Presentation on theme: "Announcements – Oct.13, 2006 Exam # 2 next Wednesday (on October 18th) Public Lecture: Dr. Jack Williams, University of Wisconsin at Madison "How will."— Presentation transcript:
Announcements – Oct.13, 2006 Exam # 2 next Wednesday (on October 18th) Public Lecture: Dr. Jack Williams, University of Wisconsin at Madison "How will species respond to future novel climate regimes? Lessons from the late Quaternary" 4:00 PM, Wednesday, October 18, 2006 B102 CLSL, Auditorium
“Slash-and-Burn” Agriculture Usually conducted in areas with nutrient poor soils (e.g., tropical forests) Cut & burn existing vegetation to provide nutrients, use land for brief period, then move to new patch land can be slow to recover Usually plant polycultures (more than 1 species) advantages: species benefit one another, avoid insect/fungal pests Only sustainable in low population densities
Labor-Intensive Agriculture Intense form of agriculture using human and animal labor to grow crops Typical farming practice until Industrial Revolution Still practiced today when: 1. Growing site won’t allow machines Mountain regions, small, oddly-shaped plots 2. Type of crop requires careful handling Rice planting, harvesting fruits 3. Economic conditions poor, human labor cheap
Mechanized Agriculture Requires large areas of land Found in areas with good soils, and necessary money and land US, Europe, USSR, South America Usually monocultures (one crop) Labor reduction in the United States: 1913: Required average of 135 hours of labor to produce 2,500 kg of corn. 1980: Required average of 15 hours.
Mechanized Agriculture Biological Problems Fields left bare, leads to erosion Organic matter often removed Planting only 1 or 2 crops Depleted nutrients Insect/Fungal problems Genetic similarity in crops Insect/Fungal problems Increased energy usage Increased reliance on fertilizers & pesticides
Energy Farming in industrialized countries is highly energy-intensive. Between 1920-1980, energy use rose directly with mechanization of agriculture US food system consumes 16% of our total energy use. Buy locally! Most foods require more energy to produce, process, and transport than we yield from them!!!
Fossil Fuel Use Takes 5.5 tons of fossil fuel to produce 1.1 tons of fertilizer. Developed world is dependent on oil to produce energy to manufacture pesticides.
Points to Know 1. What is the most common dietary problem in wealthy countries? In poor countries? 2. What is a famine? What conditions can lead to famines? 3. What three crops provide most of the world’s nutrition? 4. How is meat consumption related to the Earth’s carrying capacity? 5. What are the characteristics of the three agricultural approaches? 6. What are the benefits and problems of mechanized agriculture?
Agriculture II Lecture Objectives: 1) Learn the pros & cons of fertilizer use 2) Learn types of pesticides and their pros & cons 3) Explore the controversy over DDT
Are these increased yields solely due to mechanization? NO!
Other factors increasing production: Chemical fertilizers Chemical pesticides Intensive plant breeding & genetically modified crops (Monday)
Impact of Chemical Fertilizer 25% of crop yield because of fertilizers Price tied to price of oil raw material source of energy for industrial processing
Impact of Fertilizers Why fertilize? Replace nutrients in soil used by plants Macronutrients Nutrients plants need most of Nitrogen (N), Phosphorous (P), Potassium (K) Micronutrients Nutrients plants need in trace amounts boron, zinc, manganese
Impacts of Fertilizers Problems and limitations of fertilizers They do not replace organic matter Organic material needed for soil structure, helps maintain soil chemistry, food for soil bacteria Runoff Decreases efficiency of use Problems for aquatic systems
Next problem: Humans raise crops for ourselves and livestock to eat, but other organisms like to eat them as well… tomato fruitworm (also called corn earworm and cotton bollworm) Aphids Sugarbeet wireworm larvae
Why Are Pesticides So Widely Used? Food Production Worldwide, pests destroy 35% of crops. Economic Concerns Pesticides increase yields and profits. Health Reasons Insecticides curtail many diseases.
