. '.'.

Earth as a Living Planet

Da niel B. ot k in Profe ssor Emeritus Department of Ecology, Evolu tio n, and Marine Bio logy University of Californ ia, Santa Barbara

President The Center for the Study of the Environment Santa Barbara, California

Edward . Keller Profe ssor of Environmenta l Studies and Earth Science Univ ersity of California, Santa Barbara

@ WILEY JOHN W ILEY & SONS, INC,

---KEY TERJ\(1S ag roecosvsrcrn 2 0 7 green revoluti on 210 aqu aculture 2 05 lim iting facto r 2 0 8 crop rotation 2 0 7 rnacronutricnr 208

gen etically mod ifi ed rnariculrure 206 cro ps 21 5 micronutrient 208

ST U 0 Y O_U_~ST l 1. What wilt be the best war [0 teed the wo rld in th e

next 10 years' The next 100 years'

2. A ci ty garba ge dump is fill ed; som e suggest that the area be turned int o a farm . What factors in the dump might make it a good area to farm, and what might make it 3 poor area to farm?

3. How might we use ou r knowle dge of successio n to make agriculture sustain able ?

4. Ranch ing wild animals-that is, keeping th em fe nced but never tarncd-e-h as been suggested as <1 way to

increas e food production in Africa, where wildlife is abu ndant . Based on this chapter, what art: the en ­vironrnental ad vantages and d isadvantages of such game ranching?

5 . Explain what is meant by the following statement: Th e world food problem is one of distribution , not of production. what are the majo r solutions to this world fo od problem?

FU RTnER_BEAD Lf\­Berry, Wendell. 2004. The U;ISf:n Ji lloa! AJJUI·;,n : e li /fli rt c-A_4,.;tulnwt

(Pa perback), Sierra Club Boob, Ori~in ;lIly publi shed in 19 77 . considered a classic 10 cnviro nmeural hreratu rc. The author IS J

Kcuruckv farme r and a writ er of ticcon :1S.well J.S nonfi ction .

Clay. Iason.2004 . HorM A~rrri '/lIt Il 1'"& n wi tbeEJlr irolllJlmr: A Comm odity· o.y·CoIIIJl/Miry G" ir{( ItJ ImpnuJ trill' Pm ai ca , Washington, D.C.: Island Press. Sponsored by the: Wor ld Wildlife Fund . this book has

mon oculru re 207 o rganic farming 2 10 pasture 205

rangelan d 2 05

synergistic effect 208

6 . You an: sent int o the Amazon rain for est to look for new cro p species. In what kin ds of habitats wo uld you look' What kinds of plants wo uld you look tor?

7 . How doe s agriculture simpl ify an ecosystem ? In what ways is this simplific ation beneficial to people? In what ways docs it pose pr oblems to r a Sustainable food supply!

8. ~\ vegetable garden is planted in a vacant lot in a city. Peas and beans grow well , but tomatoes and lettuce do poorly. \l'hat is the likely problem ' HoII' could it be corrected?

9 . A second veget able garden is planted in another va­can r lor . Nothing gro ws well . Outside th e city, in otherwise similar en vironments. vegetables grow vigor ously. What might explain the differ ence!

10 . Should o rganic farming be allowed to include ge· neucally mo di fied organ isms? \Vhy or why not?

a wealth of daci abou t farming and is a good reference fOr ~'$

bookshelf.

Cu nfer, G . 2005. 0" rbcGrcm P/ni IlJ:Ag ric1IIrll utrl/r! Eltl';rollJ,w,r. Co llege Stati o n: Texas A&r-.t Umversi ry Press . Uses the his­tory of Eu rope an ag ricu lt ure arr1ied to t he Amer ican Grell Plains as a way to discuss the iutcracricn bet ween naru re ~ nd

farming.

Chapter 12 LEA R N IN G Effects of Agriculture

Ii1'"',"", nruen t

_III/ IAgriculture changes the environment in

many ways, both locally and globally. After raading truschapter. you should l11de<stand:

• Howagriculture can lead to sou erosion, how severe the prOblem is. what methods are available to minimize erosion, and how these methods have reduced soil erosion i1 the United States.

• Howtarming can deplete soil tertility andwil y agricuiture in most cases requiresthe use orfertilizers.

• Wtrf some lands are best used tor grazingand how overgrazing can damageland .

• YVhat causes desertification.

• HQI,Yfarmingcreates COnditions thattend to promote pest species . them oortancs at contro lling pests [rouding weeds). and the problems

associatedwith chemical pesticides.

• How alternative agncuitural rr.elhods-including integrated pest

management, no-tilt agriCUlture, nlxedcropping. and other method s ofSOil conseNa tion-ean provide ma,<Jr environmental benefits.

• That genetic modification at crops COUld improve food Product ion and benefit the environment but perhaps also could createnew environmental P<ObIems.

Contegraze alOIlD the ttppn· llfiJsom-i Rivo, polluting it witb their mtrmm: rrl1d illcrtfU i l tg erosionns tIJry trample theground nea,. tlu river. This is om wn)' jtlmt ngriCttltttrt trffccrsthe MllJ;'Wl1JlC1lt.

/, II

I

I I

C HA P T E R 1 1 PR ODUCING ENOUGH F OOD F OR THE WORLD

i'I I

CASE STUDY:

Cedar Meadow Farms Steve Grorffarms 200 acres in Lancaster, Pennsylvania, using no-tillagriculture . He controls weeds andother pests by keepin g some kind ofve geration cover-crops or du ring fal­101\' periods some o ther vegetation . Some of the fields in his CedarMead ow Farm have not been plowed in 15 years. The result: fewer pc:sts,SO that COSIS of pesticides have dr opped almost 50%, Groff also reports that erosion has decreased considerably, while soil organic matter hasincreased .'

Steve Groffis not alone in hisefforts to adopt farm' managem ent practices thatreducepoUurion and imp ron: water quality while improvin g his balance sheet . For ex­ample , in Kansas, 36 fume" participate in the Kansas Rural Center's Clean Water Farms Project, which began in 1995. The goal of the project is to farm in a manner beneficial both to the environment and to the economics of farm-

IIIII

1

t

subjects of this c hapter.

12.1 How Agriculture Changes the Environment

Agnculrure is both one of hurrunirv 's and civilizati on's gn::atest triumphs and the source of some o f its grear ­est cnvi ro nrnental problems. Agriculture has an ancient lineage , going back thousands of years, and it h:1S always changed the local environment.

Environmental effects of agriculture expanded greatlv with the scienrific-ind ustri al revolution . .Major enviro nmental problems that result from agricultu re include soil erosion ; sed iment rransport and dcpo­sitio n do wnstr eam; on -site pollution from overuse and secondary effect s of fertilizers and pesticides: off-site pollution of other ecosystems, of soils, wate r. and air; deforc srarion ; d cserrificarion ; degradation of aquifers; salinization; accumulation of toxic meta ls; accu m u latio n of [Oxic o rganic co mpo unds; and toss of biodi versity.

ing.' More 3J1d more farmers in many other states an:using intensive rotational grazing systems, and American farmers arenot theonly onesadopting this moreen vironmentally benign and eco nomically advantageous approach to raising livestock. A recent studv 01'280 sustainable farmin g pro]­ects in 57 of the world's poon:st nations shows that such sustainable farming practices on average increased croppro­duction bv 79%, Ar the same tim e, as wi th Ceda r Meadow Farm) these projects are making soils more sustainable and aidingbiodiversity.l.3

Intensive rot ati onal grazing is just on e of many ac­Dons that can help farmers. Others include crop rotation, co rnpcs ring livesto ck wastes, integrated pest and weed management, and redesi gni n g livestock waste manage­rncnr and watering systems.

This case study show s that practices that are environmentally benign can be

economically advantageous, With wortd food needs increasing and crops being

grown for fuel, the environmental effects of agriculture are likely to increase. In the

haste to meet demand, it is likely that shortcuts will be taken that are not environmen­

tally sound. All the more reason thatthe Cedar Meadow Farm provides an important

example for us. The environmental advantages of such alt emative approaches to

agriculture and the en vironmental effects of various forms of aqriculture are the

12.2 The Plow Puzzle There: is nothing in nature like a plow, and there arcbig differences between the soils of an unplowed forest andthe soils of previously forested land that has been plowed and used fo ..crops for several thousand years. These differences were o bserved andwritten about bv one of the originatOrs of the modern srudv of the environment, George Perkins M arsh. Born in Ver~onr in the nin eteenth century, Marsh became the American ambass ador to Iralv and Egypt, Whil e in Ital", he was ' 0 str uck bv the difl~renccs in the soils of the fore sts of his nati ve Vermo nt and the soils lb,t had been fanned for thousands of vcars on the lwun pe nins ula that he made this a major theme in his landrn3fl' bo ok Man and Nature, publi shed in 1864. The furTn1aJ\J he observed in Italv had once been fore sts . But while tb< soiJ in Verrnonr \ \ '3; rich in organic matterand had definite lavers, th e sou of Italian farmland had lime o rganic matt<' an d lacked definite layers (Figu re 12 .1 ).

C H A P T E R 1 2 EFFE CTS OF AGRI CULTURE O N THE EN VIRONMENT

Hcres the puzzle: On e would expect that f:lrming in such heaVily modified soi l wo uld even tually become unsustainable, but much o f the farm land in Italy and Fr:lnce has been in Continuous use since pre-Roman rimes and is st ill highly productive . H ow can thi s be! ....nd what has been the long-term effect of such agri ­culture on the environment? The answers lie within this

Soil

Rock

Horizons

o Horizon is mostly organicmaterials, inclUding decomposed or decomposing leavesand twigs.Thishorizon is oftenbrown or black.

chapter. Briefly, the mort altered the soil is, the greater the amounr (and the expense) of mataials that must be added each year, including fertilizers, pesticides, and even how much irrigation water. A farm er faces 3. d ear choice: Farm in wars that keep the soil and the land as narurallv fertile as possible, or spend mor e and mor e to brin g int o the so il what it lacks .

t '" ~

~ Horizon is composed of bothmineraland organic materials. The color ISoften light blackto brown. Leaching-the process of dissolving,washing, Or draining earthmaterials by percolation of groundwater or otherliquids­OCCUrs intheA horizon and movesday and othermaterials, suchas iron and calcium, to the 8 horizon.

E HOrizon Iscomposed of Itght·colored materials resulting fromleaching of clay, calcium, magnesium, and ironto lowerhorizons. The A and E horizons Iogether constrtute the Zoneof 'e~c h ing.

B HOrizon is enriched in clay, ironoxides, silica, carbonate, or othermaterial leached from overlying horizons.Thishorizonis known as the zoneat accumulation.

~ Horizon is composed of paniaJly altered(weathered)parentmaterial; rockis showner::' but thematerialcouldalsobe alluvialin nature. suchas river gravels, in other

ronments.Thishorizon may be stainedredwithironoxides ,

R Unweathered (unaltered) parent material.(Not shown)

~re 12.1 • IdcaJized di3gramof a soil , sho\\i ng soil horizons.

1 2. 2 • T H E PL OW

Zone01 leaching

Zoneof accumulation

III i

Weathered

I

Ii

I

PUZZLE

Soils To most o f us, soils arc just what we step on; we don't th ink much abo ut t hcrn-c-t hev'rc just " dirt ." Bur soil s arc J.

ke ~' to li fe 0 11 the land, 3 ftc .; (i ll ~ lite and affecte d by it. Ifvc u lo ok ·"It th em d O)e!YI so ils are q uite rem arka ble. You wo n ' t

lind anyt hin g like ~. :1 rth soil o n M ars o r

venus o r the moo n. Wh y not ! Because

water JnJ life hJ H: src ;t tl ~· altered rhe land surface. Geo log ically, soils arc earth mat erials mod ified ove r lime b~' ph vsi­

c31, chemical, and bio logical processes into J series of IJ )"t r5 called toil borizons. Each kind of sol! hJ.S its own chemical

co mpo sitio n. Soils deve lop to r a very

lo ng rime , perh aps rhousauds of years.

