August 10, 2006: Steve Groff and family
run Cedar Meadows Farm, 200 acres of mixed vegetables, grain
and seed crops situated in the heart of Lancaster County,
Pennsylvania. The bucolic setting is arguably one of the most
beautiful farming regions in the country. It’s also
a laboratory of sorts. Groff is a pioneer of sustainable agriculture
techniques, specifically no-till—which he’s been
practicing since the 1980s—and the use of cover crops
to add fertility, protect and improve the soil, reduce chemical
use and enhance water quality. Pennsylvania State University
grad students and professors are no strangers to Groff’s
farm, nor are the researchers here at The Rodale Institute.
The Cedar Meadow Farms Field Day July 14 is one of many that
have taken place on Groff’s land over the years, this
one representing a collaborative effort between Groff, Penn
State, The Rodale Institute, and the Pennsylvania Association
for Sustainable Agriculture. The theme was “Integrating
no-till practices and cover crop use to build soil quality
and manage pests.”
Groff utilizes a permanent cover cropping system that incorporates
no-till, cover crops and effective crop rotation strategies.
Several concurrent workshops July 14 drew from research that’s
taken place at Cedar Meadows Farm, with highlights including
how cover crops and crop residues encourage soil microbial
activity, how they enhance beneficial insect populations,
and how cash crops respond to different cover-cropping strategies.
Three program tracks with a total of seven possible workshops
encompassed the field day. This report centers on four of
“It’s not a perfect farm, and we’re continuing
to learn,” Groff told the crowd of about 400, sharing
his own vision “to find that perfect balance between
environmental stewardship and economic profitability”
before sending us all off in various directions across his
Cover crop selection
Timing is a critical as type and variety selection, all the
presenters agreed, and the chosen cover has to be an appropriate
match for the region, the cropping method, and the cash crop
Groff himself has been working on an early maturing hairy
vetch that can be killed up to a week sooner than traditional
varieties, thus allowing for earlier planting into the thick
living mulch the vetch forms once it’s rolled down (hairy
vetch also fixes nitrogen, most optimally if seed is inoculated
before planting). But roll down hairy vetch too early and
it comes right back. Optimum roll-down time is when at least
75 to 90 percent of the crop has begun to flower, because
the plants “think” they have done their job and
will no longer struggle to reproduce.
Groff is also growing forage radishes (diakon) as a cover
crop and is producing seed for other farmers. He offered that
a farmer can seed this crop—which biodrills deeply into
the soil; like a carrot, only bigger—for about $20-$25
an acre. Besides breaking up the soil, he said, the radishes
express some allelopathy, that is, they secrete chemicals
that keep other plants around them—namely weeds—from
“I believe the soil is meant to be covered,”
Groff told the workshop crowd gathered around a table of various
potted cover-crop samples. He cited a number of reasons for
mixing various cover crop types. For instance, he mixes vetch
with rye partially because the rye keeps the vetch off the
ground, making it easier to harvest the vetch seed.
Hairy vetch releases nitrogen on a curve, Groff explained,
so it’s critical to time the planting of a heavy feeder
such as corn to match the nutrient cycling of the cover. For
Groff, that’s around June 15. While different varieties
of cover crops have varying tolerance to winter, Groff advised,
it’s a good idea to get even the most hardy ones into
the ground at least by the second week of October (Groff farms
in USDA Cold Hardiness Zone 6).
Still riding the hairy vetch train, Rodale Institute agronomist
Dave Wilson said that a 15-30 pound seeding per acre of the
popular cover crop can deliver up to 9,000 pounds of dry biomass
and more than 200 pounds of nitrogen (the amount will vary
from year to year depending on rainfall and growing degree
days). “We use it in our organic farming system for
natural weed suppression, and it gives us all our nitrogen
for our corn,” Wilson said, explaining that the vetch
and corn residue are incorporated into the soil through tillage
once the corn has been harvested.
