Whatisorganicfarming?
At the core of the organic philosophy lies a
ban on the use of synthetic fertilizers, pesti-
cides and herbicides. That means adopting
other techniques to nourish crops and pro-
tect the soil, such as growing `cover' crops
between seasons to prevent erosion and to
restore organic matter.
Theorganicmovementalsoencompasses
such tenets as animal welfare, energy effi-
ciency, social justice and the simple agrarian
ideal of small farms growing produce for
localcommunities.Itisonthislastpointthat
the success of organic farming is starting to
divertthemovementfromitspurevision.
Although organic produce remains a
nichemarket,globalsaleshaverisenbyabout
20% per year for five years running1
. This
growth has seen some `organic' producers
turn into industrial-scale ventures that ship
their products over thousands of kilometres.
Organic proponents may aim to reduce the
fossil fuel expended in transporting crops by
encouraging farmers to sell to local markets,
but the popularity of organic food in wealthy
countrieshasspawnedahugeexportmarket.
North America and Europe account for 97%
of global organic food and drink sales, but
nearly half of the world's organic farmland is
found in Asia, Australia and Latin America
(see Map, page 794). It's hardly what the
movement'spioneershadinmind.
Organic standards also differ in their
details from country to country. Most rules
governing organic farming, including those
laid down in the European Union,Japan and
the United States, are based on standards set
by the non-profit International Federation
of OrganicAgriculture Movements in Bonn,
Germany."Anyone who is really credible will
adhere," says Bruce Pierce, deputy research
director of the Elm Farm Research Centre in
Berkshire, UK, which studies methods of
organic cultivation. But standards are not
always comprehensive: Japan, for instance,
hasnorulesfororganicmeat.
And there are important differences
between regions of the world. For instance,
an American farmer who chooses to use
Chilean nitrate, a mined source of sodium
nitrate, permitted under US rules, could not
sell the resulting produce in Europe.
Although Chilean nitrate is a natural sub-
stance,Europeanorganicstandardsconsider
it to be the equivalent of a synthetic fertilizer
because it is highly soluble and leaches read-
ily from the soil. Nor could the US farmer
market milk from a cow that had been raised
on an organic diet for less than a year --
European rules are stricter than US stan-
dards,whichrequireonlysixmonths.
Similarly, a consumer buying organic
produce in the United States cannot be sure
that it is free of contamination from geneti-
cally modified (GM) crops unless this is
explicitly stated on the label. In Europe, GM
content in all GM-free food, including
organic produce, is limited to 0.9%, and
some certifying bodies, such as Britain's Soil
Association,allownodetectableGM.
Because organic products fetch premium
prices,thereareconcernsaboutthepossibility
of cheating. Organic rules are enforced by
farminspections,butthelogisticscanbediffi-
cult, particularly in remoter parts of export-
ing countries."The inspection process is not
completely foolproof," admits Francis Blake,
standards director of the SoilAssociation and
aformerinspector."Itreliesontrust."
As a result, some researchers have begun
to look for ways to test organic products
for authenticity. Alison Bateman of the
University of East Anglia in Norwich, UK,
is developing a test based on the higher
proportion of the isotope nitrogen-15 in
organically farmed soil. This is because
nitrogen-fixing plants accumulate more of
thisheavyisotopethanispresentinsynthetic
fertilizers. Other researchers are investigat-
ing whether concentrations of trace ele-
ments such as calcium, boron, magnesium
and selenium differ between organic and
conventionalproduce.
But tests such as these address only the
final products, and so cannot verify whether
the farm from which the food came adhered
totheprinciplesof organicagriculture."They
cannot tell you if a product has been organi-
callymanagedornot,"saysBlake. LauraNelson
Isorganicfoodbetterforus?
This is the claim that attracts many of the
consumers who buy organic, so it's no sur-
prise that the movement's advocates answer
with an unequivocal `yes'. In 2001, for
instance, the Soil Association concluded
unambiguously that organic food contains
less of the bad stuff, such as pesticides, and
more of the good stuff, such as vitamins
and minerals2
.
But independent scientists are less con-
vinced. They say that many comparisons
between organic and conventional produce
are let down by poor methodology. For
news feature
796 NATURE|VOL428|22APRIL2004|www.nature.com/nature
ORGANIC FAQsIn the developed world, sales of organic produce
are growing rapidly. But how far can this trend
extend? That depends on how strictly you
define organic farming ... and the answers to
three other pivotal questions.
