Lecture 1b –Soil as a Resource

• WHAT DOES SOIL DO?• Soils define culture. • Throughout history soil has

defined human societies perhaps more strongly than any other single environmental variable. – Soil fertility defines our food, our

population and our economy. – Soil colors define our art. – Soil organisms may define our

health. • Yet, the importance of soils in

regulating human society is frequently overlooked

• Healthy soil gives us clean air and water, bountiful crops and forests, productive rangeland, diverse wildlife, and beautiful landscapes.

• Soil does all this by performing five essential functions:

Callanish Stones – Isle of LewisScotland UK, age = 4500 years

1) Regulating water. • Soil helps control where rain,

snowmelt, and irrigation water goes. • Water and dissolved solutes flow over

the land or into and through the soil.

Source: www.naturegrid.org.uk/rivers/watercyclepages/riverbasin-stages.html

Spring Snowmelt

Silt from floods in SE MnSummer 2007

2) Sustaining plant and animal life.

• The diversity and productivity of living things depends on soil.

• Often the more productive the soil, the more diversity in both the plant and animal community.

3) Filtering potential pollutants.

• The minerals and microbes in soil are responsible for :

• filtering, buffering, degrading,immobilizing,and detoxifying organic and inorganic materials.

• This includes industrial and municipal by-products and atmospheric deposits.

4) Cycling Nutrients.

• Carbon, nitrogen, phosphorus, and many other nutrients are stored, transformed, and cycled through soil.

• This is a good thing for it keeps them out of our water systems.

• WASHINGTON- “Because fewer farms are raising animals, the 350 million tons of manure they produce each year is being spread over smaller tracts of land, causing more of it to wind up in lakes, streams, and rivers”, according to a new study by the Agriculture Department.

• The department's Economic Research Service said the "competition for land for spreading manure could be severe in regions with high concentrations of animals," making it more difficult to comply with new environmental regulations for reducing farm pollution.

• States expected to have the most trouble finding enough cropland to distribute the manure include North Carolina, Virginia, Maryland, Delaware, Georgia, Alabama, Arkansas, and California, the agency said.

When manure can not be land applied it must be stockpiled in mounds or in tanks or pits.

5) Supporting Structures

Buildings and roads need stable soil for support.

The bearing capacity determines the ease of stable construction.

This road and associated bridge were built across a mangrove swamp. The bridge, supported by pylons, has not subsided. However, the road has slumped because of the low load-bearing capacity of the underlying soil material.

This building collapsed when it underwent liquefaction-induced bearing capacity failure

Digging for clues of our past- The Soil

holds the clues till we are ready.

Archeological treasures associated with human habitation are protected in soils.

The kind of the soil determines the ease of excavation and maybe the quality of the object found.

• Careful excavations are used to uncover Native American remains at U.S. Army bases.

Soil needs your respect!Will everyone, please, at some

time during the next few days take a handful of soil and show it some respect.

Put it in your hand and take a long, hard look at it.

Marvel at its color, smell, and feel. Sing in praise of its chemistry and bless its bugs. Be amazed at how it works for you.

Before placing it back from whence it came say “thank you” !

Soil is …….

• Detritus from rock or - sand, silt and clay particles along with decomposed plant remains and live organisms.

• Or• The Loose surface

of the earth that can support plants.

Soil Texture = The Sand, Silt & Clay in a soil.

• Soil texture is the single most important

physical property of the soil. Knowing

the soil texture alone will provide

information about: • 1) water flow potential,

• 2) water holding capacity,

• 3) fertility potential,

• 4) suitability for many urban uses.

Soil Texture• Soil texture is

determined by separating the amount of sand, silt and clay in a soil and determining the % of each.

• Different percentages of sand, silt and clay have been given “Textural Class Names”

• These 12 Names are put on a Textural Triangle for the various separate percentages

Soil Texture of Sandy Loam & Loamy Sand

• A sandy loam is a loam with the some characteristics of sand,

• while a loamy sand is a sand with some characteristics of a loam. (noun and adjective)

• ? Discuss two situations where you were aware of the soil’s texture.

Soil Structure

• Individual sand silt and clay particles will form together into specified shapes.

• These shaped structural peds – are given names based on their appearance.

