The Soil System

What is soil? This is the definition of soil

• Soil is a complex ecosystem

• It is a mixture of: • inorganic mineral particles

• organic material from decomposed flora and fauna

• Gasses and liquids

All of which forms the habitat for many animals

Simply putThis This

Soil is important!

• All the food we consume depends ultimately upon soil

• Plants grow in it and we either eat the plant or the animals that eat the plants

• It is a habitat for many organisms

• Holds water and mineral nutrients that the plants depend on.

• Soil filters water often altering the chemistry of water

• Stores and transfers heat so affects atmospheric temperature

Soils components

• mineral materials

• nutrients

• sand

• silt

• clay

• organisms

• dead organic matter / humus

• water

• air/gases

How do huge rocks become soil?

Rocks provide the inorganic components of soil.This happens in 2 ways. 1) weathering (the processes involved in breaking down exposed rocks) and

Don’t write background info onlyWeathering water gets into the gaps freezes and ice expands rock. This process will cause chunks of rocks to break off

How do huge rocks become soil?

2) Erosion (the movement and further breaking down of Earth’s surface by the action of water, glaciers, winds, waves, etc.)

How do huge rocks become soil?

Outline the three stages in soil formation.• stage 1: It starts out as rock (parent material) which weathers over

time.

Parent RockUnder the soil that is present. Which will get broken down and become part of the soil

Outline the three stages in soil formation.

• stage 2: As plants and other organisms begin to inhabit, their organic matter mixes with the weathered minerals from the rock.

Organic materials

Living organisms provide the organic component through their death and decay.

Some living creatures mix the various soil elements through movement and through their bodies.

Outline the three stages in soil formation.• stage 3: More and more organic matter mixes in over time and

minerals can leach down due to gravity and water, creating the different soil layers.

Humus A dark crumbly substance that is formed when organic material breaks down; it is very fertile for plant growth

Earthworms Pass a great deal of soil through their bodies helping to mix and move soil around

Moles dig around and mix soil

Leaf litter and fungi

• Soil Components graphic organizer use page 238

Fraction Constituents Function

Rock Particles

Humus

Water

Air

Soil organisms

What does soil look like?

• If you dig a trench in the ground the side of the trench creates a soil profile, a cross section

Title thissectionSoil Profile

Title this section:Soil ProfileMake sure you have both a left and right side available.

If you dig a trench in the ground the side of the trench creates a soil profile, a cross section

Soil Horizons

• In cross section soils have a profile which is modified over time as organic material leaches (washes) downward and mineral materials move upwards

• These processes sort the soil into distinctive horizons that are visible

• This profile changes as it goes down from the surface towards the underlying base rock

• It is a record of the processes that have created the soil

• It mineral composition, organic content, and chemical and physical characteristics such as pH and moisture

• Go back 2 slides

On one side of your notebook glue in the soil horizon and label each sectionOn the other side write about each section in detailUse your textbook pages 239 to write about each horizon O-R

/R

Draw the soil profile on the left

Leaching is downward flow of water in the soil, transporting and dissolving minerals, when Precipitation is > evaporation

Translocation- the movement of water either up or down in the soil layers

Water moving upwards

Salinization- Hot dry climate P<E (Precipitation is less than evaporation)• Here water is evaporating at the soil surface and water from the lower soil

layers moves upwards• It dissolves minerals and takes them to the surface where the minerals are

then left behind

Salinization also occurs in agriculture areas like San Joaquin valley

Water moving downwards

Leaching- wetter climates P>E • Here the water flows downward in

the soil layer• Dissolving minerals and

transporting them downwards• The soil layer that is leached

becomes pale do to loss of minerals• Underlying layers become red in

color • Do to iron oxide deposit

Create a diagram of an open soil system after reading the processes of soil formation on page 123.

Soil textures

• Clay is very chemically reactive. It also absorbs and holds water well, creating a “heavy” soil. Clay feels sticky when wet.

• Silt is a larger particle than clay and feels slippery when wet.

• Sand is a course particle that doesn’t hold water well creating a “light” soil. It feels gritty and falls apart easily.

state properties of two named soils

• Sandy soil

• It is possible to feel the texture of most soils. If you rub it between your fingers

• Sandy soils are gritty and fall apart easily

• Silty soils feel slippery like wet talcum powder and hold together better than the sandy soils

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

• Show rocks

Porosity, permeability, and pH

• Porosity- the amount of space between particles

• Permeability- the ease at which gases and liquids can pass through the soil

• pH- Acidification of soils

• Read pages 242-243 answer:

• Why is the pH level important?

• Is soil a sustainable/renewable resource?

state properties of two named soils

• Sandy soil

Soil textures

• Which soil is best for agriculture?

• Loamy soil is soil that has an equal mixture of all three. This soil has a balance of water-holding abilities and freely draining aerated conditions.

• The clay holds water and nutrients, the sand allows drainage for airspaces for roots to breath, and the silt holds the two together.

Is soil a renewable resource?

• Yes, soil does renew itself but it can take a very long time to form, in some cases only 1 cm of soil is formed every few hundred years.

• Since it takes such a long time it should be considered nonrenewable

Soil activityGoal: You will be able to differentiate between main soil types.

When determining soil type all 3 numbers used MUST = 100Hence..100%So if you have:50% clay, 30% sand, and 20% Silt what soil do you have?

When determining soil type all 3 numbers used MUST = 100So if you have:30% clay, 60% sand, then what part silt? ___% Silt what soil do you have?

When determining soil type all 3 numbers used MUST = 100So if you have:25% clay, 45% sand, then what part silt? ___% Silt what soil do you have?

