Certified organic at ARS
Beltsville researchers have been doing research related
to organic farming systems for more than ten years.
But how has National Organic Program implementation
in 2002 affected the research context? How much certified
organic research is going forward at BARC, and at ARS
Carolee Bull, a research plant pathologist based at
an ARS station in Salinas, California, has been cooperating
with Mike Jawson, ARS National Program Leader for Integrated
Farming Systems, and others to find answers to those
questions. Bull reports that there is now a total of
about 70 certified organic acres at ARS research stations
in Iowa, Maryland, California, Florida, Texas, Georgia,
and Minnesota. An unknown additional amount of land
is probably readily certifiable.
A key stop on Teasdale's BARC field tour is a 22-acre
field that recently became the center's first certified
organic research acreage. This spring, Teasdale and
his colleagues established their first experimental
plots on the site, a study of weed tolerance by organic
soybeans with different growth habits.
A total of six cultivars, some of them developed here
at BARC by geneticist Tom Devine, are being evaluated
in paired plots: a tall soybean vs. a standard-height
soybean; an early developing soybean vs. a standard
developer; and a large leaf vs. a normal-sized leaf.
All plots are receiving identical cultivation treatments
between the rows, but the in-row area—where weeds
are most difficult to manage—is being subjected
to three different treatments: all weeds are removed;
crop plants removed; and additional weed seeds added.
Although the facility in Salinas is so far the only
ARS station with a dedicated organic specialist position—research
horticulturalist Eric Brennan—Teasdale notes that
his lab and others began collaborating with local certified
organic farmers as early as 1999. That strategy continues:
Teasdale's lab is currently participating in an organic
high-tunnel tomato production evaluation, funded in
part by SARE and replicated at five organic farms across
the state of Maryland.
Bull, who in 2002 conducted a survey of ARS scientists
to determine levels of interest and activity in organic,
found that 81 scientists system-wide were "conducting
research in explicitly organic systems" and another
107 were interested in organic systems. In January 2005,
the agency convened a meeting in Austin, Texas, to begin
formulating an ARS organic research agenda—a step
that Bull thinks should give a needed administrative
imprimatur to organic research efforts.
In time, Bull says, "we could be the premier organic
research institution that is federally funded. As long
as the scientists on the ground communicate with one
another, we could make quantum advances in organic theory
as well as in production practices. We should be able
to ask the big questions."
Brennan, who also has a total of 22 acres either certified
organic or in transition, agrees there's a lot of interest
in organic agriculture among agency scientists and administrators
and that the Austin meeting "was an important first
step." A major challenge to establishing more certified
organic research acreage, he feels, is that particularly
for horticultural crops, "organic management is
more intensive, and so organic research is more expensive."
Because organic management requires different tools
and skills, it will take time for researchers and technicians—just
as it takes time for farmers—to make the transition.
of one wall of John Teasdale's office at the Beltsville Agricultural
Research Center is occupied by a large-scale color satellite image
of the surrounding area. On it, you can see how the fields, barns
and greenhouses of the USDA Agricultural Research Service's flagship
experiment station are ringed and threaded by the housing developments,
shopping malls and thruways of greater Washington, D.C.
Teasdale's been here long enough—26 years—to have witnessed
a good deal of that suburban encroachment. Today, when he walks
out the front door of the building that is home to the Sustainable
Agricultural Systems Lab, which he heads, and looks south, he can
see the nearest IKEA rising above the trees. Although the research
station still commands more than 7,000 acres, and lies adjacent
to another 20,000 acres of undeveloped federal property, the pulse
of the Beltway is omnipresent.
But Teasdale can also testify to other changes over the last quarter
century, changes less glaring and more broadly beneficial. While
his own interests moved toward sustainable agriculture early on,
in more recent years he's seen a dramatic increase in research related
to making agriculture more profitable for farmers and less damaging
for the environment.
"In the 1950s and '60s, ARS did mostly breeding work,"
Teasdale explains. "Now the seed industry has taken over most
of that. I was hired to do tests of chemical weed control products.
