The Living Earth

Chapter 15

Where does soil come from?

•Rocks•Minerals

•Organic Matter

Ecological definition of soil

• Soil is a mixture of mineral particles, organic matter, water, and air that is capable of supporting plant life

What is a Soil Profile?

a vertical section of soil from the ground surface to the parent rock

Bedrock

• Igneous, metamorphic and sedimentary rock of the lithosphere

Bedrock is the parent rock For soil (as it breaks down)

Pavement is the bedrockof the desert

How are climate and soil thickness related?

Sagebrush-Cold Desert

Profile is only a few cm thick due to lack of water to break down the bedrock

Desert Varnish—leaching of minerals and flowing over rocks

Permafrost

What are the main components of soil?

• Mineral Matter• Air

• Water• Organic Matter

Mineral component

• Anchorage for plant roots.• Pore space for water and air.• Source of many plant nutrients through

weathering.• Exchange sites for plant nutrients.

Organic component

• Source and exchange site for nutrient cycling.• Influences soil structure, pore space, and

water holding capacity.• Energy source for soil microbes and other

heterotrophs.

Water component

• Solvent for many essential plant nutrients.• Maintains equilibrium between cation and and

anions that are held on exchange sites.

Air component

• Contains O2 for aerobic metabolism of plant roots and soil organisms.

• Exchange of CO2 from soil respiration and which facilitates weathering.

• Provides N2 for N-fixing soil organisms.

Why are soils so crucial to ecological studies?

• They provide all or part of all essential factors for plant growth except light.• Rooting material for the plants: the platform on which trophic levels of the ecosystem are built.• Contains most of the decomposers that recycle energy

and nutrients of the ecosystem.• Contain the history of the site, which can be interpreted through paleoecological reconstructions.• The soil is an ecosystem in itself (producers, consumers, and decomposers

What are the FACTORSthat make SOIL?

TIME1000’S TO 10,000’S OF YEARS

LAY OF THE LANDTOPOGRAPHY

LIVING ORGANISMSANIMALS AND PLANTS

CLIMATEHOT/COLD, WIND/RAIN

PARENT MATERIALROCKS AND MINERALS

Major process of soil development

Physical weatheringChemical weatheringDecompositionMineralizationNitrification

Physical weathering:

• The breakdown of rock (the regolith) into finer particles through weathering

Chemical weathering:

• The breakdown and redeposition of organic and inorganic substances primarily

through the processes of oxidation, dissolving, and leaching.

Decomposition:

• The breakdown of organic matter by bacteria and fungi into simpler organic substances

(carbohydrates, lignins, proteins).

Mineralization:

• The ultimate breakdown of organic substances into nonorganic substances (minerals, carbon

dioxide, water, salts).

Nitrification:

• The transformation by soil bacteria of ammonia compounds into nitrates and nitrites.

What causes soil erosion?

WaterWind

No Vegetation

Over half of the topsoil has been lost over the past

200 years

Salinization

• Accumulation of salts in the soil

Causes: • Natural• Irrigation by raising groundwater level

temporarily and evaporation

Soil and Erosion Consequences-Topsoil loss (90% of soilfertility)– Sedimentation (rivers andcoastal ecosystems)– Desertification – loss ofwater-holding propertiesof soils

Desertification & Land Degradation

• Land Degradation happened when human activity or natural processes damage the land so that it can no long support the local ecosystem.

• Desertification is the process by which land in arid or semiarid areas become more desert like due to human impact.

What are some practices

Of

SOIL CONSERVATION?

TerracingStrip Cropping

Contour PlowingTilling

Wind BreaksGround Covers

Organic Farming

Ecosystem management rather than external inputs• Considers environmental and social impacts of

fertilizer and pesticide use• Conserves water and soil• Certification: USDA accreditation (farms must be

certified)• Organic products: 100%organic, organic (95%), > 70% organic, < 70% organic

Does Organic Farming Work?

21-y Swiss study (2002)– Yield – 20% less– Resource use reducedFertilizer (34-53%)Pesticides (97%)– Increased biodiversity• Health benefits– WHO: 3.5-5 million pesticidepoisonings per y– Nutrient content– Benefits to consumers?

How did the Canyon Lands of Utah form?

Construction

Overgrazing

Pest Control

Insects eat approx imately 13% of crops in North America

Pesticides are chemicals used to kill insects, weeds, and other crop pests.

Pesticide Issues

• Pesticide Resistance---evolution of resistance• Human Health Concerns--cancer rates; illness of workers• Pollution and Persistence--pesticides are designed to not break down

rapidily—so they accumulate in soil and magnify up the food chain

Biological Pest Control

• Introduction of a non-native species can remain unchecked and go wild unless natural predators are in ecosystem

• Pathogens—using bacteria to control pests

• Defensive Chemicals from plants--biodegradable