Chapter 7: Food and Agriculture PDF

C H A PTER 7 Food and Agriculture LEARNING OUTCOMES After studying this chapter, you should be able to answer the following questions: How many people are chronically hungry, and why does What was the Green Revolution? ­hunger persist in a worl...

C H A PTER 7 Food and Agriculture LEARNING OUTCOMES After studying this chapter, you should be able to answer the following questions: How many people are chronically hungry, and why does What was the Green Revolution? ­hunger persist in a world of surpluses? What are GMOs, and what traits are most commonly intro- What are some health risks of undernourishment, poor diet, duced with GMOs? and overeating? Describe some environmental costs of farming and ways we What are our primary food crops? can minimize these costs. Describe five components of soil. Illinois farm fields produce the world’s largest crop of corn and soybeans. ­Increasingly complex pesticide mixes are necessary to support this kind of production. ©Kostic Dusan/123RF CASE STUDY A New Pesticide Cocktail E very spring the farmers in McLean County, Illinois, set out to grow some of the biggest corn and soy crops the world has ever seen. The county with the largest crops of both ­soybeans and corn in the state with the largest soy crop and the second-largest corn crop (after Iowa), McLean County is Chemicals, seeds, and licenses to use them are expensive, and small producers, unable to compete, have largely disappeared. Since 2010, 94 percent of U.S. soy acres have been herbicide tolerant. Increasingly, these crops have “stacked traits,” or combined tolerance of multiple pesticides, to 95 ­percent cropland, and the two crops make up nearly 90 ­percent compensate for the rapid evolution of weeds and pests. of crop acres. These fields are the economic engine of the U.S. As an ecologist would point out, constant disturbance promotes agricultural economy, the world’s largest producer and exporter of evolution in a species. Constant exposure to glyphosate, the single corn and soybeans. most abundantly used herbicide in the United States (often known by To an ecologist, this is a very simplified ecosystem. It has just two its trade name, Roundup®), or to atrazine, glufosinate, or other ubiqui- dominant producer species, soy and corn, and (ideally) one consumer, tous chemicals, destroys most members of a weed population. But the farmer. But an ecologist sees a simplified system as a world of the few tolerant individuals that survive will proliferate, free of compe- niches waiting to be filled. Consumers, especially insect pests, are tition. Tolerant-trait weeds and pests come to dominate the popula- eager to move in to exploit the burgeoning productivity of crop fields. tion, making a pesticide ineffectual. For most pesticides, it takes Plant competitors, especially fast-growing weeds like pigweed and about 5 years before resistant weeds or insects begin to appear. ragweed, are poised to invade. To protect their crops, farmers depend The rapid evolution of pests and weeds, and the resulting need on chemical pesticides. Scores of these have been developed— for constantly better pesticides, is known as the pesticide treadmill. some broadly toxic, some narrowly targeted to certain pests. After the 1996 introduction of Monsanto’s “Roundup®-ready” seeds, A new stage in this eternal struggle was the introduction of it took less than 5 years for resistant pigweeds to appear. By 2017, seeds genetically modified to tolerate herbicides. Since the 1990s, at least 38 resistant weed species were known, affecting about joint chemical- and seed-producing conglomerates, especially 40 percent of the 69 million hectares (170 million acres) planted in Bayer-Monsanto and Dow AgroSciences, have produced “sys- corn, soybeans, and cotton in the United States (fig. 7.1). tems” of seeds tailored to tolerate a specific herbicide. These As herbicides become ineffectual, complex “cocktails” of chem- allow farm operators to spray herbicides liberally without harming icals become necessary. Starting in 2018, the EPA has allowed farm- crops. Seed-chemical systems have driven up profits and produc- ers in Illinois and other major farming states to use Enlist Duo®, a tion at unprecedented rates. They have also driven up costs: combination of glyphosate and 2,4-D, produced by the chemical 250 Estimated use in million pounds 200 150 100 50 < 4.52 4.52–21.12 0 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 21.13–88.06 > 88.06 No estimated use Year Estimated use on agricultural Iand, Corn Soybeans Wheat Cotton Vegetables in pounds per square mile and fruit Rice Orchards Alfalfa Pasture Other crops and grapes and hay FIGURE 7.1 Distribution and growth of glyphosate (Roundup) applications. Crops genetically modified to tolerate this herbicide were introduced in the early 1990s. Source: National Water Quality Assessment (NAWQA) project. (continued)  CASE STUDY continued manufacturer Dow Agrosciences. Both glyphosate and 2,4-D are accelerated and combined chemical use across the landscape. probably carcinogenic to humans, according to the World Health And nobody knows how long it will be effective in the race against Organization (WHO). Neither compound is a general biocide like weed evolution. DDT, but glyphosate is by far the dominant herbicide, used in major As more of us move to cities, it becomes harder for us to see crop-producing countries on dozens of crops. And 2,4-D, is one of and understand the complexities, and the implications, of our agri- the oldest and most widely used pesticides. Used since 1945, 2,4-D cultural production systems. This is how we produce the food and was an ingredient of the defoliant Agent Orange used in the Viet the trade products we depend on. Soy and corn support the inex- Nam War. In 2018, a California jury awarded $289 million in a lawsuit pensive meat products we are accustomed to eating. What are the charging that Monsanto had deliberately misled the public on the long-term effects on our ecosystems and waterways? What are the health risks of glyphosate. effects on farmers and farming communities? Those are also impor- The EPA’s approval of Enlist Duo® was controversial because tant questions. In this chapter we examine agricultural production, nobody knows the health or environmental consequences of food, and the ways we use these resources. overproduction in the United States and Europe, we pay farmers We can’t solve problems by using the same kind of billions of dollars each year to take land out of production. thinking we used when we created them. Now we have new questions in environmental science and food —albert einstein production: What are the environmental costs of intensified produc- tion? Which innovations are sustainable? Can we curb the growing health impacts of calorie-rich diets? And can we improve distribution so as to eliminate hunger that persists in so many impoverished areas? 7.1 GLOBAL TRENDS IN FOOD AND HUNGER We produce abundant food, but food security is still a global issue. Benchmark Data Average calorie and protein consumption has increased steadily Among the ideas and values in this chapter, these are a few in recent decades. worth remembering. Famines are usually triggered by conflict or misguided ­policies. 