The Living Earth Chapter 15
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
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