One big challenge of cover crops as living mulches, Groff
said, is planting into them. Another, he said, is that they
are typically aggressive. “When you plant vetch on your
farm, you will have vetch on your farm.” About
3 to 5 percent of hairy vetch seed won’t germinate the
first year, he said, yet it will remain viable up to five
years. “And you will see one seed in your wheat, because
hairy vetch seed is shiny black.”
Wilson offered other effective cover crop combination examples
of red clover, ladino clover or berseem clover frost seeded
into winter wheat. “If you want nitrogen, you grow legumes,”
he said. Non-legumes can act as a nurse crop, provide biomass
and sequester excess nitrogen after your cash crop. “Rye
sucks it up,” Wilson offered, explaining that this captured
nitrogen becomes available to crops the following year after
the rye has been incorporated into the soil. “Rye tends
to dry the soil out in the spring if you let it grow too long”
and may be a problem in a dry year, he added.
When combining covers, you’ve got to be aware of their
habits, offered Groff. “People won’t believe it
unless they see it, but radishes will outgrow anything you
have,” he said, including oats and rye. So instead of
mixing and broadcasting seed, he said, he alternates rows
when the desire is to pull in the benefits of a variety of
cover crop species that includes the aggressive forage radish.
Sometimes, Groff said, cover crops behave differently when
matched together. “I don’t know why, but rye kills
[more easily] when it’s mixed with vetch,” he
Reiterating that choosing the right cover crop or mix is
a matter of matching the right cover to the right crop, timing
your plantings in a way that the cover and cash crops best
complement each other, and having specific goals in mind,
Groff said; “You have to look at the whole program and
decide what it is you’re trying to do.”
Soil quality and beneficial organisms
Mark Goodson, Penn State Extension educator led this session
with a discussion about the glue that binds…soil particles,
that is. “Glomalin is the Superglue of the soil,”
he told the gathered crowd of the substance—a byproduct
of the interaction between arbuscular mycorrhizae fungi and
plant roots—discovered only a decade ago. This intense
binding leads to aggregate stability, he said, opening up
pore spaces for roots to grow and for water, air and nutrients
to travel freely.
Carbon dating tells us that glomalin, a combined sugar and
protein, is so stable that it lasts up to 42 years, Goodson
In the symbiotic relationship between mycorrhizae and plant
roots, he explained, the plant feeds the fungi sugar and the
fungi in turn provide the plant with nutrients (nitrogen).
All plants—with the exception of some of the brassicas—have
some sort of relationship with mycorrhiza fungi, Goodson said,
which attach to roots and grow long, thin hyphae, threadlike
filaments that reach further into the soil (up to 18 feet)
gathering water and nutrients. These fragile hyphae make glomalin
to protect themselves, then decay and slough off about every
10 days. “That glomalin goes into the soil and forms
these tight aggregates,” Goodson explained.
“One-half to one-third of the organic material in the
soil is this glomalin,” Goodson said. These levels drop
with increased tillage, he said, thus degrading the tilth,
or structure, of the soil and the ability for infiltration.
Next up, Randa Jabbour and Meredith Murray, both graduate
students in Penn State’s Department of Ecology, introduced
the concept of the soil food web. “Soil is alive,”
Jabbour said, ratting of a laundry list of underground inhabitants
that include beneficial fungi and bacteria, nematodes, worms,
insects, spiders and mites.
Murray then presented a “beetle box” that held
preserved samples of dozens of the little insects in a range
of sizes with a host of different functions. “This one
specializes in eating snails,” Jabbour explained.
At Cedar Meadows Farm, Murray, Jabbour and their colleagues
study weed seed predation by ground beetles. Murray explained
how researchers use pitfalls—homemade beetle traps fashioned
from plastic soda bottles and baited with antifreeze—to
catch beetles within a given area. By collecting beetles and
counting seed that has been placed in a given cover-cropped
area over a 14-day period, researchers get a pretty good idea
of weed-seed-predation rates. At Cedar Meadows Farm, they’ve
calculated that to be about 84 percent, with more of the weed-seed
removal attributed to vertebrates than invertebrates. “Once
rodents find a spot with a large amount of seed, they keep
coming back until those seeds are gone,” Murray said.