2,200 kcal Average human dietary energy requrements, ­according to the World Health Organization Ensuring that the earth’s soil and water resources can provide enough food for the world’s population has always been a concern in environ- > 3,500 kcal Average available per person in North America mental science. Modern industrial agriculture, as practiced in the 40–60 g Daily protein requirements American Midwest, has rewritten the story of food and hunger. While 60 g Average protein consumption in least-developed developing areas still practice small-scale subsistence agriculture, an countries increasing share of the world’s food now comes from vast operations, 110 g Average in North America often thousands of hectares, growing one or two crops with abundant 70%; 5% Percentage overweight; underweight, United States inputs of fuel and fertilizer for a competitive global market. These changes have dramatically increased production, pro- 20%; 10% Percentage overweight; underweight, China viding affordable meat protein worldwide, including in develop- 8 kg Amount of feed to produce 1 kg of beef ing areas. Food production has increased so dramatically that we 94% Percentage of U.S. soybeans genetically modified now use corn, soy, and sugar to run our cars (chapter 13). to tolerate herbicides According to the International Monetary Fund, 2005 global food 1 mm Amount of soil accumulated, per year, in ideal costs (in ­inflation-adjusted dollars) were the lowest ever recorded, ­conditions less than one-quarter of the cost in the mid-1970s. Because of 154 Principles of Environmental Science  World Least-developed countries Southern Africa Northern Africa South Asia East Asia North America Standard daily minimum (2,200 kcal, 40–60 g protein) 4,000 120 3,500 100 Energy (kcal/day/person) Protein (g/day/person) 3,000 80 2,500 60 2,000 40 1,500 20 1960 1970 1980 1990 2000 2010 1960 1970 1980 1990 2000 2010 Year Year (a) Calories (b) Protein FIGURE 7.2 Changes in dietary energy (kcal) and protein consumption in selected regions. North America and other developed regions consume more calories and protein than are needed. Source: Data from Food and Agriculture Organization (FAO) 2018. In this chapter we examine these questions, as well as the ways healthy food on a day-to-day basis, is a combined problem of eco- farmers have managed to feed more and more of the world’s grow- nomic, environmental, and social conditions. Even in wealthy coun- ing population. We also consider some of the strategies needed for tries such as the United States, millions lack a sufficient, healthy long-term sustainability in food production. diet. Poverty, job losses, lack of social services, and other factors lead to persistent hunger—and even more to persistent poor ­nutrition—despite the fact that we have more, cheaper food (in terms Food security is unevenly distributed of the work needed to acquire it) than almost any society in history. Fifty years ago, hunger was one of the world’s most prominent, Food security is important at multiple scales. In the poorest persistent problems. In 1960 nearly 60 percent of people in devel- countries, a severe drought, flood, or insect outbreak can affect oping countries were chronically undernourished, and the world’s vast regions. Individual villages also suffer from a lack of food population was increasing by more than 2 percent every year. Today security: A bad crop year can devastate a family or a village, and some conditions have changed dramatically, while others have local economies can collapse if farmers cannot produce enough to changed very little. The world’s population has more than doubled, eat and sell. Even within families there can be unequal food from 3 billion to over 7 billion, but food production has risen even security. Males often get both the largest share and the most faster. While the average population growth in the past 50 years has nutritious food, while women and children—who need food most— been 1.7 percent per year, food production has increased by an aver- all too often get the poorest diet. At least 6 million children under age of 2.2 percent per year. Food availability has increased in most 5 years old die every year of diseases exacerbated by hunger and countries to well over 2,200 kilocalories, the amount generally con- malnutrition. Providing a healthy diet might eliminate as much as sidered necessary for a healthy and productive life (fig. 7.2a). 60 percent of all child deaths worldwide. Because high infant Protein intake has also increased in most countries, including mortality is strongly associated with high population growth rates, China and India, the two most populous countries (fig. 7.2b). Less reducing childhood hunger is an important strategy for slowing than 20 percent of people in developing countries now face chronic global population growth. food shortages, as compared to 60 percent just 50 years ago. Hungry people can’t work their way out of poverty. Nobel But hunger is still with us. An estimated 900 million people— Prize–winning economist Robert Fogel has estimated that in 1790, almost one in every eight people on earth—suffer chronic hunger 20 percent of the population of England and France were effec- (fig. 7.3). This number is up slightly from a few years ago, but tively excluded from the labor force because they were too weak and because of population growth, the percentage of malnourished peo- hungry to work. Fogel calculates that improved nutrition can ple is still falling (fig. 7.4). account for about half of all European economic growth during the About 95 percent of hungry people are in developing countries. nineteenth century. This analysis suggests that reducing hunger in Hunger is especially serious in sub-Saharan Africa, a region plagued today’s poor countries could yield more than $120 billion (U.S.) in by political instability (see figs. 7.2, 7.3). Increasingly, we are coming economic growth, by producing a healthier, longer-lived, and more to understand that food security, or the ability to obtain sufficient, productive workforce.  Percentage of Total Population > 35% 20 to 35% 5 to 20% < 5% No data FIGURE 7.3 Hunger rates worldwide. Most severe and chronic hunger is in developing regions, especially sub-Saharan Africa. Source: United Nations Food and Agriculture Organization. Famines have political and social roots usually include political instability, such as wars that displace populations, removing villagers from their farms or making Famines are large-scale food shortages, with widespread starva- farming too dangerous to work in the fields. Economic dispari- tion and social disruption. Famines are often triggered by ties also drive peasants from the land. In Brazil, for example, drought or floods, but root causes of severe food insecurity wealthy landowners have displaced hundreds of thousands of peasant farmers in recent decades, first to create large cattle ranches and more recently to expand production of soybeans. World Developing regions Displaced farmers often have no choice but to migrate to the Sub-Saharan Africa Northern Africa already overcrowded slums of major cities when they lose their South Asia Eastern Asia land (see chapter 14). Latin America, Caribbean 50 45 40 35 Active LEARNING 30 Percentage Mapping Poverty and Plenty 25 Examine the map in figure 7.3. Using the map of political 20 ­boundaries at the end of your book, identify ten of the hungri- 15 est countries. Then identify ten of the countries with less than 5 percent of people facing chronic undernourishment (green 10 areas). The world’s five most populous countries are China, 5 India, the United States, Indonesia, and Brazil. Which classes do these five belong to? 0 1970 1980 1990 2000 2010 Year India has 20–35 percent; the United States has < 5 percent. ANSWERS: China, Indonesia, and Brazil have 5–20 percent malnourished; FIGURE 7.4 Changes in numbers and rates of malnourishment, by ­region. Source: Data from UN Food and Agriculture Organization, 2015. 