S.SATUSHEK/GETTYIMAGES
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2004 NaturePublishing Group

the same farm, and found 30­50% more
phenolics in the organic samples4
.Studies of
organic pears and peaches have also showed
raisedlevelsof phenolics5
.
Brandt,who tracks such studies,says that
theevidencepointstoorganiccropscontain-
ing 10­50% more secondary metabolites
than conventional equivalents. This may be
because fertilizers applied to conventional
plants supply a surfeit of nutrients, encour-
aging the plant to channel more energy into
growth,ratherthandefendingagainstpests.
Butdoplantsecondarymetabolitesreally
do us any good? Anthony Trewavas, a plant
scientist at the University of Edinburgh,UK,
andahigh-profilecriticof theorganicmove-
ment6
, questions whether we should be
trying to boost levels of secondary metabo-
lites before we know the answer to this ques-
tion. About 10,000 of these metabolites are
thought to exist. Many that have been stud-
ied seem to behave paradoxically, acting as
carcinogens at high doses and showing
anticancerpropertiesatlowdoses7
.
At the very least, it seems reasonable
to expect organic food to be free from
pesticides, which are banned or severely
restricted under organic regimes. Food-
safety authorities monitor pesticide residues
in conventional crops, but levels do occa-
sionally exceed maximum legal limits. And
according to a 1998 study by Britain's
Consumers' Association, some pesticides
remain on fruit and vegetables even after
theyhavebeenwashed8
.
But should we be worried about
this? Most researchers believe that
allowed residues are safe, although
uncertainties exist. The difficulty in
applying results from animal experi-
ments, which are the mainstay of toxico-
logical assessments, to humans is one
news feature
NATURE|VOL428|22APRIL2004|www.nature.com/nature 797
problem. Opinions can also be revised. The
chlorine-containing pesticide lindane was
banned in Europe in 2001, for example,
because of concern that it might promote
breastcancer9
.Ultimately,mosttoxicologists
urge caution in assessing and regulating
pesticideresidues,buttheydon'tseetheneed
toeliminatethementirely. Jim Giles
Isorganicfarmingbetterfor
theenvironment?
This is a more complex question than it at
first appears. In some arenas, such as bio-
diversity, organic farming has clear benefits.
But in others, such as runoff and atmos-
pheric emissions, the differences between
the two systems are difficult to establish.
Although few large, long-term studies
directly comparing the systems exist, several
literature surveys have brought together
smaller studies to build overall compari-
sons10,11
. There is general agreement on some
benefits.Forexample,organicfarmsdobetter
than conventional farms at nurturing abun-
dantanddiversepopulationsofplants,insects
and other animals.And organic farms release
no synthetic pesticides or herbicides,some of
whichhavethepotentialtoharmwildlife.
Organic farms also score points for using
lessenergy--bothperunitareaandperunit
of yield -- and producing less extraneous
waste,suchaspackagingmaterialsforchem-
icals and feed.A typical study at Washington
State University in Pullman totted up the
energy consumed by labour, machinery,
electricity, fertilizer, pesticides and weed
control to grow apples in organic and con-
ventional orchards, and found the organic
orchardtobe7%moreenergyefficient12
.
On the flipside, organic methods have a
greater environmental impact in some small
ways,studies show.Methane emissions from
organic farms are likely to be higher per unit
of food production, for example. At least in
the United States, where dairy cows receive
growth hormone, organically raised cattle
yield considerably less milk than their
hormone-assisted peers -- requiring more
cows,whichcollectivelypassmoremethane.
But findings are less definitive about
the much more significant environmental
impact of farm runoff -- through which
nitrates and phosphorus leach into streams,
rivers and lakes, causing algal blooms that
suffocate fish.Several studies have suggested
that organic methods will reduce nitrate
leaching,but according to a 2003 assessment
of the literature sponsored by the British
government, the various factors that affect
runoff mean that this is not guaranteed13
.
Too few measurements of phosphorus
runoff have been made to determine which
systemreleasesless,thereportconcluded.
