Soils and their processes IB Syllabus: 3.8.1-3.8.5 AP Syllabus Chapter 10.
Transcript of Soils and their processes IB Syllabus: 3.8.1-3.8.5 AP Syllabus Chapter 10.
Syllabus Statements• 3.4.1: Outline how soil systems integrate
aspects of living systems• 3.4.2: Compare and contrast the structure and
properties of sand, clay, and loam soils including their effect on primary productivity
• 3.4.3: Outline the processes and consequences of soil degradation
• 3.4.4: Outline soil conservation measures• 3.4.5: Evaluate soil management strategies in
a named commercial farming system and in a named subsistence farming system
Soils and living systems
Sun
Producer
PrecipitationFalling leaves
and twigs
Producers
Primary consumer(rabbit)
Secondary consumer(fox)
Carbon dioxide (CO2)
Oxygen (O2)
Water
Soil decomposers
Soluble mineral nutrients
• Links to lithosphere, atmopshere, and living organisms
• What are they?
• Inputs organic materials, parent materials, precipitation, infiltration, Energy
• Outputs leaching, uptake by plants, mass movement
• Transfers deposition
• Transformations decomposition, weathering & nutrient cycling
Soil as a resource?• Produced very slowly – almost nonrenewable• Production by…
– Weathering of rock (parent material) – chemical & mechanical this adds inorganic components
– Deposit of sediments by erosion– Introduction of living organisms – succession
the biotic component– Decomposition of organic materials and dead
organisms
• Development is slow 200-1000 years to produce 1 inch of topsoil
• Soil is different in different areas
The horizon
• Mature soils arranged in zones or layers called horizons– Different texture and composition
• Cross sectional view of soil horizons is called a soil profile
• Most mature soils have at least three horizons
Typical Horizons
• Surface litter = O horizon– Fresh and partly
decomposed organics
• Topsoil layer = A horizon– Humus mixed with
inorganics– Most life in O & A
• Subsoil = B horizon– Broken down Inorganics
• Parent material (bedrock) = C horizon
Flatworm
Rove beetle
AntCentipede
Mite
Pseudoscorpion
Groundbeetle
Adultfly
Millipede
Flylarvae
Sowbug
Mite
Earthworm
Slug
Snail
Roundworms
Protozoa
Bacteria
Organic debris
Beetle Mite
Fungi
Springtail
Actinomycetes
O & A horizon inhabitants
Living layers
• Organisms in the A & O layers are those that break down the organics to form the soil
• A & O are where plant roots are, abosorbing water and nutrients
• Humus = partly decomposed organics fertile and good for plant production
• Topsoil color indicates condition– Dark brown good lots of nitrogen and organics– Grey, yellow and red soils low in nutrients
Weak humus-mineral mixture
Mosaicof closelypackedpebbles,boulders
Dry, brown toreddish-brown, with variable accumulationsof clay, calciumcarbonate, andsoluble salts
Desert Soil(hot, dry climate)
Grassland Soil(semiarid climate)
Alkaline,dark,and richin humus
Clay,calciumcompounds
Acidiclight-coloredhumus
Iron andaluminumcompoundsmixed withclay
Forest litterleaf mold
Humus-mineralmixture
Light, grayish-brown, silt loam
Dark brownFirm clay
Acid litterand humus
Humus andiron andaluminumcompounds
Light-coloredand acidic
Tropical Rain Forest Soil(humid, tropical climate)
Deciduous Forest Soil(humid, mild climate)
Coniferous Forest Soil(humid, cold climate)
What else is in there?