“And they’ll tell all their friends.” (See
our story Free
weed-control service: Mice for more on weed seed predation
One important bit of information learned through this study
is that certain cover crops and management practices encourage
these important weed-seed predators by offering favorable
habitat. “The highest seed predation was in cropping
systems that formed a nice canopy cover,” Murray said.
“It gives [weed-seed eaters] protection from predators.”
As for cropping systems, Murray said there wasn’t a
lot of difference in beetle populations in spring but that
in fall—when beetles were most active—they thrived
more in areas were tilling was minimal or nonexistent. If
you can encourage habitat and map a weed-seed-eating insect’s
life cycle with the prevalence of weed seed on the soil surface,
she said, “You’re going to see a larger decrease
in certain weeds the following year.”
Ecological weed management
Following a scrumptious chicken barbeque prepared by Groff’s
church, those of us on Track 1 tromped into the blazing heat
behind William S. Curran, PhD, professor of weed science at
Penn State. Ecologically based weed management is about combining
many “little hammers” like allelopathy, encouraging
weed seed predation and implementing cover cropping strategies
to take the place of the “big hammers” like pesticides
and tillage, he said.
Walking into experimental corn plots—some planted in
cover crops and some not—Dr. Curran identified several
typical weeds, including lambsquarter, redroot pigweed and
foxtail. “When you’re managing cover crops properly,
you will have lots of biomass,” he said. “The
key is in trying to catch the weed-suppressive properties
of the cover crops.” These properties include:
- Creating a physical barrier.
- Reduction of light penetration.
Curran suggested a goal of at least 5,000 pounds of dry matter
per acre for adequate weed suppression. While hairy vetch
is a popular cover for its ability to deliver nitrogen, Curran
said it’s a succulent and so tends to disappear quickly.
Mixing in cereal rye, he said, combines for a more persistent
cover that offers better weed control over time. “You
can manage weeds with the residue,” he said, adding
that the most critical time for controlling weeds in corn
is at four or five weeks.
“When do weeds wake up?” This was the question
posed by Andy Hulting, a weed ecologist at Penn State, and
he brandished a poster bearing the same theme. “Typically,
you see more weeds in early planted corn than in late-planted
Timing is everything, he said. “You want to wait to
plant to allow the weeds to come up so you can manage them.”
Hulting led us to four 10’ x 80’ plots of corn
planted the same day using various cover cropping strategies.
“The weed population decreases as you go down the hill,”
he said, pointing out that as cover crop biomass decreased,
weed pressure increased.
“The timing of your weed management does matter.”
Certain weeds are common in spring, he said; “a whole
suite of different weeds become a problem later in the summer.”
Questions you have to ask yourself, he said, include:
- What weeds are a problem?
- When is the best time to think about managing them?
- What is the optimum time for planting considering the
Cover crops and rollers
“A number of years ago, we began looking at how we
could reduce tillage on our organic farm,” said Rodale
Institute farm manager Jeff Moyer. “We’ve seen
farmers who reduce tillage use more herbicides. If you reduce
something, you usually have to increase something else.”
Since increasing herbicides was not an option for organic
production, Moyer said, the farm increased its intensive management
of cover crops. Then it increased its technology, rolling
down cover crops into a living mulch and planting into them.
“We started out with a Buffalo stalk chopper, which
knocks down and chops corn stalks. It will kill most of the
cover crop as long as it’s a winter annual. We’re
trying to work with cover crops that normally would want to
Discovering that some cover crops are tenacious—particularly
when a rather easy-to-kill crop such as hairy vetch is mixed
with a tougher customer like cereal rye—Moyer and farmer
neighbor John Brubaker did what any good farmer would do;
they designed a better solution.
Protruding fins in the new roller design cut off the vascular
system of the plants by crimping stems every seven inches,
and the unit can be filled with water to regulate down pressure.