If you di ~ (.:If(' tl j ll ~· into a so il so tha t

vo u lea ve J nice, dean ver tical side, yo u

will sec: th e soil's lavers . In 3 northern

forest , ;,1 soi l is dark at (h e top, th en has

J whi rc powdery lave r, pale: as ash , th en

3. brightl y colored layer, whic h ls usua lly

much deeper th.m the white o ne and is rvpi caily o rangis h. Bele w that is :I soil

whose color is close to that of th e bed ­roc k {which geo to gisrs call "the paren t

material," for o bvious reasons}, \ ,ve 'all the lavers horizons (Figu re 12 , n.

O\'e:ral l, \\ "3.t(r no W's down th rough the so il. R..1inw';ltl: r is naru ral!y sligh tJy

Jdd b~ o: ,~us e:- it has so m..: carbon d ioxide

from the J..i r d i s.~Q\ \' t:: d in it, a.nd this for ms

c:Hbo nic Jdd. a Im ld Jcid . &1inwatcr has

a pH of about 5 .5 . As ;,1 result, minerals such .l$iron•..::akium , and magnesium are k adH.:d tr am the upper ho rizo ns (A and

E) 'J. nd may be deposited in a JOW l,;r ho ri·

zan (B) . T he uppt.:r ho rizons Jrc \b lJJ lly

r\.lll of Iii".: .l l1d 3r t:: \'ic:\\'ed by ecol og ists 3S

com plex ecosystems, o r ecosyste m units soils in th e United States Col use billions (horizons 0 and A :. Decomposition is of dollars' wort h of property d"J.nu ge th e name of the game as fuugi, bacteria, each year. an d en ...l1 ani mals 11\\: on what plants Soils wi th small day par ticles retain and animals on the surface produ ce and wa te r well and rcrard rhe movement of dep osit . A.:ru 31 che mical decom position wa ter because th e spaces betwe en the

o f o rg anic com po unds from the su rface particles are \'ery small. Soils wi th CQ1n_ is done b ~' bacteria and fungi, the great er grain s, such J S sand or grave l, have

che mical facto ries of the biosphere. So il relati vely large spaces between grains, so

animals, such as earthworms, cat leaves, water moves qu ickly through them. Soils

I

20031992 199 7 200 1 t\\i g.'i. and ot her remains and break th em

into smaller pieces th at are easier tor the fun:;i and bact eria to process. Th e ani ­

rnals atfcc t th e rate of chemical reactions in the soi l. Th ere are also predators on

soil animals, so rhere is a soil ecological

fo od chain .

The soil horizons shO\\TI in Figure 12.1

are not nece ssarily all present in any one soil. .Very ~'ou ng soils may have only J.t1 upper A horizon over a C hori zon.

whereas matu re soils may have nearly all the horizo ns Sh O\\l1 .

Soil[o 'ri/iry is th e capacity of a so il to supply nutrients necessarytOrplant growth. Soils that have formed on geologically ~ 'oung materials are ofte:n nutrient-rich. Soils in humid areas and tropics rna)' be heJ\il y Icached and reLath 'd y nutrient­poor d \ie to the high rain fall. In such soils, nutrie nts ma.~· be q'c1e:d through the orgJnic·rich upper horizons; and if forest cover is remo\'ed. reforestation l"Iu y be very difficult (see Ch3pter 13 ).

Soils th:u aCI."1.l1l1ubte certain day minerJ.ls in sc-miJrid ft.:;;)ions molYswell when they bet wet an....1 shrink .:IS they dry OU[ , crac k­

ing roads. \\";ll1s, buildings, and othe r su ua lJrCS. Expansion And ( onrral."tio n of

wirh a mix tu re ofclay and sand CJn rtcin water well enough fo r plant growth but also drain well. Soils with 3 high percent­

age: of organic muter also retain water and chemical nutrients for plant growth. It is an advan tage to have good drain­age. so a coarse-grained soil is .:I good place to bu ild your house. If you arc goi ng to farm, you' ll do best in '3. lOW! soil that has '3. mixture of par ticle sizes. Th us. the type of soil par ticles present is important in determining where to build a house and where to fum and in siring facilities such as lJndfills. where reten tion

of pollurants o n site is an objective (set Chapt er 29 ).

Coarse-grained soil" especially thO!c composed primarily of sand, ere particu­larly susceptible: to erosion by water and \\ind . Soilscomposed of Ccr.lJ"SCr (hC1\;cr) partid es or liner pmkles m" "'"usually morc coh esive (held togedler br day min· er:Lls ) are more rt'liittant to ero sion .

It is di fficu lt to thi nk o f J humJll uSC

o f th e near ·surfAce 13nd e", i ronment that doc:s nOt in\'olve consideration of the soils present. As a. resul t, the srudy of soils con ti nu ~ s to be an important fUl1 of eO\ironmentai sciences.

Eros ion on Cropland by Year (Bitllons 0' Tons)

300 1 n 2.50

2.00

1.50

1.00

0.50

0.00 1982 1987

• Sheet & Rill Erosion • Wind Erosion

CrOpland includes culti'valed and non~ltiva led cropland

United Stares So il Consen 'atio n SCT\1Ct:) the n rest udied in me 19 70s and 199 0s. Measurements at th ese th ree rimes showed that soil erosion was o nly 6% of w ha t occurred in the: 1 9 30 s , ~ ·6

The bad news is mat , in g eneral, the dec reased rate still is greater than the rate o f reg eneratio n of new so il.J

Soli erosion beca me a nati o nal issue in the United Stites in the 19305, when in tense plo"in~ . co mbined with a major dr ought) loosen ed th e so il over large areas. The soi l blew away, creatin g dust sto rms th at buried automo biles and h o uses, d estroye d m:tny farms, irnpover. ished man)' people, and led to a large migration of farm . ers from OkJahoma and other Western and midwestern 'lates to Califo mi , . Th e human tr,gedie s of the Du st Bowl were made fam ou s bv John Stei nb eck 's novel 17" Grapts of Wrarh, late r a p ~pular movie su rring Henr)' Fond, (Figure 12 .3 ).

~re 12 .3 • The: Oust Bowl. Poor agricultural pr~ctice s and ~~roug h t created the DuStBowl, which l as ~ed abou t 1,0 co". dunng the 1930 s. Hea\'il\' plowed lands b.cking "egc-taC\'," ...._~ blew a\\'ay easilr in the:: d~ \' \\" itl d ~ , crc:l.O nf. dust Storms _1nd "\Q)'lllg houses.

Figure 12 .2 Soil erosion has decreased in the United Srares-1 0%since 1982 . (S<" I1TC: U.S. Department ofAgricu lture National Resources Inventor" 2003 Annua l NRJ h rrp ://\\ '\\ '\\' .n rcs . usd:a .So \ '/t~ch n i c ai/ NRI/ 2003/images/ eros3 hanJ.irge: .gif)

T he land that becam e m e D ust BOI\'l had been part of America 's g reat prairie, wh e re grasses roo re d d ee p , creating a he avily o rganic so il a meter or more down . The dense cover provided by grass stems and the anch oring po wer of roo ts protected th e so il from the erosive forces of water and wi nd . When th e plo w turned ove r tho se roo ts) the so il was expo sed dire ctly to sun. rain , and wi nd, which further loosened the so il. It was a g reat tra gedy of th at time and . lesson people th o ught would be rernem ­bered for ever. Bur so il con tin ues to erod e,

Th e int rodu ction o f h eavy earthmoving machinery after Wo rld War II added to m e problem by fu r ther darn­aging the soil Str uc tur e so im portan t for cro p produ ction . N o · ti ll practlces d escribed in th..: chapter's o pening case s lu d~' red uce such damag e.

As the hisro n ' o f the Dust Bow l m.3kes dear, w he n a

fo reSt or prairie (s cleared fo r agriculture, the so il changes. T he original soil developed ol'a a lon g period ; it is t)'pi . I caU)' rich In org anic matte r and [h ~re fore rich in chemical

ilI'nutrients, and it also p ro vides a ph ysical stru cru re COn .

d ucive [0 p lant g rowth . \-Vhe n the: o rig in :tl "cgctari on is cleared and the land is plan ted in cro ps. most of who se:: II organic man er is ha rvested and rem oved} ther e is less inp Ut o f dea d o rganic mart er to m e soil, and m e soil is e:xposed to sunligh t, which war ms it and spee ds the I! rate of decomposition o f its o rganic m:ltter. For these n~ asons , th e .mOunt o f or ganic matt er de cl in es, an d th e I soi l's physical StrucnJre beCOml'5 less cond ucive to plan t I grO\\~ l .

Ii

Tradition ally, farme rs com bated me decline in soil fer. tility br using organic tertilizcrs, such as anim aJ manun::. T hesc have the , d,.antJge o f impr Ol'ing both chemical and plwsic-aJ characteristics o f so il. Bu , organic ferti lizers can havc drawbacks, esp ecially under intense: agriculnm: On I poo r soils. In such situations, th ey do nOt provide enough o f th e che mical dement s neede d ro rep lace what is lost.

12.3 Our Eroding Soils T he ,\ mc:rh.-an Du st Bo", 1nf thc 1930s increases the puz· zle.:: ~l bO ll t rhe plo\\' . Soils arc ker s ro stlstainabk f.1Tm ing . FJr ming e ~l s ily dam:l ge:s so ils ( s~ C' A C losr.:r Lo o k 12.1). \Vhen lal1d is c1ca n:d of its 11 3tura l \'cgetatio n , such as to r­est o r grassiJnd , the soil beg ins to lose irs tt:- rIility. So me o f thi s o...·curs b~' physical .:ro sion , T he :;ood nl:\\'s is thJt . du o..: [0 impr()\"(:d IJr m illg, pr'lI.:tk l." . ~o i l erosio n r.HeS h."i\'c

decre, sed in (he U lli(ed Scates by 40 %. In 200 1, me most n:ce nt year for which go\'e rnm~nt data are: a\-a.i lablc:, ~2 million hect ares ( 104 millio n acres) had se rious, exceSS\,'e <rosi on (Figu re 12 .2 ). Bu t (h i. was down 37% frorn 69

mill io n hecrJr es (1 70 million , cres) in 1982 ' On e outsrJnding eXJ", ple: T he drJ in, ge area of~

C reek , Wisco nsin , an ,re, of 360 km' , I13S been hea~~ tJ rmed for ~ore t~an .3 C~ nt llT Y. Thi~ stream' s w3 te~ the " ', s the subJe(( o t , dewlcd srudy 111 the 19 30. b)

C H A P T E R 1 2 E F F E C T S O F A GAI CULTU R E O N TH E E N V IR O N M E N T 1 2 .3 • OU R ER OD IN G S O I L S

Il i ~ !