• Spaces between particles hold gases mostly N2 and O2
• Precipitation, Percolates down through soil in the process of Infiltration
• Water dissolves compounds and carries them through soil = Leaching
• Nutrients in soil from breakdown of mineral components and biological cycling
Nitrogen fixingby lightning
Commercialinorganicfertilizer
10-6-4N-P-K
Organic fertilizers,animal manure,
green manure, compost
Cropplant
Deadorganic matter
Applicationto land
Nitrogen fixingby bacteria
Nitrogen fixing
Weatheringof rock
Nutrient removalwith harvest
Decomposition
Supply ofavailable plant
nutrients in soilNutrient lossby bacterialprocesses
such asconversion
of nitrates tonitrogen gas
Nutrient lossfrom soil erosion
Absorption of nutrientsby roots
Further Interactions
Detailed
Composition of Soils
• Soils vary in their content of …– Clay: very fine particles– Silt: fine particles– Sand: medium sized particles– Gravel: coarse to very coarse particles
• Soil texture determined by amounts of these components
• If mixture is relatively equal it is a loam
Texture by Feel
Moisten some soil and rub it between your thumb and forefinger
• Gritty = lots of sand
• Sticky, can form clumps = lots of clay
• Smooth like flour = silt
• Crumbly, spongy with loose clumping = loam
100%clay
Increasingpercentage silt
Increasingpercentage clay
0
20
40
60
80
80
60
40
20
0
100%sand 80 60 40 20 100%silt
Increasing percentage sand
sandyclay
clay
siltyclay
silty clayloam
clayloam
loam siltyloam
silt
sandy clayloam
sandyloam
loamy sandsand
Soil Texture
• Soil Porosity: measure of the volume of space in a volume of soil
• Fine particles = water retention
• Coarse particles = air retention
• More porous more water and air
• Size of spaces in soil determines soil permeability rate at which water and air move from upper to lower soil levels
Texture continued
• Soil structure: the organization and clumping of soil
• Loams are best for growing crops, hold water but not too tightly that plants can’t absorb it.
• Clay less porous, less permeable lead to water logged crops above
Sand Soils
1. Mineral content: moderate2. Drainage: highest3. Water-holding capacity – low, = 10%4. Air spaces: highest, = 40%5. Biota: space to live6. Potential to hold organic matter: high7. Links to primary production: pure sand =
low productivity
Clay Soils
1. Mineral content: limited2. Drainage: poor3. Water-holding capacity- highest = 40%4. Air spaces: lowest = 10%5. Biota: little space for colonization6. Potential to hold organic matter: low7. Links to primary production – water
logged crops above
Loam Soils
1. Mineral content: high
2. Drainage: intermediate
3. Water-holding capacity: intermediate = 25%
4. Air spaces: intermediate = 15%
5. Biota: highest
6. Potential to hold organic matter - good mix of organic matter
7. Links to primary production – highest productivity in balanced soil
Soil gets degraded by human activities
• Overgrazing – plants exposed to intensive grazing over long periods of time or without sufficient recovery period
• Deforestation - Removal of large sections of forest habitat
• Unsustainable agriculture – Monoculture using high chemical & fertilizer input and fossil fuels
• Irrigation – especially done in arid areas b/c evaporation leaves everything but H2O behind
• Lead to degradation by erosion, toxification, salinization, desertification
Overgrazing Impacts
• Reduces Biodiversity• Causes Desertification and Erosion• Increases Erosion by loss of cover species
and loss of roots that held the soil in place• Erosion leads to loss of organics and drop in
productivity• In marginal lands this may lead to
desertification as grassland becomes desert when productivity plummets
First year Second year Third year Fourth year Fifth year Sixth year
First year Second year Third year Fourth year Fifth year Sixth year
First year Second year Third year Fourth year Fifth year Sixth year
Pasture A
Pasture B
Pasture C
Deferred Grazedlast
Grazedsecond
Grazedfirst
Grazedfirst
Grazedsecond
Grazedfirst
Grazedsecond
Deferred Grazedlast
Grazedsecond
Grazedfirst
Grazedsecond
Grazedfirst
Grazedfirst
Grazedsecond
Deferred Grazedlast
Deforestation Impacts
• Increases rates of erosion by increasing runoff and reducing litter protection on the surface
• Roads created and machinery used also increases erosion
• Roots may hold soil in place and canopies may disperse the force of percipitation
• On steep slopes deforestation can cause landslides
Soil Erosion• Erosion = the movement of soil components
especially surface litter and topsoil, from one area to another
• Caused by WIND and WATER
• Plant roots usually anchor soils in place• Effects
1.Loss of soil fertility and water holding capacity
2.Runoff sediment pollutes water, kills organisms, clogs ditches, channels, lakes
3. Increased use of fertilizers
4. Increased runoff and flooding
2006 Cornell University Study
• The United States is losing soil 10 times faster -- and China and India are losing soil 30 to 40 times faster -- than the natural replenishment rate.
• The economic impact of soil erosion in the United States costs the nation about $37.6 billion each year in productivity losses. Damage from soil erosion worldwide is estimated to be $400 billion per year.