156 Principles of Environmental Science  7.2 HOW MUCH FOOD DO WE NEED? Malnourishment involves vitamin deficiencies as well as ­insufficient food. Weight-related issues are outpacing hunger-related ones in ­developing areas. We use much of our farmland for producing biofuels, not food. A good diet is essential to keep you healthy. You need a balance of foods to provide the right nutrients, as well as enough calories for a productive and energetic lifestyle. 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. These shortages result in devastat- ing illnesses and death, as well as reduced mental capacity, develop- FIGURE 7.5 Children wait for their daily ration of porridge at a feeding mental abnormalities, and stunted growth. station in Somalia. When people are driven from their homes by hunger or war, social systems collapse, diseases spread rapidly, and the situation quickly becomes desperate. ©Norbert Schiller/The Image Works A healthy diet includes the right nutrients Malnourishment is a general term for nutritional imbalances caused by a lack of specific nutrients. In conditions of extreme food short- ages, a lack of protein in young children can cause kwashiorkor, which is characterized by a bloated belly and discolored hair and More recently, international “land grabs” have displaced peas- skin. Kwashiorkor is a West African word meaning displaced child. ants in countries across Africa and parts of Asia. International land (A young child is displaced—and deprived of nutritious breast speculators, agricultural corporations, and developers have con- milk—when a new baby is born.) Marasmus (from Greek, to waste tracted to lease lands occupied by traditional communities but away) is another severe condition in children who lack both protein legally owned by governments. and calories. A child suffering from severe marasmus is generally Economist Amartya K. Sen, of Harvard, has shown that while thin and shriveled (fig. 7.6a). These conditions lower resistance to 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. Natural disasters or drought can contribute to violent conflict and food shortages. Some analysts have argued that recent conflict in Syria results in part from climate change that drove farmers from the land, together with a repressive government that failed to pro- vide timely assistance. Famines often trigger mass migrations to relief camps, where people survive but cannot maintain a healthy and productive life (fig. 7.5). War-torn Sudan and Somalia have experienced this upheaval. In 2011 an estimated 12 to 15 million people in the region faced starvation that was triggered by drought but was rooted in years of conflict. China’s recovery from the famines of the 1960s is a dramatic example of the relationship between politics and famine (see trends in fig. 7.2). Misguided policies from the central govern- ment destabilized farming economies across China. Then 2 years (b) Goiter of bad crops in 1959–1960 precipitated famines that may have killed 30 million people. In recent years, new political and eco- nomic policies have transformed access to food. Even though the population doubled from 650 million in 1960 to 1.3 billion in (a) Marasmus 2015, hunger is much less common. China now consumes almost FIGURE 7.6 Dietary deficiencies can cause serious illness. (a) Marasmus twice as much meat (pork, chicken, and beef) as the United results from protein and calorie deficiency and gives children a wizened look States—and much of this meat comes from livestock fed on soy- and dry, flaky skin. (b) Goiter, a swelling of the thyroid gland, results from an beans bought from Brazil or from the American Midwest. iodine deficiency. (a) ©Scott Daniel Peterson; (b) ©Lester V. Bergman/Getty Images disease and infections, and children may suffer permanent debili- Use sparingly: Red meat, processed meat & butter ties in mental, as well as physical, development. Refined grains: white rice, bread & pasta Potatoes Deficiencies in vitamin A, folic acid, and iodine are more wide- Sugary drinks & sweets Salt spread problems. Vitamin A and folic acid are found in vegetables, especially dark green, leafy vegetables. Deficiencies in folic acid have been linked to neurological problems in babies. Shortages of vitamin A cause an estimated 350,000 people to go blind every year. Dr. Alfred Sommer, an ophthalmologist from Johns Hopkins Dairy (1–2 servings a day) or Vitamin D/Calcium supplements University, has shown that giving children just 2 cents’ worth of vitamin A twice a year could prevent almost all cases of childhood Healthy fats/oils: blindness and premature death associated with shortages of vita- Olive, canola, soy, corn, sunflower, peanut & min A. Vitamin supplements also reduced maternal mortality by other vegetable oils; Seeds, beans & tofu Fish, poultry & eggs trans-free margarine nearly 40 percent in one study in Nepal. Iodine deficiencies can cause goiter (fig. 7.6b), a swelling of Whole grains: Brown rice, the thyroid gland. Iodine is essential for synthesis of thyroxin, an whole wheat pasta, oats, etc. endocrine hormone that regulates metabolism and brain develop- ment, among other things. The FAO estimates that 740 million Vegetables & fruits Healthy fats/oils Whole grains 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 iodine to table salt. Daily exercise & weight control Starchy foods, such as maize, polished rice, and manioc (tapi- oca), form the bulk of the diet for many poor people, but these FIGURE 7.7 The Harvard food pyramid emphasizes fruits, ­vegetables, and whole grains as the basis of a healthy diet. Unlike most other representa- foods are low in several essential vitamins and minerals. One cele- tions of a healthy diet, this one rests on a foundation of exercise, and it distin- brated effort to deliver crucial nutrients has been through genetic guishes the value of whole grains from that of white bread and starches. engineering of common foods, such as “golden rice,” developed by Monsanto to include a gene for producing vitamin A. This strategy has shown promise, but it also has critics, who argue that geneti- considered to mean more than 20 percent over the ideal weight for cally modified rice is too expensive for poor populations. In addi- a person’s height and sex. Being overweight increases your risk of tion, the herbicides needed to grow the golden rice kill the greens hypertension, diabetes, heart attacks, stroke, gallbladder disease, that villagers rely on to provide their essential nutrients. osteoarthritis, respiratory problems, and some cancers. About as The best human diet is mainly vegetables and grains, with mod- erate amounts of eggs and dairy products and sparing amounts of meat and oils. A solid base of regular exercise underpins an ideal diet outlined by Harvard dieticians (fig. 7.7) United States Modest amounts of fats are essential for healthy skin, cell function, and metabolism. But your body is not designed to process excessive amounts of fats or sugars, and these United Kingdom should be consumed sparingly. Canada Overeating is a growing world problem For the first time in history, there are probably more over- France weight people (more than 2 billion) than underweight people (about 900 million). In wealthy countries, more Percentage Overweight than half of adults are overweight or obese. This trend Japan 2015 isn’t limited to rich countries, though. Obesity is spread- 1960 ing around the world (fig. 7.8). Diseases once thought to China afflict only wealthy nations, such as heart attack, stroke, Underweight (2010) and diabetes, are now becoming the most prevalent causes of death and disability everywhere (see chapter 8). India In the United States, and increasingly in Europe, China, and developing countries, highly processed, sug- 0 20 40 60 80 ary, fatty foods have become a large part of our diet. Over FIGURE 7.8 While about 900 million people are chronically undernourished, more 70 percent of adult Americans are overweight. About one- than twice as many are at risk from eating too much. (Latest available data are third of us are seriously overweight, or obese—-generally shown.) Source: Data from World Health Organization, 2010. 