Then the molecular biology kick arrived and lots of people left
the field and went into the lab. I was pretty much left alone out
here." But he's emphatically not alone any more, as a tour
of the BARC research fields makes clear.
Originally from Minnesota, Teasdale received his Ph.D. in agronomy
from the University of Wisconsin in 1978 and was hired by the USDA
straight out of graduate school. "Most of my first six or seven
years were spent working with herbicides," he recalls, taking
chemicals developed for corn and soybeans and testing their applicability
for various horticultural crops.
"Especially for the smaller crops, the liability is high and
the acreage is low, so there's not much incentive for the companies
to invest there," he explains. Teasdale showed, for instance,
that when cantaloupes were grown on plastic mulch, atrazine could
be used between the rows without causing damage to the crop.
By the mid 1980s, however, Teasdale decided it was time to stretch
his wings. Herbicide companies, he realized, had little incentive
to pursue labeling even if application data were available. "Only
two things I worked on ever got a label," he says wryly. He
also decided that as a federal employee, he had a responsibility
to pursue research of the broadest possible long-term benefit—"research
that wasn't being done elsewhere."
Teasdale began by observing that the most effective weed management
strategies involved a combination of chemical and cultural controls,
including planting methods, cultivation tools and—crucially—cover
crops. For Teasdale, developing horticultural applications for agronomic
chemicals demanded an integrated approach. As he puts it, "You
thought a lot about how the cultural control was affecting the crop,
how the herbicide affected the cultural control. . . and how to
use factors like row spacing and crop density to speed up the competitiveness
of the crop."
Working on cover crops, in particular, drew Teasdale toward studying
the rest of the agroecological system, in all its beguiling complexity.
"Because cover crops have so many impacts on cropping systems,
from soil moisture levels to soil temperature levels to nutrient
movement, one's research inevitably starts to branch in to all those
different areas," he observes. "And I think we've barely
scratched the surface when it comes to understanding all those factors."
Interdisciplinary, systems-oriented research
Teasdale's impulse toward multidisciplinary investigation was facilitated
by a reorganization of BARC's human resources in the late 1990s.
Formerly, the researchers were sectioned off by discipline: weed
scientists, soil scientists, vegetable crop specialists, agronomists,
and so on. In 2000, researchers from all these fields and more were
regrouped into the Sustainable Agricultural Systems Lab, which today
consists of about 45 scientists and technicians.
But the scientists were moving toward a systems-oriented approach
well before that. In 1993, Teasdale and his colleagues set up the
Sustainable Agriculture Demonstration Project, a long-term study
focusing on reduced tillage. Because of the site's topography—a
two to 15 percent slope, running in both directions across the field—the
researchers sought to prioritize soil conservation as well as crop
yields and net returns in their experimental design. They settled
on four different management systems, all applied to a two-year
rotation of corn/winter wheat/soybean:
- a conventional no-till system with standard herbicide and fertilizer
- a crown
vetch "living mulch" system developed by Nathan
Hartwig, a professor of weed science at Penn State University,
also with standard herbicide and fertilizer inputs;
- a modified conventional system, in which cover crops were substituted
for some of the herbicide and fertilizer inputs (hairy vetch before
corn and wheat before soybeans);
- an organic, reduced tillage system, with crimson clover and
cow manure substituted for fertilizer inputs and cultivation for
The SADP is now being brought to a close, Teasdale explains, "because
the general outcome was clear." Although the crown vetch system
performed well in years with adequate rainfall, it did poorly compared
to the conventional no-till in dry years. The cover crop and organic/manure
systems did the best job of returning nutrients and organic matter
to the soil, but the organic system suffered from heavy weed pressure.
This led to lower average yields for the organic system, although
reduced inputs resulted in only slightly lower net returns—even
without the inclusion of an organic premium. (Detailed results from
the SADP can be found in the American Journal of Alternative
Agriculture 15,2: 79-87 .)