',11 I I

The development of ind ustrially p rod uced ferti lizers, co m mo nly (4 11 ~ d "c hemical" o r " art ificial" fert ilizers, \\' ;}5 a major facto r in the :;reJ t inc reases i ll crop pr od uc ­tio n in the twent iet h century, O ne o f the n-e st import ant advances W ;1S the invention of ind ust rial proces ses [Q co n­vert molecular nitrogen gJ.S in the atm osphere to nitrate th at can be used di rec tly by plants , Phosph oru s, ano ther biologically im portant d ement, is mined , usually from a fossil source that was bio logi cal in or igin, such as deposits o f bird guano o n islands used fo r nesting (Figu re 12 .4) . T he scientitic-i nd ustrial age brought with it mecha nized minin g o f phos phates and thei r lo ng -d istance tran sport. which , at a cost, led [Q sh ort-term increase s in soil fer­tility, Nitrogen, phos pho ru s, and other d ements arc co m bined in pro portions that are appropriate for specific

cro ps in spec ific loc ation s. Since [he end o f World War II, mec haniz ed farmin g

has seriou slv dam aged more th an 1 billion hectares (2.47 billio n acres) o f land . T hat's abo ut 1 0 . 5 ~; of [he worl d' s best soi l, equ al to the combined area of Ch ina and Ind ia. In ad d itio n, ove rgraz ing and def ore station have damaged app roximately 9 mi llion hec tares (22 mil­lion acres) to th e poi nt wh ere recovery will be: difficu lt; restoration of th e rest will req uire serio us 3(OOns.'

In the Un ited States, since: Europea n settleme nt , abou t o ne-third of the co u ntry' s topsoil has bee n lost, res ulting in 80 millio n hectares (198 million acres) left unprodu ctive or o nly margi nally productive ."

AgUl"8 12. 4 Boobic1 on 3 guano island. Th e birds nand 00 ,..cnruri~"s of bIrd dr op pings . Th l:y teed on oceJ.n fu h and ne1t on ish.llds. In dr y c1inul oes, their d rop pin gs J,,:~u mu I3 re . :and 1:13\'C been :l nlajof soun:c of phosphorus for ;J, gricult'U rc for (cnruries.

\

'!~!.-. - ­• ~ -r-lI -- - _

12 .4 Where Eroded Soil Goes: Sediments Also Cause Environmental Problems

Soil erode d from one location hJ.S ro go somewhere else. A lor of it travels down streams and river; and is depo sited at their mou ths . U .S. rivers carry about 3.6 billion metric [OIlS

pa year (4 billion D.S. ron s/ Y':Jf ) of scdirnent, 75"&of ir from agrirulmral lands . That's more than 25,000 po unds of sed iment for each perso n in the U nited States . Ofthis total, 2.7 billion me tri c tons /year (3 billion C .S. cons/year) are deposited in reservoirs, rivers, and lakes. Eventually, these: sedim ents fill in otherwise productive wate rs, destroying some 6sheries. In tro pical waters, sediments entering the ocean can dcstr ov coral reefs near a shore.

S, diment3tio"n has che mical enviro nmental effects as well. Nitrates, am monia, and ot he r fertilizers carried by sed ime nts enri ch the waters downst ream . This enri ch­ment , called mrropbicnt iou ; prom otes th e g row th of algae . (Eutr ophication is explained and describ ed in C hapte r 22 on water po llutio n .) It 's a st raightforward pr o cess: Fer ti lize rs that we re:meant to increase the growth of crops have th e same effect o n algae in th e: wat er. But peopl e generally do not wan t water enriched with algae, because the dead algae arc deco m pos ed by bacteria that, in turn, ((;01O\ 'C: o ":ygcn fro m th e wate r. As J result , fish can no lon ger live in th e wate r. The WOlte r bec omes thick. with :1 greenish -brown ma t, un pleasan t for recreation and a poo r base for drinking wat er, Eu t rop hication got '3. lo t of pub licity in 200 8 wh en bod ies of wate r in China became covered with algae just whe n athle tes w ere pre­parin g ro use th em for O lymp ic races . Sediments can transport to xic chemical pestic ides .

Sin ce the 19 30s, agric ultur e-induced has de creased with the decre ase in th e fate of soil erosion. Even so , taking into accou nt th e costs o f dredging and the decline in th e useful life of reser voir s, s,.:di f1lent dam­il:;e cost s the United State s abo ut 5500 rrullion a ycar,

Making Soils Sust a inable

So il form s co n rin uo usly, bur usuall y very slowly. On good lands , a layer o f soil 1 mm de ep, th inner than a piece of paper , for ms at a ta te ran ging from o ne per decade [Q onc in 40 years . In th e bcst possible farm in g­plet d v sustain able ag riculru re-the \\"ould ncver ~x ceed th c amo u nt of new soil p roduced ,

At tlus point in ou r discussi on, we have par tial answer to th e qu estion ""How co uld fanni ng be sustained fo r th ousands of \'ears, while th e so il has be<O dc::gr:1ded?" \ Vc must reca"gni ze a disti nction rh e: susrainability of J. produ (t (in this case the susrainability of th ~ ecosystem. It l ngriculw rt

I

I: I I i

I I

12 . 5 • CON T RO L L ING P E ST S

From an ecological point of view, pests are undesirable competito rs, parasites, or predators , The major agri­cultu ral pests are insects th at feed mainl y o n the live pa rtS o f plants, especia lly leaves and sterns ; nematod es (sma ll worms), which li\'e m ainly in th e so il and feed o n roots and o th er plant tissue s; bacte rial and \iral diseases ; weeds (plan ts th at co m pete lIith the crop s ); an d "erre­braces (ma inly rod en ts and bird s) th at feed o n grai n o r fi-uit . Even ro da)', wi th mo d ern techno lo gy, the total losses fro m all pests are hu ge ; in the Unit ed States, pests aCCO Unt for an csomated loss o f on e-t hird o f the poten ­tial harvest and ,bour one-tenth of the harvested cro p . Prc:har'\'est losses are d ue to co mpetitio n from weeds, d iseases, an d hc:rbi\'o rc:: s; posth arveSt losses are largel y due to herbi\·orc:s.9• 10

ver. requ ires extensiveusc of pesticides.

12.5 Controlling Pests

cenu rmtion rillng t ) invo lves not plowing the: land , using herbicid es and inte g rated pest managemen t (d is­cussed later in thi s ch ap te r) to keep d own wee d s, and allo\\; ng SOm e we ed s to grow. Stems and root s that arc nor part of t he co m me rcial crop art: le ft in th e fields and allow ed to d ec ay in pla ce ( Figu re 12.5b). In COntraSt to standard m ode rn ap p ro ach es, th e goa l in no-t ilt agr icu lture is t o suppress and co nt ro l wee ds but not to eh rninar e th em at the expen se o f so il co n­sc r\'~ti on , \Vo r l d \\' i d~ , no -till agricu lru re is increasin g bur IS PI":ICticed o n o n lv 5 '~ ; o f the wo rld 's farmland .' Paraguay leads the wo (ld wi th 55% of its farm land in nO - ~ ill. The United States, with 17 .5% in no -till , lags behind man \' o t he r nat ion s. Arge nt ina h as 4 5%, Brazil 39%, and C;nada re ach ed 30% in 2 001 , u p Ir o m 24 % a decade earlie r. An :Jdd iti o n:1 1 benefit of no -t ill agri ­~Iturt is th at it reduc~ s the releas e of carbo n dioxiden:rn the ~ oi l , which occ u rs whe n [h e soil is plowed. of Us no -ull agncultu re is o ne way to red uce t he d 'lects

global w:lrm in g .

truly and com­am ount o f soil lost

re-JChed a

bctween crops) and

, ~

sedi rnenraricn

C H A P T E R 12 E F FE CTS OF AGA I C ULTunE O N TH E: E N V I R O NM E N T

•

production can be sustai ned, but tlu: ((OSYf UJll mn.l' JlOt be. And if the ccosystem is not sustained, rhcn people mu st pro\ide ad ditio nal inputs of energy and chemical d ements to replace what is lost.

contour Plowing

plowed fu rrows make path s for wate r to flo w, and if the furro\Vs go do wnhill, then the wa te r moves rapidly along rhern, increas ing, the er osio n rate. In co n tour plowing, the land is plowed perpendicu lar to the slopes and as horizontally as possible.

Alon g with no ·till agriculture, contour plo wi ng has been one of th e mo st effective ways to red uce soil cro ­sion. Th is was demon strated by an expe rimen t on sloping land planted in pota toes. Parr of th e land was plowed in uphill and downhill rows, and parr was co ntour-plowed . That year [he uphill and downhill section lost 32 metric ronsy ha (14 .4 to nsy'acrc) of ro psoil; th e co ntour-plowed section lost o nly 0 .22 metri c ron/ ha (0 .1 ron Zacre ). It would take alm ost 150 years for th e co ntour-plowed land co erod e as mu ch as th e trad itio nally plow ed land eroded in a sing le year! In add itio n to dras tical ly red uc­ing soil erosion , co nto ur plowing uses less fuel and rim e. Even so . tod ay co nto ur plo wing is used o n o nly a small fraetion of th e land in the Un ited States, Fo r exam ple , of Minnesot a's 4 million hect ares ( 10 million acres) o f cropland, only 5 30,000 hectares (1.3 million acres ) are contour-plowe d .

No-Till Agriculture

A5 the case: srudy in trod uci ng th is chapter suggests , an even mor e efficient way to slo w erosio n is to avoid plollin g altoge the r. No-~i1I agriculture (a lso called

In)

,.. \ - ~" ...... .~ ~ .. "

~"._., ':"'

- ...~ . ,\ . - ."1< j

. -, , Il l i ~ ' - '-.. . '_ i_ " . ' . . '~ . \"~\ 'v : "-:'""'\ "'" " . . .. c!.

\ I,· \, '­

E.W (b)

Fig u re 12.5 ~ Alternative agricu ltu ral plowing and tilling meth ods : ( n ) contour strip cro ps in the:midwestern United States; ( b) no -till farming. Both meth ods reduce erosion. No -till, howe­

II I!'

I I

' ~. I'I ' iill

I i I

We rend 10 th ink th at th e major agricu ltu ral pests are insects. bur in fac t weeds are the major problem. Farming produces special environmental and ecologi­cal conditions that tend to pr om ote weeds . Remember th at rhe process o f farming is an attempt 10 ( I ) hold back the natural precesses of ecological succession, (2) prevent migrating organisms from entering an area. and (3) prevent natural interactions (including cornpeti­tion , predation, and parasitism) between populations of different species.

Because a farm is maintained in a vcry early stage of eco­logicalsuccession and is enriched b} fertilizers and wate r, it is a good place no t only for cro ps but also 1'01 other early­successional plants. These nonc rop and therefore un desir­able plants are what we call weeds. A weed is just a plant in a place: we do nor want it to be. Recall that early-successiona l plan ts tend to be fast-g rowin g and (0 have seed s that arc easily blown by the wind Orspread b)' animal s. These plants spread andgrow rapidlyin the invitinghabitatofopen , early­successional croplands,

The re are about 30 ,000 species of weeds, and in any year a typical fa rm field is infested with between 10 and 50 of them . Weeds co mpete with CtOpSlo r aUresources: ligh t, water, nu trien ts, and just plain space [Q grow. The more weeds, the less crop. Some weeds can have a devastating effect o n crops . For example, the producti o n of soybeans isreduced by 60%if a weed called cocklebur :Jrows three individuals per met e r (o ne ind ividual per fi'OI)1I

12.6 Th e History of Pestic ides

Befor e the Industrial Revoluti o n, farmers could do linle to prevent pests except remove them when they appeared or use: farming methods th at tended to d ecrease their density. For exam ple, slash- and -burn agriculture: (also known 3S swi d den agri cu ltu re) allows successio n to take place. The g reater d iversity of plants and the long time between the use of each plot red uces the den siry of pests (sec Chapter I I) . Pr eind ustrial farmers also plan ted aro ­matic herbs and other vegetatio n that repel insects.

