AP EXAM

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AP EXAM

• More review and more review

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Soil

• The weathered portion of the earths crust that
  can sustain life
• Young soils are not leached of their nutrient
• Older soils are leached and have little organic
  material remaining
• The parent material of soil is rock broken down
  by chemical and physical weathering
• Humus is the dark-colored organic material that
  remains after decomposition of leaf litter,
  droppings, and plant and animal remains
• Leaching is when minerals or matter is dissolved
  in water percolating downward
• Zone of illuviation is the area in the deeper
  levels of the soil where the leached matter is
  deposited
• Illuvial material includes iron humus and clay
  depending on soil

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Soil Organisms

• Include bacteria and fungi (function as
  decomposers)
• Algae can be present on surface of soil
• Round worms (nematodes) and segmented worms
  assist with aeration
• Insects (ants), roots, snakes, gophers,
  groundhogs and moles all tunnel and aerate soil

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Chemical Properties of Soil

• pH of the soil should range between 6 and 7 for
  most plants
• At low pH aluminum, iron, boron and manganese
  are more soluble and more available to plants (Al
  can be toxic if too much)
• Add ground sulfur or aluminum sulfate to increase
  acidity
• Alkaline soil potassium, iron and manganese are
  less available
• Add lime to make soil more alkaline
• Plants require nitrogen, potassium, phosphorus,
  calcium, magnesium, and sulfur
• Limiting Factors nitrogen and phosphorus
• Humus important for nutrients, water holding
  capacity, aeration capacity, allowing root growth
  and increasing porosity of the soil
• Salinity can be a problem, especially in
  irrigated areas

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Physical Properties of Soil

• Color
• Dark brown or black soil has lots of humus
• High organic component
• Red soil may contain iron
• Porosity pore space in between particles of soil
• Very porous soils hold more water and air
• Porosity influences the permeability
• The more porous a soil, the lower the
  permeability
• Permeability rate at which water and air move
  through the soil

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Physical Properties of Soil

• Texture of the soil determined by the relative
  amounts of different-sized inorganic particles
• Three particle sizes
• Sand 0.05-2 mm
• High permeability b/c low porosity
• Particles are so large that the spaces between
  them are large as well, resulting in good
  drainage
• Silt 0.002-0.05 mm
• Clay lt0.002 mm
• Low permeability b/c it has high porosity
• Particles are tiny which allows smaller pores
  around them, thus holding water and preventing
  water permeating through the soil
• Loam equal mixture of each type of soil

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Soil Pyramid
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Soil Horizons

• Stratified layers in soil
• A soil profile is taken to see the horizons
• O horizon organic material on the surface of the
  soil (decaying plant litter)
• A horizon topsoil (rich w/ accumulated humus)
• E horizon (eluviated) heavily leached soil that
  can develop between the A and B horizon
• B horizon subsoil- zone of illuviation for the
  leached material from A and E
• Can be rich in humus, clay or iron
• C horizon contains weathered rock and sits upon
  the parent material

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Major Soil Orders

• Spodosols form under coniferous forests
• Layer of acidic pine litter, have a white-ish,
  ashy, leached E horizon
• Soil is not suited for agriculture due to the
  acidity and nutrient leaching
• Alfisols are formed under temperate deciduous
  forests
• Topsoil is usually gray brown, indicative of high
  levels of nutrients
• High precipitation leaches the A and E horizons,
  but soil fertility is maintained by the
  constantly replaced litter

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Major Soil Orders

• Mollisols are found in temperate grasslands
• Fertile with thick, dark brown topsoil indicating
  high levels of humus
• Subject to little leaching in dry seasons
• Aridosols form in arid regions
• Little leaching b/c of little rain and little
  organics
• Histosols formed in waterlogged areas and result
  in incompletely decayed organic material
• Oxisols and Ulitsols form in hot, wet areas
• Low in nutrients b/c they are highly leached due
  to the large amounts of rainfall and lack of
  litter

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Soil Problems

• Less agricultural land is being used now than in
  previous generations b/c we have better crop
  varieties, fertilizers, irrigation, and
  pesticides
• Land productivity per unit acre has greatly
  increased over time
• Vast amounts of land are being degraded by poor
  ag practice, urbanization and pollutants
• Degraded Land soil lacks fertility
• Or is eroded
• Or surrounding water is contaminated
• Or has more runoff than is typical
• Or amount of vegetation declines
• Or area has a decreased NPP and less animal
  biodiversity

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Erosion

• Is the movement of soil from one place (desired)
  to another (less desirable)
• Erosion can be due to water, wind, or ice
• Decreasing amount of topsoil limits fertility and
  therefore plant growth
• Total amount of soil lost from cropland is
  thought to be 25 billion metric tons.