In theory, organic farms are friendlier to
the atmosphere. They should, for instance,
generatelesscarbondioxide,whichisreleased
Where there's life: the broad biodiversity supported by this organic cereal crop is clear to see.
example, some studies fail to take into
account the fact that organic farmers prefer
crop varieties that are resistant to disease,
whereas conventional farmers focus on
high-yielding strains. Such studies confuse
theeffectof productionsystemwithvariety.
Apparent benefits may also turn out to
be superficial. Several studies have shown
that organic crops contain higher levels of
nutrients such as vitamin C and iron3
, for
example, but most people in developed
countries already have enough of these
compounds in their diet. "When evaluating
relative nutritional value, these are not
important targets," says Kirsten Brandt, an
agricultural scientist at the University of
NewcastleuponTyne,UK.
On the other hand, plant secondary
metabolites, substances that may be present
at higher levels in organic food, could be an
appropriate target, says Brandt. Phenolic
metabolites, which fruit and vegetables
produce to ward off insects, are believed to
haveanticancerproperties,forexample.Last
year, food scientist Danny Asami and his
colleagues at the University of California,
Davis, looked at organic and conventionally
grownmarionberriesandmaize(corn)from
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in abundance in conventional farming by
burningfossilfuelstomanufacture,transport
andspreadnitratefertilizers.Andtheplough-
ing into the soil of crop residues and cover
crops should pull carbon back out of the
atmosphere more efficiently. Organic meth-
ods might also be expected to produce less
nitrousoxide--oneof thecausesof acidrain
--thanisreleasedbyheavilyfertilizedsoils.
Although the British assessment found
that organic farming does lead to lower CO2
emissions,it also said that a lack of firm data
made it impossible to compare emissions of
nitrous oxide -- which is also produced by
legumes and manure on organic farms. Nor
were there enough data to evaluate the effec-
tivenessofthetwosystemsassinkstocapture
atmosphericcarbon.
For organic advocates, the key environ-
mental issue is not the year-by-year balance
of farminginputsandoutputs,butratherthe
long-term sustainability of the system. By
recyclingbothnitrogenandorganicmaterial
back into the soil, they believe, organic agri-
culturecanensurethis.
Manystudiessupporttheideathatorganic
methods are good for soil quality14
."I used to
be sceptical about organic methods, but the
evidenceonorganicmaterialchangesthings,"
says Mark David, a biogeochemist at the
University of Illinois at Urbana-Champaign.
But in the absence of long-term comparative
studies, the argument about sustainability is
difficulttoprove. ColinMacilwain
Canorganicfarmingreplace
conventionalagriculture?
Not if the world wants a meat-rich diet, as
even die-hard organic proponents are will-
ing to concede. But if the world's demand
for cheap, abundant meat can be curbed,
then quite possibly it could.
Ultimately,it'saquestionofefficiencyand
yield. The elimination of pesticides and her-
bicides does not seem to reduce yields as
muchasyoumightexpect.Becausepeststend
to prefer particular plants,the crop rotations
favoured by organic farmers help to prevent
insect populations from accumulating to
damaging levels.Continuous cover cropping
in winter also keeps weeds down, so the soil
accumulates fewer weed seeds.Natural pesti-
cidesandmechanicalweedingfinishthejob.
Still, there are some regional pest prob-
lems for which no organic solution has yet
been found. Notorious in the northwestern
United States is the garden symphylan
(Scutigerella immaculata), a centipede that
canattackasparagus,maize,mintandstraw-
berries and is controlled by soil fumigants in
conventional systems.Years of research have
yielded no effective organic control -- all
organic farmers can do is replough the field
inanattempttokillthecentipedes.
Abiggerinfluenceonyieldisthemeansby
whichorganicfieldsaresuppliedwithenough
In large part, the huge nitrogen inputs
required by modern agriculture are needed
to grow sufficient grain to raise livestock:
producing a kilogram of lean meat requires
25­50 kg of grain. Even with sufficient
nitrogen, organic farms would have a hard
time meeting this demand, Smil says,
because they must grow a variety of crops to
maintain soil health and defend against
pests. Turning over entire farms to grow
maize and soya beans to feed livestock isn't a
viableoption.
