This document discusses the key components and formation of soil. It describes the six major components of soil as eroded rock, mineral nutrients, decaying organic matter, water, air, and living organisms. Soil forms through the weathering of bedrock and is influenced by physical, chemical, and biological factors. The document also outlines the horizons and properties of soil, such as texture and permeability, and explains their importance for supporting plant life. Various human impacts on and management of soil are also covered, such as erosion, conservation practices, and relevant legislation.

1. APES

2. 6 Major components of soil
 Eroded rock
 Mineral nutrients
 Decaying organic matter
 Water
 Air
 Living organisms

3. Importance of Soil
 Provides nutrients
 Recycles/filters water
 Stores water
 Soil is the basis of life on Earth…why do you think?
 Plants get nutrients from soil and plants provided
glucose and oxygen (producers)

4. Terms associated with creation of
soil
 Infiltration
 Downward movement of water through the soil
 Leaching
 Dissolving of minerals and organic matter in upper
layers carrying them to lower layers
***soil type determines degree of leaching and infiltration

5. Formation of Soil (clay + mix of
dead vegetation)
 Physical weathering
 Mechanical weathering
 Any process that breaks down rock into smaller pieces without changing
chemistry of rock
 Wind and water
 Chemical Weathering
 Result of chemical interactions between water and atmospheric gases and
the bedrock of the region
 Oxidation: reaction with O2
 Hydrolysis: rxn with H2O
 Acid action: Rxn with acids (H2CO3, H2CO4, H2SO3)
 Dissoultion: chemical weathering from acid rain
 Biological weathering
 Takes place as a result of activities of living organisms
 Can be combined with chemical processes
 Chemosynthesis of bacteria
 Roots of trees creating fissures in rocks exposing them to further mechanical
and chemical weathering

6. Soil
 1 gram of soil has over 50,000 protozoa as well as
bacteria, algae, fungi, earthworms and nematodes
 Pores between grains of minerals in soil are filled with
air or water
 Plants need water and oxygen
 Need to make glucose-use photosynthesis and cell respiration
 Size of the particles that make up the soil determine the
size of the pores between the soil particles
 USDA has many ways to categorize
 Color
 Texture

8. Soil Horizons
 O horizon (surface litter)
 Uppermostorganic matter (leaves, twigs, crop waste, animal
waste, organic matter)
 Dark, crumbly material that results from decomposition of
organic matter
 Brown or black
 A Horizon (Topsoil layer)
 Porous mix of HUMUS and some inorganic particles (weathered
rock)
 LEACHING/ELUVIATION zone
 Fertile soil=better crops
 Holds water and nutrients for plants
*** O and A are anchored by vegetation
 B Horizon (subsoil)
 Composed of inorganic minerals
 Broke down rock (clay, silt, sand/gravel)
 Receives all minerals leached out of A horizon as well as organic
material that is washed down from the topsoil above
 ILLUVIATION/ACCUMULATION zone
 accumulation of soluble or suspended organic material, clay, iron, or
aluminum
 C Horizon (parent material)
 Large pieces of rock that have not undergone much weathering
 R Horizon
 Bedrock

10. Soil Textures-3 major divisions
 Clay
 Smallest, very fine
 Less than 0.002mm in diameter
 Easily stick to each other
 Little room between particles to store water
 Extremely compact, feels sticky
 Silt
 0.002-0.05 mm in diameter
 Feels smooth
 Holds water well
 Resists filtration
 Sand
 0.05-2.0 mm in diameter
 Coarsest particle
 Too large to stick together
 Creates soil with large pores
 Water filter through
 (Gravel)
 2.0 mm and larger
 Does not hold water well

11. Acidity and Alkalinity of Soil
 What is pH?
 Most soils pH= 4-8 (neutral to slightly acidic)
 pH affects solubility of nutrients
 Determines nutrient availability for absorption by roots of
plants
 If soil in a region is too acidic or basic, certain soil nutrients
in that region will not be able to be taken up by plants
 pH too acidic=BIG problems
 Ions of heavy metals mercury (Hg) or aluminum (Al) can leach
into the groundwater
 These ions will then travel to streams and rivers=negative
impact to plants and aquatic life
 Ex. Aluminum ions can damage fish gills=suffocation of fish

12. Loamy
 Soil composed of roughly the
same amount of all three textures
(clay, silt, sand) and organic
matter
 Loose and rich
 When you squeeze it, forms a ball
that crumbles when poked
 Good at absorbing and storing
water
 Best for plant growth

13. Soil Types- Based on Water content
 Pedocal
 Dry, semi arid climate
 Little organic matter
 No mineral leaching
 High limestone content
 praries
 Pedalfer
 Enriched with aluminum and iron
 Greater organic matter and leaching
 Found in areas with high temp. and
lots of forest cover
 Laterite
 Soggiest type
 Tropical and subtropical climate
zones
 High organic matter
 Low nutrients (lots of rain)
 Aluminum hydroxide=red soil

17. Soil Porosity
 Measure of the volume of pores or air
spaces per volume of soil AND average
distance between those spaces
 Fine particles help retain water
(precipitation goes into pores)
 Large particles help create air spaces for
filtration
 Pores b/t organic solid particles and
inorganic solid particles in upper and
lower layers
 Contain varying amounts of air (N and
O) and water
 Porous soil
 Many pores
 Can hold more water
 Non porous soil
 Not a lot of spaces
 Cannot hold much water

19. Soil Permeability
 Rate at which water and air move
through the soil
 Sand
 High permeability
 Water moves through quickly
 Filters water
 Clay
 Low permeability
 Water moves through slowly
 Retain water

