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-,_ Hunger, Malnutrition,Food Supplies, andthe Environment

, -. Understanding Soils; Barriers to a Sustainable

Agricultural SystemSolutions: Building aSustainable AgriculturalSystemSpotlight on SustainableDevelopment 11-1: TheGreen Wall ofChina:Stopping the Spread ofDesert

Civilization itself rests upon the soil.- Thomas]eff erso

odern farmers typically plant huge expanses of cornand soybeans. Unfortunately, large fields containingM single crop tend to be highly vulnerable to insects,disease, and hail. An outbreak of insects can cause enormous damageIn response to this problem, some progressive Nebraskan farmers ar

breaking with the traditions of modern agriculture. Instead of plantintheir fields in one crop, they are planting two crops (such as cornand soybeans) on the same land but in alternating strips. This simplechange increases the productivity of soybeans and corn dramaticallyvVhy? In one study, researchers found that in this planting arrangementhe corn protects the soybeans from the drying effects of the wind.This, in turn , increased s0ybean output by 11%. They also foundthat the stands of corn are less dense than in a field planted fromfencerow to fencerow. This results in better sunlight penetration,which increases corn production by a remarkable 150%. Intercroppingas the practice is called, not only increases production, it reducesthe need for chemical pesticides, for reasons explained later.

Chapter II Creating a Sustainable System of


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Combinesharvesting wheaton a modern day farm.

e x e r c i s eSome agricultural interest groups object to the phrase sustainable agriculture. They argue that it implies that current agricultural practices arenot sustainable. In support of their case, they point ou t that agriculturaproductivity (the output of food per hectare or acre) has been risingsteadily in many countries- such as Canada, Australia, and the UnitedStates-thanks to widespread use of insecticides , herbicides, fertilizerirrigation, and other modern practices. They also point out that farmers in many modern agricultural countries are feeding more and morepeople every year. Is there anything wrong with this line of reasoning7What critical thinking rules are essential to analyze this issue7

Reductions in pesticide use save farmers considerable amounts of money and reduce environmentpollution.This is one example of many efforts aimed at building a more sustainable system of agricultur

Sustainable agriculture is a system that produces high-quality foods while maintaining or improvinthe soil and protecting the environment-the air, water, soil, and wealth of wild species. I t is asystem that can endure, providing benefits for centuries. This chapter tackles the subject of foodand agriculture, beginning with a look at hunger and malnutrition.

i i ; Hunger, Malnutrition, FoodSupplies, and the Envir..onment

In Chapter 9, you learned that hunger and starvation are two consequences of overpopulation. Asyou may already know, hunger and starvation arehuge problems. According to estimates from theUnited Nations, 841 million people living in lessdeveloped countries are chronically malnourished-that is, they fail to get enough protein , calories, or both. Another on e billion suffer from pro-

tein malnutrition. Thus, about 30% of the world'speople are chronically malnourished. Many of thoseaffected bythis problem are children. Malnutritionis particularly acute on the Indian subcontinent,where three-fifths o( the children suffer from ashortage of food.

Scientists recognize two types of malnutrition.The first, kwashiorkor (KWASH-ee-OAR-core),results from a lack of protein. The second , marasmu s (meh-RAZ-mess) , results from an insufficientintake of protein and calories (food that provides

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Kwashiorkor. This protein deficiency leads to swellingof the abdomen. The loss of muscle protein results inthin arms and legs. Children are phys ically andmentally stunted, apathetic, and anemic.

energy ) . ln reality, kwashiorkor an d marasmus aretwo extremes of protein-calorie deficienc y an d

most individuals who are mal-An estimated 12 mi llionpeople die each year, most lyin the less developed nations,as a resu lt of malnutritionand diseases worsened by it.

nourished exhibit symptoms ofboth. People ma y also suffer fromspecific deficiencies such as alack of vi tamin A, which maycause serious damage to th e eyes ,leading to blindness.

Figure 11-1 shows children suffering from kwashiorkor, extreme protein deficiency. Asillustrated, the legs and armsof victims of this disease arethin , and their abdomens areswollen with fluids. Victimsare weak and passive. Kwashiorkor is mos t common inchildren one to three years ofage and generally begins afterthey are weaned (thus losingthe protein-rich milk of their

Marasmus. Victims ofmarasmus (protein andcalorie deficiency) are th in butalert and active. Survivo rs ofmalnutrition may be left withstunted bodies and minds.

mothers) and have been switched to a low-proteistarchy adult die t.

Victims of marasmu s are thin an d wasted (Fure 11-2). Th ei r ribs stick out th rough wrinklskin. They of ten suck on th ei r hands and clothto appease a gnawing hunger. Unlike victims kwash iorkor, ho wever, children suffering fromarasmus are alert and active. Marasmus often ocurs in infants separated from their mothers duing breast-feeding as a resul t of maternal deathfailure of milk production (lactation ) , or th e improper use of milk sub s ti tut es . Consider th e latteln the 1970s , advertising campaigns promotipowdered milk substitutes co nvinced mawomen in the LDCs to bo ttl e-feed children u simanufactured formulas. Many we re provided wipowdere d milk free or at low cos t to introduthem to the product. After starting th ei r childron formula , ho wever, man y wo men found ththey could not afford to continue to use the prouct. By then, though, their breast mil k had driup . To compensate, some women diluted whmilk they could afford w ith water, thus reducitheir children 's intake of protein and ca lo rieMany women us ed water from contaminatestreams, so their children developed d iarrhewhich further reduced food intake an d worsentheir children's malnourishment.

Despite public outcry an d promises , Nest( th e world's largest food company) an d other companies continue to provide free an d low-cobreast-milk substitutes to hosp ita ls in the less dveloped nations .

Sadly, for every clinically diagnosed casemarasmus an d kwashiorkor in LDCs, there a re hudreds of children with mild to moderate formsmalnut rition , a condition much more difficult to dtect. Undernourishment and malnutrition are nrestricted to the LDCs of the world , however. In tUnited States, for example, an estimated 10 to 15of the population is undernourished . Hun ger most prevalent in Mississippi, Arkansas, AlabamNew Mexico, and the Dis trict of Columbia.

Malnutrition causes considerable hu ma n sufer ing. Imagine the pain of going to bed hungni ght after night. Malnutrition can lead to dea tFo r example, mild cases make people more suscetible to infectious disease s , ailments causedbacteria and v iruses tha t can be spread from operson to anothe r. A person weakened by malntrition is more likely to die from an ordinarily nofa tal disease than a perso n wh o is well nou risheln fact, malnutrition so weakens the immune sytem that normally nonthreatening diseases such

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measles and diarrhea can be fa tal among children.Making matters worse, crowding in urban centersfacilitates the spread of disease. According to theUnited Nations, an estimated12 million people dieprematurely each year from undernutrition , malnutrition, and nonfatal diseases worsened by poornutrition. Many of the victims are children-about19,000 per day'

Key ConceptsA large segment of the world's people (most of whomlive in Asia, Africa, and Latin America) either do notget enough to eat or fail to get all of he nutrients andvitamins they need-or both. Nutritional deficienciesmake people more susceptible to infectious diseaseand, if they are severe enough, can cause death.

Hunger, Poverty, and Environmental DecayMany students ask why they should study malnutrition in a course on environmental issues. One reasonis that food problems are a direct result of populationgrowth and loss of farmland caused by growing hu man population. But there's another reason. Nutritional deficiencies early in life often lead to mentaland physical retardation. The more severe the deficiency, the more severe the impairment . Mental retardation occurs because 80% of the brain's growthoccurs before the age of two. Malnourished childrenwho survive to adulthood remain mentally impaired.Typically plagued by malnutri tion their whole lives,they are often prone to infectious diseases and provide little hope for improving their ow n or their nation 's prospects. Hunger and malnutri tion, therefore ,may contribute to growing poverty, rising population , and worsening environmental conditions.

Key ConceptsHunger and malnutrition ca use mental and physicalretardation that may contribute to widespreadpoverty and population growth, which contribute toenvironmental destruction.

Declining Food SuppliesMalnutrition abounds. But what are the prospectsfor the future? Will we be able to feed the world'speople and accommodate the growing population ,which expands by about 230,000 people per day?

For many years, hope has been pinned on ourability to grow mo re food. The use of modern agricultural methods and increases in farmland causedgrain production per capita to rise approximately30% from 1950 to 1970. This resulted in a substan-

tial improvement in the diet of many of the world'speople. From 1971 to 1984 , how ever, world grainproduction bare ly kept pace with populationgrowth. Between 1984 and 1998, grain productionper capita fell 7%.

The decline in food production per capita overthe past decade results from numerous factors ,among them the warming global climate, populationgrowth, soil erosion, and soil deterioration (homcauses described in the next section). Many expertsthink tha t food production per capi ta will continueto decline throughout the next decade as a result ofthese problems. If global warming , populationgrowth, soil erosion , and other problems worsen,then hunger, poverty, and environmental destruction will beco me even more widespread.

Because of dec lining per capita food production, many countries have lost the ability to feedtheir people and have become dependent on importsfrom the more developed countries such as Canada,Australia, and the Un ited States. In 1950, grain imports by the LDCs amounted to only a few milliontons a year; in the 1980s, they rose to 500 millionton s. In 1995, they were over 1.2 billion metric tonsper year. By 2000 , they had climbed to over 1.5 billion tons per year.

