As some of you may know, The Rodale Institute®,
which publishes The New Farm®, is home to
the longest running field trials in the country
comparing organic and conventional systems of
farming called The
Rodale Institute Farming Systems Trial® (FST).
The data from that 23 years of research is a real
treasure trove of insight into the economic, ecological
and agronomic benefits of organic farming.
In addition to this long-running Farming Systems
Trial, we have a variety of other research in
progress at The Institute. David Douds, as you’ll
read in this story, has been studying soil fungi
here at The Institute’s research farm for
15 years. We’re engaged in no-till research,
weed research, compost tea research, composting
research, water quality research, and much more.
Until now, much of the light we’re generating
here on our research farm has been hidden under
the proverbial barrel, but we’re taking
off the barrel and busting it up for firewood.
We’re going let the light of the amazing
research being done here shine on farmers, consumers
and environmental activities.
Over the next year we’ll be running a series
of stories, about one a month, on the significance
of our research ... and its practical applications.
That includes a few stories on equipment construction—a
front-mounted roller for no-till, and a compost
turner converted from a junked 18-wheeler.
So sit tight, and be prepared to be amazed, starting
with David Douds’ discoveries about how
you can increase vegetable yields by 50 percent
using homemade fungal inoculants.
p.s. Interested in hearing more about how you
can take part in the mycorrhizae revolution? Click
here and let us know. Send your name, phone
number and e-mail address with your note so we
can follow-up with you.
||"Overall, Douds’ work suggests
that a small amount of mixed MF inoculant can be substituted
for a large amount of fertilizer--with no loss of yield,
greatly reduced environmental impact, and lower production
||Home-grown mycorrhizal inoculum can
be produced at a fraction of the cost of purchasing commercial
mixes. "I've done some preliminary calculations,"
says Douds. "The on-farm system produces 100 million
propagules for approximately $50, not counting the cost
of the farmer's labor, which is fairly minimal. To purchase
100 million propagules as listed on the bag of some commercial
mixes would cost anywhere from $8,000 to $40,000."
September 29, 2003: You've read the amazing
facts and figures: one teaspoon of healthy topsoil can contain
millions of individual microorganisms, all playing a part
in the functioning of the soil ecosystem. But how much do
you really know about the action of those diverse species
and how to maximize their presence in your own fields?
Ongoing research at The Rodale Institute® sheds light
on one important component of the soil community--mycorrhizal
fungi--and its impact on agricultural production. Under the
leadership of Dr. David Douds, a soil microbiologist with
the USDA's Agricultural Research Service, field trials have
shown yield gains of as much as 50% in the presence of healthy
mycorrhizae populations. Now Douds is developing a practical,
low-cost method for on-farm production of mycorrhizal soil
inoculant, promising higher yields with lower nutrient inputs.
A mycorrhizal primer
Mycorrhizae are soil-dwelling fungi that live in and around
the roots of plants ('myco-rrhizae' means 'fungus-root').
The fungi and the plants form mutually beneficial associations
in which the fungi receive carbohydrates from the plants and
the plants receive nutrients and other benefits from the fungi.
Since the first mycorrhizae species were described by a German
botanist in the 1880s, researchers have discovered that approximately
80% of all land plants form mycorrhizal associations. The
relationship is so widespread, in fact, that it is sometimes
referred to as 'the Universal Symbiosis,' and is believed
to have played a key role in the evolutionary transition from
aquatic to terrestrial plant forms.
Today, scientists divide mycorrhizae into two major types:
endomycorrhizae, which penetrate and colonize plant roots,
and ectomycorrhizae, which form sheaths around plant roots.
Whereas ectomycorrhizal relationships tend to be highly specialized--with
some 6000 fungal species worldwide associated with tree species
of the oak, beech, and pine families, among others--endomycorrhizal
associations are more generalized as well as more widespread,
with fewer than 150 fungal species opportunistically colonizing
the roots of the vast majority of terrestrial plant families.
Ectomycorrhizal inoculants are already widely used in commercial
forestry, but the possibility of developing endomycorrhizal
inoculants for production agriculture is a more recent idea.
"These are beneficial soil fungi that colonize the
roots of plants and help them take up phosphorus" and
other immobile soil nutrients, such as zinc and copper, Douds
explains. "The fungus colonizes the root and it also
grows out into the soil; the part of the fungus that's in
the soil acts as an extension of the root system, to explore
a greater volume of soil and take up nutrients and bring them
back into the root."
In addition to facilitating nutrient uptake, some mycorrhizae
secrete a gluey substance, called glomalin, which helps develop
soil structure and soil aggregation; others may help plants
fight disease. Yet because endomycorrhizae are 'obligate symbionts'--they
must have living plant roots to colonize in order to complete
their life cycle--their numbers will decline under conventional
agricultural monocultures, which have living crop covers fewer
months of the year than organic rotations. The drop in yields
typically seen after the first year of cultivation on virgin
prairie or forest soils is probably attributable in part to
the loss of native mycorrhizae, Douds says.