Even stalwart supporters of organic agri-
culture agree.But their line is that we should
eat less meat and more vegetables, and
embrace an organic future. The argument
that organic farming can't produce enough
food"only works if you assume that we con-
tinue to expand production of cheap meat",
says Peter Melchett, policy director of
Britain'sSoilAssociation. Virginia Gewin
1. Willer, H. & Yussefi, M. (eds) The World of Organic Agriculture:
Statistics and Emerging Trends (International Federation of
Organic Agriculture Movements, Bonn, 2004).
2. Heaton, S. Organic Farming, Food Quality and Human Health:
A Review of the Evidence (Soil Association, Bristol, 2001).
3. Worthington, V. J. Altern. Complement. Med. 7, 161­173 (2001).
4. Asami, D. K., Hong, Y.-J., Barrett, D. M. & Mitchell, A. E.
J. Agric. Food Chem. 51, 1237­1241 (2003).
5. Carbonaro, M., Mattera, M., Nicoli, S., Bergamo, P. &
Cappelloni, M. J. Agric. Food Chem. 50, 5458­5462 (2002).
6. Trewavas, A. Nature 410, 409­410 (2001).
7. Ames, B. N. & Gold, L. S. Mutat. Res. 447, 3­13 (2000).
8. Health Which? 8­11 (June 1998).
9. Mitra, A. K., Faruque, F. S. & Avis, A. L. J. Environ. Health 66,
24­32 (2004).
10.Stolze, M., Piorr, A., Häring, A. M. & Dabbert, S. Environmental
Impacts of Organic Farming in Europe (University of
Hohenheim, Stuttgart-Hohenheim, 2000).
11.Hansen, B., Alre, H. J. & Kristensen, E. S. Agric. Ecosyst.
Environ. 83, 11­26 (2001).
12.Reganold, J. P., Glover, J. D., Andrews, P. K. & Hinman, H. R.
Nature 410, 926­930 (2001).
13.Shepherd, M. et al. An Assessment of the Environmental Impacts
of Organic Farming DEFRA-funded project OF0405 (DEFRA,
London, 2003).
14.Johnston, A. E. Soil Use Manage. 2, 97­105 (1986).
15.Maeder, P. et al. Science 296, 1694­1697 (2002).
16.Lotter, D. W., Seidel, R. & Liebhardt, W. Am. J. Altern. Agric. 18,
146­154 (2003).
news feature
nitrogen to maintain productivity. Conven-
tional fields get a generous dose of nitrogen
each season from synthetic fertilizer, whereas
organic fields get theirs from manure and
covercrops,sometimescalled`greenmanure'.
Season to season, the two approaches can
produce comparable yields. A 21-year study
by the Research Institute of OrganicAgricul-
ture in Frick, Switzerland, concluded that
organic fields produce yields 20% lower than
conventionalfields,onaverage15
.Meanwhile,
another long-term study by the Rodale Insti-
tute in Kutztown, Pennsylvania, obtained
roughly equal yields of maize and soya beans
with the two systems. The Rodale team also
found that organic systems can achieve
20­40%higheryieldsindroughtyears16
.
Buttomaintainthesoil'snitrogencontent
inthelongterm,organicfarmersmustgrowa
legume or other nitrogen-fixing crop regu-
larly. This takes land out of commercial pro-
duction, reducing the overall yield of a plot
overtime.Althoughsomelegumesareedible,
the most efficient nitrogen-fixers, such as
clover, are not. The Rodale researchers
managed to minimize lost yield by growing
legumes over the winter, but this may not
be practical in harsher climates; nor will it
provide the same benefit in warmer regions
wherecashcropsaregrownyearround.
VaclavSmil,anatural-resourcesresearcher
at the University of Manitoba in Winnipeg,
Canada,calculates that there is an even bigger
obstacle to organic edging out conventional
farming any time soon. He says that the total
nitrogen available to organic farmers through
manureandlegumesamountstolessthanhalf
the total nitrogen consumed by the world's
farms today -- some 85 million tonnes.More
cover cropping may increase the available
nitrogen,but this is a luxury farmers in places
such as Indonesia or China can ill afford."In
these countries, you cannot plant crops that
noonewilleat,"Smilsays.
798 NATURE|VOL428|22APRIL2004|www.nature.com/nature
Soil survivor: the garden symphylan has so far proved resistant to any organic pest controls.
J.UMBLE
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