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Erosion

• Three types of water erosion
• Sheet erosion is when water moves down a slope
  and erodes topsoil evenly
• Rill erosion cuts shallow channels in soil
• Gully erosion cuts deep channels
• Is the most severe
• Occurs on steep slopes
• Streambank erosion is loss of sides of stream as
  the water flows along the soil
• Arises from cattle grazing in riparian areas or
  removal of vegetation from riverbanks

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Wind Erosion

• Occurs most severely in areas with dry seasons
  and flat terrain
• African dust can be detected in St. Petersburg,
  Florida, due to summer dust storms in the Sahara
  desert
• Soil erosion also leads to increased sediment
  flowing into surface water, which decreases water
  quality by increasing turbidity
• If the soil is contaminated with fertilizer or
  pesticides the erosion may pollute the water and
  induce eutrophication or animal death from the
  pesticide

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Nutrient Depletion

• When crops are harvested nutrients are removed
• Farmers replenish these nutrients with
  fertilizers
• Fertilizers are high in phosphates and nitrates,
  which may induce eutrophication
• Nitrates in groundwater have also been shown to
  be a problem (blue baby syndrome)

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Salinization and Waterlogging

• Salinization occurs when land is irrigated over a
  long period, especially from wells
• Salt collects in topsoil when the water
  evaporates and stunts plant growth, which reduces
  crop yields
• The excess salt could be flushed by precipitation
• To decrease salinization, irrigation can be via
  drip irrigation or underground pipes
• One option is to plant salt tolerant crops
• Water logging arises when soil is saturated
• Plant roots die due to the lack of oxygen
  required for cellular respiration

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Desertification

• Is the conversion of marginal lands to desert due
  to climate and human behavior
• Rangeland and pastures are the most likely to
  become desertified as they are too arid for crop
  cultivation
• Desertification is increased by overgrazing and
  deforestation

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Soil conservation

• Avoid conventional tillage
• Conservation tillage leaves the root residues
  from prior crops
• No Tillage seeds are planted in a furrow
• Pests and weeds may persist in the area
• Crop rotation
• Plant cover crops
• Fields can lie fallow
• Mulch can be placed over soil
• Increase water and mineral absorption by adding
  spores of basidiomycota fungi (mushrooms and
  puffballs) which form mycorrhizal relationships
  with plants

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Pesticides and Pests

• Pesticides are chemical substances that kill
  organism
• Include herbicides (plants), rodenticides
  (rodents), fungicides (fungus), nematocides
  (nematodes), and insecticides (insects)
• Biocides kill many species
• US uses about 5.3 billion pounds of pesticides
  per year
• US uses 20 percent to the worlds consumption of
  conventional pesticides
• Nearly half of that amount is the chlorine and
  hypochorites used to treat water to prevent
  waterborne illness
• Other half is conventional pesticides
• Golf courses frequently have higher pesticide
  application rates than farms

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History Lesson

• Ancient Romans burned infested locust fields to
  prevent their spread
• Sumarians used sulfur as an insecticide
• In China, Mercury and arsenic were used on
  ectoparasites and added ants to orchards to kill
  caterpillars
• Spices were valued b/c they decreased pests in
  foods
• Modern era began with DDT (dichlorodiphenyltrichlo
  rethane)
• Inexpensive to manufacture, stable, easy to apply
  and lethal to insects
• Mass production began in WWII
• Helped eradicate malaria in the US by destroying
  the Anophles mosquito Anopheles mosquito
• Birds were bioaccumulation DDT that was
  biomagnified in the top of the food chain birds

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Chemical Group of Pesticides

• Inorganic pesticides include simple compounds of
  sulfur, arsenic, copper, lead and mercury
• These chemicals are toxic and persistent
• Natural organic pesticides are usually extracted
  from plants
• Tobacco produces nicotine sulfate, toxic to
  insects and mammals
• Pyrethrum is extracted from chrysanthemums
• Rotenone is used to kill fish is from derris root
• Fumigants Carbon tetrachloride, ethylene
  dichloride and methyl bromide volatilize and
  penetrate materials sterilize soils and stored
  grain

