Soils and Their

Preservation

China’s Green Wall

What are the FACTORSthat make SOIL?

TIME1000’S TO 10,000’S OF YEARS

LAY OF THE LANDTOPOGRAPHY

LIVING ORGANISMSANIMALS AND PLANTS

CLIMATEHOT/COLD, WIND/RAIN

PARENT MATERIALROCKS AND MINERALS

Physical land features

Why is soil important?

There are different types of soil, depending on its composition. These support different types of plants and influence the ecosystem that develops.

supporting the growth of plants recycling nutrients from dead

organisms providing a habitat for organisms

such as bacteria and worms.

Soil is an essential part of the ecosystem:

The Rock Cycle

http://www.youtube.com/watch?v=pm6cCg_Do6k

How is soil created?

1. Erosion of the underlying parent rock

Soil is created in two main stages:

2. Production of topsoil This is where the other components are added. The accumulation of organic matter is affected by the climate and topology of the area.

Fragments of rock accumulate at the site of erosion. These are the source of minerals in the soil. The mineral composition of the soil therefore depends on the type of parent rock.

Uses of soil

Soil is a source of minerals. Plants produce their own food, but have to obtain minerals from the environment. Plants growing on soils that are lacking in minerals often show symptoms related to deficiencies.

Most plants grow in soil. Soil provides anchorage to hold the plant in one place.

Soil also provides plants with water. Plants obtain water via their roots. Soil traps water, providing a reliable supply for plants.

Soil Horizon

Soil separate particle diameter (mm)____________________________

Sand . . . . . . . . . 2.0 - 0.05

Silt . . . . . . . . . . 0.05 - 0.002

Clay . . . . . . . . . . <0.002

SAND

SILT CLAY

Note: clays are microscopic in size !

True or false?

Soil PropertiesTexture - Determined by the size of mineral

particles within the soil.Too many large particles leads to extreme

leaching.Too many small particles leads to poor drainage.

Oxygen and waterMost of the organisms living in soil require oxygen and water for respiration. The amount of water and oxygen that a soil can hold depends on the soil’s structure and texture.

Air can only remain in the spaces that are not filled with water. Waterlogged soils have very low oxygen levels. This is beneficial to anaerobic bacteria but not to aerobic organisms.

Large soil particles have large spaces between them, and water can drain away rapidly.

Smaller particles have smaller spaces and retain more water.

Sandy soil Clay soil

Clay mineralsphotographedwith an electronMicroscope.

Note: they are plateor flake like andare stacked on topof each other.

They are electricallycharged and act likemagnets that attractand hold plantnutrients.

Soil Structure

When subjected to pressure, pores can collapse and total pore space decrease. This is called compaction. Compaction reduces permeability of soil to water and air.

Infiltration RateThe rate of gravitational flow of water

through soil is referred to as the infiltration rate.

Soil with a high infiltration rate is easily leached. These soils can quickly become infertile without the addition of fertilizers

When soil become dry, water can be drawn upward from the water table by capillary action.

Permeability vs. PorosityPermeability is a measure of how quickly water

infiltrates soil.Highest in soil with large pores – sandy soilsLowest in soil with small pores – clay

Porosity is a measure of the space between particles of the soil.

Clay has the greatest porositySand has the lowest porosity

Porosity has an inverse relationship to permeability.

Soils and pHThe pH of most soils is 4 – 8. The solubility of certain nutrient

minerals varies with differences in pH.

Examples: At a low pH, the aluminum and

manganese in soil water are more soluble and are sometime absorbed by the roots in toxic concentration.

Calcium phosphate become less soluble and therefore less available to plants at a higher pH.

Soils and pHSoil pH affects the leaching of nutrient

minerals ;Cation exchange capacity is a soil’s ability to

hold cations (preventing them from leaching out of the soil)

Acidic soil has a reduced ability to bind positively charged ions to it (cation exchange ). Mineral ions such as potassium (K+) are readily leached out.