Fifteen years of research prove benefits
Douds has been conducting research in collaboration with
The Rodale Institute since 1989, his first year at the Agricultural
Research Service's Eastern Regional Research Center in Wyndmoor,
on the outskirts of Philadelphia. "Some employees of
The Institute farm came down to our research center as part
of a kind of an interagency show-and-tell about research programs
and facilities and what all we could do to help each other,"
Douds recalls. "Rhonda Janke"--The Institute's research
agronomist at the time--"gave a presentation about The
Rodale Institute Farming Systems Trial," a side-by-side
comparison of organic and conventional production systems.
Douds recognized it as a great opportunity to study endomycorrhizal
"Later that year I started sampling, and right off learned
that [the soils under] the conventional farming systems had
fewer mycorrhizal fungi than the soils under the low-input
farming systems. So right away we all got excited and we branched
out from there."
Since that first season, Douds' work at The Rodale Institute’s
333-acre experimental farm has progressed in three overlapping
In the first phase,
from 1989 to 1995, Douds and his team surveyed native mycorrhizal
fungi (MF) populations at Rodale and examined the impact of
different agricultural practices--including tillage regimes,
crop rotations, and soil amendments--on those populations.
The second phase, which is still ongoing, looks at the utilization
of MF by crop plants, comparing yields in the presence and
absence of different MF species. The third phase seeks to
apply those findings by devising a simple, on-farm MF inoculum
production system, so that farmers can harness the benefits
of endomycorrhizae without spending lots of money on commercial
mixes. (Commercial products already on the market include
Bio/Organics Endomycorrhizal Inoculant [$79.95 for 3 lbs,
labeled to treat 500 plants], Plant Success Mycorrhizae Tablets
[$19.95 for 100 tablets, labeled to treat 50 plants up to
1 ft tall], and Earthroots VAM Fungi by First Fruits LLC [$15
for 3 lbs, labeled to treat 200 seedlings].)
Agronomic practices that boost—or
Although the first phase of Douds's research found larger
and more diverse MF populations in organically-managed soils
than in conventionally-managed ones, it also revealed how
specific agronomic practices can boost or depress MF levels.
"Over-wintering cover crops. . . are very beneficial
to mycorrhizal fungi," Douds notes, whereas "tillage
disrupts the mycorrhizal fungi in the soil and serves to decrease
the initial colonization of the plants." Based on these
findings, Douds emphasizes that all farmers, organic or conventional,
can take steps to nurture the MF already present in their
fields: reduce tillage, he says, use fungicides sparingly,
and--most important--maximize cover cropping. "Over-wintering
cover crops give the MF a host plant to colonize when there's
no cash crop growing on the soil," Douds explains.
In the coldest part of the year the MF go dormant, but during
warm spells in early spring and late fall, the MF will try
to grow, and can exhaust their reserves if they find no plant
hosts. "During these periods. . . the fungus is still
respiring, it's still burning up its carbohydrate storage
in the spores, it's burning up the lipids that were stored,"
leaving it "less viable when the time comes finally for
the crop plant to be present." A cover crop or even just
a weedy fallow will maintain healthy MF populations, which
can then benefit the cash crop coming on to the field.
Crop rotations are another factor to consider, since a handful
of crop species belong to plant families that do not form
mycorrhizal associations (said to be 'non-mycotrophic'), including
the Brassicaceae (rape, broccoli, cabbage, turnips, etc),
the Chenopodiaceae (beets, spinach), and the Polygonaceae
(buckwheat). Not only will these crops not benefit from the
presence of MF, but MF levels in the soil will be depressed
after these crops are grown, potentially showing an effect
on any mycotrophic crops which follow.
Potatoes and peppers inoculated with mycorrhizae
get yield boosts of up to 50 percent!
In the second phase
of his research, looking at the impact of MF on crop yields,
Douds began inoculating plants in the greenhouse and then
tracking their performance in the field.
"We had some plants that were inoculated with a control
mix with no inoculum, another one inoculated with a mix of
mycorrhizal fungi, and another inoculated with just one species
commonly present in commercial inoculum," Douds explains.
"We transplanted them into the Compost Utilization Trial,"--another
ongoing experiment at The Rodale Institute--"and we found
over the course of the 3-year experiment that the mixture
of mycorrhizal fungi increased the yield of marketable-sized
peppers up to a maximum of 34% over the control. Last year
we tried inoculating potatoes, and we got up to a 50% increase
over the controls."
This year they are repeating the potato trial, measuring
yields under four different treatments: one with no added
MF; one with a commercially available MF; one with a mixed
MF inoculant grown in a leaf compost and vermiculite medium;
and one with a mixed MF inoculant grown in a dairy manure
compost and vermiculite medium. Overall, this work suggests
that a small amount of mixed MF inoculant can be substituted
for a large amount of fertilizer--with no loss of yield, greatly
reduced environmental impact, and lower production costs.
