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.
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
7.
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
9.
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
14.
15.
16.
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
18.
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
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
28.
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