When determining soil type all 3 numbers used MUST = 100So if you have:10% clay, 30% sand, then what part silt? ___% Silt what soil do you have?

When determining soil type all 3 numbers used MUST = 100So if you have:70% clay, 20% sand, then what part silt? ___% Silt what soil do you have?

When determining soil type all 3 numbers used MUST = 100So if you have:40% clay, 5% sand, then what part silt? ___% Silt what soil do you have?

Translocation- the movement of water either up or down in the soil layers

Water moving upwards

Salinization- Hot dry climate P<E (Precipitation is less than evaporation)• Here water is evaporating at the soil surface and water from the lower soil

layers moves upwards• It dissolves minerals and takes them to the surface where the minerals are

then left behind

Salinization also occurs in agriculture areas like San Joaquin valley

Water moving downwards

Leaching- wetter climates P>E • Here the water flows downward in

the soil layer• Dissolving minerals and

transporting them downwards• The soil layer that is leached

becomes pale do to loss of minerals• Underlying layers become red in

color • Do to iron oxide deposit

Soil Degradation

• Occurs when natural or human-induced processes decrease the future ability of land to support crops, livestock, or wild species.

• Soil degradation by type• water erosion

• wind erosion

• chemical degradation

• physical degradation

Soil Erosion…bad bad bad

• Soil erosion is the movement of weathered rock or soil components from one place to another.

• Erosion destroys the soil profile, decreases the water-holding capacity of the soil and increases soil compaction.

• When water can no longer percolate through the soil it runs off, taking more soil with it (positive feedback loop)

• If soil can’t hold water, crops will suffer from water shortages.

What causes soil erosion?

• Wind and water

• Human activities: • deforestation

• Burning native vegetation

• Construction

• Cultivating inappropriate land.

• Overgrazing

• Monocultures

• Row cropping

• Failing to return organic material to soil

Syria’s dead and forgotten cities. Forests were cut

down for olive groves and soil erosion followed.

Dust Bowl

• 1930s in Oklahoma, Texas, Colorado and Kansas.

• Much of the topsoil was lost because of poor cultivation practices.

• Native prairie grasses had deep roots that held the soil in place.

• Farmers would overgraze the prairies with livestock and plow up the land after harvest, then leave it exposed to high heat and winds.

1935 Soil Erosion Act

• Mandated the protection of the nation’s soil reserves.

• Established the Soil Conservation Service that carries out soil surveys, research, and provides assistance and computer databases.

Soil Conservation

• Reduce erosion and restore fertility.

• Farmers can usually reduce erosion with techniques that keep the soil covered with vegetation.

Perennial intermediate wheatgrass roots v regular wheat…..

Sunflowers

Other methods to reduce soil erosion

• Terracing: converting the land into level terraces running on a contour.

• Contour farming: plowing and planting in rows across slope rather than up and down.

• Strip cropping: alternating strips of a row crop and another crop that completely covers the soil (grass/legumes etc). The second crop catches soil and water runoff.

Terracing

Contour planting and

strip cropping

Soil conservation techniques cont.

• Cover crops: planting immediately after harvest.

• Alley cropping, several crops planted together in strips between trees and shrubs.

• Windbreaks or shelterbelts: trees to break wind and erosion (also creates habitat)

Alley cropping

Windbreaks

Desertification

• In desertification the productive potential of arid or semiarid land falls by 10% or more because of a combination of natural climate change that causes prolonged drought and human activities that reduce or degrade topsoil.

• About 1/3 of the world’s land is suffering from the effects of desertification.

Figure 14-9 Page 282

Moderate Severe Very Severe

Salinization

• Salinization: Irrigation water that contains small amounts of salts evaporates and leaves salt behind to build up in the soil.

Solutions

Soil SalinizationPrevention

Reduce irrigation

Switch to salt-

tolerant crops

(such as barley,

cotton, sugar beet)

Flushing soil

(expensive and

wastes water)

Not growing crops

for 2-5 years

Installing under-

ground drainage

systems (expensive)

Cleanup

Soil Facts

• One inch of topsoil can take up to 1,000 years to form.

• Due to extensive soil erosion in the US, more soil is lost each year than during the 1930s dust bowl.

• In 1850, soil in the prairie states averaged 14 inches of topsoil, today is half that.

• More than half of the fertilizer used today is required to replace organic nutrients lost through soil erosion.

Outline the causes of soil fertility loss

• soils may become “tired” if they are over used, e.g. crop after crop will remove vital nutrients and minerals from the soil at a rate greater than they are replaced;

• poor soil management may lead to soil erosion and the loss of essential organics and minerals from the soil as well as soil volume;

• soil may become contaminated i.e. irrigation and high evaporation rates may lead to salt accumulation and fertility problems;

describe the ways in which farmers can improve the productivity of their soil• improving fertility of the soil with (organic fertilizers/manure/chemical) fertilizers;

• reducing losses due to pests/disease with chemical treatments;

• improving nitrogen fixation by planting leguminous crops e.g. beans;

• reducing loss of nutrients due to soil erosion by terracing fields;

• reducing loss of nutrients/topsoil due to wind erosion by planting shelter belts;

• avoiding over-intensive farming by allowing fields fallow/rest periods;

• avoiding depletion of nutrients by rotating crops;

• improving yields through irrigation;

• avoiding over-compaction of soil through use of appropriate/low impact technology;

• reducing wastage by increasing field size e.g. through removal of hedgerows;

• use of GM / Green Revolution crops e.g. higher yielding varieties of rice;