ESS: Unit 5 - Soil

Transfers across soil horizons (into and out of soils)

• infiltration

• percolation

• Groundwater flow

• aeration

• erosion

• leaching
  (Transfers as they involve movement without changing the nature or state of the material)

Percolation

When water moves down through the soil, going deeper into the ground.

It's the water that soaks through the soil after rainfall or irrigation, moving down toward the groundwater.

Aeration

Air moves into the spaces (pores) between soil particles.

How oxygen gets into the soil, which is important for plant roots and soil organisms to breathe.

Leaching

When water carries nutrients or minerals down through the soil.

Rain or irrigation water washes things like salts or nutrients deeper into the ground, sometimes out of reach for plants.

Why leaching is bad

• It removes important nutrients (like nitrogen, potassium, phosphorus) from the soil, making it less fertile for plants.

• It can carry harmful chemicals (like fertilizers or pesticides) down into groundwater, polluting drinking water sources.

• It wastes resources; farmers might need to use more fertilizer to replace what's lost.

Transformations within soils changing the components or the whole soil system.

• Decomposition

• Weathering

• Nutrient Cycling

• Salinization

Decomposition

The process where dead plants, animals, or organic matter break down into simpler substances like nutrients, carbon dioxide, and water. (therefore a transfer as its being chemically broken down to a new substance)

Weathering

The breaking down of rocks and minerals into smaller pieces by physical, chemical, or biological processes.

Nutrient Cycling

The process where nutrients move through the environment, from soil to plants, animals, decomposers, and back into the soil.

A transformation due to nutrients often changing form during the cycle.

EX:

Nitrogen gas in the air → converted by bacteria into forms plants can use (like nitrates).

Organic nitrogen in dead plants → broken down into ammonium and then nitrates by bacteria.

Salinization

The buildup of salt in the soil, usually caused by the evaporation of water, leaving salt behind.

A transformation because salinization changes the soil's condition, it increases the salt content, which can affect plant growth and soil health.

Terrestrial ecosystems

Ecosystems found on land, like forests, grasslands, and deserts.

Soils as the Foundation for Terrestrial Ecosystems Medium for plant growth during secondary succession

• Seed banks: Soils contain dormant seeds that can germinate after a disturbance, kick-starting plant re-colonization.

• Water reservoir: Pore spaces in soil hold and release moisture to roots as needed.

• Nutrient store: Almost all essential plant nutrients (especially nitrogen, phosphorus, potassium) are held in the soil matrix and made available via root uptake.

• Carbon exception: Unlike other nutrients, carbon is drawn directly from atmospheric CO₂ by photosynthesis rather than from the soil.

Characterstics of highly productive soil (know atleast 4)

• presence of sufficient nutrients/minerals (N, P, K)

• Lots of nitrogen-fixing bacteria

• absence of toxic substances

• Contains adequate organic/humus content --> helps retain moisture

• a good mix/ loamy soil/ balanced clay + silt + sand --> leads to optimal infiltration

Which biomes store more carbon

• Boreal forests: cold, waterlogged soils slow decay

• Wetlands: waterlogged, low-oxygen soils let peat pile up

• Temperate grasslands: deep roots bury carbon underground

• Tundra: Cold temperatures and short seasons slow decomposition, so carbon builds up in the soil rather than being released.

• Croplands: leftover roots and plant residues add organic matter into the soil, storing carbon.

Which biomes store less carbon

• Tropical forests: High heat and humidity speed up soil decomposition, so fallen plant material in the tropics is broken down almost immediately by microbes, releasing carbon back into the air and driving a rapid carbon cycle.

• Temperature forests: moderate weather and seasons speed decay, so carbon stays in trees and leaves rather than the soil.

Reasons for food waste

• Poor agricultural practices: Ex: Overwatering tomatoes encourages fungal rot in the field, so farmers must discard large amounts before they ever reach market.

• inadequate infrastructure for transporting food

• poor storage facilities

• strict sell-buy dates

• Western demand for perfect food

Soil horizons

The distinct layers of soil, arranged from the surface down, each with its texture and composition, the darker the horizon, the more organic it is.

