Recommended
Recommended
More Related Content
What's hot
What's hot (18)
Similar to Chapt07lecture 1227030871316967-8
Similar to Chapt07lecture 1227030871316967-8 (20)
More from Cleophas Rwemera
More from Cleophas Rwemera (20)
Recently uploaded
Recently uploaded (20)
Chapt07lecture 1227030871316967-8
- 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 7 Lecture Outline
- 2. Learning Outcomes After studying this chapter, you should be able to answer the following questions: • How have global food production and population changed? • How many people are chronically hungry, and why does hunger persist in a world of surpluses? • What are some health risks of undernourishment, poor diet, and overeating? • What are our primary food crops? • Describe five components of soil. • What was the green revolution? • What are GMOs, and what traits are most commonly introduced with GMOs? • Describe some environmental costs of farming, and ways we can minimize these costs. 7-2
- 3. We can’t solve problems by using the same kind of thinking we used when we created them. –Albert Einstein 7-3
- 4. 7.1 Global Trends in Food and Nutrition • Food production has been transformed from small-scale, diversified, family operations to expansive farms of thousands of hectares, growing one or two genetically modified crops, with abundant inputs of fuel and fertilizer, for a competitive global market. 7-4
- 5. Hunger around the world 7-5
- 6. Food security is unevenly distributed • Four decades ago, hunger was one of the world’s most prominent, persistent problems. • In 1960, nearly 60 percent of people in developing countries were chronically undernourished, and the world’s population was increasing by more than 2 percent every year. • Today, some conditions have changed dramatically; others have changed very little. • The world’s population has risen from 3 billion to over 6.5 billion, but food production has increased even faster. 7-6
- 7. Food security is unevenly distributed… • Food security is the ability to obtain sufficient, healthy food on a day-to-day basis, is a combined problem of economic, environmental, and social conditions. • In wealthy countries such as the United States, millions lack a sufficient, healthy diet. • In the poorest countries, entire national economies can suffer from a severe drought, flood, or insect outbreak. 7-7
- 8. Famines usually have political and social roots • Globally, widespread hunger arises when political instability, war, and conflict displace populations, removing villagers from their farms or making farming too dangerous to carry on. • Famines are large-scale food shortages, with widespread starvation, social disruption, and economic chaos. 7-8
- 9. 7-9
- 10. 7.2 Eating Right to Stay Healthy • A good diet is essential to keep you healthy. • You need the right nutrients, as well as enough calories for a productive and energetic lifestyle. 7-10
- 11. A healthy diet includes the right nutrients • Malnourishment is a general term for nutritional imbalances caused by a lack of specific nutrients. 7-11
- 12. The Harvard food pyramid 7-12
- 13. Overeating is a growing world problem • Increasing world food supplies and low prices cause increasing overweight and obese populations. • In the U.S., and increasingly in Europe, China, and developing countries, highly processed foods rich in sugars and fats have become a large part of our diet. • Some 64 percent of adult Americans are overweight, up from 40 percent only a decade ago. About one-third of us are seriously overweight, or obese (generally considered to mean more than 20 percent over the ideal weight for a person’s height and sex. 7-13
- 14. 7.3 The Foods We Eat • Of the thousands of edible plants and animals in the world, only a few provide almost all our food. 7-14
- 15. A boom in meat production brings costs and benefits • Because of dramatic increases in corn and soy production, meat consumption has grown in both developed and developing countries. • Meat is a concentrated, high-value source of protein, iron, fats, and other nutrients that give us the energy to lead productive lives. 7-15
- 16. Meat is a good indicator of wealth 7-16
- 17. Confined animal feeding operation (CAFO) 7-17
- 18. Seafood is both wild and farmed • Overharvesting and habitat destruction threaten most of the world’s wild fisheries. • The problem is too many boats using efficient but destructive technology to exploit a dwindling resource base. • Aquaculture is providing an increasing share of the world’s seafood. 7-18
