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12.1 Introduction

Agriculture places a serious burden on the envi-ronment in the process of providing humanitywith food and fibres. It is the largest consumer ofwater and the main source of nitrate pollution ofgroundwater and surface water, as well as the prin-cipal source of ammonia pollution. It is a majorcontributor to the phosphate pollution of water-ways (OECD, 2001a) and to the release of thepowerful greenhouse gases (GHGs) methane andnitrous oxide into the atmosphere (IPCC, 2001a).Increasingly, however, it is recognized that agricul-ture and forestry can also have positive externali-ties such as the provision of environmental servicesand amenities, for example through water storageand purification, carbon sequestration and themaintenance of rural landscapes. Moreover,research-driven intensification is saving vast areasof natural forest and grassland, which would havebeen developed in the absence of higher crop,meat and milk yields. But conversely, intensifica-tion has contributed to the air and water pollutionmentioned above (Nelson and Mareida, 2001;Mareida and Pingali, 2001), and in some instancesreduced productivity growth because of soil and water degradation (Murgai, Ali and Byerlee, 2001).

Quantification of the agro-environmental impactsis not an exact science. First, there is considerabledebate on their spatial extent, and on the magni-tude of the current and long-term biophysicaleffects and economic consequences of the impact ofagriculture. Much of the literature is concernedwith land degradation, especially water erosion.Moreover, most of the assessments are of physicaldamage, although a few attempts have been madeto estimate the economic costs of degradation as aproportion of agricultural GDP. Scherr (1999)quotes estimates of annual losses in agriculturalGDP caused by soil erosion for a number of African countries, which can be considerable.Unfortunately these aggregate estimates can bemisleading, and policy priorities for limitingimpacts based on physical damage may not trulyreflect the costs to the economy at large. Second,the relative importance of different impacts maychange with time, as point sources of pollution areincreasingly brought under control and non-pointsources become the major problem. Lastly, offsitecosts can be considerably greater than onsite costs.

These important analytical limitations areapparent from recent estimates of the externalenvironmental costs of agriculture in various devel-oped countries given in Pretty et al. (2001). Theseestimates suggest that in developing countries over

Agriculture and the environment:changing pressures,

solutions and trade-offs

12CHAPTER

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the next 30 years greater consideration should begiven to air pollution and offsite damage becausetheir costs may exceed those of land and waterpollution, loss of biodiversity and onsite damage. Itshould be noted that a large proportion of theseenvironmental costs stems from climate changeand its impacts, which are still very uncertain (seeChapter 13).

It is generally accepted that most developingcountries will increasingly face the type of agro-environmental impacts that have become so seriousin developed countries over the past 30 years ormore. The commodity production and input useprojections presented in Chapters 3 and 4 providean overall framework for assessing the likelyimpacts of agricultural activities on the environ-ment over the next 30 years in developing coun-tries. Several large developing countries alreadyhave average fertilizer and pesticide applicationrates exceeding those causing major environmentalproblems in developed countries. Similarly, somedeveloping countries have intensive livestock unitsas large as those in Europe and North America thatare regarded as serious threats to waterbodies(OECD, 2001a).

Moreover, the experience of agro-environ-mental impacts in developed countries can giveadvance warning to developing countries whereagro-ecological conditions are similar to those inOECD countries. Developing countries are likely toface similar problems when adopting similarpatterns of intensification. They can use the expe-rience of developed countries to identify some ofthe policy and technological solutions to limit oravoid negative agro-environmental impacts, and toidentify the trade-offs. They can also estimate theeconomic costs (externalities) of the agro-environ-mental impacts of intensive agriculture that are notcurrently reflected in agricultural commodityprices, and these costs can provide a basis for policyand technology priority setting.

It will be argued that higher priority than iscurrently the case should be given to lowering agri-culture’s impact on air and water. The remainderof this chapter assesses the changing pressures onthe environment from agriculture, using theprojections for land, water, agrochemical input andtechnological change given in earlier chapters. Itexamines the main technology and policy optionsfor limiting agriculture’s negative impacts on the

environment and widening its positive ones.Finally, it considers the range of situations andtrade-offs that may influence the uptake of theseoptions. The important issue of climate change isexamined both here and in Chapter 13. Thischapter examines the role of agriculture as adriving force for climate change, while Chapter 13examines the impact of climate change on agricul-tural production and food security.

12.2 Major trends and forcesIt is clear from the crop production projectionspresented in Chapter 4 that the key issue for thefuture is the environmental pressure from intensi-fication of land use, rather than land cover or landuse changes alone. Some 80 percent of the incre-mental crop production in developing countrieswill come from intensification and the remainderfrom arable land expansion (Table 4.2). Thus thedominant agro-environmental costs and benefitsover the projection period will continue to be thosestemming from the use of improved cultivars andhigher inputs of plant nutrients and livestock feeds,together with better nutrient management andtillage practices, pest management and irrigation.Nonetheless, extensification of agriculture in envi-ronmentally fragile “hot spots” or areas high inbiodiversity will also remain of continuing concern.

The positive benefits of these changes willinclude a slowdown of soil erosion and at least aslower increase in pollution from fertilizers andpesticides. Likely outcomes on the negative side area continuing rise in groundwater nitrate levelsfrom poor fertilizer management, further land andyield losses through salinization, and growing airand water pollution from livestock.

The main agro-environmental problems fall intotwo groups. First, there are those that are global inscale such as, for example, the increase in atmos-pheric concentrations of the GHGs carbon dioxide(CO2) through deforestation, and nitrous oxide(N2O) arising from crop production (Houghton etal., 1995; Mosier and Kroeze, 1998). The secondgroup of problems is found in discrete locations ofthe major continents and most countries, but atpresent has no substantive impact at the globallevel. Examples are the salinization of irrigatedlands and the buildup of nitrate fertilizer residues

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AGRICULTURE AND THE ENVIRONMENT:CHANGING PRESSURES, SOLUTIONS AND TRADE-OFFS

in groundwater and surface water. These problemsfirst emerged in the developed countries in the1970s as a consequence of agricultural intensifica-tion. However, they have become of increasingimportance in some developing countries duringthe past decade or so, and are destined to becomemore widespread and more intense unless there is abreak from current policy and technological trends.

Most of the negative impacts from agricultureon the environment can be reduced or preventedby an appropriate mix of policies and technologicalchanges (see, for example, UN, 1993; Alexandratos,1995; Pretty, 1995; and Conway, 1997). There isgrowing public pressure for a more environmen-tally benign agriculture. Countries also have tocomply with the WTO Agreement on Agricultureand the UNCED Conventions (particularly theFramework Convention on Climate Change). Thisforces countries to reduce commodity price distor-tions and input subsidies, and encourages them toremove other policy interventions that tend toworsen agro-environmental impacts, and to inte-grate environmental considerations explicitly intoagricultural policies.

At the national level, there is now a range ofpolicy options available to correct past agro-envi-ronmental mistakes and to prevent or limit futureones. The main problems were first recognized inthose developed countries that embarked on agri-cultural intensification in the 1940s and 1950s, e.g.France, the United Kingdom and the United States.These countries started to formulate correctivemeasures soon afterwards. Their experience canhelp other countries embarking on intensificationto avoid or moderate some of the problems. Somedeveloping countries, for example, have introducedinstitutional mechanisms to promote environmen-tally benign technologies more rapidly than thedeveloped countries at a comparable point ofeconomic development. Moreover, the responseshave not been only at the public sector level.Farmers in both developed and developing coun-tries have also made a significant contribution byspontaneously creating or adopting environmen-tally benign technologies or management practices.

At the international level, there is now wideendorsement of the precautionary principle, underwhich countries accept the need to introduce correc-tive actions at an early stage and possibly before allof the scientific justification is in place (UN, 1993).

International action has also been taken tostrengthen research on the biophysical changes thatagriculture is causing (Walker and Steffen, 1999),and to monitor the key indicators of agro-ecosystemhealth (ICSU/UNEP/FAO/UNESCO/WMO, 1998;OECD, 1991, 2001b) so as to understand and giveadvance warning of any threats to agriculturalsustainability.

12.3 Changing pressures on the environment

12.3.1 Agriculture’s contribution to airpollution and climate change

Public attention tends to focus on the more visiblesigns of agriculture’s impact on the environment,whereas it seems likely that the non-visible or lessobvious impacts of air pollution cause the greatesteconomic costs (Pretty et al., 2001). Agricultureaffects air quality and the atmosphere in four mainways: particulate matter and GHGs from land clear-ance by fire (mainly rangeland and forest) and theburning of rice residues; methane from rice andlivestock production; nitrous oxide from fertilizersand manure; and ammonia from manure and urine.

Pollution from biomass burning. Soot, dust andtrace gases are released by biomass burning duringforest, bush or rangeland clearance for agriculture.Burning is traditionally practised in “slash andburn” tropical farming, in firing of savannahregions by pastoralists to stimulate forage growthand in clearing of fallow land and disposing of cropresidues, particularly rice. This burning has hadmajor global impacts and has caused air pollutionin tropical regions far away from the source of the fires.

Two developments should result in an appre-ciable fall in air pollution from biomass burning.Deforestation is often achieved by burning, or fireis used after timber extraction to remove theremaining vegetation (Chapter 6). The projectedreduction in the rate of deforestation will slowdown the growth in air pollution. The shift fromextensive to intensive livestock production systems(Chapter 5) will reduce the practice of rangelandburning under extensive grazing systems, althoughthe latter systems seem likely to remain dominant

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in parts of sub-Saharan Africa. The growth in thecontribution of crop residues may also slow downbecause of the projected very slow growth in riceproduction (Chapters 3 and 4). Climate changeitself, however, may cause temperatures to rise inthe dry season, increasing fire risks and thusincreasing pollution from biomass burning in someareas (Lavorel et al., 2001).

Greenhouse gas emissions. For some countries, thecontribution from agriculture to GHG emissions isa substantial share of the national total emissions,although it is seldom the dominant source. Itsshare may increase in importance as energy andindustrial emissions grow less rapidly than in thepast while some agricultural emissions continue togrow (Table 12.1). There is increasing concern notjust with carbon dioxide but also with the growth ofagricultural emissions of other gases such asmethane, nitrous oxide and ammonia arising fromcrop and livestock production. In some countries

these can account for more than 80 percent ofGHG emissions from agriculture.

The conversion of tropical forests to agricul-tural land, the expansion of rice and livestockproduction and the increased use of nitrogen fertil-izers have all been significant contributors to GHGemissions. Agriculture now contributes about 30percent of total global anthropogenic emissions ofGHGs, although large seasonal and annual varia-tions make a precise assessment difficult(Bouwman, 2001). Tropical forest clearance andland use change were major factors in the past forcarbon dioxide emissions, but are likely to play asmaller role in the future (see Chapters 4 and 6).More attention is now being given to methane(CH4) and nitrous oxide (N2O), since agriculture isresponsible for half or more of total global anthro-pogenic emissions of these GHGs (Table 12.1).