The optimum pH for soil is 6.0 – 7.0 because most nutrient mineral needed by plants are available in that pH range.

Neutralizing acidic soilThe pH of soil influences plant growth. Acidic conditions can affect enzyme function in soil organisms and alter the availability of mineral ions.

Acidic soils often occur in areas of higher rainfall because the alkaline calcium is leached out. Farmers add lime to neutralize acidic soil, a process which is called liming. Lime is a mixture of calcium compounds.

Liming releases carbon dioxide into the atmosphere. This may contribute to global warming.

Earthworms

Earthworms are present in most soil throughout the world, except in Antarctica. They improve its quality by:

burrowing through the soil, which mixes and aerates it, and improves drainage

breaking up large pieces of organic matter by dragging it into the soil, and consuming parts of it.

Soil and matter pass through their intestines and emerge as castings. Castings are higher in mineral content than topsoil. They increase the surface area of the material which is available for decomposition by bacteria and fungi.

WaterWindNo

Vegetation

Erosion - Wearing away and transportation of soil by wind, water, or ice

The Dust Bowl

How did the Canyon Lands of Utah form?

Sheet Erosion

The Problem of Soil Erosion

A. Topsoil is eroding faster than it forms on about 1/3 f the world’s cropland.

B. Losing topsoil makes soil less fertile and less able to hold water.

C. Sediment is the largest source of water pollution

1. It clogs irrigation ditches, boat channels, reservoirs and lakes.

2. It causes the water to heat up by absorbing solar energy causing fish to die.

3. Increases flood risk by filling in streams and rivers.

The Problem of Soil Erosion

D. 2/3 of the seriously degraded lands are in Asia and Africa.E. In the U.S., 1/3 of the nations original prime topsoil has been washed or blown into streams, lakes, and oceans by over cultivating, over grazing and deforestation.

Desertification: process whereby the productive

potential of arid or semiarid land falls by 10%

or more (Figure 14-19)

Desertification:

A.Causes:1. Overgrazing2. Deforestation3. Surface mining4. Irrigation techniques that lead to increased erosion5. Salt build up and water logged soils 6. Farming on land with unsuitable terrain or soils7. Soil compaction by farm machinery and cattle hoofs

Salinization1.Irrigation water contains small amount of

dissolved salts.2. Evaporation and transpiration leave salts

behind3. Salt builds up in soil

Waterlogging1. Precipitation and irrigation water percolate

downward2. Water table rises

Desertification:

B. Consequences:1. Worsening drought2. Famine3. Declining living standards4. Swelling numbers of environmental

refugees whose land is too eroded to grow crops or feed livestock.

Desertification:

C. Solutions:1. Reduce overgrazing , deforestation, and

the destructive forms of planting, irrigation, and mining.

2. Planting trees and grasses to anchor soil and hold water.

3. Removing salt from the soil.

D. Soil Erosion Act of 1935: U.S. established the Soil Conservation Service

Soil Conservation – Figure 14-21A. Tillage farming

1. Conventional tillage farming: land is plowed and then soil is broken and smoothed to make a planting surface.

2. Conservation tillage farming: disturb the soil as little as possible.

Other methods:1. Terracing: series of broad level terraces2. Contour planting: planting crops in rows

across rather than up and down the slope3. Strip cropping: a row of crops alternates in

strips with another crop.4. Alley cropping: several crops are planted

together in strips or alleys between trees and shrubs.

5. Gully reclamation: planting of shrubs, trees to prevent water runoff that forms gullies

Alley Cropping

Gully Reclamation

Soil Conservation Practices

8. Windbreaks - Planting of trees or other plants that protect bare soil from full force of the wind.

Other methods:

7. PAM: a chemical added to water during the 1st hour of irrigation. Negative PAM particles bond to positive clay particles and increase cohesiveness of surface soil particles. 8. 1985 Farm Act: established a strategy for reducing soil erosion in the U.S.

How can soil fertility be maintained?

A. Organic fertilizers B. Inorganic fertilizers