Nomadic pastoralism

Practice of moving herds of livestock to different pastures throughout the year.

Commonly used in arid to semi-arid regions where soil + water resources cannot support continuous farming. (harsh dry climates)

Strength of Nomadic Pastoralism

• In areas with low pop density, nomadic pastoralism can be sustainable as it prevents overgrazing, allowing the land time to recover as herders move.

Weakness/limitation of Nomadic Pastoralism

As populations grow or when herders are restricted to smaller areas, overgrazing can lead to soil degradation and desertification.

Slash-and-burn agriculture

A method in which forests or woodlands are cleared by cutting and burning vegetation. Resulting in nutrient-rich ash which fertilizes the soil, allowing crops to be grown for a few years before the land is left fallow to regenerate.

Strength to Slash-and-burn agriculture

In areas with low pop density, the method can be sustainable as the land is given time to recover during the fallow period. The method (slash-burn) is part of complex cycles of land use that maintain biodiversity and forest ecosystems.

Fallow periods

Planned intervals when farmland is left unplanted so the soil can recover.

Weakness/limitation to slash-and-burn agriculture

As pop increases, fallow periods become shorter, preventing the forest from regenerating and leading to deforestation, soil erosion, and loss of biodiversity.

Positive impacts of synthetic fertilizers

• High Productivity: they significantly inc crop yields, allowing farmers to inc production despite the same area.

• Rapid Plant Growth: Rapid plant growth: synthetic fertilizers supply nutrients in forms plants can absorb immediately, speeding up growth and shortening time to harvest.

• Enhanced Commercial Output: Market demand for crop staples can be met

• Reliable and immediate nutrient supply: Farmers can apply precise amounts of (N, P, K).

Negative impacts of synthetic Fertilizers

• Soil degradation: long-term use of syn fertilizers reduce organic matter + disrupting soil organisms

• Water Pollution: Runoff into water bodies = Algal blooms/ Eutrophication

• GHG emissions: The production of N-based fertilizers is energy-intensive.

Contour ploughing

A soil‐conservation technique in which farmers plough along the natural contours (level lines) of a slope rather than up and down the hill.

Prevents rainfall from running down the slope, slowing it down at each furrow, which

->reduces surface runoff velocity

->increases water infiltration into the soil

Bunding

Bunding involves building small embankments or ridges (bunds) along the field edges to form shallow pockets that catch and hold rainfall.

Bunds trap water behind each embankment, reducing flow velocity, increasing soil infiltration + lowering flood peaks

Terracing

Carving a series of flat, level "steps" into a steep slope to create horizontal planting areas.

Stops runoff by breaking the slope into segments, giving rainwater time to infiltrate rather than rush downhill.

Agroforestry

A sustainable land-use system where trees or shrubs are intentionally combined with crops and/or livestock on the same piece of land to get environmental, economic, and social benefits.

• It improves soil quality (via shade, leaf litter, and nutrient cycling)

• It reduces erosion (tree roots hold the soil)

• It enhances water use (better infiltration, less runoff)

• It boosts long-term yields by combining multiple useful products (wood, fruit, crops, livestock) on the same land

Strip Cultivation

A soil conservation technique where crops are planted in alternating strips.

A planned planting method that protects soil, improves moisture retention, and maintains productivity by carefully arranging different crops in strips to manage runoff, erosion, and nutrient use across the land.

Sand

The largest soil particles, affecting drainage and aeration

Soil Profile

A vertical section of soil that shows all its layers or horizons.

Clay

The smallest soil particles, holding nutrients and water.

Silt

Soil particles of intermediate size, between sand and clay.

Loam

A soil type with balanced sand, silt, and clay, ideal for agriculture.

Humus

Rich, dark organic material formed by decomposition of plant and animal matter.

Soil carbon sequestration

The process of capturing carbon and storing it in the soil.

Permafrost

Permanently frozen ground affecting soil formation in cold regions.