5.3 Soil Degradation and Conservation

IB ESS

Mrs. Page

SIGNIFICANT IDEAS

• Fertile soils require significant time to develop through the process of succession.

•Human activities may reduce soil fertility and increase soil erosion.

• Soil conservation strategies exist and may be used to preserve soil fertility and reduce soil erosion.

KNOWLEDGE AND UNDERSTANDINGS:

• Soil ecosystems change through succession. Fertile soil contains a community of organisms that work to maintain functioning nutrient cycles and that are resistant to soil erosion.

• Human activities that can reduce soil fertility include deforestation, intensive grazing, urbanization and certain agricultural practices (such as irrigation and monoculture).

• Commercial, industrialized food production systems generally tend to reduce soil fertility more than small-scale subsistence farming methods.

• Reduced soil fertility may result in soil erosion, toxification, salination and desertification.

• Soil conservation measures include soil conditioners (such as organic materials and lime), wind reduction techniques (wind breaks, shelter belts), cultivation techniques (terracing, contour ploughing, strip cultivation) and avoiding the use of marginal lands.

APPLICATION & SKILLS

• Explain the relationship between soil ecosystem succession and soil fertility.

•Discuss the influences of human activities on soil fertility and soil erosion.

• Evaluate the soil management strategies of a given commercial farming system and of a given subsistence farming system.

2 TYPES OF SOIL DEGRADATION

• Erosion – processes that take away the soil• Can be due to wind or water• Occurs mainly when lack of vegetation to stabilize soil

(deforestation, overgrazing)

•Making Soil Unusable• Pollutants making soil toxic• Leaching of nutrients from soil to point it cannot support

producers (deforestation, unsustainable agricultural practices)

SOIL EROSION

•Movement of soil, especially surface litter and topsoil

• Two main agents of erosion:• Wind• Flowing Water

SOIL EROSION

•Occurs due to loss of plants in the soil from:• Overgrazing• Deforestation• Irrigation

GLOBAL SOIL EROSION

Stable or non-vegetative

Some concern

Serious concern

Top Soil Erosion and Run-Off from Farm

Gully Erosion in Bolivia

Wind Removing Topsoil

Sheet Wash Erosion (Landslide) Due to Deforestation

Erosion is Harmful

• Leads to loss of fertile soil

• Increases runoff of sediment and pollutes water, killing aquatic organisms

Other Soil Issues

SALINIZATION• Irrigation water contains small amounts of dissolved salts

•Evaporation and transpiration leave salts behind

•Salt builds up in soil

Other Soil Issues

WATERLOGGING•Precipitation and irrigation water move downward

•Water table rises

•Soil saturated or impermeable

TOXIFICATION

An increase in soil acidity ( low pH = more acidic)

Caused by leaching of metalsBurning of plant material increases soil pHCan be counteracted by using lime stone to

raise the pH and reduce acidityLarge problem in the Ohio valley in the USA

due to coal power plants

UNSUSTAINABLE AGRICULTURAL PRACTICES

•Complete removal of crops after harvest (no vegetation makes soil susceptible to erosion)

•Growing crops with barren soil between rows (erosion)

•Plowing in direction of slope (creates channels)

•Overuse of pesticides (toxification)

•Overuse of chemical fertilizers (eutrophication)

• Irrigation methods (salinization)

•Monocropping (nutrient depletion)

•Overcropping (nutrient depletion)

SOIL CONSERVATION

• Improve farming Methods:•Terracing•Contour planting•Strip cropping with cover crop•Alley cropping, agroforestry•Windbreaks or shelterbelts•Conservation-tillage farming

Terracing

•Reduces soil erosion - controls water runoff by holding water at each level.

Contour Planting/ Strip Cropping

• Each row acts as a small dam to help slow water runoff and reduce soil erosion

ALLEY CROPPING

•Crops planted in alleys between trees/shrubs. Provides shade and helps slow down the release of soil moisture.

WINDBREAK

•Crops planted in alleys between trees/shrubs. Provides shade and helps slow down the release of soil moisture.

COVER CROPS

• Fast growing crops that cover soil between rows of main crop or between harvests.

•Prevents soil erosion, adds nutrients back to soil

COMPARISON OF FARMING SYSTEMS

•Commercial Grain Farming in USA• Commercial – growing

with aim of profit• Machine intensive• Mechanical large spray

irrigation• Pesticide and chemical

fertilizer intensive• Huge fields, monocrops• GMO crops common

•Patty Rice Farming Bangladesh• Subsistent farming –

growing for immediate friends and family

• Mostly human or animal labor

• Rely on nature weather patterns & river cycles

• Natural fertilizers (manure)• Small plots of land

Thinking Routine: Generate, Sort, Connect, Elaborate

• As a group – generate a list all of the words/ideas you know about SOIL.

• Sort your list into groups- discuss what the groups are and why you are placing items in each group

• Now make connections between the different groups – how are they related?

• As a group decide on a central theme or concept for your ideas

• Individually – elaborate on what you know about soil by completing the following prompt• I used to think… now I think… (support your ideas with reasoning)

HOMEWORK

Read pp. 265 – 271

Practical Work Box p. 270

(different examples from class)