158 Principles of Environmental Science many deaths result from obesity-related illnesses as from smoking frenzied Wall Street trading in wheat, food oils, and other com- every year in the United States. modities were felt in households worldwide. These changes were The obesity epidemic is not a matter of bad behavior; it is a inconvenient in wealthy countries, where prices rose on grocery symptom of poverty and food insecurity. High-calorie, low-nutrient store shelves. In poorer countries, food costs can make up as much foods are cheaper than fresh food, which has a short shelf life. Oil- as 80 percent of household expenses, and there the effect was far and sugar-rich prepared foods save time and effort for people too worse. Food riots followed in the Philippines, India, Indonesia, and busy to cook regularly or who lack cooking facilities. Healthy food many other countries. can also be expensive or hard to get, and processed food is mar- keted aggressively to food-insecure and low-income people. Biofuels have boosted commodity prices Food prices declined again after 2008, but they were shored up by More production doesn’t necessarily an additional change: new policies in the United States and Europe reduce hunger promoting biofuels. Using crops such as soy, corn, palm oil, or sug- Most strategies for reducing world hunger have to do with increas- arcane to drive our cars is an important strategy for supporting ing efficiency of farm production, expanding use of fertilizers and farm economies in wealthy countries, as the increased demand improved seeds, and converting more unused land or forest to agri- keeps prices high. These new policies also led to global increases in culture. But the prevalence of obesity, and unstable farm econo- production of these crops (opening case study; table 7.1). In the mies, suggests that lack of supply is not necessarily the principal United States, federal ethanol subsidies led to a doubling of corn cause of world hunger. An overabundance of food supplies in much prices in 2007. But in developing countries, production of soy, palm of the world suggests that answers to global hunger may lie in better oil, and other products for export often displaces food production. use and distribution of food resources. When biofuel policies compete with food supplies in Asia and For most farmers in the developed world, overproduction con- Africa, the efficiency of this market becomes less clear. stantly threatens prices for farm products. To reduce food supplies There has been much debate about the environmental and eco- and stabilize prices in the United States, Canada, and Europe, we nomic costs and benefits of biofuel production. Some studies have send millions of tons of food aid to developing areas every year. found that biofuels represent a net energy loss, taking more energy Often, however, these shipments of free food destabilize farm econ- to produce than they provide in fuel. In the United States and omies in receiving areas. Prices for local farm products collapse, Europe, the production of biofuels, especially ethanol, has not been and political corruption can expand if military groups control economically viable without heavy subsidies for growing and pro- ­distribution. Even in developing areas, lack of food production is cessing crops. On the other hand, plant oils from sunflowers, soy- not always the cause of hunger. beans, corn, and other oil seed crops can be burned directly in most There are also inefficiencies in food use. Global food waste diesel engines and may be closer than ethanol to a net energy gain amounts to some 30 percent of all food production—1.3 billion tons (see chapter 12). Brazil produces ethanol more efficiently from its annually—as food is spoiled in storage and transit, used inefficiently, tropical sugarcane crops—although the net energy balance and envi- or thrown away after preparation. We also prefer inefficient foods— ronmental impacts remain serious questions. particularly meats that require abundant feed inputs for every pound of meat we eat. In the past decade, global hunger has had two newer causes: TABLE 7.1 Key Global Food Sources* international financial speculation on food commodities and bio- CROP 1965 1990 2016 fuel production. Food has long been a globally traded commodity, Sugarcane 531 1,053 1,891 but a law passed by the U.S. Congress in 2000, the Commodities Maize 227 483 1,060 Futures Modernization Act, eliminated long-standing rules restrict- ing risky speculation on a wide variety of commodities. Global food Rice 254 519 741 products were among these commodities. Freed from restraints, Wheat 264 592 749 traders gambled on the value of future crops, which pushed up the Milk 358 524 798 price of current crops. This deregulation had far-reaching effects for Potatoes 271 267 377 ordinary people. (In the United States, a widely felt effect of the Vegetables 66 140 290 rule change was the acceleration of trade in home mortgages. This led to a financial “bubble” in home prices, followed by a collapse in Cassava 86 152 277 which millions of Americans lost their homes.) In 2008, specula- Soyabeans 32 108 335 tive trading in food commodities led to a crisis in food, as a frenzy Meat 72 158 297 of speculative trading drove prices of agricultural commodities well Barley 93 144 177 beyond their actual value. In response to this bubble in global Sweet potatoes 108 123 105 prices, local food prices rose sharply in towns and villages world- wide. The cost of some basic staples, such as cooking oil and rice, Dry beans, pulses 31 41 44 quadrupled. Farm land prices rose as well, often driving struggling *Production in million metric tons. peasant farmers from their land and livelihoods. Thus, the effects of Source: Data from UN FAO, 2017. Do we have enough farmland? 400 Corn The problem of farmland availability has always been a central ques- 350 Soy tion in debates about how to feed the world. Because we currently Wheat produce more than enough to feed the world, we probably do have 300 enough farmland to feed more people than currently live on earth—if we ate according to the recommendations in figure 7.7 and if we used 250 all farm products for food, rather than fuel and livestock feed. Could Million metric tons we expand production further by clearing new farmlands? That is 200 harder. Tropical soils often are deeply weathered and infertile, so they make poor farmland unless expensive inputs of lime and fertilizer are 150 added. Much of the world’s uncultivated land is too steep, sandy, waterlogged, salty, acidic, cold, dry, or nutrient-poor for most crops. 