unit 13/14

Having too little iron (Fe)—a component of the hemoglobin that transports oxygen in the blood—causes anemia, which causes fatigue, makes infection more likely, and increases a woman's chances of dying from hemorrhage in childbirth.

According to the WHO, one of every five people in the world—mostly women and children in less-developed countries—suffers from iron deficiency

A newer form of industrialized agriculture uses large arrays of greenhouses to raise crops indoors. In water-short, arid areas such as parts of Spain, farmers can save water by using greenhouses (Figure 12-6), because they can deliver water more efficiently to greenhouse crops than they can to outdoor crops. In addition, because the water can be purified and recycled, water use and water pollution are reduced sharply in such systems, compared to conventional crop irrigation systems.

At Growing Power, Will Allen (Core Case Study) provides jobs by hiring local people to build simple greenhouses out of arc-shaped metal hoops covered with plastic (hoop houses)—an inexpensive application of the solar energy principle of sustainability

Today, three systems supply most of our food, using about 40% of the world's land

Croplands produce mostly grains and provide about 77% of the world's food using 11% of its land area. Rangelands, pastures, and feedlots produce meat and meat products and supply about 16% of the world's food using about 29% of the world's land area. And fisheries and aquaculture (fish farming) supply fish and shellfish, which make up about 7% of the world's food supply.

More Sustainable Food Production

Eat less meat, no meat, or organically certified meat Choose sustainably produced herbivorous fish Use organic farming to grow some of your food Buy certified organic food Eat locally grown food Compost food wastes Cut food waste

A second green revolution has been taking place since 1967

Fast-growing varieties of rice and wheat, specially bred for tropical and subtropical climates, have been introduced into middle-income, less-developed countries such as India, China, and Brazil. Producing more food on less land in such countries has helped to protect some biodiversity by preserving large areas of forests, grasslands, wetlands, and easily eroded mountain terrain that might otherwise be used for farming

A growing number of scientists are urging the USDA to use a three-point strategy to promote IPM in the United States.

First, add a 2% sales tax on synthetic pesticides and use the revenue to fund IPM research and education. Second, set up a federally supported IPM demonstration project on at least one farm in every county in the United States. Third, train USDA field personnel and county farm agents in IPM so they can help farmers use this alternative. Because these measures would reduce its profits, the pesticide industry has vigorously, and successfully, opposed them. Integrated Pest Management Is a Component of More Sustainable Agriculture Several UN agencies and the World Bank have joined together to establish an IPM facility. Its goal is to promote the use of IPM by disseminating information and establishing networks among researchers, farmers, and agricultural extension agents involved in IPM.

Analysts suggest five major strategies to help farmers and consumers to make the transition to more sustainable agriculture over the next 50 years

First, greatly increase research on more sustainable organic farming and perennial polyculture, and on improving human nutrition. Second, establish education and training programs in more sustainable agriculture for students, farmers, and government agricultural officials. Third, set up an international fund to give farmers in poor countries access to various types of more sustainable agriculture. Fourth, replace government subsidies for environmentally harmful forms of industrialized agriculture with subsidies that encourage more sustainable agriculture. And fifth, mount a massive program to educate consumers about the true environmental and health costs of the food they buy

Governments use two main approaches to influence food production

First, they can control food prices by putting a legally mandated upper limit on them in order to keep them artificially low. This makes consumers happy but makes it harder for farmers to make a living Second, they can provide subsidies by giving farmers price supports, tax breaks, and other financial support to keep them in business and to encourage them to increase food production. However, if government subsidies are too generous and the weather is good, farmers and livestock producers may produce more food than can be sold

Many scientists argue that we should greatly increase the use of biological, ecological, and other alternative methods for controlling pests and diseases that affect crops and human health (Concept 12-4). Here are some of these alternatives:

Fool the pest. A variety of cultivation practices can be used to fake out pests. Examples include rotating the types of crops planted in a field each year and adjusting planting times so that major insect pests either starve or get eaten by their natural predators. Provide homes for pest enemies. Farmers can increase the use of polyculture, which uses plant diversity to reduce losses to pests by providing habitats for the pests' predators. Implant genetic resistance. Use genetic engineering to speed up the development of pest- and disease-resistant crop strains (Figure 12-25). But controversy persists over whether the projected advantages of using GM plants outweigh their projected disadvantages Bring in natural enemies. Use biological control by importing natural predators (Figures 12-22 and 12-26), parasites, and disease-causing bacteria and viruses to help regulate pest populations. This approach is nontoxic to other species and is usually less costly than applying pesticides. However, some biological control agents are difficult to mass produce and are often slower acting and more difficult to apply than synthetic pesticides are. Sometimes the agents can multiply and become pests themselves Use insect perfumes. Trace amounts of sex attractants (called pheromones) can be used to lure pests into traps or to attract their natural predators into crop fields. Each of these chemicals attracts only one species. They have little chance of causing genetic resistance and are not harmful to nontarget species. However, they are costly and time-consuming to produce. Bring in the hormones. Hormones are chemicals produced by animals to control their developmental processes at different stages of life. Scientists have learned how to identify and use hormones that disrupt an insect's normal life cycle, thereby preventing it from reaching maturity and reproducing. Use of insect hormones has some of the same advantages and disadvantages as use of sex attractants has. Also, they take weeks to kill an insect, are often ineffective with large infestations of insects, and sometimes break down before they can act. Reduce the use of synthetic herbicides to control weeds. Organic farmers control weeds by methods such as crop rotation, mechanical cultivation, hand weeding, and the use of cover crops and mulches

There are also many private, mostly nonprofit, organizations that are working to help individuals, communities, and nations to improve their food security

For example, Will Allen (Core Case Study) argues that instead of trying to transfer complex technologies such as genetic engineering to less-developed countries, we should be helping them to develop simple, sustainable, local food production and distribution systems that will give them more control over their food security. Another person who is working toward this goal on a more regional basis is National Geographic Explorer Jennifer Burney