Interestingly, Teasdale notes, a post-experiment uniformity study
(conventional no-till corn grown across all plots) is showing that
"the two treatments that did the worst in themselves"—the
crown vetch and organic treatments—"are giving the best
effects now." In other words, they did the most to build and
improve the soil, resulting in healthier crops and better long-term
yields. "What that says is that the organic system would have
done well if we could have controlled the weeds."
Other long-term organic vs. conventional systems trials, including
The Rodale Institute's Farming Systems Trial and the Integrated
Cropping Systems Trial at the University of Wisconsin, have used
a similar grain crop-based organic system with similar results,
Teasdale points out. "We had too many weeds because we tried
to just take a conventional agronomic rotation" and make it
organic. "We needed a more diverse rotation with a hay crop.
Otherwise, the weeds will just kept getting worse."
Lessons from the SADP have been folded into BARC's other long-term
trial, known as the Farming Systems Project. The FSP was also initiated
in 1993, but unlike the SADP it began with a three-year uniformity
study in which no-till conventional corn was grown across the entire
site and data were collected on growth rates, yields, and soil variables.
Experimental plots for the FSP itself were then laid out to maximize
homogeneity across plots.
Today the FSP consists of five cropping regimens, two conventional
and three organic:
- a conventional, standard tillage three-year corn-soybean-wheat
- a conventional, no-till three-year corn-soybean-wheat rotation;
- an organic two-year corn-soybean rotation;
- an organic three-year corn-soybean-wheat rotation;
- an organic four-year corn-soybean-wheat-red clover/orchard grass
Each system was tested from all possible starting points within
the rotation sequence. All of the systems included cover crops—rye
before soybeans and hairy vetch or crimson clover (or hay, in the
third organic system) before corn. The organic systems used both
standard tillage and reduced tillage, depending on the year, with
cover crops mowed or rolled prior to no-till planting.
Given the results of the SADP, Teasdale has been especially interested
in the ability of the different organic rotations in the FSP to
manage weeds. What they've found, he explains, is a "lower
seed bank and better weed control of the most troublesome weeds
in our organic plots in the longer, more diverse rotations."
(A full analysis can be found in Agronomy Journal 96: 1429-35 ).
The four-year organic rotation beginning with hay did the best job
of keeping weed seed bank levels low.
"I think for minimum-till organic systems to work, a rotation
out of annual crops and perhaps even a tillage rotation will be
important to lower seed banks and clean up perennial weeds,"
The many uses of cover crops
Long-term, multidisciplinary field experiments like the SADP and
the FSP require the collaboration of many scientists. Soil scientist
Michel Cavigelli, agronomist Mark Davis, research chemist Jeff Buyer
and microbiologist Patricia Millner are just a few of Teasdale's
colleagues who have worked on these studies. One of the strengths
of BARC and the Sustainable Ag Systems Lab (SASL) is that they allow
and encourage that kind of interdisciplinary interaction.
Another of Teasdale's colleagues is Aref Abdul-Baki, a plant physiologist
who has done extensive work on warm-season cover crops such as sunn
hemp, and who has sought to develop cover-crop-based alternatives
to methyl bromide for large-scale vegetable growers in Florida.
(Vegetable producers use the soon-to-be banned chemical as a soil
fumigant to eliminate potentially crop-damaging nematodes.) Together,
Teasdale and Abdul-Baki have studied the allelopathic effects of
cover crops like hairy vetch, demonstrating, for instance, that
the most powerful weed suppression appears to result from a synergy
between the phytotoxins released by the cover crop residue and its
action as a physical barrier.
In the field we run into entomologist Don Weber, who came to BARC
four years ago and is currently studying the effects of cover crop
mulches on Colorado potato beetles. "When I started looking
at cover crops and mulches in the 1980s, that was an effect I noticed
right away," comments Teasdale, referring to reduced CPB damage
on mulched potatoes. "I mentioned it to the entomologists,
but nobody was interested. Now at last we have people like Don,
who are interested."