With the beginning of mod em science-based agri cul ­rure , people began 10 search for chemicals that wo uld reduce the abundances of pests. More important, ehcy searched lo r a " magic bullet"- a chemical ( referred 10 as a lltJn'mp-rpecrrllllf perticidc) that would ha\'c a single rarget, just one pest , and not affect an ything clse . But th is prm'ed dush'c. \Ve have already secn that tiving: things have: many chemical reactio ns in COmmon (see Cha pte rs 4 and 6) , so a chemic.l! that is roxie ro one species is likel ~ ' to be roxjc to another. The slOry of th e scientific search for pesticide s is th e search for a bener and bemr magic buUer. Th e earli · esr pesticides were: simple inorganic compounds thou \vue

""-;':~~ - ,­

,~, ,:---.- ­

widely roxie. One of the earliest was arsenic, J chemical cleme nt toxic to all life , includi ng peop le. It was certainly effective in killing pests, but it killed ben eficial organism, as well and was verv dangerou s to usc.

A second stage in the developm ent of pesticides began in the: 1930s and involved petr oleum -based sprays and natural plant chemicals. .\hny plants produce chemicals as a defense against di Sl:3SC and herb ivores, and these cherni. cats arc effective pesticides. Nicoti ne, from the to bacco plant, is the primary agcnr in some insecticides stiUin wide usc tod ay. H oweve r, alth ou gh natu ral plant pesticides arc comparatively safe , they were not 35 effective as desired.

The third stage in the develo pment o f pes t icides was th e development of artifi cial organic co mpo unds . Some, like DDT, are broad -spe ctrum, but more ef fective than natu ral plan t chemicals. Th ese chemicals have been important (Q agriculture, but unexpected envir on men tal effe cts keep cropping up, and the rnag :c ~ "ull e t has remai ned elusive. For example , aldrin and dieldrin have been widel y used to co ntro l te rmi tes J.S well as pests on corn, potatoes , and fruits, Dieldrin is about 50 times 3S

to xic to peo plc as DDT. These chemicals are designed ro remain in the: soil and typically do so for years. but they are readily drained from tropi cal rain -forest soils. Therefore, they have spread widely and arc found in organisms in arctic waters . The chemicals accum ulate in people .

As a result , a fo ur th stage in the development of pes. ricides began , which returned <0 biological and ecological knowledge. T his was the beginni ng of modem biological control, the usc ofbiological preda to rs and parasites to can­rrol pests. One of the most effective of these isa bacterium named Bacillus thuri'ETt't1tsir, known as BT, which causes a disease that affects caterpillars and the larva e o f other insect pests. Spore s of BT arc sold co mmercially (you can buy them at your local garden store and usc thi s method fOI your home garde n). BT has been one o f the most important \\'ar~ to control epidemics of gypsy moths, an introduced mo th whose larvae periodi cally strip most of the leaves from luge areas of forests in the eastern Unit ed States. BT has proved safe and effecovc-s-safe because it causes disease onlv in specific insects and is harml ess <0 people and other mammals, and because, asa natural biological "prod uct," its presence and its decayare nonpolluting.

Another group o f effec tive biolo gical co nrro l agents aresmall wasps that arc parasites of caterpillars. The wasps lay th eir eggs On the caterpi llars; th e lall"al wasps then I<ed on the caterpillars, killing th em . Th ese wasps tend to have n~ ry specific relationships (one species of wasp \\,U be a parasite o f one species of pesr), anu so rhey an: both drecti,"e and narrow-spec uum (Figu re 12 .6 ).

And in th~ list of biolog ical control species \\ '1.:CJ~()( forger ladybugs, which arc predalO " of mmy pests. ~ ou can buy these, toO , at many garden srorcs and relC3SC them in ~'o ur garden.

. -­-

Another technique to control insects involves the use of Sex ph eromones, chemicals releasedby most species of adult insects (usu ally the female ) toattract members o f me opposite: Sex. In some species, pheromones have been shown 10 be effecti ve u p 10 4 .3 km (2.7 mil away, These chemicals have bee n identified , synth...sized , and used as baitin insect traps, in insect surve ys , or simply to confuse the mating pa tterns of the insects involved .

12.7 Integrated Pest Management

While biological control wor ks well, it has no t solved all problems with agricultural pests. fu a result, a fifth stage developed , known as integrated pest manag ement (D'M). IPM USC.\ a com bination of methods, includin g biological 'OnO'Ol, certain chemical pesticides, 3J1d some methods of planting crops. A key idea underl yi ng IP M is th at the goal can be control rather than complete elimination o f a pest. This is justified for several reasons . Eco nomical ly, it bteomcs man: and more expensi\'r: to eliminatc a greatcr ~d ,greater pcrccmagc of a IXSt, while me valuc of that e~nari on, in terms of crops to seU, becomes less and less. This SUggests that it m3.kes economi c sense to lea\'e somc of the pests and eliminate only enough 10 pl m1de beneri t . In addition , allowing some ofa peS! population to remain , small but Controlled, does less damage: to ecosystems, soils, ' '' tel, and air. Some like to thi nk ofIPM as an ecO.\\'srem apPC03ch to pest ffianage:mem, b<o:causc::: it makes use ~fthe

Figure 12.6 Integrated peS( rnanagerncnr : the bio logical co n ­trol of pests. The goal is [Q reduce the use of artificial pesticides. reduce COStS, and efficiently control pests.

characteristics of ecologicalcommunities and ecosysrcrns as discussed in C hapters 4 , 6, and 10 .

Anoth er characteristic of IPM is th.e atrernp t to move a\\'3.}' from rnonoculrure of J. single strain growing in per­tcctly regular ro« s, Studi es have show n that just the physical co mplexity of a habitat con slow the spread of parasites. In effect, a pest like a caterpillaror mite is trying to findits way through a maze . If the maze con sists ofregulsr rows of noth­ing but what the pest likes to eat, the maze problem iseasily solved by the dumb", ofanim als. But if there are several spe­cks, even two or three, arranged ina morc complex pattern, the pests have a hard rime findin;; their pre)".

N o -till o r low-till agricu ltur e is another fcaru re ofIPM , beca use th is helps natu ral enemies o f so me pests to buil d up in the soil (p lowing destroys the habitatsof these pest enemies) .

Co ntro l o f the oriental fruir moth, whic h attacks a nu m­ber of fruir cro ps, is an example of IPM biological control (Figu re 12.7). Th e moth was found 10 be a prey ofa species of wasp, 4llaCJ-ocmtrm flll ry/irortlS,9 and introducing the wasp into fields helped con trol the mo th . Inrcresringly, in peach fields the \\-asp was mo re effecti"e when Strawbe rry fields were ne.,-by. The strawberr)" fields pro"ded an alter­native habitat for the wasp, especiall)I importanr for O\"~r­

wimering.9 As this example: ~hows , spatia..! compk xiry and bio logical di"ersit)"also become part of the IPM straregj'.

Although artificial pesticides arc used , the \' arc used along with the o the r tech niques, so th e app licatio n of the se pesticides can be spari ng and specific. This wo uld also greadr reduce::: the cosrs to farmers tor pesr control.

Bacterial disease 01 insectssprayed from aircraft

C H A P TE R 1 2 EF FE CT S O F A GRI CULT URE O N THE E N V I RONME NT 12 . 7 • IN T EG R A TE D pe ST M ANAGEMENT

I

DDT 11\1 • lJ

(n J (b)

Agure 12.7 The ori ental tTuit mo th !at\ '3.C.1 pest offruit crops , is controlled bv a parasite wasp that attacks the: larvae.

( n ) T he larvae. (bl Apples dam aged by the mo th .

Cu rrent agricu lru ral pra ctice s in the Un ited States involve a combination of app roaches, bu t in most cases th e)' arc more restri ct ed than an IP M srraregy. Bio logical co ntrol methods arc used to a comparatively small extent . T hey arc t he primary tac tics fo r co ntroll ing vert ebrat e pests (mice , voles) and birds) that feed on let tuc e , rorna­roes , and strawbe rries in Californ ia but are not major techniques for grains, corton , pot atoe s, ap ples,' o r mel­o ns. Chemicals arc th e principal control method s fo r insect pes ts. Fo r weeds, the: principal con t rols arc: meth­ods of lan d cultu re. T he use of gen eti cally resistant stock is important for disease cont rol in wheat, co rn, co tton, and some veg et able cro ps, suc h as lettuc e and rornatoe s.

Monitoring Pesticides in the Environment

World us e of pesti cide s exceeds 2 .5 bil lion kg (5 billio n pounds \, and in [he U nired States it exceeds 680 million kg (1,200 milli on pounds) (Figu re 12 .8) . T he to tal amou nt paid for these pesti cid es is 532 billi on worl dw ide and Sl lbillion in the United Stares .' !

6000 - ··'-rld Market

~ "­'0 ~ c

~ ~

(nJ

O nce appl ied , th ese ch emi cals may decompose in place or may be blown bv th e wi nd or tran spor ted by surface and su bs u rface wa ters, me an w hile continuing to decom­pos e. Somet imes th e ini tial br eakdown products (the first , still complex chem icals produced from the original oesucides] are toxic, as is the case with DDT (see A Closer Look 12 .2 ). Evenruall v, the toxic compounds are deco mp osed to th eir o riginal inorganic o r simple, non­

toxic o rgan ic co mpo u nds. However, for some chemicals,

th is can tak e a \"tTY long tim e . H erbicid es account for about 60g ~ of pesticides found

in th e nation's wa te rs. Surprisingly little is known about th e history of m e co ncentra tions of pesticides in the

major rivers of America. For example, there is no well­esta blishe d program to monitor the changes in the con ­

ce ntra tion of pesti cides in the Missouri River, one: of the lo ngest rivers in the world, although rccentlv there: have been spo t measure s of this concenrrarion." The Missouri drai ns o ne -sixth o f the United States, much of it from the

major agri cultural states. Where do all th ese pesticides go> How long do they

last in the en\' iro nment, both all the site where they were:

I

Other Pesticldes

Chlorinel (6%)

Hypochl orite (530/0) Wood

PreservatiV85 (16%)

(b) (7%)

Special tBi oci de

y s Other

U.S. Market

Herbicides Inseclicides Fungicides

4000 ~1------------------1

FIgure 12.8 World tl ~ ofpcst. icld es, I n) cot:l.13mounts, (!!J pCr( .::nt3 ~': ": b ~ ' rn:lin type (SollluJ" EPA P0061"'200Q-2001

Pesticide Market E sinlJ. tc ~ : US 2;';C, " EP.\.'

EFFE CT S O F AG R IC U LTURE ON THE EN V IRONM EN TCHAPTER 12

In 20 06 , the Uni ted Nations World Hc.1lth Organiza tion endors ed wider use

of DDT in Africa to co mbat mal aria.

This cont ro versial decision is the lar­est even t in the lon g histo ry of the use

and misuse of thi s famous pesticide .The

real revolu tion in che mical pes ticides­

the develo pment of more sophis ticated pesticides-began with th e end of\Vortd

War 1I and me discovery of DDT and other chlorinate d hydrocarbo ns, inclu d ­

ing aldrin and diel drin. When DD T was first developed in the 1940s, it seemed to be the lo ng-sought magic bullet , with

no short-term effects on peop le and deadly on ly to insects . At the time , sci­

enrists believed that a chemical cou ld no t

be readily transported fro m its original site: of application unless it was water­

soluble. DDT was nor \'ery soluble in water and th erefore: did no t appear to

pose: an environmental hazard . DDT was used very wi dely unti l thr ee: th ings were: discovered.

It has long-term effects on desirab le species. Most spectac ular ly,it decr eased

the thickness o feggshel ls as they deve­loped within bird s.

It is sto red in oils and fats and is transferred up food chains as one

Animal cats ano ther . As it is passed up food chains, it becomes co ncentra ted 50 that the high er an o rga nism is o n a

food chain, th e high er its co ncentra ­tion of DDT. Thi s proc ess is knO\ \11

as food -chain con cen tra tion or bio­magnification (discussed in detail in Chapter 15 ).