So me experts believe that the safety net providedby majo r food-producing nations is in danger. One ofthe most serious threats is global warming (Chapter21). In 1988, after record high temperaturesthroughout the Midwest, U .S. grain production fellby 35%, plummeting to 190 million metric tonsbarely enough to satisfy American needs, let aloneforeign demand . Thanks to previous surpluses, do mestic and foreign demands were sa tisfied. In the fu ture, a warming trend could slow exports to a trickle ,threatening LDCs that rely on outside help.

Many experts believe that un less decisive stepsare taken- and soon-millions of people in the lessdeveloped nations cou ld perish from hunger anddiseases. The fam ines in Africa and Southeas t Asia ,in which hu ndreds of thousand s of people died inrecent years, may be a portent of what is to come .Many believe that the rich nations, to whom the lessdeveloped nations are highly indebted , will not beimmune to the up heaval that results .

Key ConceptsGrain production per capita has been on the declinefor over a deca de and a half, a t rend that bodes poorlyfor those suf fering from hunger and malnutrition- aswell as for those trying to provide food for the evergrowing human population.

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The Challenge Facing World Agriculture:Feeding People/Protecting the PlanetThree interrelated challenges face the world today:First, we must find ways to feed the malnourishedpeople alive today (an immediate challenge). Second, we must find ways to meet future needs for food(a long-term challenge). Third, we have to find waysto produce food to meet present and future needswhile protecting the soil and water upon which agriculture depends (both an immediate and a long-termchallenge). In other words, we have to ensure thatcurrent agricultural practices are sustainable.

Key ConceptsThe challenge today is to find sustainable ways tofeed current and future world residents.

''3 Understanding SoilsMalnutrition is only one of a handful of serious foodand agricultural problems facing the world todayand threatening ou r long-term future. The next section outlines many problems, such as soil erosion inthe agricultural sector, that are responsible for thedeteriorating condition of the world's cropland andthe decline in food production. Before we examinethis set of challenges and discuss ways to build asustainable agriculture, however, a brief study ofsoils is in order. This information will provide youwith some of the scientific knowledge you need toassess various solutions and their sustainability.What Is Soil?High-quality soils promote plant growth , both innatural ecosystems and in human-dominated systems such as rangeland and farmland. Because ofthis, soils are vital to our long-term health and ou reconomic well-being.

Soil is a complex mixture of inorganic and organic materials with variable amounts of air and water. The inorganic material includes clay, silt, sand,grav"el, and rocks. The organic component consistsof living and nonliving plant and animal materials.Living organisms include insects, earthworms, andmicroorganisms. The nonliving matter includesplant and animal waste and residues (remains ofdead bodies) in various stages of decomposition.

Soils are described according to six general fea-tures: texture, structure, acidity, gas content, watercontent, and biotic composition. These componentsand characteristics combine to form many differentsoil types throughout the world. A detailed discussion

Chapter l l Creating a Sustainable System of

of each soil type is well beyond the scope of this boAs you shall soon see, some soils are better suitedagriculture than others.

Key ConceptsSoils consist of four components: inorganic materials, organic matter, air, and water.

How Is Soil Formed?Soil formation is a complex and slow process, evunder the best of conditions. It results from anteraction between the parent material, the undering substrate from which soil is formed, and theganisms. The time it takes soil to develop depenpartly on the type of parent material. To formcentimeters ( l inch) of topsoil from hard rock mtake 200 to 1200 years, depending on the climaSofter parent materials such as shale, volcanic asandstone, sand dunes, and gravel beds are cverted to soil at a faster rate-in 20 years or so uder very favorable conditions. Because of the timtakes to replenish soil and because soils are so iportant to society, they should be protected acarefully managed. As discussed later in this chter, the cornerstone of sustainable agriculture is pvention-measures that preserve and protect topsso that it can remain productive indefinitely Wwe gain from soils is like interest from a bankcount. We can draw on it forever, as long as wenot deplete the soil itself, one of ou r forms of naral capital upon which society depends.

Four factors are responsible for the type of sthat forms , the thickness of the soil layer, andrate of soil formation. They are climate, parent mterial , biological organisms, and topography.

The climate is the average weather conditionotably temperature and precipitation. The parmaterial, the underlying rock or sand or gravel frwhich the mineral matter is derived, is acted onclimate and biological organisms and converted isoil. For example, heating and cooling (both ements of climate) cause barren rock to split afragment, especially in the desert biome, where datemperatures vary widely Water entering cracksrocks expands when it freezes, causing the rockfragment further. The roots of trees and large plareach into small cracks and fracture the rock. Otime, rock fragments produced by these procesare slowly pulverized by streams or landslides ,hooves of animals, or by wind and rain.

Soil formation is facilitated by numerous orgisms. Chapter 7 described how lichens eroderock surface by secreting carbonic acid. Lichens a


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capture dust, seeds, excrement, and dead plant matter, which help form soil. The roots of plants alsohelp build soil by serving as nutrient pumps, drawing up inorganic nutrients from deeper soil layers.These chemicals are first used to make leaves andbranches, which can fall and decay; thus they become part of the uppermost layer of soil , the topsoil.

Grazing animals drop excrement on the ground,adding to the soil's organic matter. The white rhinoceros, for example, produces about 27 metric tonsof manure each year, which is deposited in its habitat. A variety of insects and other creatures, such asearthworms, also participate in soil formation.

Topography, the final soil-forming force, is theshape or contour of the land surface. It determineshow water moves and how quickly soil erodes.Steeply sloping land surfaces, for instance, are moresusceptible to soil erosion. As a result, thin soilstend to form on them. Relatively flat terrain, on theother hand, suffers little from erosion. Soils tend tobe thicker in such regions. Valley floors benefit fromtheir flatness and their proximity to steeper terrainwhose soil washes away and is deposited on thefloor. Many a valley, even in the arid West, has beenconverted to valuable cropland because of the richsoil that has built up in them over many years. To-day, however, valley floors are also desirable land fordevelopment, and farmers and ranchers aresqueezed out as the population expands and newsubdivisions pop up.

Key ConceptsSoil formation is a complex process involving an in-teraction among climate; the pa rent material, whichcontributes the mineral components of soil; and bio-logical organisms. Because soil is so valuable and be-cause it takes so long to form, we should take care toprotect and manage soils.

The Soil ProfileMost of us have seen a road cu t or excavation for abuilding and noticed that soil is composed of layers.The layers, called horizons, differ in color and composition. Not all horizons are present in all soils; insome, the layering may be missing altogether.

Soil scientists recognize five major horizons(Figure 11-3). The uppermost region of the soil is the0 horizon, or litter layer. This relatively thin layer oforganic waste from animals and detritus is the zone ofdecomposition and is characterized by a dark, richcolor. Plowing mixes it in with the next layer.

The A horizon, or topsoil, is the next layer. Itvaries in thickness from 2.5 centimeters (l inch) in

0 horizonA horizon(litter andtopsoil}

B horizon(subsoil)\'

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OrganicmatterDark, richin humus

Lightcolored

C horizon { }(transition Variedzone)

o p ; ; ; ; ~ o n j ~ ~ Rock orgravelmaterial}Soil profile. Typical soils consist of five distinct layers.The topsoil is the most important to agriculturebecause it contains organic matter and nutrientsessential for plant growth.

some regions to 60 centimeters (2 feet) in the richfarmland of Iowa. Topsoil is generally rich in inorganic and organic materials and is important because it supports crops. It is darker and looser thanthe deeper layers. The organic matter of topsoil,called humus, acts like a sponge, holding moisture.Grasslands have the deepest A horizons. Thethinnest A horizons are found in coniferous forests,tundra, and tropical rain forests . As you shall soonsee, most of the land that governments view as potentially arable lies in the tropics, where the A horizon is practically nonexistent.

The B horizon, or subsoil, is also known as thezone ofaccumulation because it collects minerals andnutrients leached from above. This layer is lightlycolored and much denser than thnopsoil because itlacks organic matter. The next layer, the C horizon,is a transition zone between the parent material below and the soil layers above. The D horizon is theparent material from which soils are derived.

Th e soil profile is determined by the climate(especially rainfall and temperature), parent material, biology, and topography-that is, the same


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soil-building forces discussed in the pre vious section. Soil profiles are histor ies of the interactionamong these factors .

Soil scientists have identified 11 major soiltypes or orders. These are defined primarily by theirdiagnostic horizons-that is , as having a specific soilprofile . Soil profiles tell so il scientis ts and deve lopers whether land is best for agriculture, wildlifehabitat , forestry, pasture, rangeland , or recreation .They also tell us how suitable soil might be for various other uses such as home building, landfills, andhighway construction.

Key ConceptsSoils are typically a rranged in layers. Fo r agriculture,the most important are the upper two layers: the 0horizon, which accumulates organic waste fromplants and animals, and the A horizon, the topsoil.

Barriers to aSustainableAgricultural System

With this brief introduction to soils, we no w tumou r attention to problems facing world agriculture.We will exa min e the challenges that lie ahead as weattempt to forge a sustainable system of agriculture,beginning with the decline in food su pplies.

