Soil is a complex natural body that forms at the interface between the earth's atmosphere, biosphere, hydrosphere and lithosphere. It is composed of weathered rocks and decaying organic matter and provides a medium for plant growth. Soil formation involves physical, chemical and biological weathering processes over long periods of time. Soils perform key ecosystem functions like supporting plant growth, regulating water supply, recycling nutrients, and serving as a habitat. Understanding soil properties and managing soils sustainably is important for agriculture, the environment and human well-being.

2. Prepare by AHMAD ALI
BS Botany
5th Semester

3.  Soil is a dynamic natural body developed as a
result of pedogenic processes during and
after weathering of rocks, consisting of
mineral and organic constituents, possessing
definite chemical, physical, mineralogical and
biological properties, having a variable depth
over the surface of the earth and providing a
medium for plant growth for land plants.

4.  Soils lie at the interface of Earth's,
atmosphere, biosphere, hydrosphere and lithosphere
and interact with the hydrosphere and atmosphere.
 To understand soil requires some knowledge of
metrology, climatology, ecology, biology,
Hydrology, geomorphology, geology and many
other earth sciences and natural sciences.
 Soils play a vital role in the quality of our
environment.
 For example, soil impact the quality and quantity of
our food, and serve as foundations of our structures.

5.  Soil can be a source, a sink, or an interacting
medium for many nutrients, as well as
contaminants that impact humans, plants,
wildlife, and other organisms.
 An understanding of soil properties and
processes is therefore critical to evaluate soil
management processes.
 The word “Soil” is derived from Latin word
‘Solum’ means ‘Floor’ or ‘Ground’ “With out life,
there is no soil and without soil, there is no life
on the earth planet”.

6. Soils perform six key functions in the global ecosystem.
Soil serves as a:
1. Medium for plant growth (provides nutrients), it store and supply
nutrients to plants.
2. As an anchor for plant roots enabling plants to stand erect.
3. Regulator of water supplies (water holding tank, it absorb and
store the moisture for later use).
4. Recycler of raw materials ( Decomposition).
5. Habitat for soil organisms.
6. Landscaping and engineering medium (Soils are the base material
for roads, homes, buildings, and other structures) and It provide
space for air which creates healthy environment.

7.  Eroded rock
 Mineral nutrients
 Decaying organic matter
 Water
 Air
 Living organisms

8.  Physical weathering
 Mechanical weathering
 Any process that breaks down rock into smaller pieces without changing
chemistry of rock
 Wind and water
 ChemicalWeathering
 Result of chemical interactions between water and atmospheric gases and the
bedrock of the region
▪ Oxidation: Reaction with O2
▪ Hydrolysis: Reaction with H2O
▪ Acid action: Reaction with acids (H2CO3, H2CO4, H2SO3)
▪ Dissolution: 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

9.  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

10.  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 ofA 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

12.  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

13.  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
▪ E.g.Aluminum ions can damage fish gills=suffocation of fish

14.  Pedocal
 Dry, semi arid climate
 Little organic matter
 No mineral leaching
 High limestone content
 prairies
 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.  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

18.  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

20.  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

21.  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

22.  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

23.  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

25.  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

26.  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

28.  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

29. THE END

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