Polycultures in Modern Agriculture

8/4/2019 Polycultures in Modern Agriculture

1/7

Science

4 CSA News September 2011

Science

agriculture and the other in ecology.He belongs to the Society or RangeManagement and the EcologicalSociety o America (ESA). He holdsawards or meritorious research inagriculture and or best wildlie publi-

cation. And while he loves the scienceo ecology, he knows what it takes togrow crops. Thats why when he andhis Kansas State University colleague,ASA, CSSA, and SSSA member BobGillen, attended the ESA meetings in

2001, they were amazed to see ecolo-gists making inerences about agricul-ture rom experiments on random as-semblages o plants in small, careullytended plots.

They were interesting, Fuhlen-dor says o the studies, which aimedto test how species diversity related toproductivity. But most o them were

As a rangeland ecologist, Oklahoma State Universityprofessor Sam Fuhlendorf has always had one foot in

by Madeline Fisher

polycultures

modern agriculture?

Do

have a role in


2/7

September 2011 CSA News 5

just completely unrealistic rom anagronomic perspective.

Sensing a research niche to belled, the pair soon launched their

own experiments in two Oklahomalocations, comparing the productivityo mixtures, or polycultures, o prairiespecies, with monocultures o plantslike switchgrass and big bluestem.Later, they teamed up with OklahomaState agricultural economist FrancisEpplin, who evaluated the two crop-ping systems based on their biomassyields and production costs. The mainnding o their paper, published inthe MayJune 2011 issue oAgronomy

Journal: Economics avored the mono-cultures, at least or the locations

and conditions o their three-yearstudy. My perspective still stands,Fuhlendor concludes. There are lotso reasons to have diversity. It just sohappens that growing biomass maynot be one o them.

To many agronomists, that shouldbe the last word on the subject. But inthe meantime, the concept o di-versiying the arm landscape withperennial species and polycultures hastaken root in the scientic literature,

ueled by the push toward cellulosicbioenergy crops, such as switchgrass,miscanthus, and prairie plant mixes.Proponents argue that while todayssimplied agricultural systemsexcel at producing corn, cotton, andother vital commodities in massiveamounts, they come at the price odegraded water quality, vanishingwildlie habitat, and increased pesti-cide use. Sowing plant diversity backinto armlands, they say, could reducethese costs by providing ecological

benets, such as natural pest control,carbon storage, and nutrient retention.Others see diversication as crucial toagricultures uture resilience.

Most agronomic scientists dont

disagree; rather, its the expense, risk,and diculty o growing such cropsthat makes them wary. Still, studieslike Fuhlendors that used to appearexclusively in ecological journals are

being published more requently inthe agricultural literature, as well.And what theyre showing is thatwhile growing polycultures is hardand economically impractical rightnow, these systems do hold poten-tial that should perhaps be urtherexplored.

To do things right, however, anequally tough but promising eortmust also get underway: Agronomistsand ecologists need to work togetherto address important questions, suchas the one at hand: Are monoculturesall we should grow? Or do polycul-tures have a place, too?

I think [more collaboration]sounds wonderul, Fuhlendor says.

But, he adds with a wry laugh, itsa really big challenge.

Photo credits:page 4, clockwise: Matt Wisniewski, Great Lakes Bioenergy Research Center (GLBRC);

Kathy Eystad; David Tilman, University of Minnesota; Craig Sheaffer, University of Minnesota; and Michael

Casler, USDA-ARS, U.S. Dairy Forage Research Center;page 5, left vertical panel:Andrew Leakey;page 5,

right vertical panel: John Durling, USDA-NRCS, Rose Lake Plant Materials Center;page 5, middle horizontal

panels, from top to bottom: Gregg Johnson, University of Minnesota; Scott Bauer, USDA-ARS, Bugwood.org;

and Matt Wisniewski, GLBRC.