As already mentioned, as the world populationcontinues to expand, per capita food supplies-theamount of food available per person-are on the decline. This problem is especially acute in the less developed nations. In the more developed nations, incontrast, food surpluses are common and obesity is onthe rise. Part of the reason for the unsustainable decl ine in food production is that agricultural so ils areeroding or deteriorating in quality. In addition, manyfanns are being replaced by highways and cities.Soil ErosionThomas jefferson wrote that "civilization itself restsupon the soil." The first towns, early empires, andpowerful natioris _an all trace their origins to the deliberate use of the soil for agriculture (Chapter 8).Agricultural expert R. Neil Sampson wrote that, inmost places on Earth, "We stand only six inches fromdesolation, for that is the thickness of the topsoil layerupon which the entire life of the planet depends."

Ev erywhere one looks, soil is being washed orblow11 away-that is , eroded by wind and water.Erosion occurs when rock and soil particles are detached by wind or water, transported away, and deposited in another location, often in lakes and

streams. Soil erosion , the loss of soil from land , ison e of the most cri tical problems facing agriculturetoday. It is a problem in the MDCs as well as theLDCs.

So il erosion is classified as either natural or accelerated . As the name implies, natural erosion occurs in areas in the absence of hu man intervention.It generally occurs at such a s low rate tha t new soilis generated fast eno ugh to replace what is los t. Inother words , natural erosion generally occurs at asustainable rate. In contrast, accelerated erosionlargely results from hu man ac tivities such as overgrazing, and it occurs at a rate that ou tstrips the formation of new soil (Figure 11-4). Accelerated erosionis dangerous not just because it removes productivetopsoil , bu t because it decreases soil fertility thatmay cause declines in produc tivity. Studies on cornand wheat indicate that each inch of topsoil lost toerosion results in a 6% decline in productivity. Severe soil erosion may also resul t in the formation ofgullies that make farmland unworkable .

Soil erosion is such a pressing problem becauseas noted earl ier in the chapter, new soil forms veryslowly. Soil erosion also has a number of serious environmental impacts. For instance, pes ticides a ttachto soil particles. Transported to nearby waterwayspesti cide-laden particles may be ingested by fish andother aquatic organisms. They may then be passedto birds and human consumers in the food chainSediment deposited in waterways fills streams and

Soil erosion on rangeland. All soil erosion abovereplacement level bodes poorly fo r far mers and theworld 's people. This ra ngeland in Tunis ia is sufferingfrom ext reme erosion, wh ich not on ly ro bs the land oftopsoil but also greatly reduces its productive capac ity.

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rivers and reduces their capacity to hold water. This ,in turn, increases flooding. Furthermore, sedimentdestroys breeding grounds of fish and other wildlifeand increases the need for dredging harbors andrivers. The World Resources Institute estimates theoff-site damage from soil erosion in the UnitedStates at over $10 billion a year.Since agriculture began in the United States,one-third of the nation's topsoil has been lost to erosion , according to the Soil Co nservation Service.Unfortunately, so il erosion continues today. According to U.S. Department of Agriculture estimates,about l . 7 billion metric tons (1.9 billion tons) oftopsoil vvere lost annually from U .S. farmland from1992 to 1997-840 million tons from wind erosionand 1.06 billion tons from water erosion. Althoughso il erosion is down from earlier years (Figure 11-5) ,the average rate of erosion on U.S. farmland is approximately seven times greater than soil formation ,a situation tha t is clearly unsustainable. Should erosion continue, the U.S. agricultural system could experience substantial declines in productivity.

Unfortunately, little information is available onsoil erosion rates throughout the world. Scientistscurrently estimate that approximately one-third ofthe world's cropland topsoil is being eroded fasterthan it is regenerated. Soil erosion is especially rapidin many of the less developed nations. In China, forexample, the Yellow River annually transports 1.6billion tons of soil from badly eroded farmland tothe sea. The Ganges in India carries twice thatamount. The Worldwatch Institute (a nonprofit or ganization based in Washington, D.C.) estimatesthat 22.5 billion metric tons (25 billion tons) of

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Late 1970s 1982-1987 1987-1992 1992-1997Soil erosion on the decline in the United States. Overthe past three decades soil erosion from wind andwater has declined dramatically. Although it stillexceeds replacement level in many areas, progresshas been substantial.

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topsoil is eroded from the world's croplands each year!At this rate, the world loses about 7% of its croplandtopsoil every 10 years' To pu t this into perspective: Iferosion continues at this rate, 225 billion met ric tonswill be lost in the next decade; this is equivalent tomore than half of the topsoil on U.S. farms.

Soil erosion above the natural rate of soil formation is unsustainable. Year after year, it depletes avaluable resource needed to feed the world's people.It also will make it more difficult to feed th e growing population. Without efforts to halt soil erosion ,malnutrition and starvation could increase in thecoming century.

Key ConceptsSoil is vital to the success of a nation , indeed theworld, but agricu ltural soils are being lost at recordrates in many countries-a trend that is clearly unsustainable.

Desertification:Turning Cropland into DesertEach year millions of acres of cropland, pas tu re, andrangeland are becoming too ariel to be fanned. Thisphenomenon , called desertification , occurs most often in highly vu lnerable semiarid lands-that is,lands that are already fairly dry In such areas, evensmall changes in rainfall or in agricultural practicescan have a profound effect on the ability of land tosupport life.

Numerous factors can be blamed for this problem . On e of th e leading causes is drought: long, dryperiods. Drought may result from both natural climatic changes and changes brought about by humans. Global warming, overgrazing, and defores tation are three human causes. Overcropping semiaridlands- that is, planting th em too frequently-alsocontributes to desertification .

How do global warming, overgrazing, and deforestation cause clrought7 Global warming is discussedin detail in Chapter 21. Global warming is caused bycertain pollutants such as carbon dio xide, which trapheat in the atmosphere. Rising temperature increasesevaporation rates and thus tends to dry the so il invarious regions. Global warming also appears to bechanging climate, especially rainfall patterns. Someareas, scientists predict, will become hotter and drier.Many atmospheiic scientists believe that if globalwarming is no t stopped, changes in rainfall and average daily temperature could be severe enough torender entire agricultural regions such as the midwestern Un ited States un sui tab le for fanning.

Removing vegetation from the land also tendsto alter local climate. Deforestation , for example,

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may decrease rainfall downwind from a site. Why? Awell-vegetated surface acts like a sponge, absorbingmoisture that supports plants and replenishesgroundwater. Some water evaporates, only to fall ondownwind sites, creating a cycle of precipitation andevaporation that continues on down the line. In denud ed areas, however, water tends to run off the sur-face of the land; so less is available for replenishinggroundwater and for nourishing plants. The drierthe landscape, the less water there is to evaporate.This, in turn , tends to decrease rainfall downwind.

The loss of farmland to desertification is a serious problem, especially when combined with otherfactors, including soil erosion and climate change.

Key ConceptsThroughout the world, cropland, rangeland, and pa sture are becom in g too d ry to use because of cli matechange (natural and hum an-induced) and poor landmanagement practices such as overgrazing. Thi sphenomenon, which affects millions of hectares ofland each year, is called desertifica tion. Desertifica-tion destroys mill ions of hectares of farmland eachyear, further decreasing o ur ability to produce food .

How Serious Is the Problem? Desertifica tion is aproblem rooted in overpopulation and unsustainable land-use patterns. It afflicts numerous countriesand regions, including the United States, Africa,Au s tralia, Brazil, Iran, Afghanistan , China, and India. To begin with , a ve ry large portion of the world 'sproductive agricultural land is already experiencingdesertification. Ac cording to the Uni ted Nations Environment Programme (UNEP ), 73% of the world'srangeland and 47% of its rainfed cropland are cur-rently th reatened. About 30% of the world's irr igatedcropland is endangered as well . Making mattersworse, according to UNEP, approximately 9 to 11million hectares (22 to 27 million ac res) of croplandand rangeland become desertified each year.

Desertification is not new to humankind. In theancient Middle East, fo r instance, the des truct ion offorests, overgrazing, and poor agricultural practicescaused a deterioration of the water-absorbing capacity o f the land and redu ced the amount of rain fall.Coupled with a long-term regional warming trend ,the decline in rainfall turned once-productive pastureland and farmland in much of the Fertile Crescent (where agriculture had its roots) into desert.

A more recent example occurred in the UnitedStates in the infamous du st bowl era of the 1930s .This disaster resulted from prolonged drought combined wi th fencepost-to-fencepost cultiva tion of

fields in part to supply Europe with food in the eayears of World War II. During the prolongdrought, crops withered and died. Field after fiturned into an arid tract of dry dirt . Winds sweptparched topsoil into huge dust storms and carrthe topsoil away. Only through extensive consertion measures in the postwar years were farmers ato slowly rebuild their soils. Today, however, somethese gains hav e been lost as farmers attemp t to rafood product ion to increase thei r gross earninSmall dus t bowls are occurring in southern Ca li fnia and Texas. Colorado loses abou t 90 million toof topsoil a year to wind erosion alon e.