In some parts of the field the difference was dramatically visible:
unmulched plants skeletonized by the fat orange instars; a few rows
away, mulched plants almost untouched. "There are at least
four different things that could be going on," Weber explains
enthusiastically. The mulch could be changing the microclimate,
for instance by lowering soil temperatures; it could be altering
the biochemistry of the potato foliage; it could be directly impacting
the potato beetle in some way; or it could be affecting the pest's
natural enemies. "There's a carabid beetle that's a specialist
predator on the CPB," Weber adds, brushing aside some cover
crop residue and pointing out a small, blue-black beetle.
Elsewhere on the farm, Teasdale tells us, Weber's trialing potatoes
with a variety of different cover crops, including crimson clover,
hairy vetch, and rye, and is also experimenting with different ways
of handling the transition from cover crop to crop. "Since
potatoes go in so early, you don't get much biomass from the cover
crop if you kill it at the time of planting," Teasdale points
out. "Maybe we can develop a system in which you plant into
the standing cover crop and then mow when the potatoes start to
In the 1990s, an SASL study of tomatoes grown on hairy vetch mulches
found that the mulched plants senesced significantly later in the
season than unmulched plants. Subsequent experiments have sought
to clarify the underlying mechanism at work. A key question is how
the vetch residue, which is almost completely decomposed by mid-season,
promotes crop plant health at the end of the season. This year,
the researchers are comparing tomato plots mulched with vetch tops
only, vetch roots only, rye tops, rye roots, black plastic, white
plastic, or not mulched at all.
"We think the effect has to do with more than just the N levels
supplied by the vetch," Teasdale comments. "Dr. Autar
Mattoo, a molecular biologist in our lab, has shown that the cover
crop mulch influences the expression of many important genes in
the tomato plant."
Cover crops and N utilization
A final, fundamental role for cover crops, of course, is to supply
fertility for crops. While it's well established that cover crops
can supply all the nitrogen needed by a cropping system, much remains
to be learned about how best to manage that supply.
"That's really what I see as one of the big challenges of
sustainable agriculture," says Teasdale. "We've gotten
to the point where we can say, yes, we can provide on-farm nutrient
sources, which means they're more sustainable in terms of the environmental
costs of being produced elsewhere and transported to the farm, but
from the standpoint of keeping the N on the farm—that's still
a big challenge."
Because nitrogen supplied by cover crops and composts needs to
mineralize in order to become available to crops, calculating and
timing its availability is trickier than with synthetic N sources.
No crop is 100 percent efficient at utilizing available N, moreover—"corn
is only 50 percent efficient at using available N, and tomatoes
are more like 20-30 percent," Teasdale notes—so you have
to use too much in order to have enough. The key is to capture the
excess before it can leach out of the system and become a pollutant.
"Say you have 150 pounds of N in a hairy vetch cover crop,
the amount of N that gets taken up by the crop is quite small. A
number of different people have shown that experimentally—a
substantial part is lost to leaching and to the atmosphere. With
manure and compost, it's the same situation. It's a big challenge
to understand the mineralization process, because it's microbially
One solution, Teasdale continues, is to revise the definition of
optimum crop production, since the yield-response-to-N curve is
not linear—there's a diminishing return as you add more nitrogen
to the system. "People are thinking now that if you drop back
a bit, you would only slightly lower yields but put significantly
less surplus N into the environment."
Another is "to use cover crop mixtures where the combination
of C and N is better balanced, [so] the N becomes temporarily sequestered,"
an effect that's fairly well established scientifically, Teasdale
says. The optimum carbon-to-nitrogen ratio seems to be between 20:1
and 30:1, he adds.
Of course, a lot of farmers do use a rye-vetch mixture as cover
crop, which is a good way to achieve that C:N balance. Like other
researchers working on organic cropping systems, however, Teasdale
is keenly interested in the prospect of organic no-till, and "for
organic no-till, the mixture is harder to manage," for various
reasons. "You may get more biomass for weed suppression [with
a mixture], but all that additional residue can interfere with planting
operations." If the planting row falls right on the top of
a rye row, moreover, the rye root mass can inhibit germination.
"But none of those problems are insoluble," he emphasizes.
"They just require more work." Fortunately, BARC has a
dedicated team tackling them from a broad range of disciplinary
Laura Sayre is senior writer for NewFarm.org.