Agriculture. Development of Agriculture

Transcription

1 Agriculture Guiding Question: How has agriculture evolved? LESSON 3 Discuss the beginnings of agriculture. Explain the importance of industrial agriculture and the green revolution. Identify different types of pest control. Explain the importance of pollinators to agriculture. Reading Strategy As you read, fill in a main idea and details chart. List the main ideas of the lesson in the left column. In the right column, note important details about each main idea. Vocabulary traditional agriculture, yield, industrial agriculture, green revolution, biological pest control, integrated pest management (IPM), pollinator Can you imagine having to hunt and gather your own food every day? Can you imagine life without cotton? That was life 15,000 years ago. Agriculture arose only about 10,000 years ago. Many aspects of human civilization began about the same time. That is probably not a coincidence. Walking around all day hunting and gathering didn t leave much time for creating art or new technology! Development of Agriculture Agriculture began about 10,000 years ago, when a warmer climate enabled humans to plant seeds and raise livestock. Everything you eat and all the natural fabrics you wear are products of agriculture. If you don t run a farm, you rely on people who do. But agriculture is a relatively new development in human history. During most of the human species 200,000-year existence, we have been hunter-gatherers, depending on wild plants and animals for our food and fiber. Then about 10,000 years ago, the climate warmed following an ice age. In the warmer climate, plants grew better. People in the Middle East, China, and other areas began to grow plants from seed and to raise animals. Agriculture probably began when hunter-gatherers brought wild fruits, grains, and nuts back to their camps. Some of these foods fell to the ground, were thrown away, or were eaten but had seeds that passed through someone s digestive system. The plants that grew from these seeds likely produced fruits larger and tastier than most, because they came from seeds of fruits that people had selected. As these plants bred with others nearby that shared those characteristics, they produced new generations of plants with large and tasty fruits. You can see more details of the evolution of agriculture in Figure 13 on the next page LESSON PLAN PREVIEW Inquiry Students investigate agricultural advances throughout history. Real World Students find examples of chemical pesticide use in their environment. Differentiated Instruction English language learners study word parts to understand the terms pollination and pollinators RESOURCES In Your Neighborhood Activity, Local Planting Conditions Map It Online Lesson 12.3 Worksheets Lesson 12.3 Assessment Chapter 12 Overview Presentation Figure 12 Early Farming Tools The blades in this photo were used to harvest crops about 5000 years ago. Soil and Agriculture 365

2 Eastern United States Sahel Fertile Crescent wheat China rice sunflower Mesoamerica sorghum New Guinea corn squash Andes Amazonia West Africa Ethiopia coffee bananas potato Origins of agriculture Independent origin Possible independent origin Data from syntheses in Diamond, J Guns, germs, and steel. New York: W.W. Norton; and Goudie, A The human impact, 5th ed. Cambridge, MA: MIT Press. Figure 13 Beginnings of Agriculture Agriculture originated independently in multiple locations as different cultures selectively bred plants and animals from wild species. Areas where people are thought to have invented agriculture independently are colored green. In areas colored blue, it is not known whether people invented agriculture independently or adopted it from other cultures. The map also shows a few of the crops farmed in each region. Map it Origins of Agriculture The earliest widely accepted evidence of agriculture is from the Fertile Crescent region of the Middle East. Refer to Figure 13 as you answer the questions that follow. 1. Interpret Maps According to the map, in what four areas did agriculture most likely arise independently? 2. Interpret Maps In which part of the world were coffee crops first planted? 3. Infer Two large rivers, the Tigris and Euphrates, run through the Fertile Crescent. How did those rivers help make it a good place for agriculture? Selective Breeding and Settlement Eventually, people realized they could control what they grew. Our ancestors then began planting seeds only from those plants whose fruit they liked the most. These were the beginnings of artificial selection, or selective breeding. Selective breeding has resulted in all the food crops and livestock that feed you every day. Once our ancestors learned to cultivate crops, they began to build more permanent settlements, often near water sources. The need to harvest their crops kept them settled, and once they were settled, it made sense to plant more crops. They also began to raise animals as livestock. Increased populations resulted from settlement and more-reliable food supply and reinforced the need for both. Eventually, the ability to grow excess food enabled some people to live away from the farm, leading to the development of professional specialties, commerce, technology, cities, social classes, and political organization. Agriculture ultimately brought us the civilization we know today. Traditional Agriculture Until the Industrial Revolution of the 1800s, the work of cultivating, harvesting, storing, and distributing crops everywhere was performed by human and animal muscle power, along with hand tools and non-motorized machines such as plows. This biologically powered agriculture is known as traditional agriculture. Traditional agriculture may use teams of worker animals and use irrigation and organic fertilizer, but it does not require fossil fuels. 366 Lesson 3