Methane from ruminant and rice production.Methane is a principal GHG driving climate

Gas Carbon dioxide Methane Nitrous oxide Nitric oxides Ammonia

Main effects Climate change Climate change Climate change Acidification AcidificationEutrophication

Agricultural Land use change, Ruminants (15) Livestock Biomass Livestock (includingsource especially (including burning (13) manure applied to

deforestation manure applied farmland (44)

(estimated % to farmland) (17)

contribution to

total global Rice production Mineral Manure and Mineral fertilizers emissions (11) fertilizers (8) mineral (17)

fertilizers (2)

Biomass Biomass Biomassburning (7) burning (3) burning (11)

Agricultural 15 49 66 27 93

emissionsas % of

total anthropogenic

sources

Expected changes Stable or From rice: stable 35-60% From livestock:

in agricultural declining or declining increase rising by 60%

emissions to 2030

From livestock:

rising by 60%

Main sources: Column 2: IPCC (2001a); column 3: Lassey, Lowe and Manning (2000); columns 4, 5 and 6: Bouwman (2001); FAO estimates.

Table 12.1 Agriculture’s contribution to global greenhouse gas and other emissions

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AGRICULTURE AND THE ENVIRONMENT:CHANGING PRESSURES, SOLUTIONS AND TRADE-OFFS

change. Its warming potential is about 20 timesmore powerful than carbon dioxide.1 Globalmethane emissions amount at present to about 540 million tonnes p.a., increasing at an annualrate of 20-30 million tonnes. Rice productioncurrently contributes about 11 percent of globalmethane emissions. Around 15 percent comes fromlivestock (from enteric fermentation by cattle,sheep and goats and from animal excreta). Thelivestock contribution can be higher or lower at thenational level depending on the extent and level ofintensification. In the United Kingdom andCanada the share is over 35 percent.

The production structure for ruminants indeveloping countries is expected to increasinglyshift towards that prevalent in the industrial coun-tries. The major share of cattle and dairy produc-tion will come from feedlot, stall-fed or otherrestricted grazing systems and by 2030 nearly allpig and poultry production will also be concen-trated in appropriate housings. Much of it will beon an industrial scale with potentially severe localimpacts on air and water pollution.

The livestock projections in this report(Chapter 5) entail both positive and negative impli-cations for methane emissions. The projectedincrease in livestock productivity, in part related toimprovements in feed intake and feed digestibility,should reduce emissions per animal. Factorstending to increase emissions are the projectedincrease in cattle, sheep and goat numbers and theprojected shift in production systems from grazingto stall-feeding. The latter is important becausestorage of manure in a liquid or waterlogged stateis the principal source of methane emissions frommanure, and these conditions are typical of thelagoons, pits and storage tanks used by intensivestall-feeding systems. When appropriate technolo-gies are introduced to use methane in local powerproduction, as has been done in some South andEast Asian countries, the changes can be beneficial.If emissions grow in direct proportion to theprojected increase in livestock numbers and incarcass weight or milk output (see Chapter 5),global methane emissions could be 60 percenthigher by 2030. Growth in the developed regionswill be slow, but in East and South Asia emissions

could more than double, largely because of therapid growth of pig and poultry production inthese regions.

Rice cultivation is the other major agriculturalsource of methane. The harvested area of rice isprojected to expand by only about 4.5 percent by2030 (Table 4.11) depending on yield growthrates, and possibly on the ability of technologicalimprovements to compensate for climate-change-induced productivity loss if this becomes serious(Wassmann, Moya and Lantin, 1998). Totalmethane emissions from rice production will prob-ably not increase much in the longer term andcould even decrease, for two reasons. First, abouthalf of rice is grown using almost continuousflooding, which maintains anaerobic conditions inthe soil and hence results in high methane emis-sions. However, because of water scarcity, labourshortages and better water pricing, an increasingproportion of rice is expected to be grown undercontrolled irrigation and better nutrient manage-ment, causing methane emissions to fall. Second,up to 90 percent of the methane from rice fields isemitted through the rice plant. New high-yieldingvarieties exist that emit considerably less methanethan some of the widely used traditional andmodern cultivars, and this property could bewidely exploited over the next ten to 20 years(Wang, Neue and Samonte, 1997).

Nitrous oxide. Nitrous oxide (N2O) is the otherpowerful GHG for which agriculture is the domi-nant anthropogenic source (Table 12.2). Mineralfertilizer use and cattle production are the mainculprits. N2O is generated by natural biogenicprocesses, but output is enhanced by agriculturethrough nitrogen fertilizers, the creation of cropresidues, animal urine and faeces, and nitrogenleaching and runoff. N2O formation is sensitive toclimate, soil type, tillage practices and type andplacement of fertilizer. It is also linked to therelease of nitric oxide and ammonia, whichcontribute to acid rain and the acidification ofsoils and drainage systems (Mosier and Kroeze,1998). The current agricultural contribution to total global nitrogen emissions is estimated at4.7 million tonnes p.a., but there is great uncer-

1 Power is measured in terms of the global warming potential (GWP) of a gas, taking account of the ability of a gas to absorb infrared radiation andits lifetime in the atmosphere.

336

tainty about the magnitude because of the widerange in estimates of different agriculturalsources (Table 12.2).

Nitrogen fertilizer is one major source of nitrousoxide emissions. The crop projections to 2030 implyslower growth of nitrogen fertilizer use comparedwith the past (Table 4.15 and Daberkov et al., 1999).Depending on progress in raising fertilizer-use effi-ciency, the increase between 1997/99 and 2030 intotal fertilizer use could be as low as 37 percent. Thiswould entail similar or even smaller increases in thedirect and indirect N2O emissions from fertilizerand from nitrogen leaching and runoff. Currentnitrogen fertilizer use in many developing countriesis very inefficient. In China, for example, which isthe world’s largest consumer of nitrogen fertilizer, itis not uncommon for half to be lost by volatilizationand 5 to 10 percent by leaching. Better onfarmfertilizer management, wider regulatory measuresand economic incentives for balanced fertilizer useand reduced GHG emissions, together with techno-logical improvements such as more cost-effectiveslow-release formulations should reduce these lossesin the future.

Livestock are the other major source of anthro-pogenic nitrous oxide emissions (Mosier et al.,1996; Bouwman, 2001). These emissions arise inthree ways.

First, from the breakdown of manure applied asfertilizer, primarily to crops but also to pastures.The proportion of manure thus used is difficult toestimate, but it is probably less than 50 percent.Moreover, there are opposite trends in its use. Inthe developed countries, growing demand fororganic foods, better soil nutrition managementand greater recycling is favouring the increased useof manure. In the developing countries, with astrong growth in industrial-scale livestock produc-tion separate from crop production, and withdecreasing labour availability, there is a trend torely more on mineral fertilizers to maintain or raisecrop yields. The second source is dung and urinedeposited by grazing animals. The emissions fromthis source are higher for intensively managedgrasslands than for extensive systems (Mosier et al.,1996). Similarly, emissions from animals receivinglow-quality feeds are likely to be less than withhigher-quality feeds. Since shifts are expected from

Million tonnes N p.a. Mean value Range

Natural sources

Oceans 3.0 1-5

Soils total, of which: 6.0 3.3-9.7

Tropical soils Wet forest 3.0 2.2-3.7

Dry savannahs 1.0 0.5-2.0

Temperate soils Forests 1.0 0.1-2.0

Grasslands 1.0 0.5-2.0

Subtotal natural sources 9.0 4.3-14.7

Anthropogenic sources

Agriculture total, of which: 4.7 1.2-7.9

Agricultural soils, manure, fertilizer 2.1 0.4-3.8

Cattle and feedlots 2.1 0.6-3.1

Biomass burning 0.5 0.2-1.0

Industry 1.3 0.7-1.8

Subtotal anthropogenic sources 6.0 1.9-9.6

Total all sources 15.0 6.2-24.3

Source: Mosier and Kroeze (1998), modified using Mosier et al. (1996).

Table 12.2 Global N2O emissions

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AGRICULTURE AND THE ENVIRONMENT:CHANGING PRESSURES, SOLUTIONS AND TRADE-OFFS

extensive to intensive production systems and fromlow- to higher-quality feeds, it can be assumed thatthere will be an increase in N2O emissions fromdeposited dung and urine. The third source isfrom the storage of excreta produced in stall-feeding or in intensive production units. This mayproduce a reduction in emissions since, on average,stored excreta produce about half as much N2O asexcreta deposited on pastures (Mosier et al., 1996).

Changes in manure production over time havebeen estimated using the projected growth in live-stock populations (allowing for differences betweencattle, dairy, sheep and goats, pigs and poultry).The amounts per head have been adjusted on aregional basis to allow for projected changes incarcass weight and milk output. Emission rates havebeen adjusted for the assumed shifts from extensiveto stall-fed systems. Based on these assumptions andestimates, the total production of manure isprojected to rise by about 60 percent between1997/99 and 2030. However, N2O emissions areprojected to rise slightly more slowly (i.e. by about50 percent) because of the switch from extensive tostall-fed systems. This relative environmental gainfrom intensification has to be seen against the rise inammonia and methane emissions and the probablegrowth in point-source pollution that the intensivelivestock units will generate. This latter cannot bequantified but is a very serious problem in anumber of developed and developing countries (deHaan, Steinfeld and Blackburn, 1998).

Ammonia. Agriculture is the dominant source ofanthropogenic ammonia emissions, which arearound four times greater than natural emissions.Livestock production, particularly cattle, accountsfor about 44 percent, mineral fertilizers for 17 percent and biomass burning and crop residuesfor about 11 percent of the global total (Bouwmanet al., 1997; Bouwman, 2001). Volatilization ratesfrom mineral fertilizers in developing countries areabout four times greater than in developed coun-tries because of higher temperatures and lower-quality fertilizers. Losses are even higher frommanure (about 22 percent of the nitrogen applied).

Ammonia emissions are potentially even moreacidifying than emissions of sulphur dioxide andnitrogen oxides (Galloway, 1995). Moreover, futureemissions of sulphur dioxide are likely to be loweras efforts continue to reduce industrial and

domestic emissions and improve energy-use efficiency, whereas there is little action on reducing agriculture-related emissions. Theammonia released from intensive livestock systemscontributes to both local (Pitcairn et al., 1998) andlonger-distance deposition of nitrogen (Asman,1994). This causes damage to trees and acidifica-tion and eutrophication of terrestrial and aquaticecosystems, leading to decreased nutrient avail-ability, disruption of nitrogen fixation and othermicrobiological processes, and declining speciesrichness (UNEP/RIVM, 1999).

The livestock projections of this study are basedon changes in both animal numbers and in produc-tivity, as determined by changes in carcass weight ormilk output per animal. It is assumed that thevolume of excreta per animal, which is the mainsource of the ammonia, increases over time inproportion to carcass weight, which in turn is areflection of the increase in the use of feed concen-trates. Table 12.3 gives estimates of ammonia emis-sions in 1997/99 and 2030 using these assumptions.The projected increase for the developing countries(80 percent) is significantly higher than the increase(50 percent) given in Bouwman et al. (1997).

These projections have three main environ-mental implications. First, all the developingregions potentially face ammonia emission levelsthat have caused serious ecosystem damage in thedeveloped countries. Second, emissions maycontinue to rise in the developed countries, addingto the already serious damage in some areas. Andthird, in East Asia and Latin America, a highproportion of the emissions will come from inten-sive pig production systems, in which emissionreduction is more difficult. Since many of theseintensive production units are located where thereis a large demand, the downwind and downstreameffects are likely to be concentrated near largeurban populations, often on river plains andcoastal plains that are already subject to a highchemical and particulate pollution load.

12.3.2 Agriculture’s impact on land

In recent decades the most important environ-mental issues concerning land have been landcover change, particularly deforestation, and landuse intensification, especially its impact on landdegradation. The future picture concerning land

338

Number of animals Emissions NH31997/99 2030 1997/99 2030

(in millions) (’000 tonnes N p.a.)