• As a result of erosion over the past 40 years, 30 percent of the world's arable land has become unproductive.
• About 60 percent of soil that is washed away ends up in rivers, streams and lakes, making waterways more prone to flooding and to contamination from soil's fertilizers and pesticides.
• Soil erosion also reduces the ability of soil to store water and support plant growth, thereby reducing its ability to support biodiversity.
• Erosion promotes critical losses of water, nutrients, soil organic matter and soil biota, harming forests, rangeland and natural ecosystems.
• Erosion increases the amount of dust carried by wind, which not only acts as an abrasive and air pollutant but also carries about 20 human infectious disease organisms, including anthrax and tuberculosis.
Historical Wind Erosion
• 1930’s “ The dirty thirties”
• Combination of – drought, – removal of native plants which held in soil,– cultivation leaving land bare for months– Overgrazing
• “Dust Bowl” formed (The Grapes of Wrath)
• We may be headed for a repeat of this
Desertification
• Desertification enlargement of deserts through human activities
• The productive potential of arid or semiarid land falls by 10% due to
1. Natural climate change prolonged drought
2. Human activities reducing & degrading soil
Moderate = 10-25% productivity drop
• Severe = 25-50% drop • Very severe >50% drop = sand dunes & gullies
ConsequencesCauses
Worsening drought
Famine
Economic losses
Lower living standards
Environmentalrefugees
Overgrazing
Deforestation
Surface mining
Erosion
Salinization
Soil compaction
Causes and Consequences
Every year 11 million hectares of arable land is lost from production through the soil degradation process
Desertification Statistics• World wide 8.1 million km2 desertified in
past 50 years
• Yearly 150,000 km2 additional
• Economic losses of $42 billion / year
WE CAN
1. Reduce overgrazing, deforestation, bad agriculture practices
2. Plant trees & grasses to anchor soil, hold water, reduce global warming threat
Unsustainable Agriculture
• Characteristics of Modern Agriculture– High water input– High pesticide use– High inorganic fertilizer use
• Traditional agriculture where soil is tilled at the end of a growing season
• Idea good in practice – add nutrients to the soil – but bare soil exposed to erosion
• Tillage also deteriorates soil structure• Can cause increased erosion, toxification and
salinization
Unsustainable Agriculture Impacts
• Toxification of soil– When nonbiodegradable pesticides and
inorganic fertilizers build up in the soil they make it toxic
– Kills useful bacteria (N fixing) fungi, and decreases productivity
– Can also result from release of toxic metals like Al+3 when acidity increases (N based fertilizers mixing with water forming Nitric Acid)
• Soil erosion rates increase
Biodiversity Loss
Loss and degradation of habitat fromclearing grasslands and forests anddraining wetland
Fish kills from pesticide runoff
Killing of wild predators to protectlivestock
Loss of genetic diversity fromreplacing thousands of wild cropstrains with a few monoculture strains
Soil
Erosion
Loss of fertility
Salinization
Waterlogging
Desertification
Air Pollution
Greenhouse gas emissions from fossilFuel issue
Other air pollutants from fossil fuel use
Pollution from pesticide sprays
Water
Aquifer depletion
Increased runoff andflooding from land clearedto grow crops
Sediment pollution fromerosion
Fish kills from pesticiderunoff
Surface and groundwaterpollution from pesticidesand fertilizers
Overfertilization of lakesand slow-moving riversfrom runoff of nitrates andphosphates fromfertilizers, livestockwastes, and foodprocessing wastes
Human Health
Nitrates in drinking water
Pesticide residues in drinking water,food, and air
Contamination of drinking andswimming water with disease organismsfrom livestock wastes
Bacterial contamination of meat
Improper irrigation
• Often results from unsustainable agriculture in areas that are too arid
• Remember that water includes more than just H2O– Improper drainage or high evaporation leads
to salt deposition crop damage, reduction of productivity
– Unirrigated or underirrigated land can lead to build up of toxic agricultural waste products
Salinization can result
• Irrigation increases productivity BUT Irrigation water contains salts
• Evaporation leaves crust of salts on surface
• Accumulation of salts = salinization– Stunts crop growth– Lowers crop yields– Kills plants and ruins land
• Reduced crop yield by 21% on irrigated land
Water logging
• Attempt to solve salinization