We did not invent the use of chemicals to repel or kill other species

For nearly 225 million years, plants have been producing chemicals called biopesticides to ward off, deceive, or poison the insects and herbivores that feed on them. This battle produces a never-ending, ever-changing coevolutionary process: insects and herbivores overcome various plant defenses through natural selection and new plant defenses are favored by natural selection

There are several types of organic fertilizers

One is animal manure: the dung and urine of cattle, horses, poultry, and other farm animals. It improves topsoil structure, adds organic nitrogen, and stimulates the growth of beneficial soil bacteria and fungi. Another type, called green manure, consists of freshly cut or growing green vegetation that is plowed into the topsoil to increase the organic matter and humus available to the next crop. A third type is compost, produced when microorganisms in topsoil break down organic matter such as leaves, crop residues, food wastes, paper, and wood in the presence of oxygen

Erosion of topsoil has two major harmful effects

One is loss of soil fertility through depletion of plant nutrients in topsoil. The other is water pollution in surface waters where eroded topsoil ends up as sediment, which can kill fish and shellfish and clog irrigation ditches, boat channels, reservoirs, and lakes. This pollution problem gets worse when the eroded sediments contain pesticide residues that can be ingested by aquatic organisms and biomagnified within food webs

Scientists and producers are working on ways to make aquaculture more sustainable and to reduce its harmful environmental effects

One such approach is open-ocean aquaculture, which involves raising large carnivorous fish in underwater pens—some as large as a high school gymnasium—located up to 300 kilometers (190 miles) offshore (see Figure 11-5), where rapid currents can sweep away fish wastes and dilute them. Some farmed fish from such operations can escape and breed with wild fish. However, the environmental impact of raising fish far offshore is smaller than that of raising fish near shore and much smaller than that of industrialized commercial fishing.

More Sustainable Aquaculture

Protect mangrove forests and estuaries Improve management of wastes Reduce escape of aquaculture species into the wild Set up self-sustaining polyaquaculture systems that combine aquatic plants, fish, and shellfish Certify sustainable forms of aquaculture

Flowing water, the largest cause of erosion, carries away particles of topsoil that have been loosened by rainfall

Severe erosion of this type leads to the formation of gullies (Figure 12-14, right). Wind also loosens and blows topsoil particles away, especially in areas with a dry climate and relatively flat and exposed land

green revolution

Since 1950, about 88% of the increase in global food production has come from using high-input industrialized agriculture to increase crop yields in a process

Opponents of widespread use of synthetic pesticides contend that the harmful effects of these chemicals (Figure 12-23, right) outweigh their benefits (Figure 12-23, left). They cite several problems

They accelerate the development of genetic resistance to pesticides in pest organisms. Insects breed rapidly, and within 5-10 years (much sooner in tropical areas), they can develop immunity to widely used pesticides through natural selection and then come back stronger than before. Since 1945, about 1,000 species of insects and rodents (mostly rats) and 550 types of weeds and plant diseases have developed genetic resistance to one or more pesticides. Since 1996, the widespread use of glyphosate herbicide has led to at least 15 species of "superweeds" that are genetically resistant to it. They can put farmers on a financial treadmill. Because of genetic resistance, farmers can find themselves having to pay more and more for a chemical pest control program that can become less and less effective. Some insecticides kill natural predators and parasites that help to control the pest populations. About 100 of the 300 most destructive insect pests in the United States were minor pests until widespread use of insecticides wiped out many of their natural predators, including spiders (Figure 12-22). (See the Case Study that follows.) Pesticides are usually applied inefficiently and often pollute the environment. According to the USDA, about 98-99.9% of the insecticides and more than 95% of the herbicides applied by aerial spraying or ground spraying do not reach the target pests. They end up in the air, surface water, groundwater, bottom sediments, food, and nontarget organisms, including humans, livestock, and wildlife. Some pesticides harm wildlife. According to the USDA and the U.S. Fish and Wildlife Service, each year, some of the pesticides applied to cropland poison honeybee colonies on which we depend for pollination of many food crops (see Chapter 9, Core Case Study). According to a study by the Center for Biological Diversity, pesticides menace one of every three endangered and threatened species in the United States. Some pesticides threaten human health. The WHO and UNEP have estimated that pesticides annually poison at least 3 million agricultural workers in less-developed countries and at least 300,000 workers in the United States. They also cause 20,000-40,000 deaths per year, worldwide. According to studies by the National Academy of Sciences, pesticide residues in food cause an estimated 4,000-20,000 cases of cancer per year in the United States

Use of synthetic pesticides has its advantages and disadvantages. Proponents contend that the benefits of pesticides (Figure 12-23, left) outweigh their harmful effects (Figure 12-23, right). They point to the following benefits

They have saved human lives. Since 1945, DDT and other insecticides probably have prevented the premature deaths of at least 7 million people (some say as many as 500 million) from insect-transmitted diseases such as malaria (carried by the Anopheles mosquito), bubonic plague (carried by rat fleas), and typhus (carried by body lice and fleas). They have been known to increase food supplies by reducing food losses from pests, for some crops in some areas. They can help farmers to increase their profits. Officials of pesticide companies estimate that, under certain conditions, a dollar spent on pesticides can lead to an increase in crop yields worth as much as $4. They work fast. Pesticides control most pests quickly, have a long shelf life, and are easily shipped and applied. When used properly, the health risks of some pesticides are very low, relative to their benefits, according to some scientific studies. Newer pesticides are safer to use and more effective than many older ones. Greater use is being made of chemicals derived originally from plants (biopesticides), which are safer to use and less damaging to the environment than are many older pesticides. Genetic engineering is also being used to develop pest-resistant crop strains and genetically altered crops that produce natural biopesticides