The: storage of DDT in fats and oi ls . Uows the che mical to be t ransferr ed

biologically e:\'e:n though it is not \'er~' soluble in Water.

In birds, DDT and th e prod ucts of itscnemica.l breakdown (known as DOD

and DOE) rhinned eggshells so that they broke e:asily, reducin g the sucass of

reprodUction. T his \\'as especially severe

in birds that arc high o n the food chain ­

pred ato rs that fe ed on o the r predato rs, such as the b.:Jd eagle, the: osprey, and the pelican, which teed on fish that may

be pred ators of other fish.

As a resul t . DDT was banned in

most de veloped nations-e-banncd in the United States in I971. Since then, a dramatic recovery has occurred in th e pop ula tions of affect ed birds . The brown

pelican o f th e Florida and California

coasts, which had become rare and

endangered and whose repr oduction had been restric ted to o ffsho re islands wher e

DD T bad nor been used, became co m­

mon 3SJin. The bald eagle became abun­

danr again in the no rth wo ods, wh ere it can be see n in Voyageurs N ation al Park and the Boundary Waters Canoe Area of

northern Minnesota. H owever, DD T is still being produ ced in the United State s

for use in th e developing and less devel­

oped natio ns, especial ly 3S a control tor malaria-spreading mosquitoes .

The use of DDT has had some l-en­efits. It was primarily respo nsible fo r eliminatin g malaria and yellow fever as major diseases, reducing th e: inciden ce

o f malaria in the United States 'to rn an a\'erage of 250.000 cases a year prior

to the spraying program to fewer than 10 per year in 195 0. Even for n-esc uses, howeve r, DDT's effectiveness has declined over the yean because many species of insects have:developed :1 rests­ranee to it . Never th eless, DDT con tin ues to be used because it is che ap and suffi­cientlv effec tive and because people have become accu stome d to using it, Th e

U .S. Centers for Disease Cont:ool e:sti m.ltes that berwccn 200,000 and mo re than 1 million people die each ye,lr from malaria, 75 : ~ ofchem children in Afric.1. ,I~

About 35,000 mctri..: ton s of DDT are produced annu .~lI y in at lease five coun · tries, wd it is 1c:g;:J! ly importe:d and used

in dozens, includinG Mexico .

Although people in de \'c:lop cd nJ t.ion s bdiC' \'C' the y Arc: free from the effects of

1 2 .7 • I N TE GR AT E D

DDT, in fact th is chemical is tran sported

back to ind ustrial nations in agricul­

tu ral products fro m natio ns still using the chemical. Also, migratin g birds that

spend part of th e year in malarial reg ions

are: st ill subject to DD T. Th us, despite being banned in the develop ed na tio ns,

DD T rem ains an important wo rld issue in pest con tro l. (T he problem of de vel­

oping nation s' usc of pesticides ban ned in Other natio ns is an issue nor only for

DDT bur also for other chonicals.) Wirb the bann ing of D DT in dcvel­

op ed nations , other che micals beca me mo re: prominent , chemicals rhar we re

less persistent in the enviro nrnen r.

Among the next :::;ener:::.rion of insec­

ticides were organophospbates-c-phos­phorus-co nraining chem icals that affect the n~n'OUS system. These che micals arc

mor e specific and decay rapidl y in the soil. T herefore, th e)' do not have the:

same persistence as D DT. But they are toxic ro peop le an d must be hand! cd very carefu lly by tho se who apply them.

Chemical pestic ides have created a revolu tion in agricultu re. However, in additi on to th e negative cnvi ro rtm crt­

ral effects of chemicals such as DDT,

they have o ther major drawbacks. On e: proble m is seconda ry pest outbreaks,

which occu r after extended use (and possibly because of extended usc) or a pesu cidc. Seco ndar y pest outbreaks can

come about in re-o \\"aYs : (l) Reducing

one targ et species redu ces competition wi th ,1 second species, which then Aour­

ishes and beco mes a pest , o r (2) the

pest develops resistance to the pesti cide s

th roo ;.::h c\'o lutio n "nd narllral selec tion, which tJ.\"or those who have d gn.:;1tl:r

immunity co the chemical. Resistance

has de\'eloped with many pesticides. For e"\::J.mplc , D:J. ~ : :nit (fcnsulfothion),

an organophosphate, first introduced ill

t 970 to con ~ rol maggots thac att ".l ck

oni on s in .\1i ch : ~ran, was ori:.,rimlly suc­

cessful buc is.no\\' so in effecti\'e that it is no long\:',- used for th at Ci"Op .

P EST M A N A GEMEN T

I

- -- -- -~ ~:).,

• • • •I~_- ~

deposi ted and downstream and downwind! Wh at is the co ncentratio n o f t hese in ou r water s? 10 esta blish use ful standards to r pest icide levels in th e enviro nment, and to u nders tand the envir o nmenta l effects of pes ticides, it is neccssarv to m oni tor th e co ncc ntra tio .is. Public health stJ nd .u ds and en vironmen ta l-effects standards have been establishe d fo r so me b ut no t all of th ese co mpo u nd s. The United States Geological Sur vey has est ablished a network for mon itoring 60 sample wat ersheds through ­o ut the natio n . These arc medium-size wate rsheds, not th e e ntire tlow fro m th e: nation's major rivers . O ne such watershed is th at o f the Platt e River, a major tri bu tary of

the Missouri River. T he: mo st co m mo n herb icides used lor gro wing co rn,

sorghum , and soybeans along the Plane River were ala ­chlor, atraz iuc , cyan azinc, and m etolachlor , all organo­ni trogen herbicide s. Monitori ng of th e Plane near linco ln, Neb raska, suggested tha t du ring heavy spring ru no ff, co ncentratio ns of so me he rb icide s might be reachi ng or exceeding establ ished public health stan dards. But thi s researc h is [ust begi nni ng.and it is difficu lt to reach dcfini­rive co nclusio ns as to whether pr(sent co ncen tra tio ns are causing har m in pub lic water supplies or to wil dli fe, fish, algae in freshwate r, o r vcgeratio n. Advances in knowled ge give us muc h more in formation, o n a mor e regu lar basis, abo ut how much of man y artificial co m pou nds are in o ur\

I wate rs, but we arc s till unclear ab out th eir envi ronrnenral effects. A wide r and better program to mon itor pesticid es

! in water and soil is imp ortant to provide a sound scientific basis for dealing with pesticides .

\ 12.8 Genetically ModifiedI

i CropsI

Remem ber tram C ha pter I I t hat the gene tic mod ­I ificarion of organ ism s currently uses three method s: ( I ) faster and mor e efficient de velopment of nell' hyb rids, (2) introd ucti on of the "terminato r gene," an d (3) tra ns ­fer of gen etic pr op erties fro m wide ly diverge nt kinds o f life (Figure 12 .9 ).

- ' ~ 'l

~ ~ Yfi¥Av:0-

Eac h of th ese pos es different pot ential enviro nmental pro b lems. H er e, we need to keep in mind a ge neral ru le of enviro nm ental actions: If actions we take arc similar in kind and frequ en cy to na tura l chan ges, the n the effec ts On the environment are likely to be benign . T his is because spec ies have had a lo ng time to evo lve and adap t to th ese chan ges . In co ntrast , cha nge s th at are novel-s-that do not oc cur in nature-arc: more likclv to have negative o r undesirable environmental effects , both d ireci and indirect. \Ve can apply thi s ru le: to th e th ree categories of gen etic allv engineered crops .

New Hybrids

The development o f hybrids withi n a species is a natural phenomenon (see C hapter 7), and the d evelopment of hyb rids of maj or cro ps, especi ally of sma ll grains, has bee n 3. majo r factor in the grea t inc rease in pr od uctiv­ity of twentieth -century agri culture . So , stric tly from an envi ro nmental perspective , gene tic engineerin g to dev elop hybrids within a species is likely to be as be nign as th e deve lop ment of agri cultural hyb rids has been with co nventional me thods.

T here is an importan t cavea t, howeve r, So me: people are co ncerned th at the grea t efficie ncy of ge netic modi­fication methods ma r produce "s upe rhybrids" that are so pr oductive they can grow whe re they are not want ed and become pests. There is also co nc ern [hat so me of the nell' hvb rid cha racteristics co u ld be transferr ed bv inter­breeding with closely relat ed weeds (Figu re t z.io) . This co u ld inadverten tly create a "superwc ed" whose gro wth, persi ste nce, an d resistance to pesticides would make: it d ifficul t to co ntrol. Another env iro nm ent al concern is that n ell' hybri ds m igh t be de velop ed th at co uld grow o n more and more marginal lan ds. T he d evelopment of cro ps on suc h marginal lands migh t increase er osion and sed imentation and lead to d ecre ased biological di"ers itj' in specific bio mes . Still an other potential problem is th" "s u perhybrids" might requi re muc h more ferti lizer, pes­ticide , and wate r, This co uld lead to grea te r po lluti on and the need for mo re irr igatio n .

-"""-,, t -... ,-:. ....r -

Agur"e 12.9 .-\1\cx::lmpk of ho w crops arc g.cnc tic111~ ' mod ified , ($cc tc·u to r cxplanJu on .)

CHA PTE R 12 E F F E C T S OF AGR ICULT U R E ON T HE E NVI RO NMEN T

On th e other ha nd , gene tic engin ee ring co uld lead to h\'brids th at req uire less ferti lizer, pestici de, and wate r. F~ r example , at pre sent, o nly legu mes (p eas and th eir rc:1:lt:i\'es) ha ve symbi otic relationship s with bact eria and fungi that allow them to fix nitro gen . Attempts arc under \\' a~' to transfe r th is capability to o th er crops, so that more kinds or crops wo uld enri ch the so il with nitrogen and req uire much less e'cre rnal applicatio n of nitr ogen fertilizer_

The Terminator Gene

The term in at o r gen e makes seeds from a crop steri le . This is d on e: for envi ronmental and economic reasons . In theory, it pre \,( llts a gene tica lly modified cr op from spreading _ It also protec ts th e m arker fo r th e co rpo­ration that develo ped it : Farmers canno t get around purchasing seed s by using some of their crops ' hybrid seeds th e next yea r. But thi s po ses social and polit i­cal prob lem s. Far me rs in less-d eve lo ped na tio ns and govern me nts of na tions that lack ge netic-engineering capabi lities are conce rned th at th e term inat or gene: will allow the United Sta res, an d a lew o f its m ajo r corpo­rations, to control the world food su pply. Concerned

,ntrodUC1!On of plon l ~

Slep A: Pollen now l~wild relatives

[

Step 1: Step B: Sc.nivaI outside of cultivation Hybrid formation

~ Ste p 2: Stop C: outside of cultivation Hybrid survival

l ~ Step 3: Step 0 :

SttI-Sustainlng poouranons Hybnd reprodccucn

L ~ Step E:

Inlrogression ot gen es into wild relalives

.-JSpread and per sistence

t Economic or environmental harm

~1'812 _ 10 \\ .1:>; in whk h the t .:nctic ch.l rl ( t..: ri ~u, s 0 1 .1. lfiltd crop misht spread ,

1 2 8

obse rvers believe tha t farmers in poor nations must be able to grow nex t year 's cro ps fro m their own seeds because rhey cannot afford to buy new seeds e\'cry year. Th is is not di rec tly an enviro nm e ntal pr o ble m , but ir can become an environmental pro blem ind irectl y by affe ct ­ing total world foo d productio n, which then affec ts the hum an popu latio n and how land is used in areas that have been in agricu lture .