• Apply large amounts of water to leach salt deeper into soil
• Water accumulates underground then raises water table
• Saline water envelopes roots lowering productivity death
• 10% irrigated land is waterlogged
Prevention Cleanup
Reduce irrigation
Switch to salt-tolerant crops(such as barley, cotton, sugar beet)
Flushing soil(expensive andwastes water)
Not growing crops for 2-5 years
Installing under- ground drainagesystems (expensive)
Solving the Salty Problem
Solutions: Soil Conservation
• Goal: Reduce soil erosion, restore fertility
• Conventional Tillage Farming is bad plow land in the fall, bare & erodable all winter
• Conservation Tillage Farming disturb the soil as little as possible while planting crops
• Minimum tillage or No till farming
• Using conservation tillage on 80% of farmland would reduce soil erosion by 50%
Advantages Disadvantages
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 canharbor crop pests and fungal diseases and increase pesticide use
Requires investment in expensive equipment
Conservation Tillage Facts
Cultivation Techniques
• 1. Terracing– Convert steep slopes into a series of broad, nearly
level terraces running across the land contour– Retains water for crops controls runoff– Marginal areas, Poor farmers, little time / manpower
• 2. Contour Plowing– Plowing and planting crops in rows across the
contour of gently sloping land– Each row holds soil and slows runoff
Reducing Wind Erosion
1. Strip cropping
- planting alternative strips of (1) row crop like corn and (2) another crop like grass or legumes that completely covers the soil
- Cover strips (1) trap soil that erodes from row crop (2) catch & reduce runoff, (3)help prevent spread of pests, (4) restore soil fertility
Reducing Wind Erosion
2. Alley Cropping-Crops planted in strips or alleys
between rows of trees and shrubs which themselves are harvestable for wood or fruit
-Trees & shrubs provide
1. Shade, reducing evaporation water loss
2. Retain and slowly release soil moisture
3. Provide fruit, fuelwood, clippings for mulch (green manure)
4. Livestock fodder
3. Shelter Belts / Wind breaks
Reduce wind effects
1. Less erosion
2. Retain soil moisture
3. Supply products
4. Habitat for animals including birds and insects that eat pests
Can we Maintain & Restore soil Fertility? Soil Conditioners
• Fertilizers: compounds that partially restore important soil nutrients lost by erosion, leaching and harvesting crops
• Condition soils with– Organic Fertilizers: made of plant and animal
materials that are biodegradable– Lime: Increase alkalinity of the soil
improves fertility
Organic Fertilizer Benefits• Organic Fertilizers1. Animal Manure: improves
soil structure, nutrients, stimulates bacteria & fungus growth
2. Green Manure: Vegetation plowed into the soil increases organic content
3. Compost: Brown humus material, aerates soil, improves water holding, prevents erosion, recycles nutrients
4. Fungus spores: moisture control, disease resistance
• Inorganic Fertilizers 1. Nitrogen, Phosphorous,
Potassium 2. Easily available, transported,
stored and supplied3. Help Produce crops in 3rd
worldBUT1. Not adding humus or other
essential nutrients2. Lower oxygen, organic
matter in soil
3. Raise N2O in atmosphere (greenhouse gas)
Soil Management Strategies
• Differ depending on the agricultural system you are observing
• Comparison of Florida sugar cane farming (commercial farming) and slash and burn (subsistence farming)
Florida sugar Cane
• Soils of everglades Agricultural area are rich in organics formed from 4,400 years of sawgrass decomposition
• Soils are “muck soils” and must be drained for crop growth
• Even with high organic matter need inputs to keep soil fertile – N, P, K all added on the order of 0-30 lbs per acre each year depending on specific area differences
• Soil subsidence happening because of uptake of organics
• Water is seasonally available so may need suplementation
Slash and Burn Agriculture
• Mainly associated with Tropical Rainforest areas
• Madascar, Malasia, Central America
• Usually small scale subsistence
• Practiced in areas with poor soils
• Harvest wood, burn unusable portions
• Temporary pulse of nutrients from burning
• Ash also increases pH of soil
• Burning can drive off pests too
Slash and Burn II
• Land only fertile for a few years
• Abandoned when fertility declines
• Forces burning of more land
Review Points
• Know your horizons: O, A, B, C
• Soil composition: sand, silt, gravel, clay
• Wind and water erosion
• Desertification and Salinization
• Soil conservation Methods
• Fertilizer uses