World

Total 30.34 48.60

Cattle and buffalo 1 497 1 858 13.09 19.51

Dairy 278 391 5.35 9.98

Sheep and goats 1 749 2 309 2.02 3.50

Pigs 871 1 062 6.62 9.25

Poultry 15 119 24 804 3.27 6.35

Developing countries

Total 21.35 38.55

Cattle and buffalo 1 156 1 522 9.33 15.34

Dairy 198 312 3.63 8.08

Sheep and goats 1 323 1 856 1.59 3.02

Pigs 579 760 4.52 7.02

Poultry 10 587 19 193 2.29 5.09

Industrial countries

Total 6.67 7.24

Cattle and buffalo 254 243 3.03 3.18

Dairy 41 44 1.02 1.21

Sheep and goats 341 358 0.33 0.34

Pigs 210 220 1.51 1.58

Poultry 3 612 4 325 0.78 0.93

Transition countries

Total 2.32 2.80

Cattle and buffalo 87 94 0.74 1.00

Dairy 39 35 0.69 0.69

Sheep and goats 85 95 0.10 0.14

Pigs 81 82 0.59 0.65

Poultry 920 1 287 0.20 0.32

Note: Figures for the base year are from Mosier and Kroeze (1998).

Table 12.3 Ammonia emissions implied by the livestock projections

cover change is a continuing slowing down of theconversion of forests to areas for crop or livestockproduction; no appreciable change in grazing area; and continued growth of protected areas.However, in the case of land degradation, there arestill widely differing opinions about future trends,and the empirical basis for making firm projectionsremains weak.

Land cover change. In the past much of the pres-sure for land cover change came from deforesta-tion, but this is likely to slow down in future. Theprocess of deforestation will continue in the tropicsbut at a decelerating rate, and in a number ofmajor developing countries the extent of forest willactually increase. In Latin America, for example,governments have removed some of the policydistortions that encouraged large farmers and

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AGRICULTURE AND THE ENVIRONMENT:CHANGING PRESSURES, SOLUTIONS AND TRADE-OFFS

companies to create pastures on deforested land.However, deforestation by smallholders has notbeen reduced. In West Africa, almost no primaryrain forest is left, and over 80 percent of the popu-lation is still rural and growing at 2.5-3 percent p.a.– a situation that is likely to continue until non-agricultural employment opportunities are found.

The total extent of grassland is likely todecrease. In most developing regions the generaltrend is away from extensive grazing towardsmixed farming and improved pastures or inten-sive feedlot and stall-fed systems. It is assumedthat there will be no substantial development ofnew grassland. Some of the more marginal range-lands and pastures are likely to be abandoned asherders and other livestock producers leave theland for better-paid jobs outside agriculture, ashappened in parts of Europe after about 1950(CEC, 1980). In the absence of grazing pressurethese areas will revert to forest or scrub. Some ofthe better grazing land will be converted to crop-land or urban land, with the loss being compen-sated by improving productivity on the remainingland rather than by clearing new land. At thenational level some countries will diverge fromthis global picture. Countries such as China, someCommonwealth of Independent States countriesand parts of South America still have the potentialfor major increases in the use of natural grass-lands (Fan Jiangwen, 1998).

Net arable land expansion in developing coun-tries is projected to fall from about 5 million ha p. a.over the past four decades to less than 3.8 million hap.a. over the period to 2030 (Table 4.7). This netincrease takes into account the area of croplandgoing out of use because of degradation, which someargue is in the order of 5 to 6 million ha p.a. (UNEP,1997). It also takes into account land abandonedbecause it is no longer economically attractive tofarm or as a result of changes in government policy,and land taken up by urbanization. It does not,however, take account of the area that is restored touse for reasons other than crop production, e.g. aspart of agricultural carbon sequestration policies. Inthe future such areas could be substantial.

Even though an overall slowdown in the expan-sion of agricultural land is expected, there arethree areas of concern. First, the frequency orintensity of cultivation of formerly forested slopelands will probably increase. Second, further

drainage of wetlands will result in loss of biodiver-sity and of fish spawning grounds, with increasedcarbon dioxide but lower methane emissions.Third, high-quality cropland will continue to belost to urban and industrial development.

Cultivation of slope lands. Uplands are particularlyprone to water erosion where cultivated slopes aresteeper than 10 to 30 percent, lack appropriate soil conservation measures and rainfall is heavy.Substantial areas of land are at risk (Bot,Nachtergaele and Young, 2000), although it is notpossible to make global or even regional estimatesof how much of this is currently cropped land. InSoutheast Asia, land pressure caused by increasingpopulation has extended the use of steep hillslopes particularly for maize production. This hasled to a very significant increase in erosion onlands with slopes of over 20 percent (Huizing andBronsveld, 1991).

There are two main environmental concernsfor the future. First, more forest may be cleared forcultivation, resulting in the loss of biodiversity andincreased soil erosion. Second, existing cultivatedslopes may be cropped more intensively, leading togreater soil erosion and other forms of land degra-dation (Shaxson, 1998).

In countries such as Bhutan and Nepal withlimited flat land left to develop, almost all of theadditional land brought into cultivation in thefuture will be steep lands prone to erosion unlesswell terraced, or protected by grass strips, conserva-tion tillage, etc. In Nepal, for example, soil erosionrates in the hills and mountains are in the range of 20 to 50 tonnes/ha/p.a. in agriculture fields and 200 tonnes/ha/p.a. in some highly degraded water-sheds (Carson, 1992). Crop yields in these areasdeclined by 8 to 21 percent over the period 1970-1995. Such losses seem likely to continue, unlessthere are substantial changes in farmer incentivesfor soil conservation and wider knowledge at alllevels of the economic and environmental benefitsthat conservation provides. In countries with lessacute land pressure there may be a slowing down inthe expansion of cropped slope lands, but there willstill be pressures for the intensification of cultivationand hence the risk of greater erosion.

Deforestation of slope lands was a seriousconcern in the past but may slow down over theprojection period. On the one hand, a good part of

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the 3.8 million ha annual net new cropland overthe period to 2030 will probably come from forestconversion. A high proportion will have steepslopes and will be in zones with high rainfall, so thewater erosion risk will be high unless suitablemanagement techniques are adopted (Fischer, vanVelthuizen and Nachtergaele, 2000). On the otherhand, large areas of existing crop and grazing land– much of which is likely to be slope land – couldrevert to forest and scrub because of land aban-donment and outmigration.

Reclamation of wetlands. Historically, the reclama-tion of wetlands has made a major contribution toagricultural growth and food security. Significantparts of the rich croplands of the Mississippi basinin the United States, the Po Valley in Italy and theNile Delta in Egypt are reclaimed wetlands. Thedeveloping countries have over 300 million ha ofnatural wetlands that are potentially suitable forcrop production. Some of the wetlands willinevitably be drained for crop production. Part willbe in countries with relatively large land areas percapita but limited areas with adequate rainfall orirrigation potential, e.g. Senegal. Part will be incountries where much of the potential arable landis not well suited for sustainable agriculturebecause of steep slopes or thin, fragile soils, so thedevelopment of wetlands is therefore a moreattractive option, e.g. Indonesia.

Wetlands are flat, and by definition wellwatered. In the case of some Sahelian countriesthey are potentially important contributors to foodsecurity (Juo and Lowe, 1986). Past experience inthe inland valleys of the Sahelian belt suggest,however, that reclamation for agriculture has beenof doubtful benefit despite huge internationalinvestments. Many irrigation schemes have failedthrough mismanagement and inadequate infra-structure maintenance, civil unrest and weakmarket development. The soils in this region arepotentially productive once certain constraints areovercome, e.g. acid sulphate, aluminium and irontoxicity and waterlogging.

Assuming that the present rate of drainage ofwetlands declines, the total conversion over theprojection period will amount to a relatively smallpart of the 300 million ha they currently cover, buteven this would carry some environmental risks.There may be damage to the hydrological functions

of wetlands, such as groundwater recharge andnatural flood relief, and disruption of migrationroutes and overwintering grounds of certain birds.

In central China, for example, around half amillion ha of wetlands have been reclaimed forcrop production since about 1950, contributing toa reduction of floodwater storage capacity ofapproximately 50 billion m3 (Cai, Zhao and Du,1999). There is strong evidence that wetland recla-mation is responsible for about two-thirds of thisloss in storage capacity, and thus for about two-thirds of the US$20 billion flood damage in 1998(Norse et al., 2001). Similar links have been estab-lished for the severe 1993 floods in the UnitedStates (IFMRC, 1994). Therefore it is important tointroduce appropriate planning and regulatorymechanisms to ensure that any future wetlanddevelopment is undertaken with the necessary safe-guards, as is the case in the United States and anumber of other developed countries (Wiebe,Tegene and Kuhn, 1995).

Loss of and competition for good arable land. Aspopulations grow, much good cropland is lost tourban and industrial development, roads andreservoirs. For sound historic and strategic reasons,most urban areas are sited on flat coastal plains orriver valleys with fertile soils. Given that muchfuture urban expansion will be centred on suchareas, the loss of good-quality cropland seems likelyto continue. In fact the losses seem inevitable, giventhe low economic returns to farm capital andlabour compared with non-agricultural uses. Suchlosses are essentially irreversible and in land-scarcecountries the implications for food security couldbe serious.

Estimates of non-agricultural use of land perthousand persons range from 22 ha in India(Katyal et al., 1997), to 15-28 ha in China (Ash andEdmunds, 1998) and to 60 ha in the United States(Waggoner, 1994). The magnitude of futureconversions of land for urban uses is not certain,nor how much of it will be good arable land. Thereis no doubt, however, that losses could be substan-tial. In China, for example, the losses between 1985and 1995 were over 2 million ha, and the rate ofloss to industrial construction has increased since1980 (Ash and Edmunds, 1998).

The projected increase in world populationbetween 2000 and 2030 is some 2.2 billion.

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Assuming that the conversion of land for non-agri-cultural purposes is an average of 40 ha per thou-sand persons, the projected loss on this accountwould be almost 90 million ha. Even assuming thatall of this would be land with crop productionpotential, this would be only a fraction of the globalbalance of potential cropland that is as yet unused(see Chapter 4). However, in heavily populatedcountries such as China and India which have verylimited potential for cropland expansion, evensmall losses could be serious. In China, this issuehas been of growing concern for a number of years.Land loss to urban and industrial development incentral and southern China has been partiallycompensated by the conversion of grasslands in thenortheast to crop production (Ash and Edmunds,1998). But although this new land is very fertile,the growing season is short and allows only onecrop per year, compared with the two to threecrops per year possible on the land lost in thecentral and southern areas. However, it seemslikely that the global trading system will be able to meet China’s potential food import needs to2030 and beyond (Alexandratos, Bruinsma andSchmidhuber, 2000).

Land degradation.3 The assessment of land degra-dation is greatly hindered by serious weaknesses in

our knowledge of the current situation (Pagiola,1999; Branca, 2001). According to some analysts,land degradation is a major threat to food security,it has negated many of the productivity improve-ments of the past, and it is getting worse (Pimentelet al., 1995; UNEP, 1999; Bremen, Groot and vanKeulen, 2001). Others believe that the seriousnessof the situation has been overestimated at theglobal and local level (Crosson, 1997; Scherr, 1999;Lindert, 2000; Mazzucato and Niemeijer, 2001).

