Global soil erosion
Fig , p. 226

17. Desertification
Turning productive (fertile) soil into less productive soil (10% loss or more)
Overgrazing
Deforestation
Surface mining
Poor irrigation techniques
Poor farming techniques
Soil compaction

18. Salinization As water flows over the land, salts are leached out
When water irrigates a field it is left to evaporate typically
This repeated process causes the dissolved salts to accumulate and possibly severely reduce plant productivity
Fields must be repeatedly flushed with fresh water to remove salt build up

19. Waterlogging
When fields are irrigated they allow water to sink into the soil.
Winds can dry the surface
As more water is applied the root area of plants is over saturated reducing yield
As clay is brought to subsoil levels it can act as a boundary for water infiltration

20. Evaporation Transpiration Evaporation Evaporation Waterlogging
Less permeable
clay layer
Fig , p. 229

21. Soil conservation
Conservation tillage – (no till farming) disturb the soil as little as possible
Reducing erosion also helps – save fuel, cut costs, hold water, avoid compaction, allow more crops to be grown, increase yields, reduce release of carbon dioxide

22. Soil conservation Terracing – making flat growing areas on hillsides
Contour farming – planting crops perpendicular to the hill slope, not parallel
Strip cropping – planting alternating rows of crops to replace lost soil nutrients (legumes)
Alley cropping – planting crops between rows of trees

23. Control planting and strip cropping
Fig b, p. 230

24. Alley cropping
Fig c, p. 230

25. Fig a, p. 230
Terracing

26. Soil conservation
Gully reclamation – seeding with fast growing native grasses, slows erosion or “reverses” it
Also building small dams traps sediments
Building channels to divert water or slow water
Windbreaks – trees planted around open land to prevent erosion
Retains soil moisture (shade, less wind)
Habitats for birds, bees, etc.
Land classification – identify marginal land that should not be farmed

27. Windbreaks
Fig d, p. 230

28. Soil fertility
Inorganic fertilizers – easily transported, stored, and applied
Do not add humus – less water and air holding ability, leads to compaction
Only supply about 3 of 20 needed nutrients
Requires large amount of energy for production
Releases nitrous oxide (N2O) during production, a green house gas

29. Soil fertility Organic fertilizers – the odor is a problem
Animal manure – difficult to collect and transfer easily, hard to store
Green manure – compost, aerates soil, improves water retention, recycles nutrients
Crop rotation – allows nutrients to return to soil, otherwise same crop continually strips same nutrient, keeps yields high, reduces erosion