There are two main types of traditional agriculture

Traditional subsistence agriculture supplements energy from the sun with the labor of humans and draft animals to produce enough crops for a farm family's survival, with little left over to sell or store as a reserve for hard times. In traditional intensive agriculture, farmers increase their inputs of human and draft-animal labor, animal manure for fertilizer, and water to obtain higher crop yields. If the weather cooperates, farmers can produce enough food to feed their families and have some left over to sell for income. Traditional Agriculture Often Relies on Low-Input Polyculture Some traditional farmers focus on cultivating a single crop, but many grow several crops on the same plot simultaneously, a practice known as polyculture. Such crop diversity—an example of implementing the biodiversity principle of sustainability (see Figure 1-2)—reduces the chance of losing most or all of the year's food supply to pests, bad weather, and other misfortunes. One type of polyculture is known as slash-and-burn agriculture (see Figure 1-17). This type of subsistence agriculture involves burning and clearing small plots in tropical forests, growing a variety of crops for a few years until the soil is depleted of nutrients, and then shifting to other plots to begin the process again. Over many centuries, users of this method have learned that each abandoned patch normally has to be left fallow (unplanted) for 10-30 years before the soil becomes fertile enough to grow crops again

irrigation

a mix of methods by which water is supplied to crops by artificial means. Other technological developments include the increasing use of manufactured chemical fertilizers and pesticides to provide plant nutrients and reduce crop losses to pests

These three systems depend on

a small number of plant and animal species. Of the estimated 50,000 plant species that people can eat, only 14 of them supply about 90% of the world's food calories. About two of every three people in the world survive primarily by eating one or more of three grain crops—rice, wheat, and corn. Only a few species of mammals and fish provide most of the world's meat and seafood

Drylands in regions with arid and semiarid climates occupy

about 40% of the world's land area and are home to some 2 billion people. A major threat to food security in some of the world's water-short drylands is desertification—the process in which the productive potential of topsoil falls by 10% or more because of a combination of prolonged drought and human activities that expose topsoil to erosion

pest

any species that interferes with human welfare by competing with us for food, invading our homes, lawns, or gardens, destroying building materials, spreading disease, invading ecosystems, or simply being a nuisance. Worldwide, only about 100 species of plants (weeds), animals (mostly insects), fungi, and microbes cause most of the damage to the crops we grow

Fish and shellfish are also produced through

aquaculture or fish farming—the practice of raising fish in freshwater ponds, lakes, reservoirs, and rice paddies, and in underwater cages in coastal lagoons and estuaries or offshore in deeper ocean waters

Some synthetic pesticides, called

broad-spectrum agents, are toxic to beneficial species as well as to pests. Examples are chlorinated hydrocarbon compounds such as DDT and organophosphate compounds such as malathion and parathion. Others, called selective, or narrow-spectrum, agents, are effective against a narrowly defined group of organisms. Examples are algicides for algae and fungicides for fungi

In the United States

by law, a label of 100 percent organic (or USDA Certified Organic) means that a product is produced only by organic methods and contains all organic ingredients. Products labeled organic must contain at least 95% organic ingredients and those labeled made with organic ingredients must contain at least 70% organic ingredients. The word natural is used on food labels primarily as an advertising ploy and carries no requirement for organic content

pesticides

chemicals used to kill or control populations of organisms that we consider undesirable. Common types of pesticides include insecticides (insect killers), herbicides (weed killers), fungicides (fungus killers), and rodenticides (rat and mouse killers)

People who cannot grow or buy enough food to meet their basic energy needs suffer from

chronic undernutrition, or hunger

Other fish farmers are reducing

coastal damage from aquaculture by raising shrimp and fish species in inland facilities using zero-discharge freshwater ponds and tanks. In such recirculating aquaculture systems, the water used to raise the fish is continually recycled. For example, like the Growing Power aquaponic system (Core Case Study), the Scandinavian Silver Eel Farm in Helsingborg, Sweden (Figure 12-30), captures its fish wastes and converts them to fertilizer. This reduces the discharge of polluting wastes and the need for antibiotics and other chemicals used to combat disease. It also eliminates the problem of farmed fish escaping into natural aquatic systems. GREEN CAREER: sustainable aquaculture

On less steeply sloped land,

contour planting can be used to reduce topsoil erosion. It involves plowing and planting crops in rows across the slope of the land rather than up and down. Each row acts as a small dam to help hold topsoil by slowing runoff. Similarly, strip-cropping (Figure 12-28b) helps to reduce erosion and to restore soil fertility with alternating strips of a row crop (such as corn or cotton) and another crop that completely covers the soil, called a cover crop (such as alfalfa, clover, oats, or rye). The cover crop traps topsoil that erodes from the row crop and catches and reduces water runoff

For centuries, farmers and scientists have used

crossbreeding through artificial selection to develop genetically improved varieties of crops and livestock animals (see Science Focus 4.2). Such selective breeding in this first gene revolution has yielded amazing results. For example, ancient ears of corn were about the size of your little finger, and wild tomatoes were once the size of grapes, but most of the large varieties used now were selectively bred. Traditional crossbreeding is a slow process, typically taking 15 years or more to produce a commercially valuable new crop variety, and it can combine traits only from species that are genetically similar. Typically, resulting varieties remain useful for only 5-10 years before pests and diseases reduce their yields. Important advances are still being made with this method

iodine (I)

essential for proper functioning of the thyroid gland, which produces hormones that control the body's rate of metabolism. Chronic lack of iodine can cause stunted growth, mental retardation, and goiter—a severely swollen thyroid gland that can lead to deafness

Over thousands of years, the earth's deserts have

expanded and contracted, primarily because of climate change. However, human use of the land, especially for agricultural purposes, has accelerated desertification in some parts of the world mostly because of deforestation, excessive plowing, and overgrazing. Some 40% of the U.S. land area is dry land in the western half of the country—especially in parts of Arizona, New Mexico, and Texas. It is subject to desertification, mainly from a combination of drought and overgrazing by livestock

The world's third major food-producing system consists of

fisheries and aquaculture. A fishery is a concentration of particular aquatic species suitable for commercial harvesting in a given ocean area or inland body of water. Industrial fishing fleets harvest most of the world's marine catch of wild fish by using a variety of methods

