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  1. AP EXAM More review and more review

  2. Soil • The weathered portion of the earth’s 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

  3. 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

  4. 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

  5. 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

  6. 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 <0.002 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

  7. Soil Pyramid

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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.

  13. 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

  14. 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

  15. 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)

  16. 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

  17. 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

  18. 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

  19. 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 world’s 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

  20. 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 (dichlorodiphenyltrichlorethane) • 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

  21. 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

  22. 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

  23. 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

  24. 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

  25. 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

  26. 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

  27. 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

  28. 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

  29. 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!!!

  30. 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

  31. 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