SOIL CHARACTERISTICS

HISTORYAGRICULTURE

FUNDAMENTALS

http://www.youtube.com/watch?v=z7XzzM2sbs0&feature=plcp

CASE STUDY NO-TILL AGRICULTURE

BRAZIL

Prevents erosionReduces pollution from agri-

chemicalsadds “green” fertilizer

Works in Brazil, why not other biomes?

38% Earth’s surface is cultivated for crops (croplands) and raising

livestock (rangelands) which require healthy soil

U.S. Rangelands Japan

SOIL DEGRADATION

What is soil degradation?

What are some causes?

Why do we care?

Europe’s land - most degradedlong history of agriculture

Africa & Asia rapidly becoming degraded. Why?

Loss of topsoil containingmicroorganisms

mineralshumus

that can take hundreds of years to develop.

Text

1. overgrazing2. deforestation3. cropland agriculture

What are monocultures?

What is their effect on soil degradation?

Some History

1. Best fruits (with seeds) brought to camps ~10,000 years ago2. Some seeds dropped nearby3. Plants grew near villages/camps4. Best plants were selected & bred

Origins of agriculture (red)

Industrial Agriculture started in the early 1900’s

Use of machineryModern intensive agriculture -

requires monoculture.

Expensive machines only useful for a

single kind of cropPROS?CONS?

Traditional Agriculture

Hand tools, simple machines

Subsistence Agriculture - family produces only

enough for itself

Intensive Traditional Agriculture

Family uses animals, irrigation and fertilizer to

sell at marketPROS?CONS?

GREEN REVOLUTION - 1940’s - 70’s1. Technology initiatives increased

production pesticides, synthetic nitrogen fertilizer modern irrigation, improved crop varieties2. Energy required increased more than production.3. Crops & technology exported to countries (India & parts of Africa) experiencing famines and malnutrition.PROS? CONS?

SOIL - has both organic & inorganic components

http://www.youtube.com/watch?v=_oTFUeZyPCc&feature=plcp

FORMATION OF INORGANIC COMPONENTSParent material affects composition of soil.

Example sandstone rock transforms to sandy soil

BEDROCK: solid rock in Earth’s crust.

WEATHERING: break down of rocks and minerals. First step in soil

formation

EROSION: movement of soil from one area to another

3 kinds of WEATHERINGPhysical - wind, rain, thermal expansion &

contraction, water freezing

Chemical - dissolved

substances (acids) in water & gases

Biological - roots, lichen, moss, etc.

SOIL PROFILE

O Horizon - humusA Horizon - topsoil

E Horizon - zone of eluviationB Horizon - subsoil or zone of accumulation

Bedrock sometimes called R Horizon

Be able to identify and describe soil

horizons.

HUMUSmature compost

what is left when organic matter breaks down

helps soil retain moisturehelps soil retain nutrients

helps soil retain oxygen for organismsdark color due to carbonnecessary for healthysoil

Worms creating humus from horse

manure

SOIL CHARACTERIZATIONS

TEXTURESTRUCTURE

pHCOLOR

PERMEABILITYSMELL

OTHERS

In your soil investigations,

determine which soil

sample would be best for:

landfillcorn crop

soybean cropbuildings

SOIL TEXTURE

Clay - smallest particle sizeSilt - medium particle sizeSand - largest particle size

loam - mixture of clay, silt & sand

SOIL STRUCTURE

Description of how will the soil forms balls or

ribbonsAffected by

pore size and water & air movement.

SOIL DIFFERENCES BY BIOME

SOIL DEGRADATION & CONSERVATION

SWIDDEN (slash & burn) agriculture

In tropical rain forests, these fields are useful for

crops only one to two years. Explain.

Text

Erosion - removal of material from one place & transported to

another by wind and/or water

Deposition - arrival of eroded material at a new location

Some erosion & subsequent

depositions are natural

processes

Sediments may be deposited in valleys to create an alluvial fan, at the mouth of rivers to

create deltas & others

Flood plains usually have fertile soil due to depositions

OTHER CAUSES OF EROSION

1. Overcultivating (too much plowing)2. Overgrazing 3. Deforestation (especially on slopes)

Text

Gold mine in the Amazon Rain Forest

Farming in the Andes Mountains

Water erosioncaused by

1. force of water flow2. chemicals dissolved in water that break down rock3. sediment in water causes further erosion of riverbeds and shores

Positive or Negative Feedback?

Wind Erosion

Especially damaging in dry / desert climates

Sediments carried in wind hit landforms causing further erosion.

Positive or Negative Feedback?

Glacier Erosion - glaciers pick up huge boulders and grind them

along surfaces

Sea Erosion - salts & other dissolved chemicals erode

some rocks & carry materials up the shore.

Waves can create air pressure inside cracked rocks & carry sediment.