Plantation agriculture

form of industrialized agriculture used primarily in tropical less-developed countries. It involves growing cash crops such as bananas, coffee, vegetables, soybeans (mostly to feed livestock; see Figure 1-4), sugarcane (to produce sugar and ethanol fuel), and palm oil (used to produce cooking oil and biodiesel fuel; Figure 12-5) on large monoculture plantations, mostly for export to more-developed countries

Crops are raised by means of two types of agriculture

industrialized agriculture and subsistence agriculture

Soil conservation

involves using a variety of methods to reduce topsoil erosion and restore soil fertility, mostly by keeping the land covered with vegetation. Farmers have used a number of methods to reduce topsoil erosion. For example, terracing involves converting steeply sloped land into a series of broad, nearly level terraces that run across the land's contours (Figure 12-28a). Each terrace retains water for crops and reduces topsoil erosion by controlling runoff

A related problem is

is the increasing loss of agrobiodiversity—the genetic variety of animal and plant species used on farms to produce food. Scientists estimate that since 1900, we have lost 75% of the genetic diversity of agricultural crops that existed then. For example, India once planted 30,000 varieties of rice. Now more than 75% of its rice production comes from only ten varieties and soon, almost all of its production might come from just one or two varieties. In the United States, about 97% of the food plant varieties available to farmers in the 1940s no longer exist, except perhaps in small amounts in seed banks and in the backyards of a few gardeners

Soil, on which all terrestrial life depends

key component of the earth's natural capital. It supplies most of the nutrients needed for plant growth (see Figure 3-5). It also purifies and stores water, while organisms living in the soil remove carbon dioxide from the atmosphere and store it as organic carbon compounds, thereby helping to control the earth's climate as part of the carbon cycle (see Figure 3-17). Most soils that have developed over long periods of time, called mature soils, contain horizontal layers, or horizons (Figure 12-A), each with a distinct texture and composition that vary with different types of soils. Most mature soils have at least three of the four possible horizons. Think of them as the top floors in the geological building of life under your feet The roots of most plants and the majority of a soil's organic matter are concentrated in the soil's two upper layers, the O horizon of leaf litter and the A horizon of topsoil. In most mature soils, these two layers teem with bacteria, fungi, earthworms, and small insects, all interacting in complex food webs. Bacteria and other decomposer microorganisms, found by the billions in every handful of topsoil, break down some of the soil's complex organic compounds into a porous mixture of the partially decomposed bodies of dead plants and animals, called humus, and inorganic materials such as clay, silt, and sand. Soil moisture carrying these dissolved nutrients is drawn up by the roots of plants and transported through stems and into leaves as a key part of the earth's chemical cycling principle of sustainability (see Figure 1-2). The B horizon (subsoil) and the C horizon (parent material) contain most of a soil's inorganic matter, mostly broken-down rock consisting of varying mixtures of sand, silt, clay, and gravel. Much of it is transported by water from the A horizon (Figure 12-A). The C horizon lies on a base of parent material, which is often bedrock. The spaces, or pores, between the solid organic and inorganic particles in the upper and lower soil layers contain varying amounts of air (mostly nitrogen and oxygen gas) and water. Plant roots use the oxygen for cellular respiration. As long as the O and A horizons are anchored by vegetation, the soil layers as a whole act as a sponge, storing water and nutrients, and releasing them in a nourishing trickle. Although topsoil is a renewable resource, it is renewed very slowly, which means it can be depleted. Just 1 centimeter (0.4 inch) of topsoil can take hundreds of years to form, but it can be washed or blown away in a matter of weeks or months when we plow grassland or clear a forest and leave its topsoil unprotected

food insecurity

living with chronic hunger and poor nutrition, which threatens their ability to lead healthy and productive lives

Most of the world's hungry people live in

low-income, less-developed countries where they typically can afford only a low-protein, high-carbohydrate, vegetarian diet consisting mainly of grains such as wheat, rice, or corn. In more-developed countries, people living in food deserts (Core Case Study) have a similar problem, except that their diet is heavy on cheap food loaded with fats, sugar, and salt

To maintain good health and resist disease, individuals need fairly large amounts of

macronutrients (such as carbohydrates, proteins, and fats; see Figures 5, 6, and 9, in Supplement 4), and smaller amounts of micronutrients—vitamins, such as A, B, C, and E, and minerals, such as iron, iodine, and calcium

In the long run

making aquaculture more sustainable will require some fundamental changes for producers and consumers. One such change would be for more consumers to choose fish species that eat algae and other vegetation rather than other fish. Raising carnivorous fishes such as salmon, trout, tuna, grouper, and cod contributes to overfishing and population crashes within species used to feed these carnivores, and will eventually be unsustainable. Raising plant-eating fishes such as carp, tilapia, and catfish avoids this problem. However, it becomes less sustainable when aquaculture producers try to increase yields by feeding fishmeal to such plant-eating species, as many of them are

Desertification can be

moderate (with a 10-25% drop in productivity), severe (with a drop of 25-50%), or very severe (with a drop of more than 50%, usually resulting in huge gullies and sand dunes; see Figure 12-17). Only in extreme cases does desertification lead to what we call desert. But severe desertification can expand existing desert areas or create new deserts

In the 1930s

much of the topsoil in several dry and windy Midwestern states was lost because of a combination of poor cultivation practices and prolonged drought. The resulting severe wind erosion of topsoil led to crop failures and to the formation of a barren dust bowl, with thousands of environmental refugees migrating to other parts of the country

natural ecosystems and in many polyculture crop fields

natural enemies (predators, parasites, and disease organisms) control the populations of most potential pest species. This free ecosystem service is an important part of the earth's natural capital. For example, the world's 30,000 known species of spiders kill far more crop-eating insects every year than humans kill by using chemicals. Most spiders, including the wolf spider (Figure 12-22), do not harm humans

In the 1600s, farmers used

nicotine sulfate, extracted from tobacco leaves, as an insecticide. Eventually, other first-generation pesticides—mainly natural chemicals taken from plants—were developed. Farmers were copying nature's solutions—developed, tested, and modified through natural selection over millions of years—to apply to their pest problems

