1. 3.4 The Soil System

2. The Soil System
Soil is a complex mixture of eroded rock, mineral nutrients, decaying organic matter, water, air and billions of living organisms (microscopic decomposers).

3. Soil formation is a slow process:
Weathering of rock (mechanical).
Deposition of sediments by erosion (mechanical).
Decomposition of organic matter in dead organisms (chemical).

4. soil system integrates the biotic and abiotic

6. Mature soils are arranged in a series of zones called SOIL HORIZONS:
“O” HORIZON = freshly fallen and partially decomposed leaves, twigs, animal waste. You can find fungi and other organic materials.
“A” HORIZON = porous mixture of partially decomposed organic matter (humus) and some inorganic mineral particles.

7. These top two layers are most fertile, have the highest concentration of organic matter, and contain large amounts of living organisms.
Flatworm
Rove beetle
Ant
Centipede
Mite
Pseudoscorpion
Ground
beetle
Adult
fly
Millipede
Fly
larvae
Sowbug
Earthworm
Slug
Snail
Roundworms
Protozoa
Bacteria
Organic debris
Beetle
Fungi
Springtail
Actinomycetes

8. “B” (subsoil) and “C” (parent material) HORIZON contain most of the soil’s inorganic matter, broken-down rock.

13. Soil Content Clay (very fine particles) Silt (fine particles)
Sand (medium-size particles)
Gravel (coarse to very coarse particles)
SOIL TEXTURE is determined by the relative amounts of the different types and sizes of mineral particles.

14. Increasing percentage sand
100%clay
Increasing
percentage silt
percentage clay 20 40 60 80
100%sand
100%silt
Increasing percentage sand
sandy
clay
silty
silty clay
loam
silt
sandy clay
loamy
sand

15. Soil texture helps determine SOIL POROSITY, a measure of the volume of spores or spaces per volume of soil and the average space between those spaces.
INFILTRATION is the downward movement of water through soils.
As the water seeps down, it dissolves various soil components in upper layers and carries them down to lower layers in a process called LEACHING.

16. SOIL PERMEABILITY is the rate at which water and air move from upper to lower soil layers.
High permeability
Low permeability

17. Water-Holding Capacity
Properties of Soils with Different Textures
Texture
Nutrient Capacity
Infiltration
Water-Holding Capacity
Aeration
Workability
Clay
Good
Poor
Silt
Medium
Sand
Loam
medium

18. Absorption of nutrients
Nitrogen fixing
by lightning
Commercial
inorganic
fertilizer
10-6-4
N-P-K
Organic fertilizers,
animal manure,
green manure, compost
Crop
plant
Dead
organic matter
Application
to land
by bacteria
Weathering
of rock
Nutrient removal
with harvest
Decomposition
Supply of
available plant
nutrients in soil
Nutrient loss
by bacterial
processes
such as
conversion
of nitrates to
nitrogen gas
from soil erosion
Absorption of nutrients
by roots
Pathway of plant nutrients in soil.

19. Soil erosion is the movement of soil components, especially surface litter and topsoil.
The two main agents of erosion are wind and flowing water.
Loss of plant cover by farming, logging, construction, overgrazing by livestock, off-road vehicles, deliberate burning of vegetation and other activities leave soil vulnerable to erosion.

21. Two major harmful effects of soil erosion:
Loss of soil fertility and its ability to hold water
Runoff of sediment that pollutes water, kills fish and shellfish, and clog irrigation ditches, boat channels, reservoirs, and lakes.
serious concern
some concern
Stable areas

22. Desertification is the enlargement of deserts through human activities.
Consequences
Causes
Worsening drought
Famine
Economic losses
Lower living
standards
Environmental
refugees
Overgrazing
Deforestation
Surface mining
Erosion
Salinization
Soil compaction

23. Irrigation water contains small amounts of dissolved salts.
SALINATION
Irrigation water contains small amounts of dissolved salts.
Evaporation and transpiration leave salts behind.
Salt builds up in soil.
WATERLOGGING
Precipitation and irrigation water percolate downward.
Water table rises.
Both result in stunted plant growth,
lower crop yields,
dead plants and ruined land.

24. Evaporation
Transpiration
Waterlogging
Less permeable
clay layer

25. Soil Conservation involves reducing soil erosion and restoring soil fertility.

26. Advantages and disadvantages of using Conservation Tillage.
Reduces erosion
Saves fuel
Cuts costs
Holds more soil water
Reduces soil compaction
Allows several crops
per season
Does not reduce crop
yields
Can increase herbicide
use for some crops
Leaves stalks that can
harbor crop pests and
fungal diseases and
increase pesticide use
Requires investment
in expensive equipment

27. Contour planting and strip cropping: each row acts as a small dam to help hold soil and slow water runoff.

28. Alley cropping or agroforestry: several crops are planted together in strips or alleys between trees and shrubs that can provide fruit or fuel-wood, shade, help retain and slowly release soil moisture, and fodder for livestock.

29. Windbreaks or shelterbelts of trees reduce wind erosion, help retain soil, supply wood for fuel, and provide habitats for birds, pest-eating and pollinating insects, and other animals.

30. Terracing retains water for crops at each level and reduces soil erosion
by controlling runoff.

31. Soil Restoration Organic fertilizer Manure Compost crop rotation
No till farming
Contour farming
Terracing
Nitrogen fixation-legumes