Since the fins are mounted at an angle rather than 90 degrees,
they don’t pull the plants out of the ground and disturb
the soil, as the stalk chopper did. The elegant-yet-simple
design also sports two bearings instead of 16.
And the front-mounted roller allows for coordinated roll-down
and seeding in one pass, also saving time and energy. “All
you have to do is go back and harvest,” said Moyer.
“That’s just two trips to the field.” (Read
more about the roller and our latest research surrounding
the tool on our No-Till
Finally, Rodale Institute agronomist Dave Wilson took to
the field once more to wrap up the day with a talk about how
our farm utilizes cover crops in conjunction with limited
tillage in an organic system.
This season, he said, in the aboveground biomass produced
by the hairy vetch there was a whopping 245 pounds of nitrogen
per acre, plenty of fertility in which to plant corn. The
vetch also acts as a weed suppressor. (Later, Wilson explained
how we learned the hard way that vetch can create a hospitable
environment for “bad critters” like cutworms as
well as good ones like the weed-seed-foraging beetles discussed
above. We had to replant our corn when an earlier planting
was decimated overnight. Again, Wilson stressed, it’s
all about careful observation and timing.)
One of the biggest challenges of utilizing a cover crop
as a living mulch is direct-seeding into it, because of the
thickness of the mat, Wilson said, offering that for vegetable
crops you would need to use a no-till transplanter to be successful.
The hairy vetch at The Rodale Institute, seeded at 25 to
30 pounds per acre, also attracts an abundance of pollinators
and other beneficial insects, Wilson said, reminding everyone
that the biomass aboveground is complemented by belowground
biomass, where the root zone creates the additional benefit
of contributing to a robust soil food web.
A big difference Wilson noted between no-till and cultivated
corn systems is the cultivating action between rows actually
throws soil against the corn stalk and buries emerging weed
plants, so the weeds that grow in the organic tilled system
are in the row with the corn or soybeans. In the organic no-till
system, there are more weeds between the rows of corn and
soybeans and fewer weeds in the row with the corn or soybean
plants, he explained, so the weed-to-crop proximity is different
in the two systems.
Wilson also noted a few trick and tips when working with
different cover crops utilized for organic no-till soybeans.
“If you roll rye perpendicular to the direction of the
drilled small grains you get better cover than if you roll
it in the same direction of the drilled rolls.” Barley
and wheat can be used as cover crops but won’t deliver
as much biomass as rye. Spring oats, planted in the fall with
hairy vetch, offer a nice nurse crop (protective canopy) for
the vetch, which can be hard to get started and will winter
kill if there’s not enough growth on it before frost
arrives. “The oats sequester some of the free nitrates—the
nitrogen in the soil—and then they winter kill.”
Wilson also counseled that, for reasons of adaptability,
it’s better to get seed produced in the region where
it is to be grown. Like Groff, he stated that you have to
consider many factors—including economics, region, and
desired function—when choosing your cover or mix.
“Hairy vetch is more expensive than crimson clover,”
Wilson said, adding that as you move north, crimson clover
doesn’t overwinter as well or produce as much biomass
as vetch does.
Organic no-till differs from conventional no-till in a variety
of ways other than the absence of pesticides, Wilson said,
and the system presents particular challenges. “In most
conventional no-till systems, you’re not normally dealing
with 9,000 pounds of dry cover crop biomass,” he said.
“You’re normally cutting into a mat of crop stubble
or a killed sod or hay field.”
“We need at least four- to five-thousand pounds of
cover crop dry matter per acre for effective weed suppression;
the weed-suppression aspect is a big deal for us in organic
Whereas conventional no-till is often continuous no-till,
he said, organic no-till is rotational no till. Still, Wilson
said, conventional no-till farmers have found a way to reduce
pesticide use to 1/16 or even 1/32. That, he said, reduces
the farmers’ input costs, and reducing herbicides is
good for the environment and the farmers' well-being.