A fast-growing sector of the U.S. and world economies is

organic agriculture, in which crops are grown with the use of ecologically sound and sustainable methods and without the use of synthetic pesticides, synthetic inorganic fertilizers, and genetically engineered plants or animals. To be classified as organically grown, animals must be raised on 100% organic feed without the use of antibiotics or growth hormones. Growing Power (Core Case Study) has become a well-known model for such food production. Figure 12-7 compares organic agriculture with industrialized agriculture

Pesticides vary in their

persistence, the length of time they remain deadly in the environment. Some, such as DDT and related compounds, remain in the environment for years and can be biologically magnified in food chains and webs (see Figure 9-13). Others, such as organophosphates, are active for days or weeks and are not biologically magnified but can be highly toxic to humans

Since 1950

pesticide use has grown more than 50-fold and most of today's pesticides are 10-100 times more toxic than those used in the 1950s. Since 1970, chemists have continued to develop natural repellents and other biopesticides, again copying nature. About one-fourth of the pesticides used in the United States are aimed at ridding houses, gardens, lawns, parks, playing fields, swimming pools, and golf courses of insects and other species that we view as pests. According to the U.S. Environmental Protection Agency (EPA), the amount of synthetic pesticides used on the average U.S. homeowner's lawn is 10 times the amount (per unit of land area) typically used on U.S. croplands

One way to degrade soils is to

plant crops such as corn and cotton on the same land several years in a row, a practice that can deplete nutrients—especially nitrogen—in the topsoil. Crop rotation is one way to reduce such losses. A farmer plants an area with a nutrient-depleting crop one year, and the next year, plants the same area with legumes, whose root nodules add nitrogen to the soil. This method helps to restore topsoil nutrients while reducing erosion by keeping the topsoil covered with vegetation. A 2012 study done by Iowa State University found that rotating soy and corn crops on a 3- or 4-year cycle produced better yields than did planting the same crop year after year. This method also reduced the need for nitrogen fertilizer and herbicides by up to 88%, cut toxins in groundwater 200-fold, and did not reduce profits

It is possible to restore land suffering from desertification by

planting trees and other plants (Figure 12-17) that anchor topsoil and hold water. We can also grow trees and crops together (alley cropping, Figure 12-28c), and establish windbreaks around farm fields (Figure 12-28d).

Another change would be for fish farmers to emphasize

polyaquaculture, which has been part of aquaculture for centuries, especially in Southeast Asia. Polyaquaculture operations raise fish or shrimp along with algae, seaweeds, and shellfish in coastal lagoons, ponds, and tanks. The wastes of the fish or shrimp feed the other species, and in the best of these operations, there are just enough wastes from the first group to feed the second group. Polyaquaculture applies the recycling and biodiversity principles of sustainability

the root cause of food insecurity is

poverty

The overall aim of IPM is to

reduce crop damage to an economically tolerable level. Each year, crops are rotated, or moved from field to field, in an effort to disrupt pest infestations, and fields are monitored carefully. When an economically damaging level of pests is reached, farmers first use biological methods (natural predators, parasites, and disease organisms) and cultivation controls (such as altering planting time and using large machines to vacuum up harmful bugs). They apply small amounts of synthetic insecticides—preferably biopesticides—only when insect or weed populations reach a threshold where the potential cost of pest damage to crops outweighs the cost of applying the pesticide

Many farmers, especially those in more-developed countries

rely on synthetic inorganic fertilizers. The use of these products has grown more than ninefold since 1950, and it now accounts for about 25% of the world's crop yield. While these fertilizers can replace depleted inorganic nutrients, they do not replace organic matter. To completely restore nutrients to topsoil, both inorganic and organic fertilizers must be used. Many scientists are encouraging farmers, especially those in less-developed countries, to make greater use of green manure as a more sustainable way to restore soil fertility. Another way to restore the fertility of degraded or contaminated soils, especially in polluted urban settings, is to use biological methods. For example, Growing Power farmers (Core Case Study) have used red wiggler worms to break down the toxins present in contaminated urban soils and to improve soil fertility for raising food crops

Today, scientists are creating a

second gene revolution by using genetic engineering to develop genetically improved strains of crops and livestock animals. Engineers use a process called gene splicing to alter an organism's genetic material through adding, deleting, or changing segments of its DNA (see Figure 8, in Supplement 4). The goal of this process is to produce desirable traits or to eliminate undesirable ones by enabling scientists to transfer genes between different species that would not normally interbreed in nature. The resulting organisms are called genetically modified organisms (GMOs)

One major problem related to agriculture is

soil erosion—the movement of soil components, especially surface litter and topsoil, from one place to another by the actions of wind and water. Some topsoil erosion is natural, but much of it is caused by human activities

Despite such genetic vulnerability, since 1960 there has been a

staggering increase in global food production from all three of the major food production systems (Concept 12-2). This was made possible by technological advances such as greater use of tractors and other farm machinery and high-tech fishing equipment

Many people, most of them in less-developed countries

suffer from a deficiency of one or more vitamins and minerals, usually vitamin A, iron, and iodine. According to the World Health Organization (WHO), at least 250,000 children younger than age 6, most of them in less-developed countries, go blind every year from a lack of vitamin A. Within a year, more than half of them die

Despite some claims to the contrary, largely because of genetic resistance and the loss of many natural predators,

synthetic pesticides have not always succeeded in reducing U.S. crop losses. When David Pimentel, an expert on insect ecology, evaluated data from more than 300 agricultural scientists and economists, he reached three major conclusions. First, between 1942 and 1997, estimated crop losses from insects almost doubled from 7% to 13%, despite a tenfold increase in the use of synthetic insecticides. Second, according to the International Food Policy Research Institute, the estimated environmental, health, and social costs of pesticide use in the United States are $5-$10 in damages for every dollar spent on pesticides. Third, experience indicates that alternative pest management practices could cut the use of synthetic pesticides by half on 40 major U.S. crops without reducing crop yields