Transfer of Genes from One Major Form of Life to Another

Most environmental concerns have to do with th e- third kind of genetic modi ficatio n of cro ps: [he transfer o f genes from one major kind of life to another. T his is a nove l eftecr and th erefor e mor e: like ly to have nega tive and undesirable impacts. In several cases, th is type of gene ric modificati o n has led to unforeseen and unde..irabl e envi­ron mental effects . Perhaps th e best known invo lves pota ­toe s and co rn , caterp illars th at cat th ese crops, J. d isease of caterpillars that con trols these pests, and an endan gered specie s, m onarch burtertlies . He re is what hap pe ne d .

As discu ssed ear lier) the bacterium Bacillus thnrinqi­ensit is a succ essful pesti cid e, causin g a disease in many caterpillar> . With [he development of biot ech nology, agricu ltural scientis ts stu die d the bact eria and disc overed the to xic ch emical and th e ge ne tha t caus ed its prod uc­tio n within the bacteria. This ge ne was then transferred to po tatoes and co rn so tha t th e biologically engineered plants produced the ir own pes ticide. At first, ch is was be lieved to be a cons tructive step in pest co ntro l, beca use it was no lon ger nece ssary to spra y a pesti cide . Howeve r) the ge netically en gineered potatoes and corn produ ced th e toxi c BT substance in every cell- nor just in th e leaves th at th e ca terpillars ate , but also in the pot atoes and co rn sold as foo d , in t he flowe rs, and in the: pollen. T his has a pot ential , not yct dem on stra ted, to cre ate problems for species th at arc no t inte nd ed targets o f the BT (Figure 12 .11 ).

A strain o f rice has bee n dev elo ped that produces beta-carotene , impo rtan t in huma n nutri tion. T he rice thus has added nutri tional benefi ts that are particular ly IIvaluable for the poor of the wo rld who de pe nd on rice as a prim ary food . The gene th at ena ble s rice to make be ta -ca rotene co mes from d affod ils, bu t the mo dific a­tio n actually requi red the int rod uctio n of fou r spe-cific genes and would likelv be im po ssible wi tho ut ge neric­e ngine eri ng te chruques . That is, ~e n e: s were transfe rre d be tween pl;lnts tha.t would n Ot c:xchange bcnes in naN re . II Once again, the rule: of natu raJ change suggests tha t we sho uld monitor suc h acti ons care ful" '. II

Alth ough th e genetically modified'rice ap pears to have beneficial effc cts , the go \'ern mem of In dia has rcfused to allo\\' if to be grown in th at count ry.IS There is muc h ,I co ncern worldwide: .:.bouc the political, social, and em'(­ronm e.: lltal effe Cts o f gene tic modifi cation of crops , T his is

• G ENETI CALLY M OD IF IED CRO PS

The sp rea d o f dom estic he rbivo res around th e worl d is

. ---.~-., . 0;:-' ••

. ' ~-- . ­

(b) BT com co ntains its ow n pesticide in every cell o f the plant .

rc) Pollen from the BT com is also toxic and when it lands on milkweed, monarch buttertl ics that C3t the milkweed may die.

.-;.a .

(tf) Bacillns th"""giwsis bacterin (a natu ral pestic ide}. The: gene that caused the pesticide ( BT ) was placed in corn throu gh ge netic engineering.

Agure 12.11 Th e flow o f the BT toxin from bacteri a ( n) to corn through generic engi neering ( b) and the possible ecological transfer o f [Oxic subs tanc es [Q mon arch bu tterflies ( c).

a story in process, o ne that wilt change rapidly in th e next tew years. You can check on the se fast -m oving even ts On th e textbook's Web sit e.

12.9 Grazing on Rangelands: An Environment Benefit or Problem?

Alm ost half o f Earth's land area is used as rangeland, and about 30 % o f Earth's land is arid rangeland , lan d that is easily d amaged by grazing, espec ially during drought

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Agure 12.12 Traditional sheep grazing, a practice that has OCL1.UTCd for thousands of years and affects almost half of Earth 's h od .

(Figu re 12 .12 ). In the Uni ted St ates, more tha n 99 % of ran geland is west of th e Mississippi River, Much of the world 's ran geland is co nsid ered ro be in poor condition from overgraz ing. In the Un ited Stares , range land condi­tion s have improved since rhe 19 30s, especial lv in upland are as. H owever, land near stre ams an d the st reams them­selves co ntinue to be hcavilv affec ted by gra zin g.

Gra zing cattle -tra mplc str eam ba nks and release their waste into stream water. Maintain ing a high-qua.liry stream environment require s th at cat tle be fenced behind a buffer zone .

T he upper Miss ou ri Rive r is famo us for its beautiful "w hite cliffs." but pri vat e land s alo ng th e river that arc used to graz e cattle t ::\I,,1.: away from th e scenic splendor. C attle co me down to the Missouri River to drink in n um be rs suffi cient to damage the: lan d alo ng the river. Th e river itsel f run s heavv with ma nure. T hese effectS ex [end to an area nea r a 'federally desi gn ate d wild and scenic po rtion of th e upper Missouri River , and tourists rraveling o n the Missou ri han: co mplained . In recent years. fencing alon g th e UPP'.: i Missouri River has incre-a.sc:d, with sma ll openi ngs co allow cattle to d rink. but other­wise restri cti ng wha t th ey can do to the shoreline .

Tra d itional a n d Industria lized Use of Grazing a n d Rangelands

Traditi on al herding practices and ind ustrialized produc , tion of domestic animals have d ifferent effects on the enviro nme n t. In mod ern industri alized agri culture, carde are initially raised on open range and th en rransported to

feedlots, wh ere thcv arc fattened tor marke r. Feedlots have beco me wide lv kn ~\\1 1 in rece nt vcars 3 S sources of local

C H A P T E R 12 E F FE CT S O F AGR ICUL T URE ON TH E EN VIR ONMENT

polluti on. T he pe nned cattl e arc often crowded and arc fed grain o r fora ge th at is tran sported to th e feedl ot . Manure builds up in large mounds, Wh en it rains , th e man ure po l­lutes local stre ams. Fee dlo ts are pop ular with meat produc­ers becau se they are eco no mical to r rapid production of good- qu ality meat. However, large feedlo ts req uire in te nse usc of reso urc es and have neg ative enviro nrn ent al effects.

Traditional herding practices, by comparison , chiefly aftcet the environm ent through overgraz ing. Goats an: espc~i:ill }' dama ging ro vegetation , but all domestic hcrb i­''0'''' can destrov rangeland. The effecr of domestic he rbi ­vorcs o n the land varies grea tly wi th th eir density relative to rainfall and so il ferriliry At low to mod erate densities , the animals may actuallyaid gro wth of abovegro und vegetation bv fertilizin g soil wi th their manure and stim ulating plan t growth bv cupping off plant ends in gra zing , just as pruning stimulates plant growth . But at high densities, the vcge ta ­non is eaten taster than it can grow; some species are lost , and the growth ofothers is greatly reduced .

Th e Biogeography of Agricultural An imals

People have distributed cattl e, sheep, goa ts, and ho rses, as well as other domestic animals, around the world and then promoted the gro wth of the se animals to densities that have changed the landscape. Preind us trial people made such introduction s. For exampl e) Pol ynesian settl ers brought pigs and other domesticated animals to Hawaii and other Pacific islands . Since the age of exploration b)' Western civilizatio n) starting in the fifteenth century, domestic ani mals have been introdu ced int o Australia . New Zealand) and the Americas. H orses, cows. she ep , an d goats were bro ught to North Ame rica after th e sixteenth cen­tury. The spread of cattle brought new animal diseases an d new weeds. which arrived on th e ani mals' hooves an d in their manu re. Introductions of domestic anim als int o nc..cw habitats have man y environ me nt al effects. T wo im po rt an t effects are that (1) nati ve vegetatio n, not adapt ed to the introd uced grazers , ma l' be greatly reduced and th reatene d withextinctio n; and (2) introduced animals mal' co mp ete with native herbivo res, reducing their n umbers to a point at Which they, too, may be threaten ed with extinctio n .

A recent importane issue in cattle pro ducti on is me opening up of trop ical forest areas and th eir conv ersion to l>ngeland-for exam ple, in th e Brazilian Amazon basin . In • 'l1'ical situation, th e forest is cleared by burning and cro ps are planted for about four years. Mer that time, the soil has lost so much fertility that crops can no lon ger begrown ceo ­nonuCally. Ranchers then pur chase the land, already cleared, and run cattle bred to survive in the hot) humid conditions. Afterabout another four years, the land can no lon ger sup­t even grazing and is abandoned. In such areas, gra zing . d greatly impaired the land' s capability fo r man y uses,

uding forest gr owth." Clearly, this is an unsustainable approach to agrieulmre an d therefore un desirable . IJ1

one of (he major ways we have changed the enviro nme nt th rou gh agri cu ltu re. As th e human popu lat ion increases, and as income and expec ta tions rise, the demand to r mea t increases, As a result, we can expect grea te r dem and for rang eland an d pasrurel and in th e: next dec ades . A majo r challenge in agricultur e -vill be to develo p \\'JYs to make the pr oduction of dom estic an imals sus tainab le.

C arrying Capacity o f Gra Zing Lands

Carrying capacity is the maximum number of J species per unit arc-a mar can persist wi tho ut decreasing the ability o f that population or its ecosystem to main tain th at de nsity in the furure . The carrying capacity of land lor cattle "aries with rainfall, ropographv, soil type , and soil fertili ty.

When th e carr ying capacity is exceede d, the land is over gra zed . Overgrazing slows the growth of the ,·eg­etarion , reduc es me divcrsirv of plant species, leads to dominance by plant species tha t are relatively undesirable: to the cattle, hastens th e loss of soil by erosio n as th e plant cover is reduced , an d subj ect s the land to furth er dam age fro m th e cattle 's trampling o n it (Figu re 12 .13 ). The damaged lan d can n o longer suppor t th e same den­sity o f cattle .

.In areas with moderate to hig h rainfall evenly di s­tribured throughout the year , cattle can be maintained at high d en sities; but in arid an d sem iarid regions , the den sity dr ops gr eatl y. In th e Un ite d Stares , th e carryi ng capacity fo r cows d ro ps fro m 19 0/km' (SOO/ mi') in the East to 4 0/km' ( IOO/mi') in the regio n th at was prairie and to 4/ km ' (lO/mi' ) o r less in semiari d and desert regi on s (Figu re 12 .13 ). In Arizona, lor example , rainfa ll is low, and cattle can be m aintained o nly at low d ensiries-s­on e head o f cattl e lor 7-1 0 hectares (1 7- 25 acres). Ncar Paso Ro bles, California , in 311 area whe re rainfall is about 2S crnyvear (9.8 in ./ }'ear)-thar is, in de sert to se miarid co nd itio ns-a ranch where ca ttle are g razed wi thout an i­ficial ir rigation o r fer tilization sup ports ab out a nt: head per 6 hectares (1 5 acre s).

5000 ,0 0 '00Figure 12.13 Carrying capacity of pasture and rangeland in the United States, in avera ge num ber o f cow'Sper square kilo merer. (~lIrcc : U.S. De partment ofAgriculrurc sraristics.)

12.9 • GRA ZI NG O N R ANGELAND S : AN ENVIR ONMENT B E NE FIT O R PROBLEM ?