Deserti fica tion is especially severe in partsAfrica, especially the sub-Saharan region kn ownthe Sahel. Beginning in 1968, a long-term droughthe Sahel (coupled with overpopulation, overgring, and poor land management) began the rasou thward expansion of the d esert in Ethiopia , Mritania, Mali , Niger, Chad, and Sudan. The Saharaalso spreading northward. An estimated 100 ,0hectares (250 ,000 acres) of range land and croplaare lost in Afr ica each year.

Desertification and erosion are taking a hutoll on world food p roduc tion . In Afri ca, a continstraining un der the pressures of 770 million peoin 1999, we ll over 100 million do not have enoufood to eat. In Ethiopia, nearly one of every thpeop le is malnourished. In Chad , Mozambi qSomalia, and Uganda, four of every ten people malnourished . Food supp lies are declining in LaAmerica as well . The number of m alnourished pschool children in Peru now stands at nearly 70Infant mortality in Brazil con tinues to rise.

Key ConceptsDesertificat ion and soil erosion are dest roy ing agricutu ral land worldwide, contributing to present-day fooshortages and reducing our ab il ity to meet fu ture demands caused by expanding human population.

Farmland ConversionBesides soil erosion and desertification, valuafarmland is being lost by the conve rsion to nonpdu ctive uses , a phenome non called farmland cversion. Expanding cities, new highways, shoppmalls , and other nonfarm uses rob millions of acof farmland each year in the United Sta tes aabroad (Figuren-6) . In Canada, fa rmland near urbcent ers has sometimes been paved over and builtthen re placed. What has replaced it , howeverlower quality farmland. In the United States, an timated 1430 hectares (3500 acres) of rural land



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lost every clay. At this rate , the United States loses530,000 hectares (1.3 million acres) of farmland,rangeland, and pastureland each year. If this continues, one-third of the United States' rural farmlandwill be gone within the next 100 years.

Farmland conversion is a worldwide phenomenon. The former West Germany, for example, losesabout 1% of its agricultural land by conversion every4 years, and France and the United Kingdom loseabout 1% every 5 years. Little is known about therate of agricultural land conversion in the LDCs ofthe world, bu t it is believed to be substantial. Theloss of productive farmland is clearly an unsustainable trend that is made all the more troubling by thecontinual expansion of the world population andlosses from soil erosion and desertification.

Key ConceptsEach year, millions of hectares of productive farmlandare lost to human development-roads, airports,shopping centers, subdivisions, and so on-a phenomenon called farmland convers ion.

Declines in Irrigated Cropland Per CapitaWater is as essential to agriculture as soil and sunlight.Plants need water to grow. Water plays an importantrole in photosynthesis-the sunlight-driven conversion of carbon dioxide into organic food molecules.

Most of the world's cropland is nourished byrainfall. However, a growing percentage of theworld's cropland is irrigated-supplied with waterfrom streams and lakes (surface waters) or fromwells that draw water from the ground (groundwater). In the United States, one-eighth of all croplandis now irrigated. This land produces approximatelyone-third of the nation's food. Globally, about 17%of the world's cropland is irrigated, and that farmland produces about 40% of the nation's food.

From 1950 to 1980, irrigated cropland worldwide more than doubled. In the 1980s and 1990s,however, irrigated cropland increased at a muchslower pace. Because of this slowdown and the continual growth in the population (which grew fasterthan the increase in irrigated cropland), the amountof irrigated farmland per capita began to fall in 1978and clroppecl4% by 1998. It remained fairly stable inthe 1990s ( Figure 11-7). According to the WorlclwatchInstitute, further increases in irrigation are likely tobe modes t. Groundwater depletion and intensecompetition for surface water supplies betweenfarms and cities, for instance, are the main reasonsfor such a prediction. Groundwater is already beingpumped faster than it can be replaced in several rna-

Farmland conversion. Urban sprawl, as shown here in York County,Pennsylvania, swallows up farmland at an alarming rate throughout theworld. Homes and businesses at right occupy what were once cornfields.Once houses and other structures are built, the land is lost forever fromagricultural production, a trend with serious consequences.

jo r agricultural areas, including regions of China,India, the Middle East, Northern Africa, and theUnited States. Water shortages are also evident inmany other areas. Although such trends bode poorlyfor the long-term prospects of world agriculture,there is ho pe. Numerous sustainable solutions exist ,the most important being water conservation (atopic discussed in the next section) .

1970 1980Year 1990Irrigated farmland per capita. Thi s graph shows theworldwide decl ine in irrigated farmland per 1000 people.Because irrigated farmland produces such a largepercentage of he world's food, this trend bodes poorlyfor efforts to feed the ever-growing human population .



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Key ConceptsIrrigated cropland supplies enormous amounts offood to the world's people, but the amount of irr i-gated cropland per capita is on the decline -a t rendthat bodes poorly for world food production. Mea-sures that increase the efficiency of wa ter use mayprove helpful in providing an adequate supply of irri-gation water.

Waterlogging and SalinizationAlthough irrigation greatly increases food production , in many semiarid regions it ha s crea ted so meserious problems that could also significantly reducefood production in the coming decades , furt heradding to declines caused b y soil erosion, desertification, and farmland conversion. Two such problems are wa terlogging and salinization.

Waterlogging occurs when too much water isapplied to farmland. Irrigating poorly dr ained fields,for example, often raises the water table, the upperlevel of th e groundwater (Figure n -8) . If the watertable rises too near the surface, it can fill the airspaces in the soil and suffocate the roots of plants. Italso ma kes soil di fficul t to cultivate. Worldwide,about one-tenth of the irriga ted cropland (a n area

Salinization and waterlogging. Salts and other mineralsaccumulate in the upper layers of poorly drained soil(salinization) when irrigation-waters raise the watertable and water begins to evaporate through thesurface. The rising water table also saturates the soiland kills plant roots (waterlogging). Lowe r arrowsindicate the movement of water from groundwaterinto the topsoil. Upper arrows indicate evaporation.

slightly smaller than Idaho) suffers from waterlogging . Productivity on this land has fa llen approxima tely 20%.

Salinization occurs when irrigation water thatha s accumulated in th e soil evaporates, leaving be hind sa lt s an d minerals once dissolved in it (F igure l l -8) . If not Oushed fro m th e so il, en ormousquantities of this matter can accumulate in thesoil , greatly reducing crop production and makingsome soils im pen e trabl e.

Worldwide, about one-fourth of the irrigatedfarmland suffers from salinization. In th e Un itedStates, the produc tivity of cropland suffering fromsalinization is believed to be reduced up to 25%.Moreover, when sa line bu ildup reaches a crit i callevel, soil b ecomes unproductive an d mu st be abandoned . One expert es timates that l to 1.5 m illionhec tares (2.5 to 3. 75 million acres) of land are abando ned wo rldwide each year because of salinization.Salinization, for example , continues to be a problemin prairie soils. Alt hough it affects on ly about 2% ofthese farmlands , losses are es timated to be as high as$260 million a yea r.

Key ConceptsIrrigation can cause waterlogging, the buildup of ex-cess water in the soil, which suffocates plants. It mayalso cause salinization, the deposition of salts that aretox ic to most plan ts. Waterlogging and salin ization af-fect many mill ions of hectares of land wo rldwide.

Declining Genetic Diversity in Crops and livestockBefore the advent of modern agriculture, grains an dvegetables existed in thousa nd s of varieties . Now,only a few of these varieties are commonl y used. InSri Lanka, for example, fanners once planted 2000varieties of r ice; today, however, only 5 varieties arein use . ln India, 30,000 st rains of rice were on cegrown ; today, 10 varieties a re responsible for abou75% of the nation's rice production .

In most cases, ne w varieties are chosen becausethey are more suitable for machine ha rvesting an dbecause they respond favorably to fertilizer a nd ir rigation water. They also produce higher yields. Asimilar trend is occurring on ranches throughout theworl-d as ranchers adopt breeds developed for maximu m yield. Th e problem , as you shall soon see, isthat huge expanses planted in one spe cies are extremely vulnerable to pests , disease , and adverseweather. To combat th ese problems , notably diseaseand pests, farmers often turn to environmentallydamaging chemical pesticides.

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Key ConceptsThe number of species of cultivated plants and domestic animals has declined dramatical ly. Reducingdiversity resul ts in huge monocultures of geneticallysimilar plants, which make crops more susceptible todisease, adverse weather, insects, and other pestsand more dependent on chemical pesticides.

Th e Green Revolution The trend toward reduced genetic diversity began with development of high-yieldvarieties in the 1960s as part of a worldwide agricultural movement called the Green Revolution. Researchbegan in 1944, when the Rockefeller Foundation an dthe Mexican government established a plant-breedingstation in northwestern Mexico . The program washeaded by Norman Borlaug, a University of Minnesotaplant geneticist wh o developed a high-yield wh eatplant for which he was later awarded a Nobel prize. Before the program began, Mexico imported half of thewheat it consumed each year. By 1956, it had becomeself-sufficient in wheat production, and by 1964 it wasexporting half a million tons pe r year ( Figure 11-9) .

