5.1 - Introduction to Soil System

Soil Systems and Society - 5.1 Introduction to Soil Systems

What is soil?

a complex ecosystem that is made up of minerals, organic material, gases and liquids which forms the habitat for many animals and plants. it’s found in layers/horizons

What sphere is the soil a part of?

the pedosphere

Where is the pedosphere?

between the biosphere and lithosphere

What influences the pedosphere?

the atmosphere, hydrosphere and lithosphere

Storages in soil

Organic matter, organisms, nutrients, minerals, air and water

Transfers within soil

Biological mixing, translocation (movement of soil particles in suspension) and leaching (minerals dissolved in water moved through soil)

Inputs

Organic material including leaf litter and inorganic matter from parent material, precipitation and energy

Outputs

Uptake by plants and soil erosion

Transformations

Decomposition, weathering and nutrient cycling

Systems Diagram

Systems Diagram

What makes up rock particles?

Insoluble - gravel, sand, silt, clay, chalk
Soluble - mineral salts, compounds of nitrogen, phosphorus, potassium, sulphur, magnesium

What makes up humus?

Plant and animal matter in the process of decomposition

What makes up water?

Water either seeping down from precipitation or moving up from underground sources by capillary action

What makes up air?

Mainly oxygen and nitrogen

What makes up soil organisms?

Soil invertebrates, microorganisms, and large animals

Function of rock particles

• provides the skeleton of the soil

• derived from the underlying ___ or from ___ particles transported to the environment (ex. glacial hill)

Function of humus

• gives the soil a dark colour

• returns mineral nutrients back to the soil

• absorbs and holds on to a large amount of water

Function of water

• dissolved mineral salts become available to plants

• rapid downward movement of ___ causes leaching of minerals

• rapid upward movement can cause salination

• large volumes of ___ in the soil can cause waterlogging, leading to anoxic conditions and acidification

Function of air

• well-aerated soils provide ocygrn for the respiration of soil organisms and plant roots

Function of soil organisms

• large particles of dead organic matter are broken down by soil invertebrates like worms, leading to smaller particles

• smaller particles are then decomposed by ______________ thus recycling mineral nutrients

• larger burrowing soil animals (ex. moles) help mix and aerate the soil

Translocation

involves the movement of soil-forming materials through the developing soil profile

How does translocation occur?

by water running through soil transferring materials from upper to lower portions of the profile.

Salinization

when water is evaporating at the soil surface and water from lower soil layers moves upwards. it dissolves materials and takes them to the surface. happens in hot, dry climates when precipitation < evaporation

Leaching

in colder and wetter climates when water flows down in the soil, dissolving minerals and transporting them downwards. when precipitation > evaporation

The quality of soil influences what?

The primary productivity of an area. The better the quality of soil, the better the productivity

What is soil vital for?

• Plant survival

• Crop production

• Habitat

• Water filtration

• Foundation

• All food we depend on

• Stores & transfers heat

Factors that affect soil

• underlying rock (parent rock)

• climate

• topography

• biological factors

• time

The role of soil in water movement

• Precipitation (rain in porous soil then infiltrates the soil and gets to the roots, watering plants) or (rain in compacted soil, leading to runoff)

• Evaporation

• Transpiration when water from the soil turns into water vapor and moves to the atmosphere

The role of soil in carbon cycling

Atmospheric CO2 → Aboveground Crop → Soil Detritus → Soil CO2 → back to Atmospheric CO2

Atmospheric CO2 → Aboveground Crop → Crop root system → Soil Detritus/Soil Co2 → back to Atmospheric CO2

The soil food web

1st trophic level: Photosynthesizers

2nd tropic level: Decomposers, Mutualists, Pathogens, Parasites, Root-feeders

3rd trophic level: Shredders, Predators, Grazers

4th and 5th+ trophic level: Higher level predators

What is biota?