3 Industrial Agriculture Industrial agriculture and the green revolution have saved millions of people from starvation. The Industrial Revolution introduced large-scale mechanization and fossil-fuel engines to agriculture just as it did to industry. Farmers could replace their horses and oxen with faster, more powerful, and more efficient means of harvesting, processing, and transporting crops. In addition to the efficient farm machinery that resulted from the Industrial Revolution, other changes to agriculture came in the mid- 1900s. Many of these were reactions to the Dust Bowl of the 1930s and/or based on wartime technology. There were irrigation improvements and the introduction of synthetic fertilizers. There was also the introduction of chemical pesticides, which reduced competition from weeds and the loss of crops to pests. Because the soil was more productive, and fewer crops were lost to pests, yield increased. Yield is the amount of a crop produced in a given area. The Rise of Industrial Agriculture Mechanized farming technology, the fossil fuels it runs on, manufactured chemicals, and irrigation all allow for industrial agriculture. Industrial agriculture produces huge amounts of crops and livestock. It is also known as high-input agriculture because it relies on people to put in enormous quantities of energy, water, and chemicals. Today, industrial agriculture is practiced on more than 25 percent of the world s croplands and on most of the croplands in the United States. Because it uses large machinery and chemicals that are customized for a specific crop, to be most efficient, industrial agriculture requires that large areas be planted with a single crop, in a monoculture. You can see a monoculture in Figure 14. The planting of crops in monocultures makes planting and harvesting more efficient and can thereby increase harvests. However, monocultures have drawbacks as well. Large monocultures reduce biodiversity over large areas, because far fewer wild organisms are able to live in monocultures than in their native habitats or in morediverse plantings. Moreover, because all the plants in a monoculture are genetically similar, they are vulnerable to the same diseases and pests. For this reason, monocultures carry the risk of catastrophic crop failure. Reading Checkpoint Describe one advantage and one disadvantage of a monoculture. ANSWERS Map It 1. Mesoamerica, the Andes, the Fertile Crescent, China 2. Ethiopia 3. They supply water. Reading Checkpoint Sample answer: Advantage: efficiency; disadvantage: possible catastrophic crop failure because all the plants are vulnerable to the same diseases and pests Figure 14 Monoculture Most crop production in developed nations comes from monocultures such as this cornfield in Texas. Planting crops in large, uniform fields greatly improves the efficiency of planting and harvesting. Unfortunately, it also decreases biodiversity and makes crops susceptible to pests that have adapted to feed on that crop.

