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1、Agriculture and Pest Management,Outline,Agricultural Methods Fertilizers Pesticides Organic Farming,Development of Agriculture,Development of agriculture involved manipulating the natural environment to produce food desired by humans. Allowed increase in the size of the human population.,Slash and B
2、urn Vegetation is cleared for agriculture and burned to release nutrients Particularly useful on thin tropical soils Cleared soil useful for 3-5 years Requires a long recovery time,Labor Intensive - Favored when : Growing site does not allow mechanization. Crop does not allow mechanization. Economic
3、 condition does not allow purchase of mechanized equipment.,Typically planted with poly-culture to produce: Different microclimates Different nutrient mixes Natural insect control,Mechanized,Typical of industrialized countries Requires large amounts of energy and flat land. Often monocultures Farmer
4、s often rely on hybrid plant seeds to provide uniform monocultures.,Problems With Mechanized Agriculture,Large tracts of bare land increases soil erosion. Little genetic differentiation often leads to increased pesticide use. No crop rotation depletes soil nutrients thus increasing fertilizer use. F
5、ossil fuel energy use has replaced human muscle power.,Green Revolution has greatly increased worldwide food production.,Energy vs. Labor,In 1913, 135h to 2500kg corn/ha In 1980, 15h to 2500kg corn/ha 120h = petroleum products 5t fossil fuel = 1t fertilizer,The Impact of Fertilizer,Approximately 25%
6、 of worlds agriculture crop is directly attributed to chemical fertilizer use.,Fertilizers replace soil nutrients extracted by plants. Macronutrients 常量元素- Chemical elements used in large quantities by plants. (N, P, K) Removed after each harvest. （1% of harvesting） Micronutrients 微量元素- Chemical ele
7、ments only used in very small quantities by plants. (boron, zinc) Removed after multiple cropping. (ppb),Chemical fertilizers do not replace soil organic matter （humus）. Question: What is the function of Humus? How to keep it?,PESTICIDES,Pesticide - Any chemical used to kill or control populations o
8、f unwanted fungi, plants, or animals. Can be subdivided into several categories based on the organisms they control. Insecticides 杀虫剂 Herbicides 除莠剂 Fungicides 灭真菌剂 Rodenticides 杀鼠剂,Insecticides,Used to control insect populations. Mosquitoes are known to carry over 30 diseases harmful to humans. 300
9、0 yr. Ago, Sulfur Known for centuries that certain plant products produce repellant chemicals. Nicotine (tobacco) difficult to apply, short-lived effects other compounds were sought.,1867 - First synthetic inorganic compound. 1942- DDT First synthetic organic compound. Several new categories of comp
10、ounds have been developed.,Hard Pesticides,Chlorinated Hydrocarbons 有机氯 (DDT) Very stable, long-lasting, persistent pesticides. Tend to accumulate in soil and animal bodies. Half-life, breakdown No longer used. China banned in 1985.,Soft Pesticides,Organophosphates and Carbamates有机磷氨基甲酸酯: Both are s
11、hort-lived compounds that do not persist in the environment, but are generally more toxic to vertebrates 脊椎动物. Mechanism, halflife,Herbicides,Used to control unwanted plants. Weeds compete with crops for soil nutrients. About 60% of pesticides used in US are herbicides. Traditional weed control meth
12、ods are expensive in terms of time and energy.,Fungicides and Rodenticides,Fungicides are an important defense against spoilage of both seeds and mature crops. Rodenticides kill rats, which destroy agricultural crops, and barn grain to the extend of 30%.,Other Agricultural Chemicals,Growth regulator
13、s auxin Preservative Chemical loosening,Problems with Pesticide Use,Perfect Pesticide: Inexpensive Affect only target organism Short half-life Break down into harmless materials Newer pesticides have fewer drawbacks than early hard pesticides, but none are devoid of problems.,Problems cont.,Bioaccum
14、ulation生物积累: the process of accumulating higher and higher amounts of material within the body of an animal. Persistence, receive but unable to eliminate Biological magnification生物富集:acquiring increasing levels of a substance in the bodies of a higher-trophic level organisms. Fat soluble DDT, aquati
15、c habitat 250x in small organism 2000x in big fish,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 applica
16、tions become less effective.,Effects on Non-target Organism,Non-specificity of chemicals Kill the predator that control the pest Pest rebounding Different pest problem,Human Health Concerns,Short and long-term health effects Farmers improper uses Chronic, minute exposures to pesticide residues in food or through contamination of the env.,Why Widely Used ?,Food Production Worldwide, pests destroy 35% of crops Economic Concerns Pesticides increase yields and profits Health Reasons In
