ESS chap.5 Soil system and societies

Composition of soil

minerals

organic matter

air

water

Primary functions of soil

medium for plant growth

water storage

habitats for one-quarter of all living species (bacteria, insects..)

modifies the atmosphere through respiration (organisms + plant roots)

Spheres constituting the Earth

pedosphere (soil)

lithosphere (rocks)

hydrosphere (water)

atmosphere (air)

biosphere (living)

What factors affect soil characteristics?

climate: precipitation/evaporation balance (influence water movement)

organisms: role of decomposers

relief: elevation, aspect, and angle of the slope

parent material: original material that the soil develops from

time: amount of time the soil has had to develop

Translocation

movement of particles within the soil (up or down) through water

Salinization

when water and minerals flow up through evaporation (especially in deserts)

Leaching

when water flows down and transports/dissolves minerals (especially in places with heavy rainfall)

Cross-section of soil

O: leaf litter

where decomposition happens/most productive area

A: the organic material mixed with minerals (full of nutrients)

E: shows depletion of organic matter, clay, iron, aluminum

A + E = top-soil

B: sub-soil (rich in clay and iron)

C: where the bedrock starts breaking

R: hard bedrocks

Soil texture

Sand (0.05-2mm)

Silt (0.002-0.05mm)

Clay (<0.002mm)

loam = equal amount of sand, silt, and clay

result of parent material + type of weathering

Porosity + Permeability

the amount of space between the particles of the soil

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

the higher the porosity, the better the permeability

Acidification of soils

The high acidity in soils because of the evaporation, that soaks up the minerals out of the soil.

Inputs of soil

• minerals: from the weathering (breakdown of material by physical, biological, and chemical processes)

• organic matter: from living organisms on (ex: decomposition) and in the soil

• gases: by plants, nitrogen fixation (transforms nitrogen of the atmosphere in nitrates and ammonia) + c02 by living organisms

• water: depends on the slope

Stores of soil

• organic matter: dead organic matter (DOM) stores nutrients

• minerals: forms the parent material

• gases and water: depends on weather conditions + nbr of organisms and plant roots + soil texture

• organisms: add nutrients through waste

• nutrients: stored in the organic matter or free in the soil

Outputs of soil

lose of minerals, organic matter, water, and gases (inputs) through :

• the action of the wind: blows loose soil away

• water: leaches minerals and washes out the clay particles

• plants: take away nutrients + CO2

• animals: eat clay-based soil + herbivores

Soil properties

Sandy

• big particles

• large pores so high porosity and permeability

• warm up quickly due to high air content + subject to drought

Silt

• small particles

• smooth feel

• properties between sand and clay

Clay

• smallest particles

• small pores so low porosity and permeability

• long dry time + warm up slowly due to high water content

• rich in nutrients

Nutrient cycle

Dust Bowl

• 1930s

• USA - Texas, Colorado, New Mexico, Oklahoma, Kansas (Midwest)

Causes

• Poor farming methods: overuse of the land, left fallow

• Drought

• Windy conditions: swept topsoil formed dust storms

Consequences

• no harvest

• destruction of the land + infrastructures

• starvation

• death (dust pneumonia)

• migration of farmers

Soil inputs and outputs schema

Nitrogen cycle

large vs small farms

Case study : comparison Quesungual system in Honduras vs Large commercial farming in South Australia

SIMILARITIES

• no-till (no plough) + use of cover crops (oats)

• improved organic content and soil nutrients

• retain soil moisture and control run-off

• increase productivity

• reduce soil erosion and improve climate resilience

DIFFERENCES

• Quesungual covers the soil in mulch (compost) while South Australia also uses crop rotations, windbreaks (paravent) and advanced irrigation

• Quesungual uses tree roots on hills while South Australia uses sandy and flat soils

• Quesungual is a typre of subsistence farming so small-scale and diverse while South Australia is commercial farming so large-scale and mechanized

• Quesungual can act as a carbon sink (especially after the stop of slash and burn) while South Australia is emptier