One major environmental problem associated with aquaculture is

that about a third of the wild fish caught from the oceans are used to make the fishmeal and fish oil that are to fed to farmed fish. This is contributing to the depletion of many populations of wild fish that are crucial to the marine food web—a serious threat to marine biodiversity. Also, this is a very inefficient process. According to marine scientist John Volpe, it takes about 3 kilograms (6.6 pounds) of wild fish to produce 1 kilogram (2.2 pounds) of farmed salmon, and this ratio increases to 5 to 1 for farmed cod and 20 to 1 for farmed tuna. Another problem is that some fishmeal and fish oil fed to farm-raised fish are contaminated with long-lived toxins such as PCBs and dioxins that are picked up from the ocean floor. Aquaculture producers contend that the concentrations of these chemicals are not high enough to threaten human health. Fish farms, especially those that raise carnivorous fish such as salmon and tuna, produce large amounts of wastes. Along with pesticides and antibiotics used on fish farms, these wastes can pollute aquatic ecosystems and fisheries. Aquaculture can also end up promoting the spread of invasive plant species. An Asian kelp called wakame or undaria is a popular food product raised on some farms. But this invasive seaweed is disrupting coastal aquatic systems in several parts of the world. Yet another problem is that farmed fish can escape their pens and mix with wild fish, possibly disrupting the gene pools of wild populations. Major seed companies are now pushing to use patented genetically modified soybeans as the primary feed for farm-raised fish and shellfish. This could increase water pollution because fish that are fed soy produce more waste than other fish. It would also give a small number of seed companies control over much of the world's seafood production. And it could encourage more deforestation and loss of biodiversity that result when soy plantations replace tropical forests (see Figure 1-4). There is also controversy over the use of a type of farmed salmon that has been genetically engineered, through the combination of growth genes from a Chinook salmon and a sea eel, to grow quickly to the size of wild salmon. The genetically altered salmon requires about 25% less feed per unit of body weight, which could lower its cost and reduce pressure on fish stock used as feed. There is concern that this genetically engineered salmon could escape from fish farms and interbreed with wild salmon. Proponents say this is unlikely because the genetically engineered salmon is sterile

In undisturbed, vegetated ecosystems

the roots of plants help to anchor the topsoil and to prevent some erosion. But when we remove soil-holding grasses, trees, and other vegetation through activities such as farming (see Figure 7-12), deforestation (see Figure 10-12), and overgrazing (see Figure 10-22), the topsoil can be subject to erosion. A joint survey by the UNEP and the World Resources Institute indicated that topsoil is eroding faster than it forms on about 38% of the world's cropland

A major reason for the success in boosting productivity on farms is

the use of irrigation, which accounts for about 70% of the water that humanity uses. Currently, the one-fifth of the world's cropland that is irrigated produces about 45% of the world's food

The best way to maintain soil fertility is

through top-soil conservation. The next best option is to restore some of the lost plant nutrients that have been washed, blown, or leached out of topsoil, or that have been removed by repeated crop harvesting. To do this, farmers can use organic fertilizer derived from plant and animal materials or synthetic inorganic fertilizer manufactured of inorganic compounds that contain nitrogen, phosphorus, and potassium along with trace amounts of other plant nutrients

Another way to greatly reduce topsoil erosion is

to eliminate or minimize the plowing and tilling of top-soil and leave crop residues on the ground. This is called conservation-tillage farming, accomplished with the use of special tillers and planting machines that inject seeds and fertilizer directly through crop residues into minimally disturbed topsoil. Weeds are controlled with herbicides. This type of farming increases crop yields and greatly reduces soil erosion and water pollution from sediment and fertilizer runoff. It also helps farmers survive prolonged drought by helping to keep more moisture in the soil

Some 2.7 billion people (39% of the world's people) in less-developed countries practice

traditional agriculture. It provides about one-fifth of the world's food crops on about three-fourths of its cultivated land

Natural biodiversity and some ecosystem services are threatened when

tropical and other forests are cleared (see Figure 10-11) and when grasslands are plowed up and replaced with croplands used to produce food and biofuels For example, one of the fastest-growing threats to the world's biodiversity is the cutting or burning of large areas of tropical forest in Brazil's Amazon Basin and the clearing of areas of its cerrado, a huge tropical grassland region south of the Amazon Basin. This land is being burned or cleared for cattle ranches, large plantations of soybeans grown for cattle feed (see Figure 1-4), and sugarcane used for making ethanol fuel for cars. In Indonesia, tropical forests are burned to make way for plantations of oil palm trees (Figure 12-5) increasingly used to produce biodiesel fuel for cars. Such forests are also being cleared for food production in Africa and many other areas of Asia

Some second-generation pesticides have

turned out to be highly hazardous for birds and other forms of wildlife. In 1962, biologist Rachel Carson published her famous book Silent Spring, sounding a warning that eventually led to strict controls on the use of DDT and several other widely used pesticides

Industrialized agriculture allowed farmers to

use less land to produce more food, and this has helped to protect biodiversity in many areas by reducing the destruction of forests and grasslands for farming. However, many analysts point out that industrialized agriculture has greater overall harmful environmental impacts than any other human activity and these environmental effects may limit future food production

Hydroponics

involves growing plants by exposing their roots to a nutrient-rich water solution instead of soil, usually inside of a greenhouse