4 The Green Revolution In the mid- to late 1900s, the desire for more and better food for the world s growing population led to the green revolution, in which agricultural scientists from developed nations introduced new technology, crop varieties, and farming practices to the developing world. (Green in this context implies covered with plants rather than environmentally friendly. ) Figure 15 The Green Revolution Norman Borlaug, the Father of the Green Revolution, holds the wheat variety he bred that launched the green revolution. The high-yielding, disease-resistant wheat saved many people in developing nations from starvation. BIG QUESTION How can we balance our growing demand for food with our need to protect the environment? Perspective Have students work in pairs. Have each pair write one paragraph that evaluates how the green revolution affected our ability to meet the growing need for food. Then, have students write a second paragraph that evaluates how the green revolution affected humanity s impact on land and soil. Have students share their completed paragraphs with the class. ANSWERS Reading Checkpoint Sample answer: The green revolution introduced new technologies, crop varieties, and farming practices to developing nations. Technology The technology sharing began in the 1940s, when U.S. scientist Norman Borlaug introduced Mexico s farmers to a specially bred strain of wheat (Figure 15). It produced large seed heads, was short enough to avoid wind damage, resisted diseases, and produced high yields. Within two decades Mexico had tripled its wheat production in fact, it had surplus wheat it could export. Soon many developing nations were increasing their crop yields using selectively bred strains of wheat, rice, corn, and other crops from developed nations. Along with new strains of crops, developing nations also imported new methods of industrial agriculture from developed nations. Developing nations began applying large amounts of synthetic fertilizers and chemical pesticides on their fields, liberally irrigating crops, and using heavy equipment powered by fossil fuels. Intensive agriculture of this sort saved millions in India and Pakistan from starvation in the 1970s and eventually turned these nations into net exporters of grain. Environmental Effects The green revolution has saved millions of lives. Its technology comes at a high energy cost, however. Between 1900 and 2008, the energy used by agriculture increased by 7000 percent! On the positive side, the higher productivity of already-cultivated land preserved some ecosystems, because less additional land needed to be cleared for crops. Between 1961 and 2008, food production rose 150 percent and population rose 100 percent, while area converted for agriculture increased only 10 percent. So the green revolution has prevented some deforestation and habitat loss and preserved the biodiversity of some ecosystems. On the negative side, the intensive application of water, inorganic fertilizers, and pesticides has worsened erosion, salinization, desertification, eutrophication, and pollution. In addition, the use of fossil fuels to produce fertilizer and pesticides and to run farm equipment has increased air pollution and contributed to global warming. So the green revolution has saved human lives, but there have been environmental costs. The need to maintain this life-saving productivity while limiting environmental damage has led to attempts at more-sustainable agriculture. You will read more about these in the next lesson. Reading Checkpoint Describe the green revolution in your own words. 368 Lesson 3

5 Pests Chemical pesticides, biological pest control, and integrated pest management can all effectively protect crops from pests. What are pests? What are weeds? We call an organism a pest when it damages plants that are valuable to us, such as crops. We call a plant a weed when it competes with our plants. As you see, these are subjective terms based on our economic interests. Since the beginnings of agriculture, the pests that eat our crops and the weeds that compete with them have taken advantage of the ways we cluster plants in agricultural fields. In a monoculture, a population of a pest adapted to that plant can chew through entire fields. From the viewpoint of a pest adapted to feed on corn, for example, a cornfield is an all-you-can-eat buffet. Chemical Pesticides To prevent crop losses from pests and weeds, people have developed thousands of chemical pesticides. Roughly 400 million kilograms (900 million pounds) of active ingredients from conventional pesticides are applied in the United States each year. Three quarters of this amount is applied on agricultural land. Since 1960, pesticide use has risen fourfold worldwide. Usage in developed nations has leveled off in the past two decades, but it continues to rise in the developing world. The ability of a pesticide to reduce a pest population often declines over time as the population evolves resistance to it. Recall that natural selection occurs within populations when individuals vary in their traits. Because the populations of insects and microorganisms in farm fields are huge, it is likely that some individuals have genes that give them immunity to a given pesticide. So even if a pesticide application kills percent of the insects in a field, 1 in 10,000 survives. If an insect survives because it is genetically resistant to a pesticide and it passes the resistance trait to its offspring, the trait will become more common in the population. As a larger and larger proportion of the insects in the population become resistant to the pesticide, the chemical becomes less and less effective on that population. As a result, industrial chemists are caught up in an evolutionary arms race with the pests they battle, racing to increase the toxicity of pesticides while the pests continue to develop resistance. Figure 16 Biological Pest Control Tomato hornworms are large caterpillars that can destroy a tomato crop very quickly. Here you can see the small white eggs of a parasitoid wasp on a hornworm. When the eggs hatch, the larvae will feed on the caterpillar till it dies possibly saving a tomato plant! Biological Pest Control Because of pesticide resistance and health risks from some pesticides, agricultural scientists increasingly battle pests and weeds with organisms that eat or infect them. This strategy is called biological pest control. For example, parasitoid wasps are natural enemies of many caterpillars. These wasps lay eggs on a caterpillar. The larvae that hatch from the eggs feed on the caterpillar, eventually killing it (Figure 16). Some successful biological pest control efforts have led to steep reductions in pesticide use. Soil and Agriculture 369