Area of degraded land. The most comprehensiveglobal assessment is still the Global Assessment ofHuman-induced Soil Degradation (GLASOD)mapping exercise (Oldeman, Hakkeling andSombroek, 1991; Table 12.4).

The results are subject to a number of uncer-tainties, particularly regarding the impact onproductivity and the rates of change in the area andseverity of degradation. A follow-up study for SouthAsia addressed some of the weaknesses of GLASOD.It introduced more information from nationalstudies and greater detail on the different forms ofdegradation (FAO/UNDP/UNEP, 1994). The broadpicture for South Asia remains similar in the twostudies: 30-40 percent of the agricultural land isdegraded to some degree, and water erosion is themost widespread problem (Table 12.5).

Region Total land affected (million ha) Percentage of region degraded

Moderate Strong and extreme

Africa 494 39 26

Asia 747 46 15

Australasia 103 4 2

South America 243 47 10

Central America 63 56 41

Europe 219 66 6

North America 96 81 1

Total 1 964 46 16

Source: Oldeman, Hakkeling and Sombroek (1991).

Table 12.4 Global Assessment of Human-induced Soil Degradation (GLASOD)2

2 GLASOD defines four levels of degradation: light = somewhat reduced agricultural productivity; moderate = greatly reduced agriculturalproductivity; strong = unreclaimable at the farm level; extreme = unreclaimable and unrestorable with current technology.

3 Defined as a process that lowers the current or potential capabilities of the soil to produce goods or services, through chemical, physical or biological changes that lower productivity (Branca, 2001).

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Despite these improvements in techniques ofassessment, a number of serious difficulties remainin using them for perspective analysis. They are stillheavily based on expert judgement, for entirelyjustified reasons. There is no clear consensus as tothe area of degraded land, even at the national level.In India, for example, estimates by different publicauthorities vary from 53 to 239 million ha (Katyal et al., 1997). Land degradation is very variable oversmall areas, e.g. as a consequence of differences insoil type, topography, crop type and managementpractice, so impacts are highly site specific. Theycan also be time specific: soil erosion impacts canvary in the short term because of interannualdifferences in rainfall, with no yield reductions inhigh rainfall years but appreciable losses in dryyears (Moyo, 1998). Some forms of degradation arenot readily visible, for example, soil compaction,acidification and reduced biological activity. Lackof data and analytical tools for measuring suchdifferences prevents or limits estimation of theirimpact on productivity, and makes scaling up to thenational or regional level problematic. There areno internationally agreed criteria or procedures forestimating the severity of degradation and mostsurveys do not make reliable assessments. Few ifany countries make systematic assessments atregular intervals that permit estimation of rates ofchange. Finally, major changes in socio-economicconditions, improved market opportunities, infra-structure and technology over the medium to longterm can induce farmers to overcome degradation(Tiffen, Mortimore and Gichuki, 1994).

Impact of degradation on productivity. Does degra-dation have a serious impact on onfarm produc-

tivity, and on offsite environments through windand water dispersal of soil? Because degradation isnormally a slow and almost invisible process, risingyields caused by higher inputs can mask the impactof degradation until yields are close to their ceiling.They thus hide the costs to farmers of falling inputefficiency (Walker and Young, 1986; Bremen,Groot and van Keulen, 2001). In Pakistan’s Punjab,for example, Murgai, Ali and Byerlee (2001) ques-tion whether technological gains can be sustainedbecause of the severe degradation of land andwater resources.

Moreover, the experimental methods commonlyused to determine impacts on yields have a numberof weaknesses (Stocking and Tengberg, 1999).Estimation of the economic costs can be equallycomplex. First, there may be impacts not just onyield levels, but on grain quality (e.g. drop inprotein quality), yield stability or production costs orany combination of these (Lipper, 2000). Second, itis necessary to separate out the effect of the differentfactors involved in total factor productivity growth(Murgai, Ali and Byerlee, 2001). There are alsooffsite impacts such as siltation of streams and reser-voirs, loss of fish productivity, raising water storagecosts and the incidence of flood damage, and theseare normally more serious than the onfarm impacts.

Given the above estimation difficulties, it is notsurprising that there is little correspondencebetween global assessments of productivity loss andnational or local realities. According to GLASOD,most areas in six states of the United States wereclassified as moderately degraded. According to thedefinition, this should result in reduced agriculturalproductivity. In reality, however, crop yields in theseareas have been rising steadily for the past 40 years.

Type of land degradation Percentage of agricultural land affected

Water erosion 25

Wind erosion 18

Soil fertility decline 13

Salinization 9

Lowering of the water table 6

Waterlogging 2

Source: FAO/UNDP/UNEP (1994), p. 50-51.

Table 12.5 Shares of agricultural land in South Asia affected by different forms of degradation

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Crosson (1997) suggests that recent rates of landdegradation and particularly soil erosion have hadonly a small impact on productivity, and argues thatthe annual average loss for cropland productivitysince the mid-1950s was lower than 0.3 percent.Similarly, according to GLASOD there is almost nocultivated land in China that is not degraded in oneway or another. Almost all the areas of rice cultiva-tion in south and southeast China are classified asbeing affected by high or very high water erosion,and large wheat-growing areas southeast of Beijingare classified as suffering from medium levels ofchemical deterioration (salinization). Yet, in spite ofthis, China was able to increase its wheat productionbetween the early 1960s and mid-1990s from about16 to 110 million tonnes, and its paddy productionfrom 63 to 194 million tonnes. Moreover, moredetailed assessments suggest that there has beenlittle deterioration in China’s (and Indonesia’s) soilssince the 1950s and they may have actuallyimproved up to the 1980s (Lindert, 2000.) Watererosion from most rice fields is very low (Norse et al.,2001). Nonetheless, rising yields may have maskedproductivity losses.

Oldeman (1998) estimates the global cumulativeloss of cropland productivity at about 13 percent,but there are large regional differences. Africa andCentral America may have suffered declines of 25and 38 percent respectively since 1945. Asia andSouth America, on the other hand, may have lostonly about 13 percent, while Europe and NorthAmerica have lost only 8 percent. UNEP (1999)does not accept Crosson’s assessment and argues

that land degradation is so bad that it has negatedmany of the gains in land productivity of recentdecades. Support for this view comes from detailedanalysis of resource degradation under intensivecrop production systems in the Pakistan and IndianPunjab (Murgai, Ali and Byerlee, 2001).

Three issues arise here. First, these estimatesare global and regional averages, whereas theimplications of degradation for agriculturalproduction and food security are primarily localand national. On the one hand, there are complextrade-offs and compensatory mechanisms involvedin some forms of degradation. A high proportion oferoded soil is redeposited elsewhere in the catch-ment area, where it tends to boost productivity, butit may also silt up reservoirs and irrigation canals.For example, in the United States some 45 percentis redeposited locally, and some 46 percent in lakes,reservoirs and other impoundments (Smith et al.,2001). On the other hand, there are also a numberof so-called hot spots where the degradation isalready serious and could get worse (Scherr andYadav, 1996). These hot spots include some of thedeveloping countries’ most fertile river basins(Table 12.6), which play a vital role in food security.

Second, the most visible degradation tends tobe on marginal lands, whereas the bulk of foodproduction occurs on more favourable lands,particularly irrigated areas (Norse, 1988). On suchfavoured lands relatively low rates of degradationcould have large impacts on productivity andyields, although there are some grounds forconcluding that this will not be the case. There is

Region Salinization Erosion

South and West Asia Indus, Tigris and Foothills of the HimalayasEuphrates river basins

East and Southeast Asia Northeast Thailand and Unterraced slopes of China and North China Plain Southeast Asia

Africa Nile Delta Southeast Nigeria, the Sahel, mechanized farming areas of North and West Africa

Latin America and the Caribbean Northern Mexico, Slopes of Central America, the semi-arid Andean highlands Andean Valley and the cerrados of Brazil

Source: Scherr and Yadav (1996).

Table 12.6 Regional hot spots of land degradation

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growing evidence that farmers are able to adapt toenvironmental stress in ways that limit degradation(Mortimore and Adams, 2001; Mazzucato andNiemeijer, 2001).

Third, there are factors at work that mayreduce degradation in the coming decades. Theseinclude the wider use of direct measures to preventor reverse degradation (Branca, 2001), and indi-rect measures such as improved irrigation tech-niques and water pricing to reduce salinization.The spread of NT/CA will limit the damage causedby conventional tillage. Nonetheless the resultsfrom the Punjab show no grounds for complacencyregarding the sustainability of some high-inputcrop production systems, and point to the need forincreased fertilizer-use efficiency and reducedsalinization.

Future areas of degraded land and loss of produc-tivity. Will the area of degraded arable and pastoralland expand in the future, or deteriorate further,e.g. because of population pressure or theprojected intensification of production?

Although the projections presented in Chapter 4 do not directly address the issue of landdegradation, they do contain a number of featuresthat can be used to assess how some forms of degradation may decline or become more seriousin the future.

First, about one-third of the harvested area indeveloping countries in 2030 is projected to be irri-gated land (Table 4.8), up from 29 percent in1997/99. This is generally flat or well-terraced landwith little erosion. However, parts may be at riskfrom salinization, particularly in more arid zones(Norse et al., 2001). In addition, a quarter of theharvested rainfed land is estimated to have slopes ofless than 5 percent, which are generally not proneto heavy water erosion. Their annual soil losses ofaround 10 tonnes per ha should be reduced whereit is economically feasible to do so, but such ratescould be tolerated for several hundred years beforethey have an appreciable impact on crop produc-tion. In all, around half of the cropland will not bemarkedly prone to soil erosion, although it may besubject to other forms of land degradationincluding salinization, nutrient mining, soil acidifi-cation and compaction.

Second, the global area of rainfed land underNT/CA could grow considerably, bringing benefits

such as reduced soil erosion, reduced loss of plantnutrients, higher rainfall infiltration and better soilmoisture-holding capacity (see Chapter 11 andSection 12.4.3 below). NT/CA will have positiveeffects on the physical, chemical and biologicalstatus of soils. Organic matter levels of soils, forexample, are likely to rise. Organic matter is amajor source of plant nutrients and is the glue thatholds soil particles together and stabilizes the porestructure. Organic matter makes soils less vulner-able to wind erosion and functions as a sponge forholding water and slowing down its loss from thecrop root zone by drainage or evaporation.Moreover, the nutrients added to the soil as organicresidues are released more gradually than thosefrom mineral fertilizers and are therefore less proneto leaching, volatilization or fixation (Avnimelech,1986). In addition, higher soil organic matter levelsare commonly associated with greater levels ofhumic acid, which increases phosphate availabilityand thus can be very beneficial in those areas withstrongly phosphate-fixing soils found in sub-Saharan Africa and Latin America.

Third, fertilizer consumption and fertilizer-useefficiency are projected to rise. This will bringbenefits in terms of higher soil fertility and soilorganic matter levels. Soil erosion will diminishbecause of the positive impact on root prolifera-tion, plant growth and ground cover of increasedphosphate and potassium (associated with morebalanced fertilizer inputs).