According to some experts

one way to increase food security is to grow more of our food locally or regionally, ideally with certified organic farming practices. A growing number of consumers are becoming "locavores" and buying more of their food from local and regional producers in farmers' markets, which provide access to fresher seasonal foods. In 2012, there were more than 5,000 farmers' markets in the United States, triple the number of such markets in 1994, according to the USDA. In addition, many people are participating in community-supported agriculture (CSA) programs in which they buy shares of a local farmer's crop and receive a box of fruits or vegetables each week during the summer and fall. Growing Power (Core Case Study) runs such a program for inner-city residents. For many of these people, the organically grown food they get from the urban farm greatly improves their diets and increases their chances of living longer and healthier lives. By buying locally, people support local economies and farm families. They also help to reduce fossil fuel energy costs for food producers, as well as the greenhouse gas emissions resulting from refrigeration and transportation of food products over long distances. An increase in the demand for locally grown food could result in more small, diversified farms that produce organic, minimally processed food from plants and animals. Such eco-farming could be one of this century's challenging new careers for many young people. GREEN CAREER: small-scale sustainable agriculture Sustainable agriculture entrepreneurs and ordinary citizens who live in urban areas could grow more of their own food, as the Growing Power farm has shown (Core Case Study). According to the USDA, around 15% of the world's food is grown in urban areas, and this percentage could easily be doubled. People are planting gardens and raising chickens in many urban and suburban backyards, growing dwarf fruit trees in large containers of soil, and raising vegetables on rooftops, balconies, and patios. People are also building raised gardening beds in urban parking lots—a growing practice known as asphalt gardening. In a 2011 report, community systems expert Zaid Hassan noted that in Cuba, the government ran a program to turn the capital city of Havana's many vacant lots into urban farms or gardens. As a result, about 41% of the city's area is now used for organic agriculture that generates more than half of Cuba's vegetables. We Can Grow and Buy More Food Locally and Cut Food Waste Many urban schools, colleges, and universities are benefiting greatly from having gardens on school grounds. Not only do the students have a ready source of fresh produce, but they also learn about where their food comes from and how to grow their own food more sustainably In the future, much of our food might be grown in cities within high-rise buildings. Figure 12-27 is an architectural drawing of such a vertical farm. This building with crops growing on every floor would put into practice the three scientific principles of sustainability (see Figure 1-2). Its sloped glass front would bring in sunlight, and excess heat collected in this way could be stored in tanks underneath the building for use as needed. It could also have solar panels for generating electricity on its rooftop or on an overhang shown in the bottom of Figure 12-27. The building could also capture and recycle rainwater for irrigating its wide diversity of crops Finally, people can sharply cut food waste as an important component of improving food security (Concept 12-5). A 2011 UN study found that about one-third of all food produced globally is lost during production or thrown away. Environmental scientist Vaclav Smil and other researchers have estimated that Americans throw away 30-50% of their food supply. This wasted food is worth at least $43 billion a year, almost twice as much as the estimated $24 billion needed to eliminate undernutrition and malnutrition in the world. In some less-developed countries, food waste can be high due to spoilage from heat and pests and lack of refrigeration and food storage systems

Overnutrition

occurs when food energy intake exceeds energy use and causes excess body fat. Too many calories, too little exercise, or both can cause overnutrition. People who are underfed and underweight and those who are overfed and overweight share similar health problems: lower life expectancy, greater susceptibility to disease and illness, and lower productivity and life quality

famine

occurs when there is a severe shortage of food in an area and which can result in mass starvation, many deaths, economic chaos, and social disruption. Famines are usually caused by crop failures from drought, flooding, war (Figure 12-2), and other catastrophic events (Concept 12-1B)

Farmers can also establish windbreaks, or shelterbelts,

of trees around crop fields to reduce wind erosion (Figure 12-28d). The trees retain soil moisture, supply wood for fuel, and provide habitats for birds and insects that help with pest control and pollination

integrated pest management (IPM)

a carefully designed program in which each crop and its pests are evaluated as parts of an ecosystem, and farmers use a combination of cultivation, biological, and chemical tools and techniques, applied in a coordinated process

chronic malnutrition

a condition in which they do not get enough protein and other key nutrients. This can weaken them, making them more vulnerable to disease, and hindering the normal physical and mental development of children

In losing agrobiodiversity, we are rapidly shrinking the world's genetic

"library," which is critical for increasing food yields. This failure to preserve agrobiodiversity is a serious violation of the biodiversity principle of sustainability Individual plants and seeds from endangered varieties of crops and wild plant species important to the world's food supply are stored in about 1,400 refrigerated seed banks, as well as in agricultural research centers and botanical gardens scattered around the world. However, power failures, fires, storms, war, and unintentional disposal of seeds can cause irreversible losses of these stored plants and seeds. More secure seed banks are being built (as we discuss later in this chapter). However, the seeds of many plants cannot be stored successfully in seed banks. And because stored seeds do not remain alive indefinitely, they must be planted and germinated periodically, and new seeds must be collected for storage. Unless this is done, seed banks become seed morgues

A major pest control revolution began in

1939, when entomologist Paul Müller discovered DDT (dichlorodiphenyltrichloroethane)—the first of the so-called second-generation pesticides produced in the laboratory. It soon became the world's most-used pesticide, and Müller received the Nobel Prize in Physiology or Medicine in 1948 for his discovery. Since then, chemists have created hundreds of other pesticides by making slight modifications in the molecules of various classes of chemicals

A green revolution involves three steps

First, develop and plant monocultures of selectively bred or genetically engineered high-yield varieties of key crops such as rice, wheat, and corn. Second, produce high yields by using large inputs of water, synthetic inorganic fertilizers, and pesticides. Third, increase the number of crops grown per year on a plot of land through multiple cropping. Between 1950 and 1970, in what was called the first green revolution, this high-input approach dramatically raised crop yields in most of the world's more-developed countries, especially the United States

However, irrigation has a downside

Most irrigation water is a dilute solution of various salts, such as sodium chloride (NaCl), that are picked up as the water flows over or through soil and rocks. Irrigation water that is not absorbed into the topsoil evaporates, leaving behind a thin crust of dissolved mineral salts in the topsoil. Repeated applications of irrigation water in dry climates lead to the gradual accumulation of salts in the upper soil layers—a soil degradation process called soil salinization. It stunts crop growth, lowers crop yields, and can eventually kill plants and ruin the land

So far, several factors have limited the success of the green revolutions and may limit them in the future