The success in Mexico led to the establishmentof a second p lan t-breeding center in the Philippines.High-yielding rice strains were developed at thiscenter an d introduced into 1ndia in the micl-1960s .Again, the results were spectacular. 1ndia more thandoubled it s rice p roduction in less than a decade.

Important as it was, th e Gr een Revolution contributed greatly to the decrease in species divers ityin cultivated crops. On e of th e mos t important co ncerns was that the ne w crops were n o t as resistant todiseases an d insects. Local varieties of plants are ac climated to their environment; natural se lec tion hasensured this. New varieties, on th e o th er h and , oftenhave little such resistance.

Moreover, as diversity dwind les, huge monocul tu res becom e mo re and more common . Expansivefields of one genetic strain facilitate the sp read ofdisease an d insects. Th e potato famine in lreland inthe 1840s is on e example of the effec ts of reducingcrop diversity. At that time, on ly a few varieties ofpotatoes were p lanted i!l Ireland . When a fungu s(Phytophthora in festans) began to sp read among th eplants , there was little to s top it. Within a few ye ars,two million Irish perished from hu nger and disease ,and anoth er two million left the co untry.

In add it ion to their suscept ibility to disease ,hi gh-yield hybrids are also ge nerally less resistant todrought and flood . In 1980 , th e American p eanutcrop , co nsis ti ng of two varieties, was almos t entirelydes troyed by drought and disease .

The Green Revolution continues. Genetic researchproduced high-yie ld va rieties like the plant on th e left,which replaced lower-yield varieties (not shown) . Thewheat plant on the right is an even higher-yield varietynow under development. Although it produces a lot ofgrain, most seeds are shriveled; and plants tend totopple over under their own weight. The new variety isalso vulnerable to two serious wh eat diseases (rusts).Research is under way to correct these problems.

Th e decline in genetic diversity resulting fromthe Green Revolution an d other developments addsto the unsus tainability of modern agriculture . But italso pr ese nt s a foca l point for change, a way we canreverse th e tren d and ensure a more environmenta lly su s tainable system of food produc tion.

Key ConceptsThe Green Revolution wa s a worldwide effort to improve the productivity of important food crops: wheatand rice. It succeeded in its primary objective s but created a steady decline in genetic divers ity, whi ch makesworld food product ion mo re vulnerable to di srupt ion.



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Habitat Destruction: Contributing to the Loss ofGenetic Diversity The loss of genetic diversityamong crop species is paralleled by an equally troublesome extinction of wild species throughout theworld, especially in the tropics. The loss of speciesin the tropics could adversely affect modern agriculture. Why? Many modern crops came from tropicalregions. Many of their relatives remain there today,growing as they have for centuries. These wild relatives (as well as other species) serve as a source ofnew genetic information for domestic crops to combat drought, disease, and insects. Keeping moderncrops vital and successful, therdore, depends onkeeping their relatives alive and well. The loss ofwild species adds to the deteriorating condition ofagriculture.

Key ConceptsThe loss of wild plant species that gave rise to modern crop species throughou t the world, especia lly inthe tropics, is eroding our capacity to improve cropsand make them more resistant to pests, disease, anddrought.

Politics1 Agriculture1 and SustainabilityGove rnments also add to agriculture's growing list ofproblems , sometimes fostering unsus tainable practices. Consider some examples. Subsidies, payments mad e to farmers from their governments, cancontribute to an unsustainable system of farming. Inthe United States, for example, the federal government subsidizes farmers through price supports. Inthis program, farmers are gi ven a guaranteed pricefor certain crops such as wheat and soybeans. Thishelps keep them in business during bad years-thatis, in years when prices fall . However, this programhas many unforeseen consequences. First, it encourages farmers to plant crops that are insured by thefederal government through price support. As a result, farmers tend to plant one or a few crops. It alsoencourages farmers to plant all of the land they can,even marginal land that may be easily eroded bywind and water. Why not plant every acre if youknow the federal government will pay for you rproduct' This practice encourages huge monocultu res that are susceptible to insects and other pests.To combat them, farmers rely on an arsenal of toxicinsecticides and other chemicals. Many of thesechemicals end up in groundwater and in lakes andrivers, where they poison many species.

Government lending policies can also encourage unsustainable practices. In Mexico, for instance,most cr edit for irrigation systems and roads is givery

to farmers who produce cash crops such as tomatoeand cattle, both fo r export to the United States. Cascrop farms and cattle pastures usurp farmland oncused to produce crops for domestic consumption.

Governments may also dictate policy. IEthiopia, farmers have traditionally left semiarilands fallow for seven-year periods so that nu trienfrom the highly weathered, poor soil cou ld be replenished by natural vegetation . This practice, however, has been condemned by the Ethiopian government , which is in terested in increasing farmproduction . If land is not cultivated with in th reyears, it is confiscated. Unfortunately, bypassing thfallow period results in rapid so il deterioration.

Numerous other examples could be cited herThe important point in all of this is that to createsustainable system of agriculture, laws and policiemust be systematically reexamined and card ully rvised with global susta inability in mind.

Key ConceptsThe problems fac ing world agriculture are not all technica l. Some result from inadequate or se lf-defeatingpolicies and governmenta l intervention. Lawmakersthroughout the world have unwitt ingly fac ilitated thecreat ion of an unsusta inable system of agriculture.

Solutions: Building aSustainableAgricultural System

Providing food for the growing human populatiowill require a variety of policies and actions-botprivate and governmenta l. As is the case with othsocial and environmental issues , one of the most important solutions to famine is family planningslow the growth and perhaps reduce the size of thhuman population. Efforts must also be made to increase food supplies, and such measures must be sutainable. That is, they must no t undermine the longterm health of the global food production system . Iother wo rds , they must protect and imp rove the soiwater, and other resources upon which fanningdependent. Most analys ts recommend a multifaceteapproach that includes efforts to (l ) protect ex istinsoil and water resources ; (2) increase the amountland in production; (3) raise output per hectare farmland- th at is, increase productivity; (4) develoalternative foods; (5) eat lower on the food chain, (6reduce food losses to pests; (7 ) increase the agricutural self-suffic iency of less developed nations; (8enact legislation and policies that ensure a better ditribution of food and more sustainable productio



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methods; and (9) end wars. This sec tion describeseach part of this multifaceted strategy.

Key ConceptsA sustainable system of agriculture consists of practices that produce high-quality food in ways that protect the long-term health and productivity of soils.Creating such a sys tem will requ ire a mu ltifaceted approach , including measures to slow and perhaps stopthe growth of the human popu lat ion .

Protecting Existing Soil and Water ResourcesThe old adage that "an ounce o f prevention is wortha pound of cure" applies to many aspects of ourlives. It also applies to the task of building a sustainable system of agricultu re . In fact, few measuresare as important to creating a sustainable agricultural system as preventive ones: preventing soil erosion, desertifica tion, saliniza tion, waterlogging, andfarmland conversion.

Key ConceptsProtecti ng soil and water resources is the first line ofdefense in meeting prese nt and futu re needs for food.

Soil Conservation: Reducing Soil Erosion Protecting soil from erosion by wa ter and wind is one ofthe most important steps we can take to ensure adequa te food supplies both now and in the futu reand protect the environm en t, too. Fortunately, soilerosion can be minimized and even halted by a variety of simple, o ften cost-effec tive techniques. Thissec tion describes six s trategies: minimum tillage,contour farming, s trip cropping, terracing, gullyreclamation , and shelterbelts.

Key ConceptsOne of the highest prio rities in ma king the transitionto a sustainable system of agriculture is putting anend to excessive soil erosion . Fortunately, there aremany simp le ye t effecti ve measures that ca n ensure asustainable erosion ra te.

Minimum Tillage Farmers typicallyp low their fieldsbefore planting new crops. They then break up theclumps of soil with a device called a disc, making thesoil suitable for sowing seeds. In areas where.soil istoo wet in the spring, farmers plow and disc in thefall, leaving their land barren and subj ect to winderosion during the winter.

Wi th special implements , however, farmers canforgo these costly, time-consum ing, and energy-

Minimum tillage planter. Thi s device is des igned to dig furrows in thepresence of cro p residue, avoiding plowi ng and discing. Leaving the previoucrop residue on the land over the fallow period greatly reduces soil erosion.

in tensive steps and plant right over the previousyear's crop residue (Figure 11-10). Th is technique isone form of minimum tillage, or conse rvationtillage, a strategy that reduces the physical disruption of the soil. According to the U.S. Department ofAgriculture, minimum tillage is prac ticed on about44 million hectares (109 million acres), 37% of allU.S. farmland (Figure 11-11) . Unfortuna tely, this prac tice is not widely used in other count ries.