These conclusions are broadly consistent withprojections made by the International Food PolicyResearch Institute (IFPRI) (Agcaoili, Perez andRosegrant, 1995; Scherr and Yadav, 1996). That is,global losses to degradation are likely to be small,but losses could be significant in some localitiesand regions. However, soil productivity loss fromland degradation could be much more serious ifthe above gains from NT/CA, greater fertilizer useand fertilizer-use efficiency, and other forms of soiland water conservation are less than we estimate,and crop yield growth slows appreciably, asprojected in Chapter 4.

On the other hand, there are sound reasons to believe that some of the fragile lands most proneto degradation will be abandoned. This will notnecessarily result in additional pressures for defor-estation and cropland development, because highrates of urbanization and rural-urban migration

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are projected for the future. This outmigrationcould, for example, reduce degradation stemmingfrom the cultivation of slope lands, and lower someof the pressure on grazing land in the Sahel andother semi-arid and arid areas.

This is likely to have similar effects to those expe-rienced in western European countries from the1950s and 1960s onwards (CEC, 1980; Baldock et al.,1996), and in Eastern European countries since the1990s. Here rural outmigration and the restruc-turing of agriculture led to the abandonment ofsteep slopes and other marginal land and reducedpressure to develop any more land. Substantial areasof marginal land were abandoned and reverted toforest or scrub. In France this amounted to around3 percent p.a. in the 1960s and early 1970s (Faudryand Tauveron, 1975). In Italy around 1.5 million hawere abandoned in the 1960s, of which some 70 percent was slope land, with decreases of 20 percent in some provinces (CEC, 1980). Thedecline was very rapid, and closely related to sharpfalls in agricultural employment.

Rural outmigration and agricultural restruc-turing have also been occurring in many devel-oping countries and are projected to continue.This trend is most noticeable in countries such asChina, where urbanization is accompanied by ashift to alternative income sources. It follows,therefore, that a significant percentage of theslope land cultivated at present could be aban-doned over the next three decades in many devel-oping countries, with a substantial proportionreverting to forest. However, in densely popu-lated rural economies, such as Indonesia, wherethe rate of population growth is still over 2 percent p.a., population drift to cities has notsignificantly reduced the density of rural settle-ment, or improved the economic livelihoods ofthe majority of the rural population.

Desertification is a serious form of dryland degra-dation, given priority by the international commu-nity in the form of the United Nations Conventionto Combat Desertification (UNCCD). In the 1970sand 1980s it was argued that the Sahara wasspreading rapidly southwards as part of an irre-versible expansion of the world’s deserts. Sincethen, counter-arguments have been growing inforce, backed up by strong empirical evidence fromremote-sensing activities (Nicholson and Tucker,1998; Prince, Brown de Colstoun and Kravitz,

1998). This has shown that the desert margins arequite dynamic because of natural climate variation.The problem is more one of localized drylanddegradation because of overgrazing, excessive fuelcollection, bad tillage practices and inappropriatecropping systems.

Nonetheless, there has been some expansion ofthe deserts and dryland degradation (Dregne andChou, 1992). Degradation of vegetation and nativehabitat is the major reason for species extinction inmany semi-arid and subhumid environments.Rapid rates of species loss, particularly of beneficialinsects, birds and other predators may reduce thecapacity for natural suppression of the pests,diseases and weeds that are among the greatestthreats to current levels of agricultural production.However, quantification is not precise (Dregne andChou, 1992). The most extreme estimates suggestthat about 70 percent of the 3.6 billion ha ofdrylands are degraded, although this is likely to be an overestimate. More probing analysis is highlighting the resilience and adaptability of cropand livestock systems in vulnerable areas such asthe Sahel (Behnke, Scoones and Kerven, 1993;Mortimore and Adams, 2001).

Looking to the future, there seem to be severalongoing positive forces that could have a significanteffect. First, the contraction in extensive livestockproduction should take the pressure off somedrylands and reduce dryland degradation. Second,gains in productivity on favourable lands shouldallow some of the marginal drylands to revert torange or scrub. Third, the spread of irrigation,water-harvesting techniques and measures to avoidor overcome salinization should improve thesustainability of dryland agriculture. Fourth, thecontinued adoption of NT/CA permits greaterrainfall infiltration and improves soil moisture-holding capacity. Fifth, better drought- andgrazing-tolerant crops and grasses will be createdthrough gene transfer, although this is unlikely tohave much impact before 2015. Sixth, countriessuch as China and India are making major effortsto restore degraded land in arid areas (Sinha,1997). Finally, there are widespread efforts torestore saline and other degraded soils that havegone out of production. In the view of someanalysts, restored lands could total 200-300 millionha by 2025 (GCSI, 1999). On the negative side, atleast in the medium term, are the expansion or

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intensification of cropping in semi-arid areas andfurther losses from salinization.

Overgrazing has been one of the central environ-mental concerns related to livestock activities. It canlead to the degradation of grasslands and desertifi-cation in semi-arid areas, while on steep slopes it cancause serious soil erosion. Scherr and Yadav (1996)highlight overgrazing in parts of the Caribbean andNorth Africa, and the grazing of slopes in mid-alti-tude areas of Asia as areas of concern. UNEP’s GlobalEnvironment Outlook (UNEP, 1997) also lays emphasison devegetation and land degradation from over-grazing. However, gaseous emissions and waterpollution from livestock systems could be of greaterglobal and more widespread national concern thanovergrazing, although the latter will remain aserious threat in some areas. This is consistent withthe detailed analysis of the impact of livestock on theenvironment given in de Haan, Steinfeld andBlackburn (1998).

There is a growing consensus that the impor-tance of overgrazing has been misjudged in thepast, particularly in sub-Saharan Africa. This was inpart caused by poor understanding of rangelandecology, and in part by the lack of appreciation oftraditional range management practices in aridand semi-arid areas (Behnke, Scoones and Kerven,1993). The alleged overgrazing in the Sahel, forexample, is mainly a consequence of naturalclimate variability, i.e. low rainfall in some years,and poor stock management rather than over-stocking per se (Fleischhauer, Bayer and Lossau,1998). There is very little lasting impact on thevegetation, which is more robust than oncethought. In recent decades, however, the establish-ment of permanent watering-points and therestrictions placed on traditional migratory routesthrough border checks have led to greater impactin drought periods than probably occurred in thepast. In Australia, for example, poor planning andmanagement of water-holes have led to seriousovergrazing and reductions in pasture species. Theperiodic overstocking that does occur is often theconsequence of institutional and infrastructuralproblems constraining the marketing of livestock.

Looking ahead to 2030, it is reasonable toassume that overgrazing will not cause majorincreases in land degradation globally. Pastoralistswill continue to move their livestock around toexploit spatial differences in growing conditions if

they are allowed to. The lack of opportunities to raise the productivity of extensive livestocksystems, and changing income sources and aspira-tions among livestock producers will continue tocause shifts to more intensive systems on the betterlands closer to urban markets, or out of agriculturealtogether. Finally, some of the institutional andinfrastructural constraints that have encouragedovergrazing in the past will be reduced as growingurbanization and income growth stimulate marketimprovements.

12.3.3 Environmental dimensions of water use and water pollution by agriculture

Many water management and pollution issues havegrown in importance in recent decades, such asgrowing competition with the urban and industrialsectors for the available water supply; poor irriga-tion water-use efficiency; overextraction of ground-water; reduced infiltration of rainwater into soilsand reduced water recharge because of deforesta-tion and land degradation; declining crop yieldsand water quality related to waterlogging andsalinization; contamination of groundwater andsurface water from fertilizers, pesticides and animalwastes; and the risk of greater aridity and soil mois-ture deficits towards the end of the projectionperiod in some areas of sub-Saharan Africa andSouth Asia because of climate change.

Overextraction of groundwater. Overextraction ofgroundwater is widespread in both developed anddeveloping countries. It arises when industrial anddomestic and agricultural withdrawals of waterexceed the rate of natural recharge. In some areas,particularly in the Near East/North Africa region,irrigation draws on fossil aquifers that receive littleor no recharge at a level that is not sustainable(Gleick, 1994). In substantial areas of China andIndia groundwater levels are falling by 1-3 metresp.a. The economic and environmental conse-quences are serious and will get worse in theabsence of appropriate responses. Irreversible landsubsidence, especially in urban and peri-urbanareas, causes serious structural damage to build-ings, drainage systems, etc. Overextraction incoastal areas causes saltwater to intrude into fresh-water aquifers, making them unfit for irrigation or

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drinking-water without costly treatment. Loweringof the water table increases pumping costs. It willtake many years to achieve the investments andother changes required to limit overextraction, soseveral million ha of irrigated land may either goout of production or be faced with unsustainableoperating costs.

Waterlogging and salinization. Both these problemsare commonly related to irrigation mismanage-ment. Waterlogging restricts plant growth. It arisesfrom overirrigation and inadequate drainage, andin many cases precedes salinization. Over 10million ha are estimated to be affected by waterlog-ging (Oldeman, Hakkeling and Sombroek, 1991).

Salinization results from the buildup ofdissolved solids in soil and soil water, and can occurin rainfed areas with inherently susceptible soils (asin parts of Australia) as well as in irrigated areas.UNEP considers that salinization is the secondlargest cause of land loss, but there are wide differ-ences in the estimates of the area affected and of thearea going out of production. Oldeman, Hakkelingand Sombroek (1991) estimate the total affectedarea to be over 76 million ha but do not differen-tiate between irrigated and rainfed areas. It seemspossible that some 20 percent of the total irrigatedarea is affected and some 12 million ha of irrigatedland may have gone out of production (Nelson andMareida, 2001). The problem can be very serious atthe subregional and national level. India, forexample, has lost about 7 million ha (Umali, 1993;FAO/UNDP/UNEP, 1994; FAO, 1999b). In somesemi-arid countries, 10 to 50 percent of the irri-gated area is affected to a greater or lesser degree(Umali, 1993; FAO, 1997b, 1997e), with averageyield decreases of 10 to 25 percent for many crops(FAO, 1993a; Umali, 1993). Unfortunately there arelittle or no time series data to allow reliable esti-mates of the rates of change in the salinized area. Itcould be 1-1.5 million ha p.a. and increasing(Umali, 1993) but it is difficult to quantify. Of partic-ular concern are those irrigated areas in semi-aridregions that support large rural populations, suchas the western Punjab and Indus valley where largeareas of waterlogged saline land are spreadingthrough the intensively irrigated plains.

Pollution by fertilizers. Since the 1970s extensiveleaching of nitrate from soils into surface water and

groundwater has become an issue in almost allindustrial countries (OECD, 2001a). In large areasof the EU, for example, concentrations are near toor exceed the maximum permitted concentrationof 50 mg per litre or 50 ppm (parts per million).This nitrate poses a risk to human health andcontributes to eutrophication of rivers, lakes andcoastal waters. The bulk comes from diffusesources arising from mineral fertilizer and manureuse on both crops and grasslands. The problem isnow serious in parts of China and India and anumber of other developing countries, and will getworse (Zhang et al., 1996).