- 19. Fish pins • Net pens anchored in nearshore areas allow spread of diseases, escape of exotic species, and release of feces, uneaten food, antibiotics, and other pollutants into surrounding ecosystems. 7-19
- 20. Increased production comes with increased risks • There are many environmental worries about this efficient production. – Land conversion from pasture to soy and corn fields raises the rate of soil erosion. – Constant use of antibiotics raises the very real risk of antibiotic-resistant diseases. 7-20
- 21. 7.4 Soil Is a Living Resource • Soil is a marvelous substance, a living resource of astonishing complexity and frailty. • It is a complex mixture of: – mineral grains weathered from rocks, – partially decomposed organic molecules, and – a host of living organisms. • Soil can be considered a living ecosystem by itself. 7-21
- 22. What is soil? Soil is a complex mixture of six components: – sand and gravel-mineral particles from bedrock, either in place or moved from elsewhere, as in wind-blown sand. – silts and clays -extremely small mineral particles; many clays are sticky and hold water because of their flat surfaces and ionic charges; others give red color to soil. – dead organic material-decaying plant matter stores nutrients and gives soils a black or brown color. – soil fauna and flora -living organisms, including soil bacteria, worms, fungi, roots of plants, and insects, recycle organic compounds and nutrients. – water -moisture from rainfall or groundwater, essential for soil fauna and plants. – air -tiny pockets of air help soil bacteria and other organisms survive. 7-22
- 23. 7-23
- 25. 7.5 Ways We Use and Abuse Soil • Agriculture both causes and suffers from environmental degradation. • The causes of this extreme degradation vary: – In Ethiopia, it is water erosion. – In Somalia, it is wind; and in Uzbekistan, salt and toxic chemicals are responsible. – In Sweden and Finland, fallout from the Chernobyl nuclear reaction explosion has contaminated large amounts of grazing land and farmland. 7-25
- 26. Causes of Soil Erosion and Degradation 7-26
- 27. Farming accelerates erosion • Erosion is an important natural process, resulting in the redistribution of the products of geologic weathering, and it is part of both soil formation and soil loss. • Where erosion has worn down mountains and spread soil over the plains or deposited rich alluvial silt in river bottoms, we farm it. 7-27
- 28. Wind and water move soil • Sheet erosion: water flowing across a gently sloping, bare field removing a thin, uniform layer of soil. • Rill erosion: when little rivulets of running water gather together and cut small channels in the soil. • Gully erosion: if rills enlarge to form bigger channels or ravines that are too large to be removed by normal tillage operations. • Desertification: conversion of productive land to desert. 7-28
- 29. Wind and water are the main agents that move soil around. 7-29
- 30. Wind can equal or exceed water in erosive force • In extreme conditions, windblown dunes encroach on useful land and cover roads and buildings. • Over the past 30 years, China has lost 93,000 km2 (about the size of Indiana) to desertification. • Advancing dunes from the Gobi desert are now only 160 km (100 mi) from Beijing. 7-30
- 31. 7.6 Other Agricultural Resources • Irrigation is necessary for high yields – Agriculture accounts for the largest single share of global water use. – Salinization: mineral salts accumulate in the soil due to evaporating water from irrigation. • Fertilizer boosts production – Much of the doubling in worldwide crop production since 1950 has come from increased inorganic fertilizer use. • Modern agriculture runs on oil • Pest control saves crops 7-31
- 32. 7.7 How We Have Managed to Feed Billions • In the developed countries, 95 percent of agricultural growth in the twentieth century came from improved crop varieties (the green revolution) or increased fertilization, irrigation, and pesticide use, rather than from bringing new land into production. 7-32
- 33. The green revolution has increased yields • Most of this gain was accomplished by use of synthetic fertilizers along with conventional plant breeding: geneticists laboriously hand-pollinating plants and looking for desired characteristics in the progeny. • Starting about 50 years ago, agricultural research stations began to breed tropical wheat and rice varieties that would provide food for growing populations in developing countries. 7-33