All the plants, animals, algae, fungi and microbes in an ecosystem

Role of biota in soil formation

• Plants hold parent material in place

• Roots bind soil particles together and increase water filtration into the soils, reducing runoff and erosion

• Roots growing in cracks and fissures break apart rocks, speeding up soil formation

• Lichens on rocks increase weathering

• Vegetation is the initial source of the carbon fixed by photosynthesis that becomes organic matter in the soil

How does vegetation affect microclimates with relation to the role of biota in soil formation?

• slowing wind speeds

• shading soil surface

• retaining snow

resulting in cooler and more moist soil environments

Soil Upper Levels

Have been altered due to the climate or organisms

Soil lower boundary

Hard rock that is devoid of biological activity

What is included in a soil profile?

O - Humus

A - Zone of leaching of soluble salts (top soil)

B - Zone of accumulation of salts (subsoil)

C - Weathered parent material (bedrock)

Gradational Contact

Fresh parent material (bedrock)

What is included in soil horizons?

O Horizon - Organic material/leaf litter

A Horizon - Mixed mineral-organic (humus layer)

E Horizon - Eluvial or leached

B Horizon - Illuvial or deposited

C Horizon - Weathered rock from which the soil forms

R Horizon - Parent material (bedrock)

The soil system

Soil Structure

Made up of: Clay, Silt, Sand

Clay Soils are

< 0.002 mm in diameter

• consist of very small particles with tiny gaps holding water by surface tension

• feel sticky and can be rolled up into a ball easily

• rich in nutrients and organic matter

• not evenly mixed or easily available to plants

• become waterlogged due to poor drainage

• poorly aerated

Low primary productivity and low biodiversity

Silty Soils are

0.002 - 0.05 mm in diameter

• feel slipper like wet talcum powder and hold together better than sandy soils

Sandy Soils are

0.005 - 2 mm in diameter

• gritty and can fall apart easily

• have large spaces between large particles (leading to large air spaces) making sandy soil well drained and well aerated

• have low nutrient availability to plants because minerals and nutrients are easily washed out (LEACHING)

low biodiversity due to low potential to hold organic matter, low primary productivity and little biota

Loam Soils:

• have particles of a variety of sizes

• mineral particles are held together by humus which holds water, nutrient ions, and mineral particles

• Larger structures made of mineral particles are called “crumbs”

• humus contains abundant biota

• bacteria and fungi are important in the nitrogen and carbon cycle

• soil organisms greatly contribute to soil fertility, removing and digesting detritus from the soil surface and then releasing nutrient ions which roots can take

• worm channels improve drainage, help aeration and help root growth

• crops grow better in the presence of earth worms

Soil Texture Triangle

Follow the direction of the arrows

Porosity

The amount of space between particles (with relation to a soil’s texture)

Permeability

The ease at which gases and liquids can pass through the soil.

Acidification of soils

Major impact on forestry in Northen Europe where ____ rain cause by industrial pollution has made the soil more ___.

Soil Sustainability

Fertile soil is a non-renewable resource

It is not inert and stable. It develops, evolves, and changes

Soil formation takes 1000s of years

Soil use often exceeds soil formation

Main nutrients in fertile soil

nitrates, phosphates, and potassium. These _____ can be leached out of soil or removed when a crop is harvested

How can nutrients be replaced in agricultural soils?

via chemical fertilizer, growing legumes, crop rotation, or through the application of organicmatter (manure/compost)

O Horizon

Organic material/leaf litter

A Horizon

Mixed mineral-organic (humus layer)

E Horizon

Eluvial or leached

B Horizon

Illuvial or deposited

C Horizon

Weathered rock from which the soil forms

R Horizon

Parent material (bedrock)

Soil pH influences

• soil bacteria

• nutrient leaching

• soil structure

pH in soil

Affects whether the plant can use nutrients or not

Term for low pH soil

Acidic Soil

Term for high pH soil

Alkaline Soil

Compare and Constrast table