3/7

Science


Science

Ecologists Paper Sparks

Agronomic Research on

Polycultures

I the challenge was already big,University o Minnesota ecologist Da-vid Tilman likely made it bigger whenhe published a paper in Science in2006. An expert on prairie ecosystems,Tilman has or years examined therelationship between productivity andspecies diversity in restored prairieson extremely nutrient-poor sites incentral Minnesota. His work had littleto do with agricultureuntil biou-els came barreling along. Suddenlyeveryone wanted to grow perennialgrasses and in Tilman jumped with

his paper, reporting that mixtures o16 native grasses, legumes, and orbsyielded 238% more bioenergy thandid monocultures ater a decade ogrowth. The plots were also unertil-ized and watered only during estab-lishment, suggesting high-diversitypolycultures would be more environ-mentally riendly than corn ethanol orsoybean biodiesel.

The paper drew intense criticismrom agronomists, however. Some

argued that Tilmans small, hand-weeded research plots held little sig-nicance or commercial agriculture.Others questioned his methods; orexample, his practice o burning hisstands returned nutrients to the soil,critics said, whereas harvesting bio-mass at seasons end would obviouslyremove nutrients and reduce produc-tivity over time. Iowa State Universityagronomy proessor Ken Moore alsonotes that plant diversity naturallydepends on soil conditions, and richsoils are more likely to let single spe-cies dominate than are nutrient-poorsites like Tilmans. Five years later,Moore still holds strong opinionsabout the work. I would state, says

the ASA and CSSA Fellow, that stud-ies that articially create and maintaindiversity have no relevance to the realworld.

At the same time, some agrono-mists decided to launch their ownstudies o polycultures, one o whomwas orage agronomist and ASA andCSSA Fellow Craig Sheaer. A col-league o Tilmans at the Universityo Minnesota, Sheaer credits theecologist with sparking agronomic

research on the subject. We wouldntbe having this conversation right nowwithout his work, he says.

Like Fuhlendor, Sheaers goal

wasnt to investigate whether diver-sity was correlated with productivity,however, but to nd the croppingsystem that oered the highest, mostreliable yields o biomass at produc-tion scales. To this end, he and hiscolleagues, Don Wyse and MargaretMangan,launched a series o experi-ments in eight sites in Minnesota thatspan a range o ecoregions. At each lo-cation, they established stands o 1, 4,8, 12, or 24 species o native, tallgrassprairie plants and ollowed them ortwo years without applying ertilizer.

As reported in the MarchApril2011 issue oAgronomy Journal ,themost productive plots were eithermonocultures or ones containing aneight-species mixture o grasses andlegumes. Indeed, an increase in spe-cies rom one to eight boosted yields

by an average o 28%, suggestingthat a strategic combination o a ewspecies might achieve the highest bio-mass during the establishment phase,Sheaer says. Seeding more than


4/7


eight species oered little additionalbenet, though, and Sheaer wasntsurprised to see something else hap-pening in the mixtures, as well: Onaverage, a single, dominant speciesaccounted or 75% o the biomass.

What we report in our paper isnot that unique rom an agronomicperspective, he says. I you seed30 species on the landscape, yourenot going to get 30 species growing.Thats why armers ocus on simplemixtures, he adds, such as alalagrass mixes that include one or twograsses. There arent 26, Sheaersays, because we know enough aboutthe species that will persist and beproductive.

That point may be patently obviousto him, but its one that ecologistsoten ail to get, says Matt Liebman,who is both an ASA Fellow and ESAmember: Rather than going or themaximum number o species, agrono-mists are willing to sacrice some di-versity or the merits o certain plants.Theres a reason we grow corn andsoybean in Iowa, says Liebman, theWallace Chair or Sustainable Agri-culture at Iowa State University. Its

There is a reason we grow corn and

soybean in Iowa. Its not that werehell bent on eliminating diversity. Its

that those species are very

well adapted here.

not that were hell bent on eliminatingdiversity. Its that those species arevery well-adapted here.