6 Find Out More Contact your local division of the USDA and ask if an introduced predator or parasite has ever been used to control a pest in your area. If so, what was the result? If not, ask if they would ever consider doing so. ANSWERS Find Out More Answers will vary. Students responses should indicate that they have contacted the local division of the USDA to learn about introduced predators or parasites. Reading Checkpoint No one knows what effects the predator or parasite will have on nontarget organisms because they have never lived in the same ecosystem before. Bt A widespread modern biological pest control effort is the use of Bacillus thuringiensis (Bt). Bt is a naturally occurring soil bacterium that produces a protein that kills many caterpillars and the larvae of some flies and beetles. Farmers have used the natural pesticidal activity of this bacterium to their advantage by spraying spores of it on their crops. When used correctly, Bt can protect crops from pest-related losses. Introduced Predators and Parasites In some cases, biological pest control requires the introduction of an organism from a different ecosystem. Unfortunately, this means that no one can know for certain in advance what effects the biological pest control organism might have. In some cases, biological pest control organisms have become invasive and harmed nontarget organisms organisms other than the pests. Benefits and Costs If biological pest control works as planned, it can be a permanent solution that requires no maintenance and is environmentally harmless. However, like all invasive species, invasive biological pest control organisms can have wide-ranging ecological and economic impacts, as did the cactus moth in Figure 17. And if nontarget organisms are harmed, the damage may be permanent because halting biological pest control is far more difficult than stopping the application of a pesticide. Because of such concerns, researchers study biological pest control proposals carefully before putting them into action, and government regulators must approve those proposals. But there is never a surefire way of knowing in advance whether a biological pest control program will work as planned. Reading Checkpoint What is one risk of introducing a predator or parasite from a different ecosystem? Figure 17 Risks of Biological Pest Control Cactus moth larvae eat the pads of prickly pear cactus. The story of the cactus moth is one of both great success and environmental destruction. The cactus moth was imported from Argentina to Australia in the 1920s to control prickly pear cactus that was invading rangeland. Within just a few years, millions of hectares of rangeland were free of the cactus. Following the cactus moth s success in Australia, it was introduced in other nations. Unfortunately, cactus moths introduced to Caribbean islands spread to Florida and ate many rare native cacti there. If these moths spread to Mexico and the southwestern United States, they could destroy the many native and economically important species of prickly pear there. Biologist Colothdian Tate (inset) has worked to prevent this ecological disaster. 370 Lesson 3