Without huge inputs of water and synthetic inorganic fertilizers and pesticides, most green revolution and genetically engineered crop varieties produce yields that are no higher (and are sometimes lower) than those from traditional strains. These high inputs also cost too much for most subsistence farmers in less-developed countries. Scientists point out that where such inputs do increase yields, there comes a point where yields stop growing because of the inability of crop plants to take up nutrients from additional fertilizer and irrigation water. This helps to explain the slowdown in the rate of growth in global grain yields from an average increase of 2.1% a year between 1950 and 1990 to 1.3% annually between 1990 and 2011. Can we expand the green revolutions by irrigating more cropland? Since 1978, the amount of irrigated land per person has been declining, and it is projected to fall much more between 2012 and 2050. One reason for this is population growth, which is projected to add 2.6 billion more people between 2012 and 2050. Other factors are wasteful use of irrigation water, soil salinization, and the fact that most of the world's farmers do not have enough money to irrigate their crops. In addition, according to many scientific studies, projected climate change during this century is likely to melt some of the mountain glaciers that provide irrigation and drinking water for many millions of people in China, India, and South America. Can we increase the food supply by cultivating more land? We have already cleared or converted about 38% of the world's ice-free land surface for use as croplands and pastures. By clearing tropical forests and irrigating arid land, we could more than double the area of the world's cropland. The problem is that such massive clearing of forests would greatly speed up and magnify climate change and biodiversity losses. Also, much of this land has poor soil fertility, steep slopes, or both, and cultivating such land would be expensive and probably not ecologically sustainable. In addition, during this century, fertile croplands in coastal areas, including many of the major rice-growing floodplains and river deltas in Asia, are likely to be flooded by rising sea levels resulting from projected climate change. Food production could also drop sharply in some major food-producing areas because of longer and more intense droughts and heat waves, also resulting from projected climate change. Crop yields could be increased with the use of conventional or genetically engineered crops that are more tolerant of drought, which are in the early stages of being tested. Commercial fertilizers have played a role in green revolutions, but their use in most of the more-developed countries has reached a level of diminishing returns in terms of increased crop yields. However, there are parts of the world, especially in Africa, where additional fertilizer could boost crop production

Alley cropping, or agroforestry

another way to slow the erosion of topsoil and to maintain soil fertility. One or more crops, usually legumes or other crops that add nitrogen to the soil, are planted together in alleys between orchard trees or fruit-bearing shrubs, which provide shade. This reduces water loss by evaporation and helps retain and slowly release soil moisture

Aquaculture, the fastest-growing type of food production, is sometimes called the

blue revolution

Soil

complex mixture of eroded rock, mineral nutrients, decaying organic matter, water, air, and billions of living organisms, most of them microscopic decomposers. Soil formation begins when bedrock is slowly broken down into fragments and particles by physical, chemical, and biological processes, called weathering. Figure 12-A shows profiles of different-aged soils

Agricultural activities, including the clearing and burning of forests to raise crops or livestock

create a great deal of air pollution. They also account for more than a quarter of all human-generated emissions of carbon dioxide , which is helping to warm the atmosphere in a process of climate change that is projected to play an important role in making some areas unsuitable for growing crops during this century

Farmers have two ways to produce more food:

farming more land or getting higher yields from existing cropland

Soil is

literally the foundation of life on land (Science Focus 12.1). Specifically, the fertile top layer of many soils, called topsoil, is a vital component of natural capital, because it stores the water and nutrients needed by plants

Most of the world's aquaculture involves

raising species that feed on algae or other plants—mainly carp in China and India, catfish in the United States, tilapia in several countries, and shellfish in a number of coastal countries. However, the farming of meat-eating species such as shrimp and salmon is growing rapidly, especially in more-developed countries. Such species are often fed fishmeal and fish oil produced from other fish and their wastes. In the next major section, we examine the harmful environmental impacts of aquaculture that could limit its growth

A more sustainable form of meat production and consumption would involve

shifting from less grain-efficient forms of animal protein, such as beef, pork, and carnivorous fish produced by aquaculture, to more grain-efficient forms, such as poultry and plant-eating farmed fish (Figure 12-32). Such a shift is under way. Since 1996, poultry has taken the lead over beef in the marketplace, and within a decade or so, herbivorous fish farming may exceed beef production

Perhaps the biggest problem resulting from excessive irrigation in agriculture is

that it has contributed to depletion of groundwater and surface water supplies in many areas of the world

Food security

the condition under which all or most of the people in a population have daily access to enough nutritious food to live active and healthy lives

Industrialized agriculture, or high-input agriculture

uses heavy equipment (Figure 12-4) along with large amounts of financial capital, fossil fuels, water, commercial inorganic fertilizers, and pesticides to produce single crops, or monocultures. The major goal of industrialized agriculture is to steadily increase each crop's yield—the amount of food produced per unit of land. Industrialized agriculture is practiced on 25% of all cropland, mostly in more-developed countries, and produces about 80% of the world's food

feedlots

very crowded pens and cages in huge buildings called concentrated animal feeding operations (CAFOs). Most veal calves, pigs, chickens (Figure 12-11), and turkeys that are raised in more-developed countries spend their lives in CAFOs

Other obstacles to food security are

war, bad weather (such as prolonged drought, flooding, and heat waves), and climate change (Concept 12-1B), along with corruption and political upheaval

Another problem with irrigation is

waterlogging. in which water accumulates underground and gradually raises the water table, especially when farmers apply large amounts of irrigation water in an effort to leach salts deeper into the soil. Waterlogging lowers the productivity of crop plants and kills them after prolonged exposure, because it deprives plants of the oxygen they need to survive. At least 10% of the world's irrigated land suffers from this worsening problem

Whether farmers have a good or bad year depends on factors over which they have little control:

weather, crop prices, crop pests and diseases, interest rates on loans, and global markets.

Largely because of the two green revolutions

world grain production more than tripled between 1961 and 2011 (Figure 12-8, left). Per capita food production increased by 31% between 1961 and 1985, but since then it has generally declined slightly (Figure 12-8, right)