Still, crop diversity matters greatlyto Liebman, and hes spent his careerstudying its impacts on actors suchas weeds, soil ertility, and long-termproductivity. Unlike Sheaer andFuhlendor, however, when he andhis ormer graduate student, ValentnPicasso, compared monocultures andpolycultures in a 20032005 study,they sowed not only prairie plants,such as Maximilian sunfower andIllinois bundlefower, but also agro-

nomic species including alala andorchardgrass. This may be one reasonwhy their ndings diered, as well: In

their experiments, published in 2008in Crop Science, polycultures o two tosix species clearly outyielded mono-cultures under all conditionsonaverage by 73%.

Like the other studies, though, spe-cies in Picassos plots that producedthe most biomass in monoculture alsodominated any polyculture in whichthey were present, with other speciescontributing relatively little to yield.Moore adds that this kind o shit can


5/7

Science


Science

happen even in very simple grasslegume mixtures, which his group has

been investigating as a way to reducecostly nitrogen ertilizer applicationsto bioenergy crops.

Given its [way], the plant com-munity will transition to a quasi-equilibrium state dierent rom theinitial one, he says. It takes careulmanagement to maintain a benecialequilibrium.

Why Mixtures?

It seems a air question, then: Whymess with mixtures at all? Althoughhe is an unabashed an o plant diver-sity in agricultural systems, rangeland

ecologist Randy Jackson understandsthe concern, having experienced thepitalls o polycultures himsel. Threeor our times during the last decade,explains the University o WisconsinMadison (UW-Madison) agronomyproessor, prairie plants seeded byhis group or agronomic experimentshave ailed to take, orcing a costlyreplanting eort.

So, its a dicey proposition, saysJackson, who is currently comparing

polycultures and monocultures obiouels crops as part o the U.S. De-partment o Energy-sponsored GreatLakes Bioenergy Research Center(GLBRC) based at UW-Madison andMichigan State University. Peopleknow how to grow corn everywhere.But growing switchgrass or diverseprairie, youve got to be in it or thelong haul and willing to throw somemoney at it, because its expensiveright now. And its risky.

Even so, these crops have one criti-cal advantage, he adds: The ecologi-cal benets they oer, also known asecosystem services. As orageagronomists well know, or example,deep-rooted perennials easily outper-

orm annual, row crops at prevent-ing erosion, retaining nutrients, andsequestering carbon. Diversity inarmlands can also boost natural pestcontrol: Some o Jacksons GLBRCcolleagues have shown that insectpredators such as ladybeetles devourmore soybean aphids and other croppests when eeding in elds nestledwithin woodlands, grasslands, andcroplands than in those surrounded

by a monotony o corn. Even aesthet-

ics is considered an ecosystem service,with people valuing grasslands notonly or their plants, but also the wild

birds they attract.

Still, why mixtures exactly? Cantmonocultures o switchgrass providethese services just as well when sownon the landscape amid row crops? Itsa key question, Jackson says, and akey reason why his team is comparingnot just the productivity o various

bioenergy cropping systems, includ-ing continuous corn, switchgrassmonocultures, and native prairie,

but the level o services they oer, aswell. The idea is that because dierentspecies presumably occupy dierentecological niches, mixtures can better

retain nutrients, or resist droughtand disease, than any one species canon its own. Even i this hypothesisis supported, however, its unclearwhether these benets will outweighthe downsides.

We havent really done the ullaccounting yet, Jackson says. Okay,the diverse system is less productive,

but what does it do or greenhousegas emissions, carbon accumulation,and nitrogen retention? Are we seeing


6/7


extra benets there? Or is a switch-grass monoculture just as good on allthose accounts as a diverse prairie,especially on rich soils?

Liebman has documented better

weed suppression in polyculturesthan in monocultures. But ecosystemservices arent the only reason to con-sider mixtures, he emphasizes: The re-silience o agricultural systems is alsocritical. As Picassos work showed,he says, picking the best-adaptedspecies or a given set o conditionsleads to high yields in monocultures.But imagine you dont know the exactconditions or the best-adapted spe-cies. In this case, including a ull seto possible species, rom which thewinner can emerge, makes sense.