12.10 Desertification: Regional Effects and Global Impact

D esert s o ccur naturally wh er e th ere is t OO lit tl e wa ter fo r su bs ta nt ial plant growth . Because the plants t hat do g ro w arc: to o sparsel y spaced and u nproduct ive: to ere­are a so il rich in or ganic m att er, de sert soils are mainly ino rganic, coa rse, and typ ically sandy (see the discus­sio n o f succe ssio n and soils in Chap ter 10 ). Wh en rai n do cs co me, it is often hC3\1', and ero sion is seve re , T h c princip al cl ima t ic conditio n th at lead s to de sert is low o r undependable precipitation . T he warmer the climate, the greater th e rai nfall req u ired [0 co nvert an area from desert to nondesert , such as grassland. But even in coole r climates o r at highe r alti tudes , deserts m ay fo rm if precipita tio n is [00 low ( 0 support more: t han spa rse: pl ant life . The crucia l fact o r is the am ou nt o f wat e r in t h e so il available for plants to u se . Facto rs that destroy t he abili ty o f a so il to st ore wate r can e re ­

ate a desert. Earth has five na tu ral war m de sert regi ons, all ofwhich

lie pri ma rily between lati tudes 15 ' and 30 ' no rth and sou th of the equator. These inclu de the deserts o f the southwestern United States and Mexico ; Pacific Coast deserts of Chile and sou thern Ecua dor; th e Kalaha ri De sert o f southern Africa ; th e Au stra lian des erts that cov er mos t o f th at co ntinent ; and the gr eatest d esert regio n of all- the de sert th at exte nds fro m the Atlantic Coast o f N o rth Africa ( the Sahara) eas twa rd to the des­er ts o f Arabia, Iran, Rus sia, Pakistan , Ind ia, and China.!" Only Europe lacks a major warm desert ; Europe lies north of th e desert latitudi nal ba nd .

Based o n climate, about o ne -thi rd of Ear th 's lan d area sh ou ld be des ert, but estimates suggest that 4 3% o f the land is de sert . T his ad di tional de sert area is believed to

be a result o f human activities.II Deser tifi cati on is the deterioration of land in arid , semi arid , and drv sub hu mi d areas d ue to changes in climate and human a~thitie s .I "

Desertification is a serious globa l p roblem . It affects o ne -sixth of th e wor ld's population (abo ut 1 billion peop le) and threatens 4 billio n he ctar es, o ne-thi rd of Earth 's land area" In the United States it threatens 30%of th e land . Land de gradation caused by peop le has alte red 73 % of dri er rangelands (3 .3 billion hal and th e so il fertil ity and sirucrure o f 4 7% of dr yland areas with marginal rainfal l for cro ps. Land de grad ation also affec ts 30% o f dryl and area s with high popul ati on density and

agri cultural pote ntial . A large part o f deserti ficatio n oc cu rs in th e poorest

co untries . T hese regi o ns include Asia , Africa , and So uth Am erica. w orldwi de, 6 mi llion hectares o f land per year arc lo st to th is proce ss, with an estimated econ om ic 10 55

o f 54 0 bi llio n . And th e cost of reco very o f the se land s

co uld reach S10 billion per year."

~-

~~;-': . · ,t~ ----,-

W h a t C auses Deserts?

Some areas o f Eart h are mar gin al land s; even light graz ­ing and crop production can rurn th em in to de serts . In sem iarid regions, ra infall is just barely en ough (0 enable th e land to produ ce ma rc veg etatio n th an a desert, and eve n light 'g razing is a problem. The leadin g hu man cause s o f de sertifi cation arc bad farmin g p ractices, such ;10;, failure to use contour plowi ng o r limp'.l' roo milch [M ming; overgrazing (Figu re 12.14 ); th e co nversion of ran geland s to cro pla nds in marginal areas where rainfall is no t sufficient to support cro ps over the lon g term; and poo r forestry practices, inclu ding cutting all th e trees in an area ma rginal for tree growth.

(b)

Figure 12.14 (n ) Gully soil erosion on cleared and plO'vcd . farmland in South Australia. ( b) Agricultural runoff ' .lrrying ha \l sedim ent IOJd.

In no rt he rn C hin a, areas th at we re o nce g rassla nds were o vergraze d , and then some of these ra ngelands were co nve r ted to cro p lands. Bo th pr actices led to the co nversion of t he lan d to desert . Betwe en 19 4 9 and 19 80 , so mc 65 ,000 km ' (25,100 mi' , an ar ea Luger than Den mark) became d esert, and an additional 160,000 km ' (61,760 m i' ) arc in d ang er of bec omin g deser t . As 3 resul t o f d esertificati on , th e freq uency o f S3ndst or m s inc reased fro m abou t three d ays pe r yea r in the earlv 19 50 s to an average of 17 d a)'sjl'car in the next decade and to mo re th an 25 da )'sjl'ear by the earlv 19 80s "

Des e rt likc areas can be cre at ed anywhere br poi son ­ing of th e soi l. Po iso nin g can result fro m the ap plicat io n of per sistent pesticid es o r o ther to xic o rga nic chemi ­cals; from ind ustr ial pro cesses thar lead to improper disposal of to xic che mic als; and fro m air born e pol ­lutant acid ifica tio n, excessive man ur in g in feed lo ts, and oil or che mical sp ills. Al l o f th ese ca n po ison so il, forcing abando nm ent o r red uced ag ricu ltural usc of lands. Worl d wi de , che mical s accou nt fo r abou t 12' , of all so il degradation . Iro nically, irri gation in a rid ar eas can also lead to descr t ificario n . V,'hen ir rigation wate r evapo rat es , a residue o f sal ts is left behi nd . Althou gh these salts ma y have bee n in ver y low co nc ent ratio ns in the ir rig at ion wat er, ove r time th e salts can bui ld up in th e soi l to the po int at wh ich th ey bec ome to xic. This effect ca n so m eti m es be reversed if irrigation is increased g reatly; th e: larger vo lu me of wa re r th en redissolves the salts and ca r ries them with it as it pe r ­colates down into the water tab le .

Preventing Desertification

The first ste p in prevent ing deser ti fica tion is detec tion o f initial sympto m s. The m ajor sym pto ms o f deserti fication arethe following:

Lowering of th e water table (wells have to be: du g deeper and d eepe r) .

• Increase in th e salt content of th e: so il.

Reduced su rface wat er (s tream, an d po nds de y up ).

• Increased so il erosion (th e dry soil, losing its organi c matter, begin s to be blown and washe d away in heavy rains).

loss of nati ve veget ation (not having adapte d to desert conditions 1 native vegetation can no lon ger survive ].

Preventing desemficad on beg ins with moni toring the se f1cto~_ Mon itoring aquifers and soi ls is impo rtant in ~trglnal agricultu ral land s. When we o bserve undesir ­~ le chang es, We can tty to co ntrol th e activiti es produc ­~ng these chan ges. Prope r me th od s uf so il con ser vation , cresr managem ent , and irriga tio n can hdp pre ven t th e

spread o f deserts. (See C hapters 11 and 2 1 for a back­g ro und di scussion of soil an d far ming and irrigation prac­tices.) In addition to th c practices discu ssed earlie r, good so il con servation includes th e usc of windbreaks (narrow lines o f tree s th at help slow the wind ) to prevent wi nd erosion of the so il. A landscape with tre es is a land scape with a good chance of avoi ding deserti fication . Pract ices tha t lead to defo restati o n in marginal areas sho uld be avoide d . Refo restatio n, including the planting of wi nd ­breaks, should be encou raged .

12 .11 Does Farming Change the Biosphere?

People ha ve lon g recognized local and regio nal impacts of agricu ltu re, but it is a recen t idea th at farming might affect Earth 's entire life -suppo rt system . Thi s possib ility came to people 's att ention in the twentieth cen tury, first with e, cn ts like the Am erican Dust Bowl , discussed car­lier in thi s chapter, wh ich led so me to specu late tha t suc h disaste rs could beco me worldwi de." The idea gained supp orters in the late twe nti eth centu ry as sate llites an d astr o nau ts gave us views of Ear th from spa ce and th e idea o f a global ecol ogy began to de velop . H ow might farm ­ing change the biosphere? First, ag ricu lture changes land cover, resulting in changes in th e reflection of ligh t bv the land su rface , th e evap oratio n o f wa te r, th e: roughne ss o f die sur face , and th e rate of exchange of chemicaI co m ­pounds (such as carbo n dioxide) produced end re moved by livi ng things. Each o f thes e changes can have re gional and global clim atic effects.

Secon d, modern agriculture incr eases carbon d ioxide (C O ,,) in [\-\ '0 ways. As a ma jor user of fm :,i1 fuels, it increases carbo n dio xide in th e atmosp here, addi ng to the buildu p o f greenhouse gases (discussed in detail in Ch apter 2 3). In add ition , clearing land for agri cu lture sp..e ds the deco mpo sitio n of organic matt er in th e soi l, tran sferri ng the ca rbo n sto red in the organic matter int o carbon dio xide , which also increases th e CO, co ncentra ­tion in th e:atm osp here . .

Ag ricul tur-: can also affect clima te th rough fire . Fi res associated wi th clearing land fo r agricu ltu re , especially in t ro p ical countries, ma y ha ve sig nificant effect s o n the cli mate because th ey add sm all par ticu late s to the at mosp her e . Anothe r gl obal eff ect o f ag ricul tu re resu lts from t he art ificial pr oduct ion o f nitrogen co m ­pou nd s for u se in fer tilize r, wh ich ma l' be lead in g to

signi ficant ch anges in g lob al biogeochemical cycles (sec C ha pter 3) ,

Finally, ag ricultu re affec ts spec ies divers iry The loss of compe ting ecosysrerns (because of ag ricu ltu ral land use ) red uces biolo gical diversity an d increas es th e nu m be r of enda ngered species.

1 2 .1 1 I:J D OE S FA RMIN G C HA N G E THE B I O SP HER E ? C HAP T E R 1 2 EF FE C T S O F AG R I C ULT U R E O N THE EN V IRO NMENT

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S h o u ld Rice Be Grown in a Dry Climate? wcrer is a precious resour ce, especially In California , where the average ramtall is low (38- 5 1 em/ year, o r 15-20 in./year) , the population- -33 millio n --is large and growin g, and agricultural water use is high. (Farmers usc 46 % of the state's wate r to irri ­

oJIC' 3 .5 million hectar es (8 .6 million acres), mort: than in anv other StJ.I C. ) l Q, · O .

\Virh cities and industri es, not to mention fish and other wildlife, in need o f Wa [C'T, (; I'OWlI lg cro ps that requ ire a lor o f

\,..Her h3.S come under hC;J\'Ycriticism, especialI}' because:much o f the water that tanners receive ;s su bsidized by the govern ­nH:IH. Some farmers have responded by reducing the acrC"3gc of water-intensive cro ps and switchin g to crops that requ ire less water, such 35 fruits , vegetables, and nuts .