- 34. Genetic engineering could have benefits and costs • Genetic engineering: splicing a gene from one organism into the chromosome of another. • Genetically modified organisms (GMOs): organisms with entirely new genes, and even new organisms, often called “transgenic” organisms. 7-34
- 35. Is genetic engineering safe? • The greatest danger is the ecological effects if these organisms spread into the native populations. • There are social and economic implications of GMOs. Will they help feed the world, or will they lead to a greater consolidation of corporate power and economic disparity? • Are GMO’s required if we hope to reduce malnutrition and feed eight billion people in 50 years. 7-35
- 36. 7.8 Alternatives in Food and Farming • Soil conservation is essential – With careful husbandry, soil is a renewable resource that can be replenished and renewed indefinitely. – Water runoff can be reduced by grass strips in waterways and by contour plowing, plowing across the hill rather than up and down. – Terracing is shaping the land to create level shelves of earth to hold water and soil. 7-36
- 37. Soil conservation is essential 7-37
- 38. 7.9 Consumer Choices Can Reshape Farming • You can be a locavore – Locavore: a person who consumes locally produced food. • You can eat low on the food chain – Since there is less energy involved in producing food from plants, you can reduce your impact by eating more grains, vegetables, and dairy and a little less meat. • You can eat organic, low-input foods – If you buy organic food, you are supporting farmers who use no pesticides or artificial fertilizers. 7-38
- 39. Practice Quiz 1. What is Brazil’s Cerrado, and how is agriculture affecting it? 2. Explain how soybeans grown in Brazil are improving diets in China. 3. What does it mean to be chronically undernourished? How many people in the world currently suffer from this condition? 4. Why do nutritionists worry about food security? Who is most likely to suffer from food insecurity? 5. Describe the conditions that constitute a famine. Why does Amartya Sen say that famines are caused more by politics and economics than by natural disasters? 6. Define malnutrition and obesity. How many Americans are now considered obese? 7. What three crops provide most human caloric intake? 7-39
Editor's Notes
- Food production has been transformed from small-scale, diversified, family operations to expansive farms of thousands of hectares, growing one or two genetically modified crops, with abundant inputs of fuel and fertilizer, for a competitive global market. These changes have dramatically increased production, lowered food prices, and provided affordable meat protein in developing countries from Brazil to China. Food production has increased so dramatically that we now use edible corn and sugar to run our cars (chapter 12). According to the International Monetary Fund, 2005 global food costs (in inflation-adjusted dollars) were the lowest ever recorded, less than one-quarter of the cost in the mid-1970s. In the United States and Europe, overproduction has driven prices low enough that we pay farmers billions of dollars each year to take land out of production.
- Mapping Poverty and Plenty: Examine the map in figure 7.3. Using the map of political boundaries at the end of your book, identify ten of the hungriest countries. Then identify ten of the countries with less than 5 percent of people facing chronic undernourishment (yellow areas). The world’s five most populous countries are China, India, United States, Indonesia, and Brazil. Which classes do these five belong to? Answers: China, Indonesia, and Brazil have 5–20 percent malnourished; India has 20–35 percent; the United States has <5 percent.
- Nobel Prize-winning economist Amartya K. Sen, of Harvard, has shown that, while natural disasters often precipitate famines, farmers have almost always managed to survive these events if they aren’t thwarted by inept or corrupt governments or greedy elites. Professor Sen points out that armed conflict and political oppression are almost always at the root of famine. No democratic country with a relatively free press, he says, has ever had a major famine.
- The United Nations Food and Agriculture Organization (FAO) estimates that nearly 3 billion people (almost half the world’s population) suffer from vitamin, mineral, or protein deficiencies.