Because fields are protected much of the year bycrops or crop res idues, so il erosion can be decreasedsubstantially- in some cases by as much as 90%.Minimum tillage also reduces energy consumption byas mu ch as 80% and conserves soil moisture by reducing evaporation. Crop residues can increase habitat for predatory insects that prey on pests, reducing

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Terracing and contour farmingeach reduce soi l erosion byabout so%. When combined,they reduce erosion by 75%.Minimum tillage red uces soilerosion by go%. Whencombined with terracing andcontour farming, soil loss canbe slashed by g8%.

the need for pesticides and subsequen t contamination of the environment (Chapter 23) . Curtailingthe use of heavy machinery on farmfields also has the benefit of reducing soil compaction , which makessoils harder, increases surfacerunoff, and impairs root growth.Thus, by cutting back on machinery use, farmers may find that cropsactually grow more rapidly and

produce more food.Despite its benefits, minimum tillage has seve ral

drawbacks. For example, herbicides, chemicals thatkill weeds, are often used in place of mechanical cultivation to control weeds. In addition, crop residuesmay harbor insec ts that damage crops. Minimumtillage also requires new and cos tly farm equipment.Already strapped for cash, many farmers can't affordthe new equipment. In Canada, this problem hasbeen partially solved by th e Provincial governmen t ofManitoba , which purchased or leased conservationseeding equipment , then made it available to farmersfor a nominal fee . As a resul t , hundreds of thousandsof acres have been brought into minimum tillage.

Key ConceptsReducing the amount of land disturba nce by mi n i-m izing tillage protects the soil from the erosive forcesof wind and rain. This technique, while effective in re-ducing energy demand and erosion, often requiresadditional chemical herbicides to control weeds.

Contour farming. This land is farmed along the contour lines to reduce soilerosion and surface runoff, thus saving soil and mo isture.

Contour Farming On hi lly terrain, crops can beplanted along lines that follow the contour of theland, a technique called contour farming (Figure 11-12) .Planting crops across the direction of water flow onhilly terrain reduces the rate at which water flowsacross the land, resulting in a 50 to 80% reduc tion insoil erosion and a marked increase in water retention.This technique therefore also reduces demand for irriga tion water.

Key ConceptsPlanting crops perpendicular to th e s lope-that is,along the lan d contour lines-reduces so il erosionand increases water retent ion .

Strip Cro pping As Figure 11-13 shows, strip crop ping is a measu re in which fa rme rs alternate st r ipsof two or more crops in single fields on flat or hillyterrain . Strip cropping redu ces wind and watereros ion and in creases productivity. For examp le,farmers ma y alternate row crops such as corn withcover crops such as alfalfa on hilly ter rai n. Wate rflows more easil y through row crops and begins togain momentum , bu t when it reach es the covercrop, its flow is n early stopped. Strip croppingcan be combined with con tour farming to furthe rred uce erosion.

Key ConceptsCrops can be planted in alternating str i ps , a practiceca lled strip cropping. When combined with contourfa rming, th is technique greatly reduces so il erosion.

Strip cropping. St rips of wheat protect rows ofwatermelon in this field in Ch ina .

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Terracing Fo r thousands of years many peopleshave grown cro ps in moun tainous regions using ter-races, small earthen embanl


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Shelterbelts. Rows of trees planted along the margin of farm fie lds protectsoil from the erosive effects of wind and pro tect crops from drying out, too.

rows of trees as windbreaks, or shelterbelts, onfarms in the Great Plains to slow the winds thatcarry soil away (Figure 11-15). Thousands of kilometers of shelterbelts were planted from Texas to NorthDakota.Besides decreasing soil erosion from wind, shelterbelts prevent snow in fields from being blownaway, thus increasing soil moisture. This in turn reduces the demand for irrigation water during thegrowing season and helps replenish groundwatersupplies. Shelterbelts can also improve irrigation efficiency by reducing the amount of water carriedaway from sprinklers by wind. In addition, shelterbelts provide habita t for animals, pest-eating insects,and pollinators. They also protect citrus groves fromwind that blows fruit from trees. Planted aroundfarmhouses , shelterbelts also reduce heat loss onwindy winter clays.

Key ConceptsShelterbelts are rows of trees planted along theperimeter of fields to block wind and reduce soilerosion. Shelterbelts have the added benefit of preventing snow from blowing away from fields, thus increasing soil moistu re content. In addition, she lterbelts provide habitat for u;;eful species, such asinsect-eating birds that help control crop pests .

Overcoming the Economic Obstacles to Soil Erosion Controls Soil erosion control is one of themost important measures needed to build a sustainable system of agriculture. In many less developed na-

tions, however, farmers struggle to meet their basicneeds and claim that they have neither the time nothe means to care properly for the land. Fe>v can seethe benefits of soil conservation because the gaintend to materialize slowly and usually take the formof a decrease in food production rather than an increase in output.Economics and short-term thinking impair soilerosion conuol efforts in the more developed nations as well. Caught between high production costand low prices for grains, fa rmers often ignore soierosion and offset any losses in production by applying synthetic fe rtilizers. These additives artificially help farmers maintain yield, despite the loss insoil and valuable soil nutrients. Despite the importance of soil erosion controls to sustainable agriculture, many farmers are reluctant to invest in thesepractices. Such a view, while understandable, ignores the long-term cost of permitt ing unsustainableloss of soil-an erosion of the productive capacity ofarmland.Governments can promote soil conservation in avariety of ways. One landmark attempt to end the devastating loss of U.S. topsoil was the 1985 Fann BillThis law created a land conservation program (theConservation Reserve Program) that directs the federal government to pay farmers to retire their moshighly erodible cropland from production for 10 yearsand plant trees, grasses, or cover crops to stabilize andrebuild the soil. By 1993, farmers had retired an estimated 14.7 million hectares (36.4 million acres), cutting erosion by an estimated 900 million tons per yearIn 1996, the U.S. Congress passed a farm bill that extended the Conservation Reserve Program to 2002maintaining the protected acreage at slightly less than15 million hectares (36.4 million acres).The 1985 Farm Bill also es tablished a federaprogram that called on farmers to develop soil erosion plans in exchange for eligibility for federal cropinsurance, subsidies, and other benefits . So far, 1.5million farmers have signed up for the program andhave worked with the U.S. Soil Conservation Serviceto develop plans fo r 134 million acres, about 25% oU.S. farmland. These efforts could cut soil erosionon some of the most productive soils in the countryThe 1996 Farm Bill provided additional support fothese efforts by providing $200 million annually toassist farmers technically and financially with conservation measures. Half of the money is earmarkedfor livestock operations. This program is known athe Environmental Quality Incentives ProgramCost-benefit calculations showed that for every dollar invested in the program, the nation saved twodollars in reduced erosion and pollution.



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Key ConceptsFarmers are sometimes reluctant to take measures tocontrol erosion because of their costs. Careful lycrafted government policies can provide econom icincentives to protect soils from the erosive forces ofwind and water.

Preventing Desertification Protecting soil fromdesertification is also needed to preserve croplandand rangeland. Several of the measures designed toprevent soil erosion will be helpful in this vitalgoal. For example , shelterbelts protect soil fromthe drying effects of wind. More direct actions arealso possible. In China, for instance, agriculturalofficials have embarked on an ambitious programto plant a 6900-kilometer (4300-mile) "greenwall" of vegetation to stop the spread of desert inthe northern region (see Spotlight on SustainableDevelopment l l-1) . Contour farming and ter racing both increase soil moisture content and combat desertification. In Australia, huge semicircularbanks of soil are created in the windswept plainsto catch seeds and encourage regrowth in areas denuded by livestock. Better land management-forexample, controls on the number of livestock onrangeland-is also necessary (Chapter 13) . Pollution controls to slow down global warming arealso vital to this effort (Chapter 21) .

Key ConceptsMany measures that protect soil fro m erosion alsomake it less susceptible to desertification. Whencombined with measures to reduce global warmi ng,these steps could help to slow desertification.

Reducing Farmland Conversion Efforts to prevent the spread of cities, the proliferation of highways, and other nonfarm uses of arable land are alsovital to protecting farmland and creating a sustainable future. Slowing the growth of the population isessential. Careful city planning and new zoninglaws could help reduce farmland conversion by ensuring that homes, roads, airports, and businessesare not built on agricultural land. (For more on thistopic, see the Spotlight on Sustainable D e v e l o p ~ e n t and the discussion on urban growth controls inChapter 18.)

Key ConceptsNumerous techniques are available to prevent farm-land conversion, the loss of arable land to highways,airports, subdivisions, and other nonfarm uses.

Saving Irrigated Cropland/Using Water More Effi-ciently As you learned ea rlier in this chapter, irrigated cropland produces a large portion of theworld's food supplies, but huge expanses of irrigatedland are being salinized and waterlogged. Groundwater supplies are also declining very seriously inkey agricultural areas such as the midwesternUnited States. You also learned that the growth in irrigated cropland is not keeping pace with population growth. One of the reasons for this is a lack ofavailable surface water and groundwater.

One way to solve all of these problems is to useexisting water more efficiently. The efficient use ofresources, of course, is a key to building a sustainablesociety. Farmers, for instance, can improve irrigationefficiency through many simple and cost-effectivemeasures. Lining irrigation ditches with cement orplastic can cu t water losses by 30 to 50%, thus freeing up tremendous amounts of water to irrigate otherland. Transporting water in pipes can result in evengreater savings. Subsidies that help support thesecostly efforts can assist farmers all over the world. Itis taxpayer money well spent, say supporters. Farmers can also use drip irrigation systems to deliver water directly to the roots of fruit trees and a few othercrops (Figure 11-16) . Conventional center pivot irrigation systems that once sprayed water into the air(with tremendous losses to evaporation) can bemodified to spray water downward, at a considerablesavings (Figure 11-17). Computer systems can helpfarmers monitor soil moisture so they apply wateronly when it is needed and in the amount required

Increasing the efficiency of irrigation. Trickle sys tems deliver water to roots,cutting evaporation losses substantially. Trickle systems can be used on ly focertain crops, among them strawberries (shown here) and fruit trees.

