Soils

What is soil made up of

Rocks, pebbles, humus, clods, plant roots, small animals, microorganisms

How did soil become what it is today?

Through the interaction of factors like parental material, climate, vegetation, living organisms, topography and time

What is the solid part of soil made of?

Mineral and organic matter

Aerated soil

Soil that has a healthy amount of air-filled pores

Small pores

contains water

Larger pores

contains air

A-horizon

The topsoil that contains more organic matter than the lower layers

What two layers may or may not be present in the soil profile

O horizon and E horizon

B horizon

The subsoil that usually contains more clay and lighter in colour than the topsoil

C horizon

The “parent material” found at the bottom and extends down to bedrock

How is the parent material formed as the 1st step in the development of soil?

Result of weathering of rocks from various sources

Volcanic activity

igneous rock

Depositing by glaciers, water or wind

sedimentary rock

Igneous or sedimentary rocks changed by great pressure, heat or both

metamorphic rock

Where is the soil poorly developed because of little weathering from rain

desert

What do bacteria and fungi do in soil

decompose organic mater like falling leaves and dead plants and animals

How do roots and living organisms play a role in dissolving minerals?

Roots and living organisms produce CO₂ which combines with the soil water to form an acid that increases the rate at which minerals dissolve

In what kind of areas would organic composition be much higher

In wet areas because there is a lack of oxygen therefore this prevents normal microorganism activity

On steep slopes how would soil wash/erode away?

Gravity, wind, water and ice

What kind of topography is ideal for soil development

Topography permitting drainage and little erosion

How is soil texture measured

relative to proportions of sand, silt and clay in soil

What does it mean when they say clay particles are sheet like, negatively charged?

Attract, exchange or retain positively charged ions for plant growth ( Mg²⁺, K⁺ and Ca²⁺⁾

List the soil textures components in ascending order

clay, cilt, sand

What are the best agricultural soils?

loams ( 40% silt, 40% sand, 20% clay)

Light/ course soils

High sand and low clay content therefore don’t retain lots of water

Heavy soils

High clay content therefore have a high water holding capacity and allow little water to pass through

What elements are found in the mineral composition

O, H, Si, Al, Fe, K, Ca, Mg, Na

What is an aggregate

the arrangement of the soil particles into groups

When do aggregates develop?

Develop when clay particles clump together and mainly a result of soil organism activities.

What do productive agricultural soils contain

Granular with pore spaces that take up 40-60% of the total soil volume

Why can too wet soils be harmful

Can create anaerobic conditions which interfere with the plants growth and can leach mineral nutrients leading to a slower release of N

Hydroscopic water

Physically bound to the soil particles and unavailable to plants

Gravitational water

Drains out of pore spaces after rain

Capillary water

Water held in soil pores against gravity forces, water is mainly taken up by plants

What factors determine the amount of capillary water available to the plant

Soil texture, structure, OM, density and the location of the underground water tables

Field capacity

Remaining water after draining

When do plants readily absorb water from the soil

when the soil is at or near field capacity

Plant available water ( PAW )

soil water between field capacity and permanent wilting point

What happens to the water films around soil particles when the soil dries out

Becomes thinner, more difficult for the roots to uptake, more tightly bound - leads to plants wilting

what pH conditions do tea and cranberries thrive under

acidic conditions

What plant does not survive in soils with pH extremes

Mycorrhizae

What do highly acidic soils inhibit

Inhibit the growth of nitrogen fixing bacteria

Why are acid soils more common in areas of high precipitation

Where base minerals ( Ca, Mg, K ) are leached from the topsoil

Liming

add compounds od calcium or magnesium to counteract soil in agriculture

How can we make alkaline soils more acidic?

Adding sulfur which bacteria convert into sulfuric acid

How can we lower the pH

N fertilisers