- Malnourishment is a general term for nutritional imbalances caused by a lack of specific nutrients. In conditions of extreme food shortages, a lack of protein in young children can cause kwashiorkor, which is characterized by a bloated belly and discolored hair and skin. Kwashiorkor is a West African word meaning “displaced child.” (A young child is displaced—and deprived of nutritious breast milk—when a new baby is born.) Marasmus (from Greek, “to waste away”) is another severe condition in children who lack both protein and calories. Deficiencies in vitamin A, folic acid, and iodine are more widespread problems. Both are found in vegetables, especially dark green leafy vegetables. Deficiencies in folic acid have been linked to neurological problems in babies. Effects of vitamin A shortages cause an estimated 350,000 people to go blind every year. Dr. Alfred Sommer, an ophthalmologist from Johns Hopkins University, has shown that giving children just two cents’ worth of vitamin A twice a year could prevent almost all cases of childhood blindness and premature death associated with shortages of vitamin A. Vitamin supplements also reduced maternal mortality by nearly 40 percent in one study in Nepal. Iodine deficiencies can cause goiter (fig. 7.7), a swelling of the thyroid gland. Iodine is essential for synthesis of thyroxin, an endocrine hormone that regulates metabolism and brain development, among other things. The FAO estimates that 740 million people, mostly in Southeast Asia, suffer from iodine deficiency, including 177 million children whose development and growth have been stunted. Developed countries have largely eliminated this problem by adding a few pennies’ worth of iodine to our salt. Starchy foods, such as maize, polished rice, and manioc (tapioca), form the bulk of the diet for many poor people, but these foods are low in several essential vitamins and minerals.
- The best way to make sure you’re healthy is to eat lots of vegetables and grains, moderate amounts of eggs and dairy products, and sparing amounts of meat, oils, and processed foods. Modest amounts of fats provide lipids (chapter 2) that are essential for healthy skin, cell function, and metabolism. But your body is not designed to process excessive amounts of fats (or sugars). Unsaturated plant-based oils, such as olive oil, are recommended by dietitians; trans fats (found in hydrogenated margarine) are not recommended. A food pyramid developed by Harvard dieticians provides a useful guide for healthy eating, together with a solid base of regular exercise (fig. 7.8).
- Being overweight substantially increases your risk of hypertension, diabetes, heart attacks, stroke, gallbladder disease, osteo-arthritis, respiratory problems, and some cancers. Every year, about 400,000 people in the United States die from illnesses related to obesity. This number is approaching the number related to smoking (435,000 annually). Paradoxically, food insecurity and poverty can contribute to obesity. In one study, more than half the women who reported not having enough to eat were overweight, compared with one-third of the food-secure women. Lack of good quality food may contribute to a craving for carbohydrates in people with a poor diet. A lack of time for cooking, limited access to healthy food choices, and ready availability of fast-food snacks and calorie-laden soft drinks, also lead to dangerous dietary imbalances for many people.
- About a dozen types of grasses, three root crops, twenty or so fruits and vegetables, six mammals, two domestic fowl, and a few fish species make up almost all the food we eat (table 7.1). Two grasses, wheat and rice, are especially important because they are the staple foods for most of the 5 billion people in developing countries. In the United States, corn (another grass, also known as maize) and soybeans have become our primary staples. We rarely eat either corn or soybeans directly, but corn provides the corn sweeteners, corn oil, and the livestock feed for producing our beef, chicken, and pork, as well as industrial starches and many synthetic vitamins. Soybeans are also fed to livestock, and soy provides protein and oils for processed foods. Because we have developed so many uses for corn, it now accounts for nearly two thirds of our bulk commodity crops (corn, soy, wheat, rice).
- Meat is a good indicator of wealth because it is expensive to produce, in terms of the resources needed to grow an animal (fig. 7.12). As discussed in chapter 2, herbivores use most of the energy they consume in growing muscle and bone, moving around, staying warm, and metabolizing (digesting) food. Only a little food energy is stored for consumption by carnivores, at the next level of the food pyramid. It takes over 8 kilos of grain fed to a beef cow to produce a single kilo of meat. (Actually, we raise mainly steers, or neutered males, for beef.) Pigs, being smaller, are more efficient. Just three pounds of pig feed are needed to produce a kilo of pork. Chickens and herbivorous fish (such as catfish) are still more efficient. Globally, some 660 million metric tons of cereals are used as livestock feed each year.