100 About 11 percent of the earth’s land area, some 1,400 million ha, is used for agricultural production. This land area amounts to 50 about 0.2 ha per person (1 ha = 100 m × 100 m). Arable land per person has fallen from about 0.5 ha per person in 1960, mainly 0 because of population growth. Population projections suggest we 1960 1970 1980 1990 2000 2010 will have about 0.15 ha by 2050. In Asia, cropland will be even more Year scarce—0.09 ha per person by 2050. FIGURE 7.9 U.S. production of our three dominant crops—corn, Much of the world’s uncultivated land could be converted to ­soybeans, and wheat. Source: Data from USDA, 2015. cropland, but this land currently provides essential ecological services on which farmers depend. Forested watersheds help maintain stream flow, regulate climate, and provide refuge for biological and cultural (table 7.1). Two grasses, wheat and rice, are especially important diversity. Wetlands also regulate water supplies, and forests and grass- because they are the staple foods for most of the 5 billion people in lands support insect pollinators that ensure productive crops. developing countries. Despite the importance of these services, the conversion of In the United States, corn (a grass, also known as maize) and tropical forests and savannas to farmland continues, spurred by soybeans have become our primary products. We rarely eat either global trade in export crops, such as soy, palm oil, sugarcane (for corn or soybeans directly, but corn provides sweeteners; corn oil; ethanol), and corn (maize, largely for animal feed), as well as beef the livestock feed for producing our beef, chicken, and pork; indus- and other livestock. The FAO reports that 13 to 16 million ha of trial starches; and many synthetic vitamins. Soybeans are also fed to forest land are cleared each year, about half of that in tropical livestock, and soy provides protein and oils for processed foods. Africa and South America. Brazil, for example, has cleared Because we have developed so many uses for corn, it now accounts cleared vast expanses of Amazon and Atlantic rainforest in order for nearly two-thirds of our bulk commodity crops (which to become a global leader in exports of soy, sugar, beef, poultry, include corn, soy, wheat, rice, and other commodities). and orange juice, and it is emerging as a leading producer of rice Together, corn and soy make up about 85 percent of commodity and corn. crops, with an annual production of 268 million tons of corn and Most of these export crops serve those who already have 88 million tons of soy (fig. 7.9). enough to eat, however: According to FAO data, 85 percent of global crop exports are bound for Europe, North America, China, Rising meat production is a sign of wealth Japan, and other wealthy countries. Meanwhile, human rights Largely because of dramatic increases in corn and soy production, groups protest that land conversions have displaced traditional meat consumption has grown worldwide. In developing countries, communities and subsistence farmers across South America, meat consumption has risen from just 10 kg per person per year in Africa, and much of Asia. the 1960s to over 26 kg today (fig. 7.10). In the United States, our meat consumption has risen from 90 kg to 136 kg per person per 7.3 WHAT DO WE EAT? year in the same 50 years. Meat is a concentrated, high-value source of protein, iron, fats, and other nutrients that give us the energy to Producing meat takes more resources than producing vegetables lead productive lives. Dairy products are also a key protein source: and grain. Globally, we consume more than twice as much dairy as meat. But Farmed seafood depends mainly on wild-caught feed. dairy production per capita has declined slightly, while global meat production has more than doubled in the past 50 years. Antibiotic overuse is making our antibiotics ineffective. Meat is a good indicator of wealth because it is expensive to Of the thousands of edible plants and animals in the world, only a produce in terms of the resources needed to grow an animal (fig. 7.11). few provide almost all our food. About a dozen types of grasses, As discussed in chapter 2, herbivores use most of the energy they 3 root crops, 20 or so fruits and vegetables, 6 mammals, 2 domestic consume in growing muscle and bone, moving around, staying warm, fowl, and a few fish species make up almost all the food we eat and metabolizing (digesting) food. Only a little food energy is stored 160 Principles of Environmental Science  (a) 400 140 350 Production (tons) 120 FIGURE 7.10 Meat and dairy consumption has quadrupled in the past Area harvested (hectares) 40 years, and China represents about 40 percent of that increased demand. 300 100 Millions of hectares ©William P. Cunningham Millions of tons 250 80 200 for consumption by carnivores, at the next level of the food pyramid. 60 150 For every 1 kg of beef, a steer consumes over 8 kg of grain. Pigs are 40 more efficient: Producing 1 kg of pork takes just 3 kg of pig feed. 100 Chickens and herbivorous fish (such as catfish) are still more effi- 50 20 cient. Globally, some 660 million metric tons of cereals are used as 0 0 livestock feed each year. This is just over a third of the world cereal 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 use. As figure 7.11 suggests, we could feed at least eight times as many people by eating those cereals directly. A number of technological and breeding 8 (b) innovations have made this increased production FIGURE 7.12 (a) Feedlots have expanded the global market for corn and possible. One of the most important is the con- soybeans. (b) Brazil’s soy production, which supports feedlots globally, has fined animal feeding operation (CAFO), where grown from near zero to being the country’s dominant agricultural product. animals are housed and fed—mainly soy and (a) Source: Photo by Jeff Vanuga, USDA Natural Resources Conservation Service; (b) Source: Data from UN Food and Agriculture Organization, 2015. corn—for rapid growth (fig. 7.12). These opera- tions dominate livestock raising in the United corn, soy, and animal protein (parts that can’t be sold for human States, Europe, and increasingly in China and food) that maximize their growth rate. New breeds of livestock have other countries. Animals are housed in giant been developed that produce muscle (meat) rapidly, rather than sim- enclosures, with up to 10,000 hogs or a ply getting fat. The turnaround time is getting shorter, too. A U.S. million chickens in an enormous barn chicken producer can turn baby chicks into chicken nuggets after just complex (fig. 7.13), or 100,000 cat- 3 8 weeks of growth. Steers reach full size by just 18 months of age. tle in a feed lot. Operators feed Increased use of antibiotics, which are mixed in daily feed, make it the animals specially pre- possible to raise large numbers of animals in close quarters. About pared mixes of 2 90 percent of U.S. hogs receive antibiotics in their feed. 1.5 1 Seafood, both wild and farmed, depends on wild-source inputs The 140 million metric tons of seafood we eat every year is an impor- tant part of our diet. Seafood provides about 15 percent of all animal protein eaten by humans, and it is the main animal protein source FIGURE 7.11 Number of kilograms of grain needed to produce 1 kg of for about 1 billion people in developing countries. Overharvesting bread or 1 kg live weight gain. and habitat destruction threaten most of the world’s wild fisheries,  FIGURE 7.13 Most livestock grown in the United States are raised in large-scale, concentrated animal-feeding operations. Up to a million animals can be held in a single facility. High population densities require heavy use of antibiotics and can cause severe local air and water pollution. FIGURE 7.14 Fish farms produce much of our seafood, but most rely on ©Novastock/PhotoEdit ­wild-caught fish for feed, and pollution and disease are common concerns. ©WaterFrame/Alamy Stock Photo however. Annual catches of ocean fish rose by about 4 percent annu- ally between 1950 and 1988. Since 1989, 13 of 17 major marine study of fish catches for fish farms has shown that global declines fisheries have declined dramatically or become commercially unsus- of seabird populations, such as puffins and albatrosses, closely tainable. According to the United Nations, three-quarters of the track the increase in farm-raised carnivorous fish. world’s edible ocean fish, crustaceans, and mollusks are declining In tropical areas, coastal fish and shrimp-rearing ponds have and in urgent need of managed conservation. replaced hundreds of thousands