Its context dependent, obviously.I youre in a world with a stable cli-mate and cheap ertilizer and perectmoisture conditions, you can probablypick the winning species, Liebmansays. But i you dont operate in thatkind o a world or the cost o inputsis becoming limiting or protableproduction, then you begin to look atorms o biological diversity not justas ways to hedge your bet, but also to

We havent really done the full

accounting yet... the diverse system isless productive, but what does it do

for greenhouse gas emissions,

carbon accumulation, [and]

nitrogen retention?

maintain productivity in the ace o

economic and biophysical challenges.Nick Jordan, Sheaers and Til-

mans colleague at the University oMinnesota, agrees, noting that a 2010study led by Bruce Dale at MichiganState University suggests perennial,

biomass crops could be grown prot-ably or animal eed and biouels onroughly 50 million U.S. hectares thattoday produce annual crops or eedand export. Such a transormationo our agricultural land base, Jordan

says, would not only provide useul

goods and substantial environmentalbenets, but could also help buerU.S. agriculture against the widervariability in weather thats beingorecast or the uture.

The prediction, at least, is thatwere talking about signicant dier-ences in the distribution o rainall,so that we have more big storms anddrought, he says. So we need toinvest in 50 million hectares o peren-nials in a way that will be resilient to


7/7

Science


Science

that kind o variation, or at least weshould consider it.

Lab Land Concept

Considering it is one thing, how-ever; getting there is quite another.Answering agronomic questions canhelp in this regard, o course. But or

Jackson, those questions arent themain ones.

We have to do this work to under-stand the agronomic limitations, the

best practices, and that sort o thing,he says. But the real leverage pointsare how people behave, what choicesthey make, how society incentiv-izes these things. We can understand

everything there is to know aboutwhether a diverse prairie is moreproductive or not, but i people arentgoing to plant it, then it isnt going tomatter.

A means to make that societal shithas thus become another researchocus o Jackson and Jordan. Clearly,creating these unprecedented sys-temsblends o perennial and annualagriculture on unprecedented, land-

scape-wide scaleswe have no ideahow to do that in advance, Jordansays. The only way to gure it out isto try to build pilot-scale landscapesthat we can learn something rom,without betting the arm on them.

To this end, the pair has beendeveloping a Lab Land concept,with their colleague Doug Landis oMichigan State University. It compris-es, rst o all, spatial decision supporttools that would allow stakeholders,such as armers and land managers,to turn the dials on a watershed orother landscape, Jackson saysadd-ing to elds o corn, or example,strips o diverse prairie plantings orstreambank buers o switchgrass or

willow. The tools would then let themsee not only how actors such as pro-ductivity, water quality, greenhousegas emissions, and wildlie habitatwould be aected, but the actuallook o the new armlands, as well.Another ingredient are mechanismsor bringing multiple stakeholderstogether to design supply chains,markets or ecosystem services, andother needed inrastructure to make

the new landscapes lucrative. And thenal ingredient, Jordan says, is policy.

I weve got a landscape peoplecan agree on and a supply and value

chain that looks promising, he says,then what kind o policy environ-ment do we need to support them?

The Land Lab isnt the only pos-sible solution, o course, but thelarger point is that we need some wayto move orward. Otherwise, it willremain tough to bridge the divide

between the benets o diversity thatecologists see and the need or prot-able production that agronomistsknoweven when both sides are will-ing to cross it.

Here at Minnesota, at Iowa State,at Wisconsin, were studying these na-tive plants [as crops] because we areaware o the importance o ecosystemservices, Sheaer says. But I alsolike to think that as agronomists, wepretty much have our eet on theground in terms o the reality o thesituation.

M. Fisher, lead writer forCSA News magazine

Documents

Polycultures in Modern Agriculture