Soil Formation, Horizons & Conservation

Soil Formation

• Soil is composed of organic matter, minerals, gases, liquids, and organisms.
• Soil forms from the weathering of rocks (physical and chemical).

Soil Horizons

• O Horizon: Humus (organic matter).
• A Horizon: Topsoil, mix of organic and mineral material, subject to leaching.
• B Horizon: Accumulation of metals and nutrients, location for testing.
• C Horizon: Least weathered, similar to parent material.
• R/D Horizon: Unweathered/partially weathered bedrock.

Soil Conservation

• Contour Plowing: Plowing follows land contours.
• Windbreaks: Rows of trees to prevent wind erosion.
• No-Till Farming: Growing crops without disturbing the soil.
• Cover Crops: Crops rotated to replenish nutrients and ground cover.

Soil Composition

• Soil particles (smallest to largest): Clay → Silt → Sand.
• Loam is the best soil for agriculture.

Porosity vs. Permeability

• Porosity: Measure of open spaces in soil.
• Permeability: How easily fluids move through soil.

Watersheds

• Watersheds are areas where streams and rivers drain into a larger body of water.
• Runoff impacts downstream water quality.

Biogeochemical Cycles

• Carbon Cycle: Key for photosynthesis, atmospheric reservoir is CO2. Humans impact through fossil fuel use and deforestation.
• Nitrogen Cycle: Essential nutrient for life, atmospheric reservoir is N2. Humans impact via synthetic fertilizers and fossil fuel burning.
• Phosphorus Cycle: Essential for DNA, ATP, and RNA; found in sedimentary rock. Human impact through erosion.
• Water Cycle: Moves nutrients through ecosystems; ocean is the largest reservoir. Human impacts include impervious surfaces causing flooding.

Detailed Nitrogen Cycle

• Nitrification: Ammonia changes to nitrite and nitrate.
• Denitrification: Nitrate turns into nitrogen gas (N2).
• Assimilation: Producers create proteins from nitrogen.
• Nitrogen Fixation: Bacteria convert atmospheric N2 to usable forms.
• Ammonification: Bacteria/fungi convert nitrogen in waste to ammonium.

Clearcutting

• Clearcutting: Removing most or all trees.
• Environmental Impacts: Habitat loss, biodiversity loss, soil erosion.

Green Revolution

• Increased crop production using fertilizers, pesticides, and high-yield varieties.
• Innovations: Chemical fertilizers, pesticides, fossil fuels, farm machinery.

Agricultural Practices & Impacts

• Organic Compounds: Contain carbon AND hydrogen. (ex: alcohol, proteins)
• Inorganic Compounds: Lack carbon-hydrogen bonds (ex: water, phosphate)
• Humans began agriculture ~10,000 years ago.
• Global food production (highest to lowest): Corn → Rice → Wheat.
• Tilling: Plowing impacts soil erosion, structure, and runoff.
• Slash-and-burn: Releases CO2, harms habitats, and reduces biodiversity.
• Organic Fertilizers: From plants/animals
• Inorganic Fertilizers: Synthetic, more prone to runoff.

Irrigation Methods

• Drip irrigation is the most efficient.
• Furrow irrigation is the least efficient.

Salinization

• Buildup of salts in soil from irrigation or aquifer overexploitation.
• Solutions: irrigation improvements, drainage, desalination, aquifer replenishment.

Aquifers

• Body of permeable rock holding groundwater.
• Ogallala Aquifer (Great Plains, USA) primarily used for agriculture.
• Impervious surfaces prevent aquifer replenishment.

Pest Control & IPM

• DDT: Broad-spectrum pesticide, banned due to environmental impacts.
• Integrated Pest Management (IPM): Uses multiple methods including biological control.

GMOs

• Genetically modified organisms (GMOs) created in labs.

Meat Production

• Meat production is inefficient due to high resource use.
• Developed countries consume more meat.
• Overgrazing: Damages vegetation, leading to desertification.
• Free Grazing: Cows graze freely.

Ecological Footprints

• Ecological footprint: Environmental impact of a person/community.
• Developed countries have larger footprints due to higher consumption.

Sustainable Agriculture & Forestry

• Sustainable agriculture: Planting vegetation strips, no-till farming.
• Sustainable forestry: Reforestation, wood reuse, ecologically sustainable wood, prescribed burns.

Sources of Pollution

• (Note: A table comparing point and non-point sources is not included here.)

Human Impacts on Ecosystems

• Range of tolerance: Ideal abiotic conditions for species survival.
• Oil spills: Harm marine organisms, negatively impact the economy.
• Ocean dead zones: Caused by excess nutrients, leading to oxygen depletion.
• Mercury: Enters through acid mine drainage and fossil fuels. Methylmercury biomagnifies.
• Litter: Creates hazards and introduces toxins.
• Sediment pollution: Reduces light penetration, harming producers.

Endocrine Disruptors

• Chemicals that interfere with the endocrine system.

Wetlands & Mangroves

• Wetlands provide water purification and flood protection.
• Mangroves are threatened by development and fish farming.

Eutrophication

• Excessive nutrient enrichment (nitrates/phosphates).
• Hypoxia: Lack of oxygen.
• Oligotrophic vs eutrophic waterways.

Thermal Pollution

• Warmer water holds less oxygen.

Persistent Organic Pollutants (POPs)

• Synthetic, carbon-based molecules that don't easily break down.
• Bioaccumulate in fatty tissues.

Bioaccumulation & Biomagnification

• Bioaccumulation: Substance builds up in an organism's tissues.
• Biomagnification: Concentration increases up the food chain. DDT impacted Bald Eagles. Mercury, PCBs affect human health through biomagnification.

This lesson covers the process of soil formation, its physical and chemical weathering, and the composition of organic matter, minerals, gases, liquids, and organisms including soil horizons, and different methods, such as contour plowing, windbreaks and crop rotation used for soil conservation. Loam is described as best for agriculture.