of hectares of mangrove forests and The problem is too many boats using efficient but destructive wetlands, which serve as irreplaceable nurseries for marine technology to exploit a dwindling resource base. Boats as big as ocean species. Net pens anchored in near-shore areas encourage liners travel thousands of kilometers and drag nets large enough to spread of diseases, as they release feces, uneaten food, antibiotics, scoop up a dozen jumbo jets, sweeping a large patch of ocean clean and other pollutants into surrounding ecosystems (fig. 7.14). of fish in a few hours. Longline 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 Biohazards arise in industrial production nets across the bottom, scooping up everything indiscriminately and Increasingly efficient production has a variety of externalized reducing broad swaths of habitat to rubble. One marine biologist (unaccounted for) costs. Land conversion from forest or grassland compared the technique to harvesting forest mushrooms with a bull- to crop fields increases soil erosion, which degrades water quality. dozer. In some operations, up to 15 kg of dead by-catch (nontarget Bacteria in the manure in the feedlots, or liquid wastes in manure species) are dumped back into the ocean for every kilogram of mar- storage lagoons (holding tanks) around hog farms, escape into the ketable food. Nearly all countries heavily subsidize their fishing environment—from airborne fecal dust around feedlots or from fleets, to preserve jobs and to ensure access in the unregulated open breaches in the walls of a manure tank. When Hurricane Floyd hit ocean. The FAO estimates that operating costs for the 4 million boats North Carolina’s coastal hog production region in 1999, some now harvesting wild fish exceed sales by $50 billion (U.S.) per year. 10 ­million m3 of hog and poultry waste overflowed into local rivers, The best solution, according to a United Nations study on eco- creating a dead zone in Pamlico Sound. In 2018, Hurricane Florence system services, is to establish better international agreements on caused similar overflows. These disasters were especially severe, but fisheries. Instead of a free-for-all race to exploit fish as fast as pos- smaller spills and leaks are widespread. sible, nations could manage fisheries for long-term, sustained pro- Constant use of antibiotics has been associated with antibiotic- duction. Just as with hunting laws within a single country, agreement resistant infections in hog-producing areas. Eighty percent of all anti- to international fishery rules could improve total food production, biotics used in the United States are administered to livestock. This fishery employment, and ecosystem stability. massive and constant exposure kills off most bacteria, but occasional Aquaculture is providing an increasing share of the world’s strains that resist the effects of the antibiotics can survive. These seafood. Fish can be grown in farm ponds that take relatively little survivors then reproduce freely, creating new strains that are untreat- space but are highly productive. For cultivation of plant-eating fish able in human hosts. Thus, overuse is slowly rendering our standard such as tilapia, these systems can be very sustainable. Cultivation of antibiotics ineffective for human health care, and thousands of peo- high-value carnivorous species such as salmon, however, threatens ple have died from antibiotic-resistant infections. The next time you wild fish populations, which are caught to feed captive fish. A 2012 are prescribed an antibiotic by your doctor, you might ask whether 162 Principles of Environmental Science she or he worries about antibiotic-resistant bacteria. What would you do if your prescription were ineffective against an illness? Although the public is increasingly aware of these environmental and health risks of concentrated meat production, we seem to be will- ing to accept these risks because this production system has made our favorite foods cheaper, bigger, and more available. A fast-food ham- burger today is more than twice the size it was in 1960, especially if you buy the kind with multiple patties and special sauce, and Americans love to eat them. At the same time, this larger burger costs less per pound, in inflation-adjusted dollars, than the 1960 version. As a conse- quence, for much of the world, consumption of protein and calories has climbed beyond what we really need to be healthy (see figs. 7.2, 7.8). As environmental scientists, we are faced with a conundrum: 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? Should we consider FIGURE 7.15 Terracing, as in these Balinese rice paddies, can control reducing our consump­tion to lower environmental and health erosion and make steep hillsides productive. These terraced rice paddies costs? How might we do that? have produced two or three crops a year for centuries because the soils are carefully managed and organic nutrients are maintained. ©William P. Cunningham 7.4 LIVING SOIL IS A PRECIOUS RESOURCE 2. Silts and clays (extremely small mineral particles; many clays Soil consists of mineral, organic, and living ­components. are sticky and hold water because of their flat surfaces and ionic charges; others give red color to soil) Soil fauna capture, process, and store nutrients for plants. 3. Dead organic material (decaying plant matter stores nutrients Erosion and degradation make millions of hectares of farmland and gives soils a black or brown color) ­useless each year. 4. Soil fauna and flora (living organisms, including soil bacteria, Understanding the limits and opportunities for feeding the world worms, fungi, roots of plants, and insects, recycle organic com- requires an understanding of the soil that supports us. In this sec- pounds and nutrients) tion we examine the nature of soils and the ways we use them. Many 5. Water (moisture from rainfall or groundwater, essential for soil of us think of soil as just dirt. But healthy soil is a marvelous sub- fauna and plants) stance with astonishing complexity. Soil contains mineral grains weathered from rocks, partially decomposed organic molecules, 6. Air (tiny pockets of air help soil bacteria and other organisms and a host of living organisms. The complex community of bacteria survive) and fungi is primarily responsible for providing nutrients that plants Variations in these six components produce almost infinite variety in need to grow. Soil bacteria also help filter and purify the water we the world’s soils. Abundant clays make soil sticky and wet. Abundant drink. Soil can be considered a living ecosystem by itself. How can we manage our soils to maintain and build these precious systems? 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 Active LEARNING 1 mm per year. With careful husbandry that prevents erosion and adds organic material, soil can be replenished and renewed indefi- Where in the World nitely (fig. 7.15). But many farming techniques deplete soil. Crops consume the nutrients; plowing exposes the soil to erosion by wind Did You Eat Today? or water. Severe erosion can carry away 25 mm or more of soil per Make a list of every food you ate today or yesterday. From this year, far more than can accumulate under the best of conditions. list, make a graph of the number of items in the following categories: grains, vegetables, dairy, meat, other. Which food What is soil? type was most abundant? With other students, try to identify the location or region where each food was grown. How many Soil is a complex mixture of six components: come from a region more than halfway across the country? 