7 Integrated Pest Management Because both chemical and biological pest control approaches have their drawbacks, agricultural scientists and farmers have developed more-complex strategies that combine the most-useful aspects of each. In integrated pest management (IPM), different techniques are combined to achieve the most effective long-term pest reduction. IPM may include biological pest control, close monitoring of populations, habitat alteration, crop rotation, reduced soil tillage, mechanical pest removal, and chemical pesticides. In recent decades, IPM has become popular in many parts of the world. Indonesia is an important example. Indonesia s government had financially supported chemical pesticide use for years, but its scientists came to understand that the pesticides were actually making the pest problems worse. Pesticides were killing the natural predators of the brown plant-hopper, an insect that devastated rice fields as its population exploded. Concluding that supporting pesticide use was costing money, causing pollution, and decreasing yields, in 1986, the Indonesian government acted. It banned imports of 57 pesticides, slashed financial support for pesticide use, and encouraged IPM. Within four years, Indonesia s pesticide production fell to less than half its 1986 level, pesticide imports fell to one third, and financial support for them was phased out, saving $179 million annually. After these actions, rice yields rose 13 percent. Pollinators Insects and other animals are essential to the reproduction of many crops. Pests are such a major problem in agriculture that it is easy to fall into a habit of thinking of all insects as destructive. But in fact, most insects are harmless to agriculture, and some are essential. Pollination Pollination is the process by which male sex cells of a plant (pollen) fertilize female sex cells of a plant. Without pollination, plants cannot reproduce sexually. Plants such as conifer trees and grasses are pollinated by pollen grains carried on the wind. These plants are fertilized when, by chance, pollen grains land on the female parts of other plants of their species. Plants with showy flowers, however, are typically pollinated by animals, such as insects, hummingbirds, and bats. These animals are called pollinators. Pollinators are among the most vital, yet least appreciated, factors in agriculture. When pollinators feed on flower nectar, they collect pollen on their bodies and take it to the next flower, which might then be fertilized. Our important grain crops, such as corn and wheat, are wind-pollinated, but many other crops, such as fruits, depend on insects for pollination (Figure 18). The most complete survey to date lists 800 species of cultivated plants that rely on bees and other insects for pollination. Figure 18 Pollinators Many agricultural crops depend on insects to pollinate them. Our food supply, therefore, depends partly on conservation of these vital animals. Flowers such as these apple blossoms have shapes and sweet scents that advertise nectar to pollinators such as honeybees. Soil and Agriculture 371

8 Figure 19 Pollinator-Safe Gardening Japanese beetles can destroy rosebushes very quickly. The canister (inset) contains a pheromone (chemical signal) that attracts only Japanese beetles, destroying them and conserving pollinators while protecting rosebushes. ANSWERS Lesson 3 Assessment For answers to the Lesson 3 Assessment, see page A 18 at the back of the book. Declining Pollinators Unfortunately, pollinator populations have declined. One example is the alkali bee, a native pollinator of Utah, Nevada, and other dry areas of western North America. Alkali bees are a major pollinator of alfalfa, which is a very important livestock feed and cover crop. When pesticide use rose in the mid- 1900s, alkali bee populations plummeted, and alfalfa yields fell, threatening both crop and livestock agriculture. Farmers have changed the way they use pesticides in alkali bee habitat, but alkali bees are now extinct in many of their former breeding areas. Preserving the biodiversity of native pollinators is especially important because our most common domesticated pollinator, the honeybee, is declining sharply. North American farmers regularly hire beekeepers to bring colonies of this introduced bee to their fields when it is time to pollinate crops. Honeybees pollinate more than 100 crops, which together make up one third of the U.S. diet. In recent years, two accidentally introduced parasites have swept through honeybee populations, destroying hives. In addition, starting in 2006, entire hives began dying off for an unknown reason. Scientists are racing to discover the reasons for this mysterious syndrome, which is called colony collapse disorder, before it threatens our food supply. Pollinator Conservation Farmers and homeowners can help maintain populations of insect pollinators, such as bees, by reducing or eliminating pesticide use. Otherwise, they risk killing the good bugs along with the bad bugs. Pest control measures that target specific pests, such as the pheromone trap in Figure 19, are pollinator-safe alternatives to pesticides Communicate Write a paragraph describing when and how agriculture likely began. End with a description of the beginnings of selective breeding. 2. Infer How have industrial agriculture and the green revolution affected the world s population? 3. Compare and Contrast How do (a) chemical pesticides, (b) biological control, and (c) integrated pest management protect crops from pests? 4. Review How are pollinators important to crop agriculture? 5. Suppose that you were the resource manager for a national wildlife refuge with a pest problem. You have been told that you can import predators of the pest from Asia to begin a biological pest control program. What three questions would you ask before you began that program? 372 Lesson 3