The problem occurs primarily when N applica-tion rates exceed crop nutrient uptake. The riskdepends on crop type and yield, soil type andunderlying rocks (Goulding, 2000). The risk ofhigh nitrogen (and some phosphate) lossesthrough leaching and runoff can become seriousunless there is good fertilizer management (Hydro,1995; MAFF, 1999). There are large regional andcrop differences in fertilizer application rates perhectare (Daberkov et al., 1999), and large spatialand temporal differences in nutrient levels andfertilizer-use efficiency on similar soil types. Hencethe projected changes in average application ratesgiven in Table 4.15 are not a good indicator of therisk of nitrate losses. In the United Kingdom, thepresent average application rate for all arable cropsis about 150 kg N/ha, but the range is 25-275 kgN/ha with application rates of more than 150 kg onover 35 percent of arable land. In parts of Chinathe situation is even more extreme with some ricefarmers applying over 870 kg N/ha, almost fourtimes the national average. As stated above, highapplication rates as such should not be a problemas long as crop yields are commensurate, but theybecome problematic when application rates exceedcrop nutrient uptake. In contrast, most cropproduction in sub-Saharan Africa takes placewithout the benefit of mineral fertilizers and soilfertility remains very low or declining (Chapter 4).

Chapter 4 assumes substantial gains in fertilizer-use efficiency and hence a relatively modest aggre-gate growth rate in N fertilizer demand, projected todecline to less than 1 percent p.a. by 2030. However,extensive areas in both developed and developingcountries already receive large nitrogen fertilizerapplications that are not commensurate with theavailability of adequate soil moisture, other nutrients

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and management practices needed to attain highyields. Even modest increases in nitrogen fertilizerapplication could cause problems when yield growthstagnates, leading to nutrient-use inefficiencies andsevere pollution. Four difficulties arise here. First,these losses can occur at N application rates belowthe economic optimum, since current fertilizerprices do not include the cost of environmentalexternalities (Pretty et al., 2001). Second, maxi-mizing the efficiency of N use is complex and diffi-cult (Goulding, 2000). Third, it may take many yearsfor improvements in fertilizer-use efficiency to resultin reductions in nitrate losses and decades forgroundwaters to recover from nitrate contamina-tion. Fourth, the situation could be particularlyserious for the production of vegetables, becausethey are often grown in or close to urban areas sothat there is fairly direct contamination of thedrinking-water sources for large numbers of people.

Water pollution arising from agriculture hasother dimensions. Nitrogen and phosphate enrich-ment of lakes, reservoirs and ponds can lead toeutrophication, resulting in high fish mortality andalgae blooms. This is important because of thegrowing importance of aquaculture (Chapter 7).Algae blooms release toxins that are poisonous tofish and humans. The human risks are a growingproblem in some developed countries and poten-tially even more serious in warmer developingcountries with more intense sunshine (Gross, 1998).

Further intensification of fertilizer use may alsoadd to the widespread problem of soil acidification(Scherr, 1999). A combination of improved nutrientmanagement and liming could limit this butammonia emissions from livestock and nitrogenfertilizers, discussed above, also add to soil acidifi-cation through acid rain. The conjunction iscausing serious ecosystem damage in some devel-oped countries, and this could also occur in devel-oping countries, particularly in East Asia with therise of industrial-scale pig and poultry production.

Pesticide pollution. Pesticide use has increasedconsiderably over the past 35 years. Recentregional growth rates have ranged between 4.0 and5.4 percent (Yudelman, Ratta and Nygaard, 1998).This has led to serious water pollution in OECDcountries (OECD, 2001a). Pesticide pollution isnow appearing in developing countries as well,exacerbated in some instances by the availability of

cheap, out-of-patent, locally produced chemicals.Future pesticide consumption is likely to grow

more rapidly in developing countries than indeveloped ones (Morrod, 1995), although theintroduction and spread of new pesticides mayoccur more rapidly in the latter. The environ-mental implications of this growth are difficult toassess. For example, application rates per hectarehave gone down, but the new pesticides are biolog-ically more active. Improved screening methodsfor pesticide safety and environmental health legis-lation have helped to reduce the mammalian toxi-city of pesticides and to assess other potentialenvironmental damage. On the other hand, theadoption of improved application techniques hasnot progressed sufficiently in the past decade,particularly in the case of sprayers, so that a highproportion of pesticide still fails to reach the targetplant or organism (Backmann, 1997). This situa-tion is unlikely to change in the near future.

Over the period to 2030 several factors couldcreate significant breaks from recent trends inpesticide use, and could reduce pesticide contami-nation of groundwater and surface water, soil andfood products. Developed countries are increas-ingly using taxes and regulatory measures toreduce pesticide use (DME, 1999; DETR, 1999).The rapid growth in demand for organically grownfood will continue to reduce the use of pesticides.Research in “smart” pesticides using advances inbiotechnology, knowledge of insect hormones andinsight into the ecological basis of pest control, etc.is likely to result in safer control methods withinthe next decade or so (Thomas, 1998). There willbe further development of IPM for crops otherthan rice, which should help to reduce the use ofinsecticides and, to a lesser extent, fungicides andherbicides (Yudelman, Ratta and Nygaard, 1998).However, shortages of farm labour, the reduceduse of flood irrigation for rice and the spread ofminimal tillage systems could lead to majorincreases in the use of herbicides and herbicide-resistant crops.

Pollution from livestock wastes. Water pollutionalso arises from intensive dairying and from thelandless rearing of pigs and poultry, particularly inEast Asia. Here peri-urban industrial-scale pig andpoultry production has caused serious environ-mental damage, especially water pollution, unpar-

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alleled in the industrialized world (de Haan,Steinfeld and Blackburn, 1998). The problemarises from discharges or runoff of nitrogen andother nutrients into surface waters because of badwaste management and from environmentalimpacts of feed and fodder production (Hendy,Nolan and Leng, 1995; de Haan, Steinfeld andBlackburn, 1998). In the medium term these prob-lems seem bound to increase, although the techno-logical means of overcoming them are neithercomplex nor very costly.

12.3.4 Loss of biological and ecological diversity

In the main, recent land cover changes havereduced the spatial distribution of species ratherthan causing their extinction, although this hashappened and will continue to happen on a morelimited scale. The loss of wild relatives of crops andof native crop varieties that are better adapted tounfavourable or changing environmental condi-tions could be particularly serious for crop intro-duction or breeding programmes to adapt toclimate change.

The projections of land cover and land usechange do not explicitly examine changes in biodi-versity,4 but they do provide some proxy indica-tors. These can help in assessing how the impacts ofagriculture on biodiversity might evolve over theprojection period. The focus of this chapter is onthe environmental and ecosystem impacts of thechanges, rather than on plant genetic resourceissues. Pressures on non-agricultural biodiversityfrom land clearance and the inappropriate use ofagrochemicals may in future grow more slowlybecause of the increase in protected areas and landrestoration.

However, there will be increasing pressures onbiodiversity within agricultural production systems.This will stem primarily from the intensification ofproduction. Together with economic forces, intensi-fication will lead to farm and field consolidation;reduction of field margins; clearance and levellingof adjacent wastelands so that they can be culti-vated; further expansion in the use of modern vari-eties; greater use of pesticides; and higher stockingrates for grazing animals. These trends can lead to

the destruction of the habitats of beneficial insectsand birds that help to keep crop pest populationsunder control, and to other losses in biodiversity.However, assessment of these losses in developingcountries is severely limited by lack of data on quan-titative and qualitative changes in pesticide use, live-stock densities and wildlife populations.

The effects of agriculture on non-agriculturalbiodiversity can be positive as well as negative,depending upon the situation. In the UnitedKingdom, for example, the intensification ofpastoral systems has been an important factorbehind the decline in bird populations. On theother hand, in Norway around half of the threat-ened species depend on agricultural landscapesand therefore the conservation of biodiversity isclosely related to the protection of such landscapes(Dånmark, 1998), including grazing systems thatprevent pastures from reverting to scrub or wood-land.

Nonetheless, intensification will have a majorpositive impact by reducing the need to convert newland to agriculture. CGIAR has estimated that landsaved through yield gains over the past 30 yearsfrom CGIAR research on seven major crops is equiv-alent to 230-340 million ha of forest and grasslandthat would have been converted to cropland in theabsence of these gains (Nelson and Mareida, 2001).Their estimate excludes the land savings thatstemmed from research on other crops, fromnational and private research systems and fromfarmers’ own research and development. Some esti-mates of land savings resulting from all past researchefforts and agricultural intensification amount tomore than 400 million ha (Goklany, 1999).

Agriculture’s main impacts on wild biodiversityfall into four groups. First, there is the loss of naturalwildlife habitat caused by the expansion of agricul-ture. This has been a major force in the past, andwill continue in the future, although much moreslowly. The projections of Chapter 4 suggest that anadditional 120 million ha of arable land will berequired over the next 30 years. Inevitably these willinvolve a reduction in the area of natural forests,wetlands and so on, with attendant loss of species.

Second, there is the general decline in speciesrichness in managed forests, pastures and fieldmargins, and the reduction of wild genetic

4 Biodiversity includes genetic differences within each species, diversity of species and variety of ecosystems.

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resources related to domesticated crops and live-stock. There are comprehensive and well-main-tained ex situ germplasm stocks for the major crops,and gene transfer and other advanced plantbreeding tools have opened up new possibilities forgenetic improvement. Nevertheless, these losses inthe wild could be serious for future crop and livestock breeding. They cannot be quantified atpresent, although advances in molecular biologymay provide the tools needed for more robustmonitoring.

Third, there is the reduction of wild species,including micro-organisms, which help to sustainfood and agricultural production, for examplethrough soil nutrient recycling, pest control andpollination of flowering crops. This can be regardedas damage to the life support system for agriculture,given the vital role some of these species play in soilfertility maintenance through nitrogen and carboncycling. Such losses are of increasing importancewith the shift to integrated farming and the growingemphasis on IPM. The intensive use of mineralfertilizers is known to change soil microbe popula-tions (Paoletti, 1997), but does not appear to disruptnutrient recycling. Intensive grazing lowers plantspecies richness in pastures but the long-termconsequences of this are not known. In developedcountries, loss of insect-eating bird species, as aresult of reduction or removal of field margins orpesticide use, has been firmly linked with increasesin crop pest damage. This problem may ariseincreasingly in developing countries.

Lastly, there is the reduction in wild species thatdepend for habitat, food, etc. on agriculture and thelandscapes it maintains – the habitats, flora andfauna that would not exist without agriculture.Richly diverse chalk grasslands, for example, wouldrevert to scrub or woodland without grazing pres-sures, with the loss of ground-nesting bird species,butterflies and herbaceous plants. The reduction ofwild species is most apparent in those EU countriesthat have lost large areas of hedges, ditches, shrubsand trees through field and farm consolidation.Losses have also arisen from extensive use of insec-ticide and herbicide sprays with consequent spraydrift on to field margins and other adjacent ecolog-ical niches. Increased stocking rates on extensivepastoral systems have led to a decline in birds thateither nest on such land or are predators of rodents,etc. living on these lands.

The impact of livestock production on biodiver-sity takes two main forms: high grazing pressuresand reseeding of pastures. Grazing pressures arelikely to rise with time in some areas, particularlywhere marketing infrastructure is weak and thereare few alternative livelihoods, even though there isa continuing shift to limited or zero grazing such asfeedlots and stall-feeding systems. In other areas,however, the area of grazing land and pastures willprobably decline as the more marginal areas areabandoned. Some pastures will be converted intocropland and urban and industrial land. Such land use changes can be appreciable. In westernEurope, for example, the area of meadows andpastures declined by 10 percent between 1970 and1988 (OECD, 1991). This decline was associatedwith the rise in stocking rates. On rough pasturesthese commonly increased by 50 to 100 percentbetween 1970 and 1990 (Pain, Hill and McCracken,1997) and they have risen even more on improvedpastures. Such increases in stocking rates havebeen linked to the loss of certain bird species fromlarge areas of the United Kingdom and Europeand lower populations elsewhere (Pain andPienkowski, 1996). Similar stocking rate increasesare projected for parts of sub-Saharan Africa andAsia, so they are also likely to suffer losses in birdand other wildlife populations. It is also likely thatthere will be a shift to more intensive pasturesystems. This will most probably involve somereseeding of natural meadows, and hence loss ofnative grassland plants. Intensification of pasturesnormally also involves the application of high levelsof organic or mineral fertilizers, leading to nitrateor phosphate loss to water systems. The experienceof the developed countries indicates that theseimpacts can be substantial.