- A number of technological and breeding innovations have made this increased production possible. One of the most important is the confined animal feeding operation (CAFO), where animals are housed and fed—mainly soy and corn—for rapid growth (fig. 7.13). These operations dominate livestock raising in the U.S., Europe, and increasingly in China and other countries. Animals are housed in giant enclosures, with up to 10,000 hogs or a million chickens in an enormous barn complex, or 100,000 cattle in a feed lot (fig. 7.14).
- Boats as big as ocean liners travel thousands of kilometers and drag nets large enough to scoop up a dozen jumbo jets, sweeping a large patch of ocean clean of fish in a few hours. Long-line fishing boats set cables up to 10 km long with hooks every 2 meters that catch birds, turtles, and other unwanted “by-catch” along with targeted species. Trawlers drag heavy nets across the bottom, scooping up everything indiscriminately and reducing broad swaths of habitat to rubble. One marine biologist compared the technique to harvesting forest mushrooms with a bulldozer. In some operations, up to 15 kg of dead and dying by-catch are dumped back into the ocean for every kilogram of marketable food. The FAO estimates that operating costs for the 4 million boats now harvesting wild fish exceed sales by $50 billion (U.S.) per year. Countries subsidize fishing fleets to preserve jobs and to ensure access to this valuable resource. Fish can be grown in farm ponds that take relatively little space but are highly productive. Cultivation of high-value carnivorous species, however, such as salmon, sea bass, and tuna, threaten wild stocks exploited to stock captive operations or to provide fish food. Building coastal fish-rearing ponds causes destruction of hundreds of thousands of hectares of mangrove forests and wetlands, which serve as irreplaceable nurseries for marine species.
- There are many environmental worries about this efficient production. Land conversion from pasture to soy and corn fields raises the rate of soil erosion (discussed in the next section). Bacteria in the manure in the feedlots, or liquid wastes in manure storage lagoons (holding tanks) around hog farms, can escape into the environment—from airborne dust around feedlots or from breaches in the walls of a manure tank. This massive and constant exposure produces antibiotic-resistant pathogens, strains that have adapted to survive antibiotics. This use, then, is slowly rendering our standard antibiotics useless for human health care. Next time you are prescribed an antibiotic by your doctor, you might ask whether she or he worries about antibiotic resistance, and you might think about how you would feel if your prescription was ineffective against your illness. As environmental scientists, we are faced with a conundrum, then. Improved efficiency has great environmental costs; it has also given us the abundant, inexpensive foods that we love. We have more protein, but also more obesity, heart disease, and diabetes than we ever had before. What do you think? Do the environmental risks balance a globally improved quality of life? Or should we consider reducing our consumption to reduce environmental costs? How might we go about making changes, if you think any are needed?
- Soil is a marvelous substance, a living resource of astonishing complexity and frailty. It is a complex mixture of mineral grains weathered from rocks, partially decomposed organic molecules, and a host of living organisms. Soil can be considered a living ecosystem by itself. Building a few millimeters of soil can take anything from a few years (in a healthy grassland) to a few thousand years (in a desert or tundra). Under the best circumstances, topsoil accumulates at about 1 mm per year. With careful husbandry that prevents erosion and adds organic material, soil can be replenished and renewed indefinitely. But many farming techniques deplete soil. Crops consume the nutrients; plowing exposes the soil to erosion by wind or water. Severe erosion can carry away 25 mm or more of soil per year, far more than can accumulate under the best of conditions.