Californ ia produces 20':" of the nation's rice. nu kin g it the second -largest rice-growing stare in the United Sta res. Th e rice produ ced has a mark et value of about 52 15 million and it uses enou gh water to supply cue- fourt h of the stare's po pula ­tio n. Although rice grow ers arc not the biggest water when the evapotranspiration is much lower users in th e state , the y have been particular targets of atta ck because the flood ed fields required fo r rice ere a vi sible remin der of the am oun t o f water used by agriculture . In addrrion to hi£!hwater usc. rice growi ng has had other adverse cnvir on mcntci effec ts: It, hig h pesticide:

and herbicide m e co ntaminates titers and drinking supplie s, and the: burn ing o f stubb le left after harvestin g contri butes to air

pol lution in the: valley. i Rice growers have respon d ed [Q pressure ro clean up their I

I act in .1 num ber o f W;JyS . In th e 199 0s they decreased warcr usc by 32'; and pesticide usc by 98 %, Th ey have switched to biode gra dable pesticides ; J ud th ey have: decre ased the burn ing o f stubble by plowin g it unde r. harvesting it , o r flooding th e fields in wi nte r when {he evapo transpiration is much lower and allo wing UH: or:;:.lnie nurrCf to rOt Experts .1rc: 31so crying to lind WJ ~'S [Q protc ct youn g 5<1 11110 n . which ru n in the ri\'crs o f the SaCr3.01CmO Valley, fro m being pump ed into the channels· 1 ~ J.d i ng to the rice ti dd ~ " Alth ou gh d rawing "':lte r OUt of the rin :rs might h;l\'c a negative impact on salmo n , th e release of \Y~.Hc r at the end of rhe wim er, whe n the ri'"ers arc low, (QuId

hd p the spring run o f salmon . And the titld s do protide J. wetland habirat tor many migr.n ·

inr- birds Jnd other sp~.:: jc s , ~o that " inter nooding bene fits an ( \"cn wida diversiry and greate r numbcr of species , \Vaterfo wl :lf e o f partkll!Jir in te rest because thei r nu mbers d.:c1ined fro m 10-12 million in 1967 to 4-5 millio n in 1990, J pe riod in which the stat e lo st 9 0% of irs wetlands to dc\'dopment and agriculture, Abo ut 79 % of the year h' destru crion of wctlands is ;ln n burcd to agricu ltura l pf;l...:ti ..: es, T he dl.linagc o f wetl:lnds adds to th e loss br ;tbo ut 117 ,000 Acres per )'car, SO the nct loss to Jgri culrur:ll l:lnds is 2 ,38 millio n acre s per ye arY~

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FIgure 12.15 The Padric flyw3 Y, used by m3JW birds tha( ~ t() P at .1gri..-ulrur.11 \"etland, in Co1lifo m i.:l, (&'1/ 1'((;' CJlifomia Rice Co mmission 200 3,)

C H A P T E R 1 2 E FF E C T S O F AGRI CU LTU R E O N THE E N VIRONM E N T

Critical Thinkin g Ques tio ns 3. Althou gh birds can feed o n rice grains in dry fields, they get :J more balanced diet by feeding in flooded fields. Why would

1. Most of the areas where rice is grow n han alkaline , hardpan th is be so ?

soil, unsuited [ 0 other crops, If rice were not gro wn on the land . 4 . Two o f the un knowns in thi s system are the: long-ter m it prob3.bly wo uld be developed for hous ing. EAch acre of rice

ctfeces of tlood ing o n the ability of the soil to sup po rt rice requires five acre-feet o f water . Less than o ne acre-foo t co uld growing and the lon g-term effects on d rvland species. such as supply wate r tor a family of four for J r CM, If housing lots WeTC rattlesnak es and rats. What is .1 scientific wa}' of investigating one-eighth acre:and 411housed families offour, how many acre­o ne o f these questi on s? feet of war er per acre of housing wo uld be used in a rear? which

USe1 more , an acre o fric e or an acre of peop le! How would real 5 . The new rice-growin g practices arc referred to as "win­win ." \Vl13t is meant br the term in general, and how docs this

situatio n illustra te th e term! estate devel opment affect wild life l1.3.bic'u :

2. Farmers tind th::u the presence ofwaterfowl in flood ed fields speeds up the rott ing of stub ble. Can you think of at lean two

reasons fo r this?

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• The Industrial Revolution and the rise o f cgric u lrura l sci­ • Deserti fication is a serio us problem that ( :10 be caused ences have led to J revolu tio n in agricultu re, with many by po or farm ing p ractices and by t he: con version benefits and some serious dra wba cks. Th ese drawbacks o f margina l grazing lands to croplands. Additional have includ ed an increase in so il los s, erosio n , and resul t ­ dese rtification can be avo ided by impro ving farming ing downs tream sedimentation, as well as th e pollution prac tices , planting trees as windbreaks, and m onit or­of soil and water with pesticides, fertilizers , and heavy ing land fo r syrnpto rns of de se rtification . met als th at are co ncentra ted as a resul t of irrig atio n ,

Two revol u tio ns are occurring in agriculture, one • Modern ferti lizers have gr eatly increased the yie ld

eco log ical and the o th er genetic. In th e eco logical pcr unit area . Mod em chemistr y has also led to the

app roac h to agricultu re , pest co n tro l will be domi­developm en t o f a wi de variety o f pe sticides tha t have

na ted by integrated pes t managem ent. Agri cu ltu re will reduced ) but no t elimi na ted, the loss of crops to weeds ,

be ap p ro ac he d in terms o f ecosys tems an d biomes, diseases, and herbivores.

taking into account the co mplexity of these systems. Soil • Most twentieth-c entu ry agricu lture has relied o n rnachin­ co nservatio n th rough n o -till agricultu re and co ntou r

cryand the usc of abundant ene rgy. \\ith relatively little plowing will be: emphasized, alo ng with wat er ce nser­ Iattention paid to th e los, of so ils, the limits of ground ­ vario n, th rough met ho ds d iscussed in Ch apter 21 . Th e water, and the negative effectS of chemica! pesticides . gene tic re"olurion is already th e subject ofco ntro\,e rsy.

• Ove rgrazing h as cJ used se\'ere dJ.m age: to lan d s. It o tTering bo th be nefi ts and environmental dangers . is important to p roperly m an :lge li\"l: sro ck , including Dangers will result if ge ne tic m o d ificati on is used \\ith ­using appropriat e land s fo r gra zing and keep ing live ­ Out cons i d c ri n~ th e ecosys te m , land scape, bi ome , 30d

stock at a sllstainable d t:nsiry. g lob al co ntext in which it is done . II I, II I i

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SU M M A, R Y

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bio lo gical co ntro l 2 2 8

carrying capaci ty 2 3 5

co ntour plo wing 2 27

Agri culture is the wo rld 's o ldest and largest indust ry; marc t han o ne -half o f all th e peo ple in th e wo rld still live o n farms. Becau se the pr odu ction, pr o ­cessing , and d istr ibuti on o f food alter th e environ me nt, and becau se o f th e size of t he indu stry, large effects o n th e en viro nme nt an: una vcida'alr

Alrernadvc ag ricul tural me thods appear to o ffe r th e greates t ho pe of sustain ­ing agri cultu ral ecosystems an d habitats over the: lon g term , bu t mo re tests and be tter me th od s are needed . As the experience: with European agricu ltu re sho ws, crop s 'an be: prod uced o n th e same Lan ds fo r th ou sand s o f years as lon g as su ffi cien t fe r tilizers and water arc available; however , th e so ils and o th er aspe cts o f th e original ecos yste m arc g reatly changcd-e-rhc se are not sustained . III ngriculwrt:, prodnct ion cml be sustai ned , but tbc ceoI)'SU1I1 ",flY

not be.

Agricultu re has nu merou s g lo bal e ffec ts. It ch anges land co ver, affec n ng climate at regi o nal and glo ba l levels, increasing carbon dio xid e in the atm o ­sphe re an d addi ng to th e build up o f gre enhouse gases, w hich in turn affects clim at e (d iscussed in derail in C ha pter 23 ). Fires associate d wi th d e,ring lan d fo r agricu ltur e may ha ve significant e ffects o n the climate be cause of th e: small parti culates they ad d to the atm osph er e . Genetic m od ification is 3

new global issue having not o nly envi ronmental bu t also poli tical and social

effects .

T he agricultural revol u tion enables fewe r and fewe r peop le to produce ma rc and mo re. to ad and leads to greater productivity per acre. Fret:d from dep enden ce o n far min g. pe ople floo d to cities . T his leads to increased urban effec ts o n the land. T hus , agricultu ral e ffects o n th e envi ro nme nt ind irectly

extend to the ci ties .

Farming is o ne o f th e most d irect an d large-scale ways that peo ple affect nature. Our o wn su srainabiliry, as well as the qu ality of ou r lives . depends

hea vily o n how \\ c farm.

Human activit ies have se rio us ly damaged one -fo urt h o f the world 's tot al land area, imp act ing o ne-sixth o f the wo rld 's po pulation (abo u t 1 billion pe ople ). Six mill io n hect are s o f land pet year are lo st to dese r tification. A large part of desertification occ urs in th e po ores t countries . O"agrazing, deforestati on , an d dest ructive cro p prac tices have: caused so much dam ­age th at recover y in so me areas will be d ifficu lt; restoration of th e rest "ill requi re se rio us acti o ns. A majo r va lue jud gm ent we must mak e in th e furor( is w hether ou r socklies will alloc ate funds to res tore th ese d am aged lands­Resto ra tio n req uir es scie nti fic kn o wledge, both ab out present co"nditi ons 3.nd abo ut acti o ns requir ed for restor ation . W ill we see k th is knowledge:and pay th e COSt S fo r it ?

d esertificatio n 236 overg razing 235

integrated pest managem ent 229 term inat or gene 233

no -ti ll ag ricu ltu re 227

C H A PT E R 1 2 E F F E C T S O F AGR I C U L TU R E O N TH E E N VI R ON M ENT

1. D esign an in teg rated pest -m anagem e nt scheme for use in a small vegetab le garde n in a ci t)" lo t be hin d a

. house . H ow wou ld this scheme differ fro m rPM used on a large farm ? Wh at asp ects o f rPM co uld not be emplo yed? H ow migh t th e: arti ficial stru ctu res of a city be put ro usc to benefit IPM?

2. You arc: given 5 10 billio n [Q red uct: th e nu mber of death s wo rldwide fro m maim " . (a) You have one year to act. (b) You have ten yea rs to act. In each case, mala: a plan of act ion , being specific about the usc of pesticide s.

3 . Under wha t co nd itio ns might g razing catt le be: sus ­rainable wh en gro wi n g wheat is not? U nd er wh at can ­dirio ns m ight a her d o f biso n pro- i de , sustai nable supply o f meat wh en cows mi ght not?

4. Pick one of the nation s in Mica th at has a major food shortage. Design a prog ram to increase its food pro ­ducti on . D iscuss how reliable tha t progr.J.m migh t be given t he un certainties th at nation face s.

Mu o)"er. ~....Iarcel, and Laurence Rood ar. 2006 . A HinD')' of W",1d Ji5ricnl fUrt : Fro'" the Ncolir l,i, Age til fix CItM'Wf Crisis. Mon th l ~'

Re-.i tw Press. By two Frenc h pro fessors of agriccl rure, this book. argues tha t the world is abOUI to reach :r.new fu ming crisis, which an be und erstood from the history of agricultu re.

t.kNctly, J. A., and S. J. Scherr. 2003 . Etol'tl1ricrt/trtrt. \ \'3:shington, D.C.: Island Press.

5. H ow can we avoid an o th er Du st Bowl in the: U nited States!

6 0 Should ge netically m od ified crops bc co nsid ere d ac ­ccp rable to !""o rganic" farming!

7 . A lead ing expert proposc:s a major . expen sive pr03r.1m to increase ur ban gardens arou nd th e wor ld . H e claims th is is one way to soh" the world food sap. Decide whet her ur ban garde ns co u ld be a major so urce of food . As mu ch as possib le, make use of scientific data presented in th is chap ter , and make necessar y calculi ­Don s £0 de term ine th e possible increases in wo rld food prod uction tr am ur ban gardens .

8. You are abo ut to buv yo ur mo th er a bouquet of 12 roses for Mother' s D av, but vou discove r tha t th e roses

O

were genetic ally mod ified W give th em a more brilliant co lo r and to prod uce a na tural pesti cide th rough gene ­tic energy. Do you bu v th e flowers? Ex plain and j usti~ o

yo ur ans wer based o n th e ma teri al prese nted in th is cha p ter.

Smil, V. 2000 . Fttdi"l1 ,I", n orM. Cambridge, Mus.: MIT Press.

Terrence, J. Toy, Georg e R. Foster, Uld Kenne th G. Renard. 2002 . Soil Erosion: p,.ocm (s, Prrdi, ri tfll • .lferrm rtlJltllf, nJ,d Clm n-o/. New York: John W ilev,

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FURT H E R RE A DI N G