12.3.5 Perturbation of global biogeochemical cycles

Agriculture plays a significant role in the anthro-pogenic perturbation of several biogeochemicalcycles, notably the nitrogen, phosphate and sulphurcycles. In the nitrogen (N) cycle, ammonia andnitrous oxide emissions from agriculture are signifi-cant, but there is also perturbation of N fixation.The manufacture of nitrogenous fertilizers, burningof fossil fuels and cultivation of leguminous crops have resulted in anthropogenic N fixation

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exceeding natural N fixation since about 1980, by anincreasing margin. Some analysts suggest that “overthe next few decades this alteration (of the N fixa-tion cycle) will undoubtedly become even moresevere” (Walker and Steffen, 1999), for example, ifthe use of nitrogen fertilizer more than doublesbetween 1990 and 2050, thereby causing a pro rataincrease in direct and indirect N2O emissions(Smith, 1999). However, the projections of N fertil-izer use and leguminous crop cultivation given inChapter 4 and of manure production discussedearlier in this chapter all point to a slowing down inthe growth of agriculture’s contribution to thisperturbation. Moreover, there are a number ofother changes, e.g. in land use management, whichshould also reduce perturbations of the N cycle. Forexample, the expected increase in the area underNT/CA and other measures to counter soil erosionshould reduce the loss of nitrogen in eroded organicmatter from arable land. But in contrast, other landmanagement practices such as burning may result inincreased nitrogen losses, particularly if climatechange results in increased summer maximumtemperatures and greater fire risk in savannah andother fire-prone ecosystems (Lavorel et al., 2001).

12.4 Current and emerging solutions

It is clear from Section 12.3 that some of the mostserious environmental pressures stem from agri-cultural intensification. This process started in thedeveloped countries over 50 years ago and some ofthe environmental problems became clear in the1960s (Alexandratos, 1988). A number of themhave been overcome while others remain and seemlikely to grow in severity for the next decade or so(OECD, 2001a). The policy and technologicalsuccesses and failures of developed countries canbe of great help to those developing countries thatare now suffering the environmental damages ofintensification. They may even help those countriesand farmers who have yet to intensify productionto avoid some of the environmental problems thatcould arise. Many of the required policy, regulatoryand technological actions are known. If pursued,such actions could result in a more favourableagro-environmental future than that outlined inthe preceding section.

Reduction of pollution by fertilizer. The EU andNorth America have used a number of researchand regulatory measures to limit pollution fromfertilizers, such as research on slow release andother less polluting formulations; tighter emissionand discharge standards for fertilizer factories andhigher fines; public and private advisory (exten-sion) services; physical limits on the use of manureand mineral fertilizers; and application of thenutrient budget approach.

These actions have not been enough toprevent serious buildup of nitrate in drinking-water sources and the eutrophication of rivers,lakes and estuaries (OECD, 2001a, 2001b; EEA,2001). Since the early 1990s an increasing numberof countries have been introducing economicmeasures in the form of pollution taxes onmineral fertilizers.

All of these actions are or will be relevant todeveloping countries. They can be formulated inthe framework of a strategy for integrated plantnutrition (see Chapter 11). Some countries willhave to remove a number of other distortions, suchas direct and indirect subsidies to mineral fertilizerproduction or sales (e.g. energy subsidies tonitrogen fertilizer). They will also need to phaseout low-efficiency fertilizers such as ammoniumcarbonate, and provide adequate funding to exten-sion services so that they are not even partiallydependent on the sale of fertilizer.

The consumer-led drive towards organic agri-culture will limit fertilizer pollution in some areas,as will the adoption of NT/CA over a much largerarea.

Reducing pesticide pollution. A number of impor-tant lessons can be drawn from past experience.First, rigorous testing procedures must be in placeto determine the safety of pesticides before they areallowed on the market. The developed countrieshave suffered in the past from weaknesses in thisregard, and have had to tighten their procedures.It is important that pesticide safety information isshared with developing countries through theInternational Plant Protection Convention (IPPC)and other mechanisms. In addition, as more devel-oping countries become pesticide producers anddevelop their own products, it is essential that theyimplement their own testing, licensing and controlprocedures.

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Second, even where the above measures are inplace, environmental problems can arise from theaccumulation of pesticide residues along the foodchain, in soils and in water, e.g. the buildup ofatrazine in water supplies in Europe and theUnited States. There must be comprehensive andprecise monitoring systems to give early warning ofresidue buildup. The international sharing ofinformation, e.g. through the Codex Alimentarius,provides valuable support to developing countriesthat lack adequate monitoring and testing facilities.Moreover, in the context of consumer safety andthe WTO agreements, rigorous procedures mustbe in place to ensure food safety and enable agri-cultural exports.

Third, pest control measures should be imple-mented in a strategic framework for IPM (Chapter11), which aims to avoid or minimize the use of pesti-cides. In recent years a number of developed coun-tries have concluded that even with the abovemeasures some farmers are still applying too muchpesticide, or pesticide accumulation in the environ-ment has not been reduced. They have decided,therefore, to use economic as well as regulatorymeasures, and to impose pollution taxes on pesti-cides so as to create economic incentives to reducetheir use. Such taxes appear to be a valid option fora wider range of countries and situations, although itmay be some time before many developing countrieshave the institutional capacity to implement them.

Development and expansion of no-till/conservationagriculture. The biological, environmental andeconomic advantages of NT/CA have been describedin Chapter 11. The wider adoption of NT/CAdepends on raising awareness among politicians andfarmers of the benefits of conservation agriculture.Government policies need to be directed towardscreating the appropriate conditions for its uptake.Farmers need to see how it meets their specificneeds. The lessons learned from the farmer-to-farmer training approach used successfully for IPMin Asia could be of help. For example, Brazilianfarmers who have benefited greatly from NT/CAcould share their experience with farmers in Africaand help them to adapt the technique to their ownconditions. Greater national research and develop-ment efforts and international assistance will beneeded to develop the technique for other agricul-tural environments and production systems.

Improving water management. Water scarcity andintersectoral competition for water are major prob-lems. Reduced groundwater recharge because ofdeforestation and soil degradation is also an impor-tant issue. The most serious direct environmentalproblem is salinization. Three main actions couldbe used to limit salinization: (i) greater investmentin better drainage and distribution canals, eventhough planners have been slow to act on thisoption in the past; (ii) better water management,for example through the increasing involvement offarmers in water users’ associations and similarbodies; and (iii) stronger economic incentives forwater conservation, which are growing as govern-ments increasingly implement water-pricing poli-cies and as competition from other sectors drivesup the price.

Promotion of organic farming. While the techno-logical approaches described above are measures toreduce the negative effects of conventional agricul-ture on the environment, organic agriculture (forenvironmental reasons) does not use any industrialfertilizer or pesticide inputs at all. The use of suchinputs commonly has negative effects on the envi-ronment; however, their non-use does not neces-sarily make agricultural production sustainable.Soil mining and erosion, for example, can be prob-lems in organic agriculture. Organic farming canalso cause serious air and water pollution – forexample, the overuse of manure or badly managedapplications can increase ammonia in the air andnitrate in groundwater.

The rapid expansion of organic productionduring the past decade has already made an appre-ciable contribution to pollution reduction and agri-cultural sustainability in Europe (FAO/COAG, 1999).Three aspects need to be clarified. First, badlymanaged organic agriculture can result in some ofthe same pollution problems that arise from conven-tional agriculture, but not in others such as thoseassociated with the use of industrial inputs andproduction systems described in the precedingsections. Second, although the rate of expansion hasbeen fast, the proportion of agricultural landinvolved is small. Current policies in many EU coun-tries aim at a considerable increase in the agriculturalland under organic farming (see Chapter 11). Third,most of the pressure for the switch to organic farmingis in the developed countries (FAO/COAG, 1999).

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The environmental and economic benefits oforganic farming can be increased in a number ofways. These include introduction of policies thatbring prices of industrial inputs in line with theirfull economic costs, including externalities;improvements in product standards, certificationand labelling to give consumers confidence thatthey are buying genuine organic foods (FAO,1999f); establishment of an internationally agreedaccreditation mechanism, particularly proceduresto gain international equivalence of organicproduct standards; greater government assistanceto farmers wishing to switch to organic farming;regulations to enforce or encourage the use oforganic farming as a means of overcoming orreducing problems such as the buildup of nitrate ingroundwater; increased research to widen therange of organic agricultural techniques; improve-ments in the availability of or access to organicinputs, e.g. GMO-free seed, rock phosphate andmanure; and capacity building in extensionsystems, farmers’ cooperatives and national accred-itation bodies to remove barriers to the expansionof organic farming, particularly in extension serv-ices that still promote approaches centred on theintensive use of mineral fertilizers and pesticides.

Improving livestock waste management. Themain actions required here are the following.Development of national strategies for livestockwaste management to provide the general frame-work for local action; improved policy and regulatory framework, with clearly defined andenforceable discharge and emission standards andeffective waste disposal charges; meaningful penal-ties for breaches in regulations, and an expandedrange of economic instruments to discourage poorlivestock waste management, e.g. pollution taxes tolimit waste discharges from livestock farms andfisheries; well-targeted programmes to disseminatebest practices; strengthened guidelines to optimizethe location of livestock production units and toprohibit the development of certain types of inten-sive livestock units in unsuitable areas; increasedsupport for the adoption and dissemination ofappropriate technological measures, with emphasison introducing better techniques for livestockwaste management already available in developedcountries; drawing lessons from North Americaand the EU on the failure of regulatory approaches

alone to achieve adequate livestock waste manage-ment; and improved donor coordination and envi-ronmental impact assessment (EIA) to ensure thatinternational projects have adequate provision forsound livestock waste management.

12.5 Physical and economic trade-offs

Earlier sections have shown that agriculture is anindustry with substantial environmental conse-quences upstream and downstream as well asonfarm. It is evident that crop production and foodsecurity cannot be achieved at zero environmentalcost. The issue therefore is whether environmentalcosts can be minimized so that future food securityis not at risk.

The trade-offs involved are multidimensional.They vary over time and space, between differentenvironmental goods and services, and betweendifferent developmental goals. It is for society todecide which trade-offs are acceptable and whichones can be mimimized, but this raises the questionof whose society, and who in society should decide.A few examples of the various types of trade-offs arementioned below.

Between countries and regions. The increasingswitch in developing countries to intensive, grain-fed livestock production systems close to urbanmarkets has reduced or prevented overgrazing ofrangeland. But it has transferred part of the envi-ronmental burden to developed country exportersof feedgrains, because row crops such as maize aremore susceptible to soil erosion and nitrate leaching(although improvements in farming practices havebeen reducing this damage in recent years). Thepast high rates of growth for dairy, pigs and poultryin some major developing countries were onlypossible through the use of large quantities of feedconcentrates imported from North America andother developed countries.