- 1. sand and gravel (mineral particles from bedrock, either in place or moved from elsewhere, as in wind-blown sand) 2. silts and clays (extremely small mineral particles; many clays are sticky and hold water because of their flat surfaces and ionic charges; others give red color to soil) 3. dead organic material (decaying plant matter stores nutrients and gives soils a black or brown color) 4. soil fauna and flora (living organisms, including soil bacteria, worms, fungi, roots of plants, and insects, recycle organic compounds and nutrients) 5. water (moisture from rainfall or groundwater, essential for soil fauna and plants) 6. air (tiny pockets of air help soil bacteria and other organisms survive)
- Healthy soil fauna can determine soil fertility: Soil bacteria, algae, and fungi decompose and recycle leaf litter into plant-available nutrients, as well as helping to give soils structure and loose texture (fig. 7.16). Microscopic worms and nematodes process organic matter and create air spaces as they burrow through soil. These organisms mostly stay near the surface, often within the top few centimeters. The sweet aroma of freshly turned soil is caused by actinomycetes, bacteria that grow in fungus-like strands and give us the antibiotics streptomycin and tetracycline.
- Most soil fauna occur in the uppermost layers of a soil, where they consume leaf litter accumulates. This layer is known as the “O” (organic) horizon. Just below the O horizon is a layer of mixed organic and mineral soil material, the A horizon (fig. 7.17), or surface soil. The B horizon, or subsoil, tends to be richer in clays than the A; the B horizon is below most organic activity. The B layer accumulates clays that seep downward from the A horizon with rainwater that percolates through the soil. If you dig a hole, you may be able to tell where the B horizon begins because the soil tends to become slightly sticky. If you squeeze a handful of B soil, it should hold its shape better than a handful of A soil. A and B horizons. The E layer is loose and light-colored because most of its clays and organic material have been washed down to the B horizon. The C horizon, below the subsoil, is mainly decomposed rock fragments. Parent materials underlie the C layer. Parent material is the sand, wind-blown silt, bedrock, or other mineral material on which the soil is built. Your food comes mostly from the A horizon: Ideal farming soils have a thick, organic-rich A horizon. The soils that support the corn belt farm states of the U.S. Midwest have rich, black A horizon that can be over two meters thick, although a century of farming has washed much of this soil down the Mississippi River to the Gulf of Mexico. Most soils have less than half a meter of A horizon.
- It is estimated that, every year, 3 million ha (7.4 mil lion acres) of cropland are ruined by erosion, 4 million ha are turned into deserts, and 8 million ha are converted to nonagricultural uses, such as homes, highways, shopping centers, factories, and reservoirs. Over the past 50 years, some 1.9 billion ha of agricultural land (an area greater than that now in production) have been degraded to some extent. About 300 million ha of this land are strongly degraded (meaning that the soil has deep gullies, severe nutrient depletion, or poor crop growth or that restoration is difficult and expensive). Some 910 million ha—about the size of China—are moderately degraded. Nearly 9 million ha of former croplands are so degraded that they no longer support any crops at all.
- Water and wind erosion provide the motive force for the vast majority of all soil degradation worldwide (fig. 7.20). Chemical degradation includes nutrient depletion, salt accumulation, acidification, and pollution. Physical degradation includes compaction by heavy machinery or trampling by cattle, water accumulation from excess irrigation and poor drainage, and laterization (solidification of iron and aluminum-rich tropical soil when exposed to sun and rain).
- An estimated 25 billion metric tons of soil are lost from croplands every year due to wind and water erosion. The net effect, worldwide, of this widespread topsoil erosion is a reduction in crop production equivalent to removing about 1 percent of the world’s cropland each year. Many farmers are able to compensate for this loss by applying more fertilizer and by bringing new land into cultivation. Continuation of current erosion rates, however, could reduce agricultural production by 25 percent in Central America and Africa and by 20 percent in South America by 2020.