SOIL EROSION - topsoil carried away from farmlands and cause

infertility.Humans are the primary cause

Does rapid population growth affect the rate of soil erosion?

Explain.

DESERTIFICATION - loss of >10% productivity (biomass growth) of

soil due toErosionSoil compaction - causes?Forest RemovalOvergrazingDroughtSalinization (accumulation of salt)Climate ChangeDepletion of water resources

Rangeland in Colorado. Salts dissolved in the soil accumulate at the surface.

THE DUST BOWLSediment from eroded

farmlands from the plains (Oklahoma) ended up in New

York, Washington D.C. and the Atlantic Ocean

Poor agricultural practices and years of sustained drought caused the Dust Bowl. Plains grasslands had been deeply plowed and planted to wheat. During the years when there was adequate rainfall, the land produced bountiful crops. But as the droughts of the early 1930s deepened, the farmers kept plowing and planting and nothing would grow. The ground cover that held the soil in place was gone. The Plains winds whipped across the fields raising billowing clouds of dust to the skies. The skies could darken for days, and even the most well sealed homes could have a thick layer of dust on furniture. In some places the dust would drift like snow, covering farmsteads.

U.S. SOIL CONSERVATION ACT OF 1935

Established theSOIL CONSERVATION SERVICE

(SCS) CREATED. Agents worked with farmers to teach them how

to conserve their soil.

SOIL CONSERVATION & DOMESTIC ALLOTMENT ACT OF 1936 provided cost-sharing funds to landowners

for soil & water protection, including tree planting.

PREVENTION - RESEARCH & PRESENT

Crop rotationContour farmingIntercroppingTerracingShelterbeltsConservation tillageNo-till farming (Brazil)

Definition, visual, how it works, where it’s mostly

used, pros, cons.

IRRIGATION - artificial provision of water to support agriculture

70% of ALL FRESHWATER

used by humans.

WATERLOGGING - over irrigation can raise the water table, & suffocate plant roots, soil

microbes die.

SALINIZATIONEvaporation in arid areas

draws water up through the soil along with dissolved salts.

Irrigation causes repeated evaporation, bringing more

salts up. READ CASE STUDY: HISTORY OF MONO

LAKE

Prevention: plant crops that do not require irrigation, use water

with low salt concentration, irrigate efficiently

LAB QUESTIONSWhat is the salt toxicity level for plants?What is the salt toxicity level for seed

germination?

Salinization refers to a build up of salts in soil, eventually to toxic levels for plants. (3,000 - 6,000 ppm salt results in trouble for most

cultivated plants.) Salt in soils decreases the osmotic potential of the soil so that plants can't take up water from it.

When soils are salty, the soil has greater concentrations of solute than does the root, so plants can't get water from soil. (Remember osmosis -- water "tries" to accomplish dilution -- it moves from areas with lower concentration of dissolved substances to areas with higher concentration?) The salts can also be directly toxic, but plant troubles usually result primarily from inability to take up water from salty soils.

WHAT WOULD HAPPEN TO AN ONION CELL IN PURE WATER? IN 0.5% SALT CONCENTRATION? IN

5% SALT CONCENTRATION?

Three main types of forces which contribute to the energy state of soil water include: 

•Gravitational water has a positive energy and can flow out of the soil through the large pores. 

•Osmotic potential is due to the attraction that salts have for water through the phenomenon of osmosis. This energy is negative relative to free water. 

•Matric Potential, the potential energy of water attracted to soil solids. It too is negative. 

TextProblems with salinization are most commonly associated with excessive water application, rather than with too little.

Where does the salt come from?

Text

All irrigation water contains dissolved salts derived as it passed over and through the land, and rain water also contains some salts. These salts are generally in very low concentration in the water itself.

However, evaporation of water from the dry surface of the soil leaves the salts behind.

Which soil type is most susceptible to salinization?

Salinization is especially likely to become a problem on poorly drained soils when the groundwater is within 3 m or less of the surface (depending on the soil type). In such cases, water rises to the surface by capillary action, rather than percolating down through the entire soil profile, and then evaporates from the soil surface.

Even if farmers irrigate extensively, salinization isn't really a problem if during the winter, there is enough water to flush the salts that were deposited during the summer irrigation.

Salinization is a worldwide problem, particularly acute in semi-arid areas which use lots of irrigation water, are poorly drained, and never get well flushed. These conditions are found in parts of the Mideast, in China's North Plain, in Soviet Central Asia, in the San Joaquin Valley of CA, and in the Colorado River Basin; all areas where the soil profile never (or rarely) gets well flushed.

Globally, something on the order of 20% of the world's irrigated acreage is estimated to be affected by salinization, with salt concentrations high enough n about 10% of irrigated acreage to decrease yields significantly. (This is one of those places where you can read all kinds of figures -- estimates of affected acreage range from the relatively conservative 20% that I cite above to upwards of 50% of irrigated acreage!)