Spatially within countries. This expansion of inten-sive livestock production has also led to a number ofenvironmental trade-offs within countries. First, ittends to shift the environmental burden from non-point to point pollution, with greater discharges ofconcentrated liquid and solid wastes, causingserious water pollution. Second, it reduces thegrazing pressures on vulnerable semi-arid pastures

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and steep slopes, but it separates arable and live-stock production. This limits or prevents thereturn of livestock manure to cropland, which isoften vital in raising crop yields and maintainingsoil fertility. Hence some countries, notably theNetherlands, have introduced regulations onstocking rates or manure recycling. Moreover, theproduction of large quantities of feedgrain andfodder crops can lead to serious soil erosion, andto environmental problems stemming from fertil-izer and pesticide use. The higher stocking rates ofintensive systems lead to loss of biodiversity fromtrampling and reseeding (Pain, Hill andMcCracken, 1997), and more concentrated emis-sions from manure and urine, causing ecosystemacidification locally and GHG accumulation glob-ally (Bouwman et al., 1997).

Over time within countries. The European experi-ence shows how forest clearance for food produc-tion can buy time while technology andinternational trade catch up with populationgrowth, allowing marginal cropland eventually tobe reforested (Norse, 1988). Most European coun-tries converted forests to cropland prior to theapplication of mineral fertilizers and modern cropbreeding techniques. However, the loss of biodiver-sity from such deforestation may be permanent,and it may be impossible to re-establish the originalforest ecosystem.

Over space and time. Erosion from steep slopesthat are difficult to cultivate and inherentlyunstable is commonly followed by the redepositionof sediments in reservoirs, in river valleys and estu-aries up to 1 000 km or more away. The result withtime is the creation of flat lands that are easy tocultivate. In South and East Asia such lands havebeen able to sustain crop production for thousandsof years. On the other hand, by reducing thestorage capacity of drainage systems this erosioncan contribute to severe flooding, loss of human lifeand serious economic losses (FAO, 1999g), and itmay be impossible to restore eroded slopes to theiroriginal vegetation.

Between food security and the environment. Poorfarmers in various parts of the world are miningsoil nutrients because they lack access to sufficientorganic manure or mineral fertilizer (Bremen,Groot and van Keulen, 2001). They know thattheir land use practices cause environmentaldamage that may ultimately endanger future food

security but immediate food needs take priority(Mortimore and Adams, 2001).

Greater intensification of cropland use versus greaterloss of biodiversity and GHG emissions from deforesta-tion. The introduction of new technologies thatlead to higher yields or returns on existing landreduces the need for further land development.This can save a considerable amount of forest andrangeland (Nelson and Mareida, 2001) and even-tually allow marginal cropland to be taken out ofproduction and used for more sustainable systems,e.g. agroforestry, forestry, pastures and recreation.However, even under well-managed sustainablesystems such as IPNS and IPM, intensification canlead to more fertilizer and pesticide pollution(Goulding, 2000), greater GHG emissions fromnitrogen fertilizer and loss of biodiversity on inten-sively grazed pastures.

Reduction of soil erosion and water pollution versusgreater pesticide use. NT/CA, minimum tillage andrelated approaches to land management havemultiple environmental and farm income benefits,yet may require greater use of herbicides. However,initial fears that NT/CA would lead to greater use ofherbicides have not been fully confirmed, as herbi-cide use can be reduced or eliminated in systemsfollowing all the principles of NT/CA, once a newagro-ecosystem equilibrium has been established.Using green cover crops to reduce nitrate leachingduring the autumn and winter may increase carry-over of weeds, pests and diseases and lead to greaterpesticide use.

The potential environmental benefits versus risks ofGM crops. As discussed in Chapter 11, GM crops canhave a number of environmental benefits such as (i)reduced need for pesticides, particularly insecti-cides (e.g. Bt maize and cotton) and herbicides (e.g.Ht soybeans), although these gains are not neces-sarily permanent as pests can overcome the resist-ance of GM crops; (ii) lower pressures for croplanddevelopment and deforestation because of higheryields from existing land; and (iii) increased oppor-tunities to take marginal land out of production forset-aside or to cultivate some crops less intensively.The technologies involved can produce cultivarsthat can tolerate saline soils and thereby help toreclaim degraded land. On the other hand, thereare a number of possible environmental impactsand risks, such as the overuse of herbicides withherbicide-tolerant varieties and accumulation of

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herbicides in drinking-water sources; herbicidedrift from cropped areas, killing plants in fieldmargins, and hence leading to the death of insectsand birds in or dependent on field margins; deathof beneficial insects feeding on GM crops; andcrossing of GM crops with wild relatives and partic-ularly with related weed species, e.g. red rice,possibly leading to the development of herbicide-resistant weeds.

The most vocal concerns about agriculturalpollution and ecosystem damage tend to come fromenvironmentalists in developed countries. But in anumber of respects an improved environment is a luxury good that these countries can now afford.In earlier times they had different priorities(Alexandratos, 1995). Until the 1960s, when mostpeople were concerned with improving theirincomes, diversifying their diets and generalwelfare, protection of the environment was a lowpriority for all but a small minority (Reich, 1970;Nicholson, 1976), and some serious environmentalproblems arose. Since then income growth, educa-tion and better understanding of the environmentalconsequences of different agricultural practices and lifestyles have led to a growing consensus that governments should do more to protect the environment and that the public should pay morefor environmental protection and food safety.

Industrial countries have the economic andtechnical capacity to introduce additional measuresto protect the environment, and can afford thehigher food costs that may follow as a consequenceof these actions. In short, they are more able to payfor trade-offs between environment and develop-ment, although current actions seem unlikely toprevent some growth in agricultural pollution overthe next 20 years or so (OECD, 2001a).

Environmentalists and government officials indeveloping countries are no less aware of the nega-tive environmental consequences of agriculturalgrowth. However, their responses are constrainedby inadequate finance for the necessary research,particularly in sub-Saharan Africa; lack of institu-tions and support services that could raise aware-ness of potential ways to minimize or eliminatetrade-offs; and the need to avoid measures thatraise food prices because a high proportion ofpeople are unable to buy adequate food even atcurrent prices.

12.6 Concluding remarksIt has been argued that during the next decadesenvironmental trade-offs will be more difficult thanin the last few decades, with fewer win-win situa-tions and more obvious losers than winners(OECD, 2001a). This is not necessarily the case foragriculture in many developing countries if marketsignals are corrected so that they include the valueof environmental goods, services and costs; givefarmers everywhere the incentive to produce in asustainable way; overcome the negative impacts ofintensive production technologies; give resource-poor farmers the support they need to react toenvironmental and market signals (Mortimore andAdams, 2001); and North and South work togetherto remove production and trade distortions(McCalla, 2001).

There are many opportunities for placing agri-culture on a more sustainable path over the nextdecades, with benefits for both farmers andconsumers. For example, measures resulting inhigher nitrogen fertilizer-use efficiency and IPMreduce production costs for the farmer andprovide safer food, and at the same time they are cheaper than drinking-water treatment inreducing nitrate and pesticide residues.

Future agro-environmental impacts will beshaped primarily by two countervailing forces.Environmental pressures will tend to rise as a resultof the continuing increase in demand for food andagricultural products, mainly caused by populationand income growth. They will tend to be reducedby technological change and institutional responsesto environmental degradation caused by agricul-ture. The early implementation of available policyand technological responses could reduce negativeagro-environmental impacts or slow their growth,and speed up the growth of positive impacts.

Agricultural intensification is required for foodsecurity and for the conservation of tropical forestsand wetlands. The main priority is to decoupleintensification from the environmental degrada-tion caused by some current approaches to intensi-fication, by reshaping institutional structures andmarket signals. Research and farming practicesmust also be redirected towards greater use ofbiological and ecological approaches to nutrientrecycling, pest management and land husbandry(including soil and water conservation).

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This decoupling has already started in somecountries, but it will take time before it has appre-ciable effects. Hence agro-environmental impactsin the nearer future will be largely a continuationor acceleration of present trends. In particular,there will be a further slowdown in deforestationand rangeland clearance for crop production.Thus the main quantitative impacts on the envi-ronment will stem from the intensification ofproduction on existing cropland, rather than fromexpansion of cropland. There will be increasingpressure on some marginal lands, but progress inresearch and better off-farm employment opportu-nities seem likely to lead to the abandonment andnatural recovery of some marginal lands in Asiaand Latin America. There will also be moderateincreases in the area under irrigation. Drainagedevelopment and better irrigation water manage-ment will help to limit or reduce soil damage fromwaterlogging and salinization. Lastly, increasedintensification of production on existing arableland will have two main characteristics. There willbe enhanced use of precision farming and otheradvanced technologies, for example sophisticatedplant breeding and controlled release of mineralfertilizers. And the growth of fertilizer and pesti-cide use will slow down because of regulatory meas-ures and consumer demand for organically grownproduce.

The focus of concern is likely to shift from theonfarm impacts of physical land degradationtowards chemical and biological impacts, and fromonsite towards offsite and downstream impacts ofair and water pollution. Soil erosion may bereduced in important crop production areas by the projected shifts in technology. However, air and water pollution from mineral fertilizers andintensive livestock production will increase, withmore widespread nitrate contamination of waterresources, eutrophication of surface waters andammonia damage to ecosystems.

The slowing down of deforestation will reducethe rate of loss of biodiversity, but the intensifica-tion of cropland and pasture use seems likely toincrease such losses. The general picture for deser-tification is less certain, but the abandonment orreduced use of extensive semi-arid grazing landsshould lower the risk of desertification.

The overall pattern of future agro-environ-mental impacts is one of trade-offs between

increased agricultural production and reducedpressures on the environment. Intensification ofcrop production on existing cropland reduces thepressure to deforest, but tends to increase waterpollution by fertilizers and pesticides. Similarly, theswitch from extensive to intensive livestock lowersgrazing damage to rangelands but, for example,may increase water pollution from poorly managedmanure storage.

On the other hand, intensification of produc-tion on the better lands allows the abandonment oferosion-prone marginal lands, and improvementsin fertilizer-use efficiency and IPM together withthe expansion of organic farming are projected toslow down the growth in use of mineral fertilizersand pesticides. Similarly, the concentration of live-stock into feedlots or stalls makes it more feasible tocollect and recycle manure and to use advancedsystems for water purification and biogas produc-tion.

In an increasing number of situations the trade-offs are becoming less serious. Thus, for example,NT/CA may reduce overall pesticide use; reducesoil erosion, fossil energy inputs and droughtvulnerability; and raise carbon sequestration,natural soil nutrient recycling and farm incomes.Factors such as these lead to the overall conclusionthat agro-environmental impacts need not be abarrier to the projected production path becausethey can be reduced considerably through theadoption of proven policies and technologies.

It is one thing to project the potential for areversal or slowdown in the growth of agriculture’snegative impacts on the environment. It is quiteanother matter to make such a future a reality. Thiswill need a multidimensional approach and theintegration of environmental concerns into allaspects of agricultural policy. Such actions werefirst proposed more than a decade ago (FAO, 1988)but are only now being pursued in a partial mannerby some developed countries. Governments need toexploit the complementary roles of regulatory,economic and technological measures. Actions areneeded at the global, regional, national and locallevel. None of these actions will be easy, but the realachievements of some countries and local commu-nities over the past 30 years in promoting sustain-able agricultural development show what could beachieved over the next 30 years, given morecoherent efforts.