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

vocabulary

• Soil

• Soil profile

• Biodegradable

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

Draw Diagrams linking the soil to the atmosphere, lithosphere and living things

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

Profiles from different biomes, will show different horizon size

and composition

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

Water Water

High permeability Low permeability

Particle Size and Permeability

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

http://en.wikipedia.org/wiki/File:Canjuers_Moutons.jpg

DO NOT POST TO INTERNET

DO NOT POST PHOTOS TO INTERNET

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

Areas of serious concern

Areas of some concern

Stable or nonvegetative areas

World Erosion concerns

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.

Colorado Kansas

DustBowl

Oklahoma

New Mexico

Texas

MEXICO

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

Moderate Severe Very Severe

World Desertification concerns

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

Unsustainable irrigation

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

Severe Salinization

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

Evaporation

Evaporation

Transpiration

Evaporation

Waterlogging

Less permeableclay layer

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

Terracing Contour planting and strip cropping

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

Strip Cropping

Alley cropping

Windbreaks

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

Big Sugar and Florida An Uncertain Future

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

References

• http://www.mo15.nrcs.usda.gov/