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202

on Sustainable Development

11-1 The Green Wall of China: Stopping the Spread of DesertChina is a nation in trouble. With a growing population of over 1.25 billion people, China's land isfalling into ruin. Centuries of overgrazing, pooragricultural practices , and deforestation haveresulted in severe erosion and rapidly spreading deserts that gobble up the once-productivecountryside.

The spread of deserts affects the lives of millions of peasants in China. In the highlands ofnorthern China, for example, the land is cut withgullies, some hundreds of meters deep. Erosionfrom the raw, parched Earth is an astounding30-40 metric tons per hectare (12-16 tons of opsoil per acre) per year-far above replacementlevel. In all, some 1.6 billion metric tons are carried into the Yellow River annually, making it oneof the muddiest rivers in the world.

According to one estimate, an area largerthan Italy has turned into desert or semidesert inChina in the last 30 years. Although most of thedesertification is occurring in northern China, fewareas are immune to this problem.

In 1978, the Chinese government launched areforestation project to stem the tide. By plantingtrees, shrubs, and grasses, they hope to form a giant green "wall" across the northern reaches ofthe nation . When completed, the wall will extend6700 kilometers (4000 miles) and will be 400 to1700 kilometers (250 to 1000 miles) wide. This

ambitious project is designed to return much ofthe land now fa ll ing into ruin to productive use.

Between 1979 and 1993, 13 mill ion hectares(32 million acres) were replanted, and 6 millionhectares (15 million acres) were naturally regenerated in mountainous and sandy areas. The nationplanted 5-5 billion trees. Eleven million hectares(27 million acres) of farmland were protectedfrom desertification. Although the program continues, information on the gains are not available.They are most li kely substantial, however.

The Yulin district is one of China's successstories. Before 1949, more than 400 villages and6 towns had been invaded or completely coveredby sand. Today, four major tree belts have beenplanted in the area, decreasing the southwardpush of the desert by 8o% (Figure 1) . Toweringsand dunes now peep through poplar trees, andrice paddies sparkle in the sunshine. Grain production has been replaced by a diversified agricu ltural system, including animal husbandry,forest ry, and crop production. The trees provideshade and help reduce wind erosion that causesthe sand dunes to shift . Shrubs and grasses nowthrive on land once stripped of its rich vegetation. Trees and shrubs grow in gullies, andgrasses carpet slopes. Revegetation helps tohold the soil in place and reverse the local climate change.

Center pivot irrigation. (a) The standard device sprays water into the air, but much of the water evaporates before it hitsthe ground on hot days. (b) By turning the spray nozzle's downward, much more water makes it to the plant.



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Local residents have built a diversified economy in what was once an unproductive desert.Juice from the cherry trees, which thrive in thedesert climate, is rich in vitamin C and aminoacids; it is used to produce soft drinks, pre serves, and beer. Twigs of the desert willow areused to make wicker baskets and trunks , which

Figure 1 Greenbelt_ These trees planted in Ch ina arepart of the effort to stop the spread of desert.

by crops. Applying irrigation water at night or earlyand late in the day when evaporation is lowest canreduce demand by 50% or more. Improvements insoil organic matter through application of manureand compost can also help because organic matteracts as a sponge, holding water in the soil. Efforts toprotect aquifer recharge . zones, areas in whichgroundwater supplies are recharged, c;an also ensurefanners a re liable supply of water (Chapter 14 .

Key ConceptsWater efficiency measures help free up water to ex-pand irrigated cropland.

Preventing Salinization and Waterlogging All wa-ter efficiency meas ures help increase irrigation waterand expand cropland under irrigation, bu t certain

earn local residents $2 million in U.S. currencyevery year.

Despite the encouraging signs in China, areport by the Shanghai-based Wor ld Economic Tribune says that while nearly 10 million hectares(4000 square miles) are planted every year, twicethat amount is still being lost. In the northernprovince of Heilongjiang, home of China's largestconcentration of virgin forest, loggers have re-duced the tree cover from so to 35% in just 30years. Government pricing po licies promote overcutting.

The reforestation project is also plagued by ashortage of money and technical expertise. Be-cause of short-sighted land-use practices, China'sYangtze River, the nation's longest watercourse,could become a second Yellow River. Each year,its tributaries turn muddier from erosion.

Reforestation is an attempt to restore theEarth's vegetative surface, which is vital to building a sustainable future . Efforts such as China'sare needed on most continents to help reversecenturies of land abuse that have spawned thespread of deserts. Replanting forests not onlyslows the spread of deserts; it also helps restorewildlife populations and can help reduce globalwarming, which now threatens the world climate.Adapted from: L. Ming (1988). "Fighting China's Sea ofSand." International Wildlife 18 (6): 38-45, with permission.

measures can reduce salinization and waterlogging.This, in turn, could reduce the annual loss of farm-land. By using computerized sensors that measuresoil moisture, for example, farmers can apply onlythe amount of water needed by crops. This not onlyfrees up water for other crops, it reduces salinizationand waterlogging. Special drainage systems can alsobe installed to draw off excess water and prevent thebuildup of salt and the potential for waterlogging,although such measures are quite costly. As you willsee in Chapter 12, water drained from farm fieldsmay carry high levels of potentially toxic sub-stances. Special care must be taken to avoid solvingone problem (salinization) while creating another(surface water pollution) . Government programscould also discourage irrigation in soils susceptibleto these problems.



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Key ConceptsMore frugal application of irrigation water to cropsand special drainage systems can reduce sa linizationand waterlogging in soils susceptible to the problem.

Soil Enrichment ProgramsSoil erosion controls help preserve farmland from being washed or blown away. Because soil contains nutrients that are essential to plant growth, soil-erosioncontrol methods also protect soil fertility As anygood farmer will tell you, protecting or even enhancing the fertility of the soil is vital to maintaining orincreasing its productivity

Soil fertility can be enhanced by the use of fertilizers and crop rotation. In many locations throughout the world, agricultural soil fertility is maintainedby applying human wastes from homes or sewagetreatment plants-an activity that returns the nutrients of foods we eat to their origin.

Key ConceptsFarming mines the soil, robbing it of valuable nutri-ents, but numerous methods such as applying or-ganic fertil izer and rotating crops can replenish nutri-ents and maintain the health of he soil over the longterm.

Organic Fertilizers On e of the most effectivemeans of replenishing soil fertility is to apply organic fertilizers to cropland and pasture. Organicfertilizers can be waste materials such as cow,chicken, and hog manure and human sewage. Allof these replenish the soil's organic matter and addimportant soil nutrients such as nitrogen andphosphorus.

There are many sources of organic fertilizer.Currently, there are hundreds of millions of head ofsheep, cattle, hogs, and other animals that producebillions of tons of waste. Putting it to good use -making cropland more productive-makes greatsense. It helps recycle nutrients and prevents pollution of water supplies.

Organic lertilizers also include green manureplants grown in a field (hat rather than being-harvested are plowed under. Especially valuable are theleguminous plants such as alfalfa and clover, whichare often grown during "he off-season and plowedunder before food crops are planted.

Soil enrichment wi th organic fertilizers of all sortsprovides many benefits vital to building a sustainableagricultural system. First and foremost, it increases orhelps to maintain soil fertility and crop yield. Because

organic matter acts like a sponge in the soil, orgafertilizers increase the water-retention capabilitiethe soil. Organic matter also provides an environmconducive to the growth of bacteria necessary fortrogen fixation. Organic fertilizers help prevent shin soil acidity, and they tend to prevent the leachinminerals from the soil by rain and snowmelt. In ation, careful application of human wastes on farmlhelps to reduce water pollution by municipal sewtreatment plants (Chapter 22).Organic wastes have been successfully appliesome countries, such as China and India, for myears, bu t this practice is not without its probleone of these is the cost of transporting waste to faby pipelines or trucks, for many cities are situamany miles from arable land. Another problemthat organic waste from municipal sewage treatmplants may be contaminated with pathogenic (disecausing) organisms such as bacteria, viruses,parasites. Theoretically, some of these organicould be taken up by crops and therefore enterhuman food chain. In industrialized nations, muipal waste may be contaminated with toxic hemetals such as mercury and lead coming from faries connected to the plant. Better controls at sewtreatment plants or at the factories that prodthese materials could alleviate the problem.

Key ConceptsUse of organic fertilizers helps farmers maintaineven improve soil conditions and boost crop prodution. This strategy also returns nutrients to the sothus helping to close nutrient cycles and prevent polution of waterways.

Synthetic Fertilizers In the more developed cotries such as Canada, Australia, and the UnStates, farmers apply millions of tons of synthfertilizer to their land each year to boost cropduction. Without these fertilizers, world food duction would fall 40% or more, according toWorldwatch Institute.