1. Sand and gravel (mineral particles from bedrock, either in from another country? place or moved from elsewhere, as in windblown sand)  Springtail Wood roach Pseudo- scorpion Termite Snail Mite Centipede Sow bug Carabid (ground) beetle Slug Nematode and Soil fungus nematode-killing Ant constricting fungus Earthworm Cicada nymph Wireworm (click beetle larva) Soil protozoan FIGURE 7.16 Soil ecosystems include countless organisms that consume and decompose organic material, aerate soil, and distribute nutrients through the soil. organic material and sand make the soil soft and easy to dig. Sandy disturbance. Too much rain washes away nutrients and organic mat- soils drain quickly, often depriving plants of moisture. Silt particles ter, but soil fauna cannot survive with too little rain. In extreme are larger than clays and smaller than sand, so they aren’t sticky and cold, soil fauna recycle nutrients slowly; in extreme heat, they may soggy, and they don’t drain too quickly. Thus, silty soils are ideal for work so fast that leaf litter on the forest floor is taken up by plants growing crops, but they are also light and blow away easily when in just weeks or months—so that the soil retains little organic mat- exposed to wind. Soils with abundant soil fauna quickly decay dead ter. Frequent disturbance prevents the development of a healthy soil leaves and roots, making nutrients available for new plant growth. ecosystem, as does steep topography that allows rain to wash away Compacted soils have few air spaces, making soil fauna and plants soils. In the United States, the best farming soils tend to occur grow poorly. You can see some of these differences just looking at where the climate is not too wet or dry, on glacial silt deposits such soil. Reddish soils are colored by iron-rich, rust-colored clays, the as those in the upper Midwest, and on silt- and clay-rich flood kind that store few nutrients for plants. Deep black soils are rich in deposits, like those along the Mississippi River. decayed organic material and thus are generally rich in nutrients. Most soil fauna occur in the uppermost layers of a soil, where they consume leaf litter. This layer is known as the “O” (organic) horizon. Just below the O horizon is a layer of mixed organic and Healthy soil fauna can determine soil fertility mineral soil material, called the A horizon (fig. 7.17), also known as Soil bacteria, algae, and fungi decompose and recycle leaf litter into topsoil or surface soil. plant-available nutrients, as well as helping to give soils structure The B horizon, or subsoil, lies below most organic activity, and and loose texture (fig. 7.16). Microscopic worms and nematodes it tends to have more clays than the A layer. The B layer accumu- process organic matter and create air spaces as they burrow through lates clays that seep downward from the A horizon with rainwater soil. These organisms mostly stay near the surface, often within the that percolates through the soil. If you dig a hole, you may be able top few centimeters. The sweet aroma of freshly turned soil is to tell where the B horizon begins, because the soil tends to become caused by actinomycetes, bacteria that grow in funguslike strands slightly more cohesive. If you squeeze a handful of B soil, it should and give us the antibiotics streptomycin and tetracycline. hold its shape better than a handful of A soil. The health of the soil ecosystem depends on environmental Sometimes an E (eluviated, or washed-out) layer lies between conditions, including climate, topography, and parent material (the the A and B horizons. The E layer is loose and light-colored because mineral grains or bedrock on which soil is built), and frequency of most of its clays and organic material have been washed down to 164 Principles of Environmental Science  material in the United States was transported to its present site by glaciers, wind, and water and is not related to the bedrock forma- tions below it. Organic layer: O Decomposing Your food comes mostly from the A horizon leaves and organics Ideal farming soils have a thick, organic-rich A horizon. The soils Topsoil: that support the Corn Belt farm states of the U.S. Midwest have Organic matter, A organisms, roots, rich, black A horizon that can be more than 2 meters thick, although inorganic minerals a century of farming has washed away much of this soil. Most soils have less than half a meter of A horizon. Desert soils, with slow rates of organic activity, might have almost no O or A horizon Eluviated (washed- out) layer: (fig. 7.18). E Clays and humic Because topsoil is so important to our survival, we differentiate acids leached to soils largely according to the thickness and composition of their lower layers upper layers. The U.S. Department of Agriculture classifies the thousands of different soil types into 11 soil orders (http://soils.usda.gov/technical/classification/orders/). Mollisols (mollic = soft, sol = soil), for example, have a thick, organic-rich A horizon that develops from the deep, dense roots of prairie grasses. Alfisols have Subsoil: Enriched in clays a slightly thinner A horizon, with slightly less organic matter. B and other material Alfisols develop in deciduous forests, where leaf litter is abundant. leached from upper In contrast, the aridisols (arid = dry) of the desert Southwest have layers little organic matter, and they often have accumulations of mineral salts. Organic-rich mollisols and alfisols dominate most of the farm- ing regions of the United States (fig. 7.19). FIGURE 7.17 An idealized soil profile showing common horizons. Soils How do we use and abuse soil? vary greatly in composition and thickness of layers. Below the B horizon, there is generally a C horizon of weathered rock, sand, or other parent Agriculture both causes and suffers from environmental degra- material. Depth is marked in 10-cm increments. ©Mary Ann Cunningham; dation. The International Soil Reference and Information Centre Courtesy Soil & Land Resources Division, University of Idaho in the Netherlands estimates that, every year, 3 million ha of cropland are made useless by erosion, 4 million ha are turned the B horizon. The C horizon, below the subsoil, is mainly decom- into deserts, and 8 million ha are converted to nonagricultural posed rock fragments. Parent materials underlie the C layer. Parent uses, such as homes, highways, shopping centers, factories, material is the sand, windblown silt, bedrock, or other mineral and reservoirs. Over the past 50 years, some 1,900 million ha material on which the soil is built. About 70 percent of the parent of agricultural land (an area greater than that now in (a) (b) FIGURE 7.18 Soils vary dramatically among different climate areas. Temperate grassland soils tend to have a thick, soft, organic-rich A horizon (a). Arid land soils may have little or no workable A horizon, as in this Libyan valley (b). (a) ©Ingram Publishing/SuperStock; (b) ©imageBROKER/Alamy Stock Photo  erosion also is a problem in farmland streams, where soil washes away from streambanks. Cattle and other livestock often accelerate streambank erosion, as they trample and graze down the veg- etation that holds a bank in place. Sheet and rill erosion cause most soil loss on farmland, even though this process is often too gradual to notice. Studies in Iowa farm fields have found areas with as much as 50 metric tons lost per hectare during winter and spring runoff, more than 12 times the rate considered tolerable or officially acknowl- edged by state soil scientists. That loss repre- sents just a few millimeters of soil over the whole surface of the field, but repeated years of storms and spring runoff are gradually sending Iowa’s productive capacity down- Cultivated Cropland stream to the Gulf of Mexico. Percentage of land area, by county All this waterborne sediment damages 0–9 