20. Topography
 Mapping of the land by contours and physical features of areas
 Since water runs downhill, it is easy for soil to be carried away during a heavy
rainstorm
 Slope percentage affects the speed of the water’s down hill path
 Ex. 5% grade= more erosion than 1% grade

21. Soil Formation is influenced by 5
interrelated factors

22. How Soil is Formed

23. Soil Problems For and Caused By Humans
 Properties humans look for in soil
 Top soil
 Nutrient rich soil layer, millimeters to meters deep
 Contains a mix of organic matter and minerals
 Renewable when replenished and cared for properly
 Currently, thousands of acres bare due to erosion, nutrient deficiency,
overtillage, and misuse
 Arable: soil suitable/fertile for plant growth…
 Fertility refers to soils ability to provide essential nutrients: N, K, and
P
 Humus also important b/c its rich in organic matter
 Loamy soil
 Composed of same amount of clay, silt, sand
 Ability to aggregate (clump)
 Best soils are aggregates of different soil types bound together by
organic matter

24.  Tillage
 Repeated plowing
 Breaks down soil aggregates leaving
“plow pan” or “hard pan”
(hard, unfertile soil)
 Opening up Earth to plant new seeds
 Increases soil erosion
 It is done b/c it is thought to increase
soil nutrients
 Today, narrow chisel plows are used
that leave 75% of crop residue on
surface and open up only a thin ridge
for seeds
 No-till methods are beneficial
 Pierce seeds through ground cover
without opening up a seam in the earth
 Keeps soil in place and prevents erosion

25.  Monoculture
 Planting of just one type of crop in large area
 Decrease in genetic diversity of crop species
 Lack of genetic variation=increased susceptibility to pests and
diseases
 Consistent planting of one plant in area LEACHES soil of specific
nutrients needed for plant growth
 Prevention Method: CROP ROTATION
 Different crops are planted in growing area in each growing season
 Machinery
 Large machines
 Agriculture industry is a huge consumer of energy
 Energy is consumed by:
 Production of pesticides
 Production of Fertilizers
 Use of fossil fuels to power farm machinery

26.  Green Revolution=boom in agricultural productivity
 Industrial revolution  mechanization of farming  increase world
wide agricultural productivity in last 50 years of =detrimental to
environment
 Drawbacks
 Increase in irrigation = Over irrigated soils= SALINIZATION
 Soil becomes water logged and when it dries out, salt forms a layer on the
surface, which leads to land-degradation
 Drip irrigation is one way scientists have started combating problem
 Allots area only necessary amounts of water
 Water delivered straight to roots
 Chemical pesticides=new insect species that are pesticide-resistant
 Recently GM plants are helping solve pesticide problem

27. Soil Erosion
 Bare soil=soil in which no plants are growing
 More susceptible to erosion than soil covered by organic matter
 Erosion: normal and natural process
 Constant movement of wind and water on Earth’s surface
 Drawbacks:
 Removes valuable top soil
 Over 25 billion tons of soil lost due to wind and water erosion
 Erosion can lead to DESERTIFICATION
 Deposits soil in undesirable places (i.e. bodies of water)
 Farmers need healthy soil for planting
 Humans rely on water uncontaminated water for drinking/living
 Soil can contaminate water with pesticides and other harmful chemical
 Causes
 Deforestation
 logging and slash-and-burn
 Plants anchor in O and A horizons of soil
 Removal of plants make soil susceptible to erosion
 Over-cultivation of agricultural fields
 Overgrazing
 Urbanization
***All of these will continue to make ARABLE land for farmers hard to find
***New techniques must be utilized to preserve the integrity of the soil

29. Effects of Erosion
 Top soil blown away by wind or washed
away by rainfall
 Weakened land Leads to…
 Downstream flooding
 Reduced water quality
 Increased river and lake sedimentation
 Build up of silt in reservoirs and
navigation channels
 Dust storms
 Air pollution
 Health issues
 Allergies
 Eye infections
 Upper respiratory problems

30. Soil Conservation
 Several management practices utilized to conserve soil
resources
1. Return organic matter to soil
2. Slow down effects of wind
3. Reduce amount of damage done to soil by tillage (plowing)
 Examples:
 Use animal waste and the residue of plants to increase the
amount of organic material in soil
 Modify tillage practices to reduce the breakup of soil and
reduce the amount of erosion (contour plowing and strip
planting)
 Use trees and other wind barriers to reduce forces of winds

31. 
Soil conservation
Contour planting
 Plant across a hillside (instead of up and down),
slows run off
 Strip farming
 Planting alternating crops in strips across land
 In combination with contour planting, this slows
erosion
 Terracing
 Similar to strip farming
 Land is shaped…level ridges of land are created to
hold water and soil in place
 More expensive and time consuming but allows
cultivation on steep grades and increases
sustainability (this is how rice is grown in Asia)
 Perennial plant growing
 Coffee and tea
 Plants that grow during several seasons
 Do not have to harvested yearly AND hold soil
longer
 Ground cover plants (alfalfa) hold and protect soil
from erosion if planted right after initial harvest

32. Soil Laws
 1977 Soil and Water Conservation Act
 Soil and water conservation programs to aid landowners
and users
 Sets up conditions to continue evaluating the condition
of the US soil, water and related resources
 1984 Food Security Act “Swampbuster” Act
 Discouraged conversion of wetlands to non-wetlands
 1990 federal legislation denied federal farm supplements
to those who converted wetlands to agriculture
 Provided restoration of benefits to those who
unknowingly converted lands to wetlands