Synthetic fertilizers contain three nutrients:trogen, phosphorous, and potassium. Becausethis, synthetic fertilizers only partially restore fertility. Most importantly, they do nothing toplenish organic mat ter or micronutrients (nutrirequired by p l ~ n t s in very small quantity) necesfor proper plant growth and human nutrition.land that is fertilized solely with syntheti c fertilizsoil fertility slowly declines over time. Moreoexcess fertilizer may be washed from the landrains and end up in streams, causing a numbe



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problems (Chapter 22). To prevent the gradual depletion of nutrients and to help develop a mo re sustainable society, many agricultural experts call formuch wider use of organic fertilizers.

Key ConceptsSynthetic fertilizers help boost soil fertility but theyonly partially replenish agricultural soils because theycontain just three of many nutrients needed forhealthy soil: nitrogen, phosphorus, and potassium.

Crop Rotation In modern agriculture, syntheticfertilizers and pesticides have allowed farmers togrow the same crops year after year on the sameplots. This way, farmers can concentrate their effortson crops that they know well. However, this processis generally viewed as unsusta inable because it oftendepletes soil nutrients, increases soil erosion, andcreates serious problems with pes ts and croppathogens.Crop rotation is a practice in which farmers alternate the crops they plant in their fields from oneseason to the next. For example, corn may beplanted for one or two years, followed by alfalfa, acover crop. The cover crop reduces soil erosion andreplenishes soil nitrogen. If the cover crop is plowedunder, it helps to rep lenish organic matter and re turn a variety of valuable nutrients to the soil.Therefore, this simple practice helps build the soi l.Crop rotation has two additional benefits: It redu cespest damage and reduces the need for costly and potentially harmful chemical pesticides (substancesthat kill damaging insec ts, weeds, and otherspecies). Th e reasons for this benefit are explainedin Chapter 23. Properly planned and executed , croprotation can boost yields by 10 to 15%.

Key ConceptsCrop rotation, alternating crops planted in a field oneseason after an other, offers many benefits. Plantingthe proper crops can help replenish soil nutrients . Italso helps reduce erosion, pest damage, and theneed for costly and potentially harmful pesticides.

Increasing the Amount of land in ProductionThere are several ways of meeting increasing demand for food. The previous sec tion described apreventive approach-strategies such as erosioncontrol and organic fertilizers. The other strategy isto develop new supplies. In the past, virtually a ll nations solved the problem of rising food demand byopening up new lands to the plow. Today, however,

that option is quickly vanishing. In most pans of theworld, potentially arable land is in short supply. Inmost of the major industrial nations, for example,farmland reserves are relatively small. In Ca nada,less than 5% of the land is capable of supportingcrops, and virtually all of that land is in production.In Southeast Asia , 92% of the potential agriculturalland is being farmed. In southwestern Asia, mo reland is currently being used than is considered suitable for rain-fed agriculture. Consequently, percapita food production in Asia has begun to fall asthe population continues to grow.

For those countries that have little farmland reserve, efforts to protect soils, manage urban growth ,and reduce population growth offer the greatesthope for meeting future food demand.

Africa and Sou th America have large surplusesof land that could be farmed. Some exper ts be lievethat the nations of these continents should developthis land. However, much of this land is currentlycovered by tropical rain forests. As noted in Chapter6, although the tropical rain forests are rich in plantand animal species, the soils they grow on are poorin nutrients. when stripped of vegetation, thesesoils also are prone to erosion in the intense tropicalrains and may become hardened when exposed tosun (Chapter 6) . The potential for expansion onthese continents is therefore not as great as somewould lead you to believe.

Tapping un farmed grasslands may be an optionin some areas. These soils are rich and productive,bu t this st rategy cou ld severely deplete wildli fe populations and disrup t many of the free services provided by nature-for example, flood control and local climate control.

Key ConceptsGrasslands and forests can be converted to farmlandto meet the risi ng demand for food . In many parts ofth e world, tho ugh, and especially in th e more devel-oped nations, farmland reserves are small. Even incountr ies where there is an abundance of reserveland, much of this land is covered with poor so ils.Furthermore, the ecolog ical cost of converting wildland to farmla nd would be enormous.

Increasing the Productivity of Existing land:Developing Higher-Yield Plants and AnimalsAnother way to increase food supplies is to developnew, higher-yield plants and animals. New, highyield var ieties of rice and wheat developed duringthe Green Revolution, for example, produ ce three to



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five times as much grain as their predecessors. Newvarieties of plants are created by breeding closely related plants to combine the best features of the parents; these are called hybrids.

As the new hybrids were introduced into manypoor nations, the hopes of the Green Revolutiondimmed, however. Farmers soon found that the hybrids required large amounts of wate r and fertilizer,which were una vailable in many areas. Withoutthese inputs, farm yields were not much higher thanthose of local variet ies. In some cases, they were actually lower. Another problem was the high cost ofth e new varieties, which prevented many smallfarmers from buying them. Moreover, new plantswere often more susceptible to insects and disease.

These setbacks stimulated new research to produce varieties that would increase productivitywithout hu ge inputs such as fertilizer. Today, plantbreeders throughout the world are attempting to develop crops with a high nutritional value and greaterresistance to drought, insects, disease, and wind.Plants with a higher photosynthetic efficiency arealso in the offing. Efforts are even under way to inco rporate the nitrogen-fi xing capability of legum es(C hapter 5) into cereal plants such as wheat-achange that would decrease the need for fertilizersand r e d u c ~ : nitrogen depletion.

One exciti ng improvement is a new variety ofcorn, a staple fo r 200 million people worldwide. Because corn is such an important source of caloriesand protein, researchers spent nearly two decadesdeveloping a new variety, quality-protein maize(QPM). Studies show that only about 40% of theprotein in comm on corn is digested and used byhu mans. In cont ras t, roughly 90% of QPM's proteincan be digested and used. In areas where corn is astaple, such as Africa and Mexico , QPM could helpcurb malnutrition . It could also help the residen tso[ these areas become more self-sufficient in foodproduction.

So me researchers are also exploring the use ofperennial crops for agriculture. A perennial is aplant that grows from th e same root system year after year-such as grasses. Today, most agriculturalcrops are annuals, plants that only last one season.Annuals are grown from seeds each year. Preliminary research suggests tha t productivity from perennials may be equal to or sligh tly lo wer than conventional annuals such as wheat, bu t the benefits fromsoil conserva ti on, so il-nutrien t retention , and energy savings may overwhelmingly favor them . Ju s tas new varieties of plants help increase yield, so dofas t-growing varieties of fowl and livestock.

Key ConceptsNumerous efforts are under way to increase the yof plants and the growth rate of animals to increfood production.

Selective Breeding and Genet ic Engineeringforts are being mad e to improve plants and liveby selective breeding. In selec ti ve breeding, oisms containing valuable characteristics are brhopes of acquiring offsprin g with these charactics. This technique, used for hundreds of yeaeffective bu t rather slow. Another, more recenvelopmem being used to improve livestock andspecies is genetic engineerin g.

Genetic engineering is a complex processigned to mechanically transfer desirable genesthe genetic material of an organism. Genes that catt le grow faster, for example, can be transferredthe ova of cattle. If the genes are incorporated intDNA of the ova, the offspring would then carrgene and pass it on in tum to their o ffspring

Ge netic engineering may be used in otherthat improve agriculture. A new strain of bacdeveloped by scientists at the Universi ty of Cania, for example, inhibits the formation of froplants, which may provide farm ers with a way ducing crop damage from early frost. Ot her stists are working on genes that give plants resisto herbicides used to control weeds. A group oentists at the Monsanto Company has develostrain of bacteria that grows on the roots of cornother plants. When eaten by insec ts, the bacterlease a toxic protein that kills the pest. Genethave also introduced certain genes that allow othrive in sa lty soils, and researchers are experiming with genetically engineered bacteria thathelp plants absorb nutrients more efficiently,increasing crop yields. In Canada, genetic engihave developed a new strain of potatoes that pColorado potato beetles. Animal geneticists areworking on ways to improve livestock, combgenes from one species with those of another tprove efficiency of digestion, weight gain, ansistance to disease.

Genetic engineerin g was once touted as a sfor world agriculture. However, researchers a reing that it is more difficult to apply to agricuand much slower than proponents once thoNevertheless, the successes of genetic enginehave fostered ex traordinary enthusiasm in the ness community. Dozens of new companiesformed in recent years, and billions of dollars



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been invested in the fledgling industry. Still, safetyquestions remain. Will the genetically engineeredbacteria escape into the environment , upsetting theecological balance7 Experts agree that, once unleashed, a new form of bacterium or virus would beimpossible to retrieve. Controlling it could provecostly and damaging.

Some individuals have criticized genetic engineering as a means of tinkering with the evolutionaryprocess. Deliberate genetic manipulations, such as thetransfer of chromosomes from one species to another,are different from anything that ordinarily occurs during evolution. Is it right, critics ask, to interfere withthe genetic makeup of living organisms7 Will these intrusions alter the evolution of life on Earth?

Recent research suggests that the dangers of genetic engineering have been blown out of proportion and that genetically engineered bacteria are notgenerally a threat to ecosystem stability. Most scientists agree.At least two studies now indicate that genetically engineered bacteria th

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