aquatic systems, too. Increased sediment loads 10– 24 erode rivers and reduce water quality in lakes. FIGURE 7.19 Distribution of cropland in the United States, by Excess nutrients create eutrophic “dead zones” 25–49 county. Dark blue areas especially highlight the fertile Farm Belt of in estuaries and coastal waterways, most 50–74 the Midwest and Great Plains, as well as the Mississippi river bottom. famously in the Gulf of Mexico. Infrastructure 75– 100 Source: U.S. Census of Agriculture. such as reservoirs and harbors also can be badly impacted by sediment deposits. production) have been degraded to some extent. About 300 ­million ha of this land are strongly degraded, with deep gullies, severe Wind is a close second in erosion nutrient depletion, or poor crop growth, making restoration diffi- Wind can equal or exceed water in erosive force, especially in dry cult and expensive. regions, and where vegetation is sparse (fig. 7.20c). When plant Water and wind erosion cause a vast majority of global soil cover and surface litter are removed from the land by agriculture or degradation. Chemical degradation, a secondary cause of soil deg- grazing, wind lifts loose soil particles and sweeps them away. In radation, includes nutrient depletion, salt accumulation, acidifica- extreme conditions, windblown dunes encroach on useful land and tion, and pollution. Physical degradation includes factors such as cover roads and buildings. Over the past 30 years, China has lost compaction or loss of soil structure after cultivation by heavy 93,000 km2 (about the size of Indiana) to desertification, or conver- machinery, waterlogging from excess irrigation, and laterization— sion of productive land to desert. Advancing dunes from the Gobi rock-hard solidification of tropical soils exposed to sun and rain. Desert are now only 160 km (100 mi) from Beijing. Every year more than 1 million tons of sand and dust blow from Chinese dry- lands, often traveling across the Pacific Ocean to the west coast of Water is the leading cause of soil erosion North America. Since 1985, China has planted more than 40 ­billion Erosion is an important natural process that redistributes the prod- trees to try to stabilize the soil and hold back deserts. ucts of weathering. Erosion contributes to soil formation, creating Intensive farming practices are largely responsible for this situ- regions of windblown silt that form much of the U.S. Farm Belt, ation. Row crops, such as corn and soybeans, leave soil exposed for and to soil loss, as well as rich river bottom soils on which early civi- much of the growing season. Deep plowing and heavy herbicide lizations were built. Erosion also depletes farmland soils when they applications create weed-free fields that look tidy but are subject to are left bare or worked at the wrong time. erosion. Farmers, under pressure to maximize yields and meet loan Some erosion occurs so rapidly that you can watch it happen. obligations, often plow through grass-lined watercourses (low areas Running water can scour deep gullies, leaving fence posts and trees where water runs off after a rain) and pull out windbreaks and standing on pedestals as the land erodes away around them. But most fencerows to accommodate the large machines and to get every last erosion is more subtle. Sheet erosion removes a thin layer of soil as a square meter into production. sheet of water flows across a nearly level or gently sloping field. When An estimated 25 billion metric tons of soil are lost from crop- small rivulets of running water form and cut small channels in the lands every year due to wind and water erosion. The net effect, soil, the process is called rill erosion (fig. 7.20a). Where rills expand worldwide, of this widespread topsoil erosion is a reduction in crop to form bigger channels or ravines, too large to be removed by cultiva- production equivalent to removing about 1 percent of the world’s tion, we call the process gully erosion (fig. 7.20b). Streambank cropland each year. 166 Principles of Environmental Science (a) Sheet erosion (b) Gully erosion (c) Wind erosion FIGURE 7.20 Land degradation affects more than 1 billion ha yearly, or about two-thirds of all global cropland. Globally, erosion by water accounts for about 56 percent of soil loss from fields (a, b). Wind erosion accounts for another 28 percent (c). (a) Source: Photo by Lynn Betts, courtesy of USDA Natural Resources ­Conservation Service; (b) Source: Photo by Jeff Vanuga, courtesy of USDA Natural Resources Conservation Center; (c) Source: Natural Resource Conservation Service 7.5 AGRICULTURAL INPUTS Irrigation is required for most high-yielding agriculture. Fertilizers, especially N, P, and K, are widely used and ­overused. Pesticides vary greatly from general biocides to narrowly targeted compounds. Soil is the foundation of food production, but there are many other critical factors. Reliable water resources, nutrients, favorable tem- peratures and rainfall, productive crop varieties, and the mechani- cal energy to tend and harvest the crops are also essential. Strategies for applying these different inputs vary greatly among regions and among contrasting farming strategies (Key Concepts, p. 168). High yields usually require irrigation Agriculture uses at least two-thirds of all fresh water withdrawn (a) from rivers, lakes, and groundwater. Although estimates vary widely, about 15 percent of all cropland, worldwide, is irrigated. Some countries are water rich and can readily afford to irrigate farmland, while other countries are water poor and must use water very carefully. The efficiency of irrigation water use varies greatly. In some places, high evaporation and seepage losses from unlined and uncovered canals can mean that as much as 80 percent of water withdrawn for irrigation never reaches its intended destination. Poor farmers may overirrigate because they lack the technology to meter water and distribute just the amount needed. In wealthier countries, farmers can afford abundant uses of water, including center-pivot irrigation systems (fig. 7.21). They can also afford water-saving methods such as drip irrigation, which waters only the base of a crop, reducing evaporative losses. Excessive use not only wastes water but also often results in waterlogging. Waterlogged soil is saturated with water, and plant roots die from lack of oxygen. Salinization, in which mineral salts accumulate in the soil, is often a problem when irrigation water dis- (b) solves and mobilizes salts in the soil. As the water evaporates, it FIGURE 7.21 Pivot irrigation systems (a) deliver water to many leaves behind a salty crust on the soil surface that is lethal to most U.S. farm fields. These systems create green circles visible in aerial plants. Flushing with excess water can wash away this salt accumula- images of the landscape (b). (a) ©Cecilia Lim/123RF; (b) ©Kris Hanke/ tion, but the result is even more saline water for downstream users. Getty Images  How can we feed the world? KEY CONCEPTS The world’s population has climbed from 3 billion to 7 billion we managed to increase food production so rapidly? What in about two generations (since 1960). Despite this growth, are the pros and cons of these strategies? What additional the proportion of chronically hungry people has declined choices do we have? Presented here are three main strate- from 60 percent to about 20 percent in developing coun- gies in food production. tries, where most population growth has occurred. How have KC 7.1 The Green Revolution involved development of high responders— crops that grow and yield well with increased use of fertilizer, irrigation, Circular green fields, irrigated by and pesticides. center-pivot sprinklers, produce the