Peds are formed in the soil by wetting, drying, freezing and thawing and are held by clay and organic matter

Kinds of Soil Structure (see Unit 3 chap. 1)

• Granular• Platy• Sub-angular

Blocky• Prismatic• Good structure

promotes healthy soil

Once the virgin land is used for agriculture – the quality of the soil resource will begin to degrade, the rate of decline will depend

on the skill of the land manager.

U.S. Fish and Wildlife Service

Overgrazing• According to the

Sierra Club, the National Cattlemen's Beef Association, the U.S. Forest Service, and the Bureau of Land Management: – Overgrazing is

what happens when there are too many animals on the land.

• What grass plants need is sufficient recovery time between bites. Therefore, timing and grazing management, not numbers, is the critical factor.

• But this is something that everybody already "knows"--that the solution to overgrazing is to reduce or eliminate the grazers.

• Increasing the area available to the animals is not nearly as effective as shortening the time period during which the plant is exposed to grazing.

• Grazed BLM land on the left side of the fence, desert wildflowers on the right.

• In 1991, Congress's General Accounting Office (GAO) completed a report (RCED-92-12) that analyzed the BLM's permitting of livestock grazing in the desert. The GAO concluded that,

• "the lands we visited provided enough evidence of the high environmental risk and low economic benefit associated with livestock grazing in America's hot deserts for us to conclude that the program as currently conducted merits reconsideration”.

• Or some would say that “cows don’t belong in the desert”

• source: www.jdburgessonline.com/ grazing/desert.html .

Deforestation

• The main contributors to land degradation are: – erosion and soil

compaction, as a result of extensive removal of vegetation, exposure of the soils to heavy rainfall,

– increased evaporation,– and later wind action.

• The main reasons for vegetation removal are: – commercial logging and

tree cutting to provide domestic fuel,

– clearing of forests for commercial or subsistence cultivation.

• Soils in many tropical areas rapidly decline in productivity after logging.

Agriculture• Agriculture may last

for a few hundred years or it may last for thousands of years.

• These terraces have been in place for thousands of years in Bali. (Island in South Pacific)

• Stone tools and earthenware vessels, which were estimated to be 3000 years old, were unearthed near Cekik (west Bali).

• Source: http://www.promotingbali.com/bali-essential/bali-history/

• Agave production on these fields in Mexico may last for fewer than 50 years due to soil erosion which results in the loss of valuable topsoil.

• Tequila is an alcoholic drink made in the arid highlands of central Mexico from fermented and distilled sap of the agave plant, a succulent.

• Archeologists say the agave has been cultivated for at least 9,000 years but not on the fields here

http://www.ianchadwick.com/tequila/

Water Erosion

• Water erosion is the wearing away of soil particles.

• Raindrops detach the soil particles.

• As infiltration is reduced, water moving down slope takes the soil with it.

Wind Erosion

• Wind erosion is the detachment of soil particles by the wind and moving them to another location.

• Snirt = ?

DYAD

• Where have you seen some kind of soil degradation?

Chemical Degradatio

n• Chemical spills

can pollute the soil beyond which it can recover naturally.

• Soil remediation can reclaim the soil, making it useful again.

Manure Spill- a chemical degradation• Manure spills are

chemical spills and they result in polluting soils, surface water and groundwater.

• Problems may occur during any of the steps of manure management including:– collection, transfer,

storage and application.

• If a manure spill reaches a stream it can create serious problems for aquatic life as well as for people and livestock.

Human Activities Influence Planet Earth

• Human activities globally now move ten times as much earth and rock as all natural processes. 

• One of the side effects of this is soil erosion that is causing the progressive loss of farmlands at the same time that the human need for them is growing. 

• Driving this has been our rapidly increasing human population. 

• Research done by Bruce Wilkinson of the University of Michigan has shown that this human-caused erosion began to exceed nature's ability to repair it nearly 1,000 years ago (Wilkinson Geology

28, 843-846, [2000]). 

Geologic Erosion

Human Induced Erosion

Human influence on the soil : Blue = no change, Red = significant impact on soil

Soil – A Sustainable Natural Resource

• Having a sustainable soil system is everyone's responsibility!• Healthy soil gives us clean air and water, bountiful crops and

forests, productive rangeland, diverse wildlife, beautiful landscapes and beautiful soils.