Topic-5.1-Introduction-to-soil-systems.pptx

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Topic 5: Soil and terrestrial food production systems and societies

Topic 5.1: Introduction

to soil systems

Starter:

1. What is soil?

2. Why is soil so important?

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Soil is a complex

ecosystem

• Minerals (Rocks)

• Organic material (Humus)

• Gases (Air)

• Liquids (Water)

• The exact mix of these four portions which give soil its characteristic.

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The majority of food we

consume depends

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“Too many people have lost sight of the

fact that productive soil is essential to

the production of food”

• _{Hugh Hammond Bennett was a}

pioneer in the field of soil conservation.

• _{He was convinced that soil erosion}

was a serious problem facing the planet.

• _{Reduces areas in which crops can be}

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Soil systems are dynamic

• _{Many complex systems are interlinked}

• _{Water cycle}

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5.1.U1 The soil system may be

illustrated by a soil profile that has a layered structure (horizons).

• _{The soil interacts with the atmosphere, lithosphere,}

biosphere and hydrosphere. The water cycle moves through the soil by infiltration and water may

evaporate from the surface.

• _{The atmosphere may contain particulate matter that is}

deposited on the soils and particles may blow up into the atmosphere.

• _{Rocks in the lithosphere weather to form soils, and soils}

at depth and pressure may form rocks.

• _{Plants in the biosphere may extract nutrients from the}

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Soil Horizons

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Soil Horizons

O Horizon:

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Soil Horizons

A Horizon:

Build up of humus.

Partially decomposed organic matter and fine mineral particles.

Dark layer or brown or black organic material – humus layer

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Soil Horizons

E Horizon:

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Soil Horizons

B Horizon:

Clay and Iron salts

deposited in this horizon.

Soluble minerals and

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Soil Horizons

C Horizon:

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Soil Horizons

R Horizon:

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Soils are important to humans in

many ways:

• soil is the medium for plant growth, which most of foods for humans are grown in

• soil stores freshwater, 0.005% of world’s freshwater

• soil filters materials added to the soil, keeping quality water

• recycling of nutrients takes place in the soil when dead organic matter is broken down

• soil is the habitat for billions of micro-organisms, as well as other larger animals

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Water carries particles up or down

the layers - translocation _{In colder, wet}

climates water flows down into the soil, dissolving minerals and transporting them downwards.

This is known as

leaching.

P>E

In hot, dry climates precipitation is less that evaporation (P<E).

This means that water moves up through the layers.

As water evaporates it leaves the minerals behind, this is called salinization.

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What type of soil?

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• _{Porosity –}_{The space between the particles}

• _{Permeability –}_{The ease at which gases and liquids}

can pass through the soil

Clay soils – High porosity (macropores), low permeability, high nutrients but inaccessible.

Sandy soils – High porosity (micropores), high permeability

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5.1.U2 Soil system storages

include organic matter,

organisms, nutrients,

minerals, air and water.

• _{Soil has matter in all three states:}

organic and inorganic matter form the solid state

• _{soil water(from precipitation, groundwater and}

seepage) form the liquid state

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Loam soils are best for

agriculture

• _{Sand ensures good drainage and good air supply} • _{Clay retains the nutrients}

• _{Silt hold the sand and clay together and make the}

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5.1.3U Transfers of material within the soil, including biological mixing and leaching (minerals dissolved in water moving through soil),

contribute to the organization of the soil

• _{Translocation involves the movement of}

soil-forming materials through the developing soil profile. Translocation occurs by water running

through the soil transferring materials from upper to lower portions of the profile. Burrowing animals like earth worms, ants, etc., move soil materials

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5.1.U4 There are inputs of organic material including leaf litter and inorganic matter from parent

material, precipitation and energy.

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Weathering (input)

• _{Rock weathering is one of the most important}

long-term sources for nutrients. However, this process adds nutrients to ecosystems in relatively small quantities over long periods of time. Important nutrients released by weathering include:

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Atmospheric (Input )

• _{Large quantities of nutrients are added to}

ecosystems from the atmosphere. This addition is done either through precipitation or by a number of biological processes.

Carbon - absorbed by way of photosynthesis.

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Biological Nitrogen

Fixation (Input)

• _{Biological nitrogen fixation is a biochemical process}

where nitrogen gas from the atmosphere is chemically combined into more complex solid

forms by metabolic reactions in an organism. This ability to fix nitrogen is restricted to a symbiotic associations with legumes and other

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Soil Erosion (Output)

• _{Soil erosion is probably the most import means of}

nutrient loss to ecosystems. Erosion is very active in agricultural and forestry systems, where cultivation, grazing, and clearcutting leaves the soil bare and

unprotected. When unprotected, the surface of the soil is easily transported by wind and moving water. The top most layers of a soil, which have an

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Leaching (Output)

• _{Leaching occurs when water flowing vertically}

through the soil transports nutrients in solution downward in the soil profile. Many of these

nutrients can be completely lost from the soil profile if carried into groundwater and then horizontally transported into rivers, lakes, or

oceans. Leaching losses are, generally, highest in disturbed ecosystems. In undisturbed ecosystems, efficient nutrient cycling limits the amount of

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Gaseous Losses (Output)

• _{High losses of nutrients can also occur when}

specific environmental conditions promote the export of nutrients in a gaseous form. When the soil is wet and anaerobic, many compounds are

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5.1.U5 Transformations include

decomposition, weathering and

nutrient cycling.

• _{The transformation and movement of materials}

within soil organic matter pools is a dynamic

process influenced by climate, soil type, vegetation and soil organisms. All these factors operate within a hierarchical spatial scale. Soil organisms are

responsible for the decay and cycling of both macronutrients and micronutrients, and their

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5.1.U6 The structure and properties of sand, clay and loam soils differ in many ways, including mineral and nutrient content, drainage, water-holding capacity, air spaces, biota

and potential to hold organic matter. Each of these variables is linked to the ability of the soil to promote

primary productivity

• _{Primary productivity of soils depend on mineral}

content • _drainage

• _{water-holding capacity} • _{air spaces}

• _biota

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Applications and skills

• _{5.1.A1 Outline the transfers, transformations,}

inputs, outputs, flows and storages within soil systems.

• _{5.1.A2 Explain how soil can be viewed as an}

ecosystem.

• _{5.1.A3 Compare and contrast the structure and}

properties of sand, clay and loam soils, with