- Wind can equal or exceed water in erosive force, especially in a dry climate and on relatively flat land. When plant cover and surface litter are removed from the land by agriculture or grazing, wind lifts loose soil particles and sweeps them away. In extreme conditions, windblown dunes encroach on useful land and cover roads and buildings (fig. 7.21c). Over the past 30 years, China has lost 93,000 km2 (about the size of Indiana) to desertification, or conversion of productive land to desert. Advancing dunes from the Gobi desert are now only 160 km (100 mi) from Beijing. Every year more than 1 million tons of sand and dust blow from Chinese drylands, often traveling across the Pacific Ocean to the West Coast of North America. Since 1985, China has planted more than 40 billion trees to try to stabilize the soil and hold back deserts. Many areas of the United States and Canada have very high erosion rates. The U.S. Department of Agriculture reports that 69 million ha (170 million acres) of U.S. farmland and range are eroding faster than 1 mm per year (10 tons/ha/year), the rate at which soil accumulates in the best conditions. These erosion rates steadily deplete long-term productivity. Intensive farming practices are largely responsible for this situation. Row crops, such as corn and soybeans, leave soil exposed for much of the growing season. Deep plowing and heavy herbicide applications create weed-free fields that look neat but are subject to erosion.
- Irrigation is necessary for high yields: Agriculture accounts for the largest single share of global water use. At least two-thirds of all fresh water withdrawn from rivers, lakes, and groundwater supplies is used for irrigation (chapter 10). Irrigation increases yields of most crops by 100 to 400 percent. Although estimates vary widely (as do definitions of irrigated land), about 15 percent of all cropland, worldwide, is irrigated. Salinization, in which mineral salts accumulate in the soil, is often a problem when irrigation water dissolves and mobilizes salts in the soil. As the water evaporates, it leaves behind a salty crust on the soil surface that is lethal to most plants. Flushing with excess water can wash away this salt accumulation, but the result is even more saline water for downstream users. Fertilizer boosts production: In addition to water, sunshine, and carbon dioxide, plants need small amounts of inorganic nutrients for growth. The major elements required by most plants are nitrogen, potassium, phosphorus, calcium, magnesium, and sulfur. Nitrogen is a key component of all living cells (chapter 2), and nitrogen is the most common limiting factor for plant growth. Thus nitrogen, potassium, and phosphorus are our primary fertilizers. Calcium and magnesium often are limited in areas of high rainfall and must be supplied in the form of lime. A good deal of the doubling in worldwide crop production since 1950 has come from increased inorganic fertilizer use. In 1950 the average amount of fertilizer used was 20 kg per hectare. In 2000 this had increased to an average of 90 kg per hectare worldwide. Modern agriculture runs on oil: Farming as it is generally practiced in the industrialized countries is highly energy-intensive. Fossil fuels supply almost all of this energy. Between 1920 and 1980, direct energy use on farms rose as gasoline and diesel fuels were consumed by increasing mechanization of agriculture. Indirect energy use, in the form of synthetic fertilizers, pesticides, and other agricultural chemicals, increased even more, especially after World War II. On intensively fertilized farms, indirect energy use may be five times that of direct energy. The energy price shocks of the 1970s encouraged energy conservation that has reduced farm energy use, even though total food production has continued to rise. Pest control saves crops: Biological pests reduce crop yields and spoil as much as half of the crops harvested every year in some areas. Modern agriculture largely depends on toxic chemicals to kill or drive away these pests, but there are many serious concerns about the types and amounts of pesticides now in use.
- In fact, less land is being cultivated now than 100 years ago in North America, or 600 years ago in Europe. As more effective use of labor, fertilizer, and water and improved seed varieties have increased in the more developed countries, productivity per unit of land has increased, and much marginal land has been retired, mostly to forests and grazing lands. In developing countries, at least two-thirds of recent production gains have come from new crop varieties and more intense cropping, rather than expansion into new lands. Although at least 3,000 species of plants have been used for food at one time or another, most of the world’s food now comes from only a few widely grown crops (see table 7.1). Many new or unconventional varieties might be valuable human food supplies. The spread of new high-yield varieties around the world has been called the green revolution. It is one of the main reasons that world food supplies have more than kept pace with the growing human population over the past few decades.