Types of Pesticides Pesticide: any chemical used to kill or control unwanted organisms Insecticides: control insects Herbicides: control plants Fungicides: control fungal pests Rodenticides: control mice/rats
Other attributes to keep in mind… Which species does the pesticide affect? Target organism: the one you’re trying to kill Non-target organism: anything else affected How long does the pesticide last? Persistent pesticides: stable compounds that remain active for long periods of time Nonpersistent pesticides: break down quickly
Insecticides Insect pests can cause serious economic problems (e.g., corn rootworm) Many insects also spread human diseases
Insecticides DDT was first synthetic organic insecticide Long lasting, deadly to insects DDT is a Chlorinated hydrocarbon Banned in US in 1972
Three main types of organic insecticides Chlorinated hydrocarbons Organophosphates Carbamates
Chlorinated hydrocarbons DDT, toxaphene, aldrin, dieldrin, heptachlor Thought to affect insect nervous system Cons: Extremely persistent Bioaccumulation Non-target species Pros: Extremely persistent Helps prevent disease Banned in many parts of the world
Organophosphates and Carbamates Malathion, Parathion, Diazinon (used in gardens) interferes with nervous system results in continuous nerve impulse, leads to uncontrolled spasms Organophosphates more toxic than carbamates Pros: Less persistent than chlorinated hydrocarbons Cons: Are not insect specific Usually much more toxic to humans
60% of pesticides used in US are herbicides Used to control “weeds” - unwanted plants rights-of-way, lawns, crops Why control weeds? Compete with desirable species Need to separate from crop at harvest Traditionally controlled manually
Herbicides Some kill seeds, other plants Most act by disrupting physiological processes growth regulators interfere with plant compounds others interfere with photosynthesis, stop cell division, etc. Some toxic to all plants, some selective Can depend on concentration
Fungicides and Rodenticides Fungicides some fungi decompose organic matter some fungi act as parasites Rodenticides Mice/rats can destroy food supplies, carry disease, damage crops in field warfarin - causes internal bleeding in all mammals in many cases, safer to build rodent proof storage buildings
Problems with Pesticide Use Perfect Pesticide: Inexpensive Always 100% effective Only affect target organism Short half-life Break down into harmless materials But it doesn’t exist!! Newer pesticides have fewer drawbacks than early pesticides, but all have problems.
Problems With Pesticide Use Pesticide Resistance — Insecticides only kill susceptible individuals. Most surviving individuals have characteristics that allowed them to tolerate the pesticide. Survivors pass on genetic characteristics for tolerance. Subsequent pesticide applications become less effective.
Problems With Pesticide Use Effects on Non-Target Organisms Most pesticides are not species specific, and kill beneficial species as well as pest species. Many kill predator and parasitic insects that normally control pest insects.
Problems With Pesticide Use Human Health Concerns Acute poisoning during application. Inadvertent exposure to small quantities. Chronic minute exposure. Migrant workers
Pesticides in People Recent study led by Mount Sinai School of Medicine (NY) Blood and urine work on nine volunteers Found 167 chemicals 76 cause cancer in humans or animals 94 are toxic to the brain and nervous system 79 cause birth defects or abnormal development
Problems With Pesticide Use Persistence — Persistent pesticides become attached to small soil particles and are easily moved by wind or water. May be distributed throughout world from local applications. DDT is still one of the most commonly detected pesticides in breast milk DDT can stay in the environment for as long as 90 years
Problems With Pesticide Use Bioaccumulation and Biomagnification Bioaccumulation — Accumulating material within an organism’s body. Many persistent pesticides are fat soluble and build up in fat tissues. Biomagnification — Acquiring increasing levels of a substance in bodies of higher trophic-level organisms. DDT, Mercury, PCBs
1930s, DDT was considered a miracle chemical Inexpensive, seemed harmless Came into wide agricultural and commercial usage in US in the late 1940s First used in WWII as a delousing agent DDT (Dichloro-Diphenyl-Trichloroethane)
Environmental Impacts In the 1960s, noticeable decline in populations of peregrine falcons, bald eagles, brown pelicans and other predatory birds In humans, large doses result in tremors and seizures In small doses: Increased chance of having a premature baby Reduction in the duration of lactation Possible ties to cancer Possible ties to falling sperm counts
Diseases carried by Mosquitoes At least 30 known human diseases are carried by mosquitoes West Nile Virus Encephalitis Yellow Fever Malaria Mosquito bites infected person, gets the disease, then transfers it to the next person
Mosquito Life Cycle Mosquitoes require water Can try to control both the adult stage and the larval stage
Should DDT be banned Worldwide? Negative environmental impacts Possible effects on human health 40% of the world’s population at risk of contracting malaria 300 to 500 Million cases a year 1 to 3 million deaths per year
Points to Know 1) What 4 factors are responsible for the increases in food production over the last 50 years? 2) Why are chemical fertilizers tied to the price of oil? What 6 nutrients do fertilizers provide (3 macro, 3 micro)? What are the problems and limitations of chemical fertilizers? 3) Know the 4 categories of pesticides and their target species. 4) What is the perfect pesticide? Besides cost, how do the attributes of a perfect pesticide relate to the problems with pesticide use? 5) What is the controversy over DDT use?
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