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Organochlorines

• Chlorinated hydrocarbons are toxic and nearly all
  are banned or restricted in the US
• DDT, aldrin, kepone, dieldrine, chlordane, and
  toxaphene
• Nerve toxins that acutely cause nausea, vomiting,
  concusions, and death by respiratory failure by
  interfering in nerve impulses
• Linked to all fertility disorders
• Probable human carcinogens
• Highly persistent and fat soluble and biomagnify

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Organophosphates

• Malathion, parathion, and tetraethylpyrophosphate
• WWII nerve agents
• Inhibit enzyme that breaks down the
  neurotransmitter acetylcholine
• Break down relatively quickly and not likely to
  bioaccumulate
• More expensive to produce
• and more toxic in lower amounts b/c they are
  rapidly absorbed

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Organophosphates

• Subacute doses induce headache, slow heart beat,
  confusion, vomiting, and difficulty breathing
• Acute doses may lead to paralysis, tremors, coma
  and death
• Roundup (glyphosate) does not affect the nervous
  system

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Carbamates

• Are used as insecticides, herbicides and
  fungicides
• Have the same mode of action, toxicity and lack
  of persitence and bioaccumulation as
  organophosphates
• Sevin (carbaryl) and Temik (aldicarb)
• Toxic to bees!!!!
• Many pesticides have chronic health effects that
  include cancers, birth defects, immunological
  problems, neurological problems, and endometriosis

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Pesticide Benefits

• Eradicated many insect vectors, including
  mosquitoes (malaria, dengue and yellow fever),
  rat fleas (bubonic plague), typhus (lice and
  fleas), and tsetse flies (African Sleeping
  sickness)
• Many countries feel the health risks are small
  compared to the benefits of saving lives from
  illness.
• Increased food supply and decreased cost of
  producing food

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Pesticide Problems

• Pesticides often kill nontarget species
• Ecological pest controls are killed (spiders)
• Kill honeybees and other insect pollinators
• resulting in decreased fruit production
• Pest resurgence insects that survive spraying
  b/c of resistance
• Positive feedback loop as farmer increases
  application
• Secondary pest outbreaks can occur
• Grasshopper Effect chemicals migrate from the
  site to condense and precipitate in colder
  regions where bioaccumulation occurs in top
  carnivores

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Relevant Pesticide Legislation

• Three federal agencies regulate
• EPA
• Food and Drug Administration (FDA)
• US Department of Agriculture (USDA)
• 1938 Food, Drug, and cosmetic act allows the EPA
  to set tolerance levels for pesticide residues in
  food
• 1958 Delaney Clause- no chemicals would be added
  in food if they cause cancer
• 1947 FIFRA (Federal insecticide..) allows EPA to
  regulate sale and use of pesticides
• EPA licenses pesticides if they will not pose
  significant risk
• FDA and USDA enforce levels set b the EPA
• 1996 Food Quality Protection Act accounts for
  aggregate exposure
• Banned Dursban b/c of risk to children
• CCA, chromate copper arsenate, treated lumber,
  banned in homes

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Relevant Pesticide Legislation

• 2001, 127 countries banned persistent organic
  pollutants (POPs)
• Aldrin, chlordane, deledrin, DDT, mirex,
  toxaphene, PCBs, diocins, and furans
• Production of chemicals in US continues
• Sent back to US on imported crops
• Cycle of Poison!!!

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Bhopal

• December 1984
• Local Union Carbide plant producing SEVIN
• Released many gases used to generate the
  pesticide, including methyl isocyanate
• Plant next to shanty town
• 15,000 instant deaths
• 800,00 people exposed
• Union Carbide paid India 470 million in
  compensation
• Monies not paid to victims

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Integrated Pest Management

• IPM uses low doses of nonpersistent,
  nonbiomagnified pesticide to reduce pest numbers
  for specific pests
• Increase crop diversity
• Strip cropping or polyculture
• Crop rotation prevents population buildup
• Shelterbelts for insect eating birds and
  predators
• Plant around insect hatching
• Create trap crops around desired crop
• Marigolds planted around garlic