- So far, the major improvements in farm production have come from technological advances and modification of a few well-known species. Yield increases often have been spectacular. A century ago, when all maize (corn) in the United States was open pollinated, average yields were about 25 bushels per acre (bu/acre). In 2000 the average yield from rainfed fields in Iowa was 138 bu/acre, and irrigated maize in Arizona averaged 208 bu/acre. The highest yield ever recorded in field production was 370 bu/acre on an Illinois farm, but theoretical calculations suggest that 500 bu/acre (32 metric tons per hectare) could be possible. Most of this gain was accomplished by use of synthetic fertilizers along with conventional plant breeding: geneticists laboriously hand-pollinating plants and looking for desired characteristics in the progeny. Starting about 50 years ago, agricultural research stations began to breed tropical wheat and rice varieties that would provide food for growing populations in developing countries. The first of the “miracle” varieties was a dwarf, high-yielding wheat developed by Norman Borlaug (who received a Nobel Peace Prize for his work) at a research center in Mexico (fig. 7.25). At about the same time, the International Rice Institute in the Philippines developed dwarf rice strains with three or four times the production of varieties in use at the time. The spread of these new high-yield varieties around the world has been called the green revolution. It is one of the main reasons that world food supplies have more than kept pace with the growing human population over the past few decades.
- Genetic engineering, splicing a gene from one organism into the chromosome of another, has the potential to greatly increase both the quantity and the quality of our food supply. It is now possible to build entirely new genes, and even new organisms, often called “transgenic” organisms or genetically modified organisms (GMOs), by taking a bit of DNA from here, a bit from there, and even synthesizing artificial sequences to create desired characteristics in engineered organisms (fig. 7.27). Most GMOs have been engineered for pest resistance or weed control: Biotechnologists have created plants with genes for endogenous insecticides. Bacillus thuringiensis (Bt), a bacterium, makes toxins lethal to Lepidoptera (butterfly family) and Coleoptera (beetle family). The genes for some of these toxins have been transferred into crops such as maize (to protect against European cutworms), potatoes (to fight potato beetles), and cotton (to protect against boll weevils). This allows farmers to reduce insecticide spraying. Arizona cotton farmers, for example, report reducing their use of chemical insecticides by 75 percent. Most European nations have not approved Bt-containing varieties. Fear of transgenic products has been a sticking point in agricultural trade between the United States and the European Union.
- The first genetically modified animal designed to be eaten by humans is an Atlantic salmon (Salmo salar) containing extra growth hormone genes from an oceanic pout (Macrozoarces americanus). The greatest worry from this fish is not that it will introduce extra hormones into our diet—that’s already being done by chickens and beef that get extra growth hormone via injections or their diet—but, rather, the ecological effects if the fish escape from captivity. The transgenic fish grow seven times faster and are more attractive to the opposite sex than a normal salmon. If they escape from captivity, they may outcompete already endangered wild relatives for food, mates, and habitat. Fish farmers say they will grow only sterile females and will keep them in secure net pens. Opponents point out that salmon frequently escape from aquaculture operations and that, if just a few fertile transgenic fish break out, it could be catastrophic for wild stocks. Finally, there are social and economic implications of GMOs. Will they help feed the world, or will they lead to a greater consolidation of corporate power and economic disparity? Might higher yields and fewer losses to pests and diseases allow poor farmers in developing countries to stop using marginal land and avoid cutting down forests to create farmland? Is this simply a technological fix, or could it help promote agricultural sustainability? Critics suggest that there are simpler and cheaper ways other than high-tech crop varieties to provide vitamin A to children in developing countries or to increase the income of poor rural families. Adding a cow or a fishpond or training people in water harvesting or regenerative farming techniques (as we’ll discuss in the next section) may have a longer-lasting impact than selling them expensive new seeds. On the other hand, if we hope to reduce malnutrition and feed eight billion people in 50 years, maybe we need all the tools we can get. Where do you stand in this debate? What additional informationwould you need to reach a reasoned judgment about the risks and benefits of this new technology?