One unexpected finding of Douds' work at Rodale "is
that mycorrhizae can be used to increase the yield of crops
even in soils that are very high in phosphorous." Some
of the soils at the Rodale Farm which have been heavily composted,
Douds notes, "have available P in excess of 300 parts/million"--well
above the level at which mycorrhizal responses are typically
seen, around 20-50 ppm available P. "The generalization
would be that P as high as 300 would be a situation in which
the plant can take up all the P that it needs by itself without
relying on the mycorrhizal fungi." Douds believes that
at high nutrient levels, some of the other benefits of MF--enhanced
disease resistance, improved soil aggregation and better water
relations--could be showing an effect.
Build your own on-farm inoculum production
The third phase
of Douds' research at Rodale Farm focuses on developing an
inexpensive, practicable system for on-farm production of
mycorrhizae inoculant. As obligate symbionts, endomycorrhizae
have so far resisted attempts to create what scientists call
axenic (or isolated, single-species) cultures--they can only
be grown in the presence of a host plant. Douds' system works
within this constraint, using bahiagrass (Paspalum notatum),
a tropical grass native to the southeastern US, as a host.
The basic procedure is for the farmer to construct a simple
enclosure out of landscape fabric (75 cm square and 20 cm
high), fill it with a mixture of compost and vermiculite,
and then transplant pre-colonized bahiagrass seedlings into
the mixture. Over the course of the growing season the bahiagrass
spreads within the enclosure and the mycorrhizal fungi spread
and reproduce along with it. When the grass dies back in the
winter, the farmer is left with a concentrated mycorrhizal
inoculant that can be incorporated into his or her potting
mix when starting seedlings in the greenhouse the following
This year, Douds gave inoculated bahiagrass seedlings and
other materials to a few Pennsylvania farmers to see how the
method fares in the real-life conditions of farming. Meanwhile,
Douds has 12 soil enclosures growing at the Rodale Farm in
an experimental grid designed to identify optimum growth media.
Douds chose three different kinds of compost--yard-clippings
compost, controlled microbial compost, and dairy manure-leaf
compost--and then diluted each kind with vermiculite at four
different ratios, ranging from 1 part compost:2 parts vermiculite,
down to 1 part compost:49 parts vermiculite. Each soil enclosure,
finally, has nine separate sections, three with no inoculant
and three each with two different mixtures of MF.
At the end of the season, says Douds, "we'll sample
the mixtures from within each enclosure, quantify the inoculum
production, and then hopefully develop a prediction formula,
where the optimum ratio [of compost to vermiculite] is a function"
of the nutrient analysis and other properties of the compost.
All the farmer will need to do, then, is get the nutrient
analysis of his or her compost, plug it in to the formula,
and find the optimal ratio of compost to vermiculite to use
for his or her farm.
"On-farm methods have several advantages over commercial
inoculants," Douds explains. In the first place, whereas
commercial formulae typically only contain a single MF species
(frequently Glomus intraradices), Douds' method yields a diverse
inoculum containing many MF species. This is crucial because
MF show significant 'functional diversity'--"some are
good at holding the soil together, some are good at gathering
nutrients," others help fight disease.
A second, related advantage is that by mixing in some soil
from a nearby woodland, prairie, or hedgerow, the farmer can
use Douds's system "to produce the native or indigenous
strains of mycorrhizal fungi. . . the ones that are already
adapted to his [or her] particular soil conditions."
This could be especially important on problem soils, such
as those with high aluminum, say, or high or low pH, where
commercially-produced fungi may not survive.
Last but not least, home-grown mycorrhizal inoculum can be
produced at a fraction of the cost of purchasing commercial
mixes. "I've done some preliminary calculations,"
says Douds. "The on-farm system produces 100 million
propagules [in a single enclosure] for approximately $50,
not counting the cost of the farmer's labor, which is fairly
minimal. To purchase 100 million propagules as listed on the
bag of some commercial mixes would cost anywhere from $8,000
to $40,000." Commercial inoculants are sold in a peat-
or vermiculite-based medium, so purchasers have to buy (and
pay to have shipped) a large volume of material to get a small
number of viable MF propagules--another reason it makes more
sense to grow your own.
At the moment, Douds' system (like commercial MF inoculant)
is suitable for two types of farms: vegetable growers on any
scale who produce their own seedlings and can mix the inoculum
into their potting mix; and smaller, labor-intensive farms
or urban gardens where "the inoculum can be incorporated
by hand, directly into the planting furrow or planting hole."
Farmers growing field crops on a large scale can only take
advantage of MF inoculants if they want to try them out in
a relatively small area. "Delivery of MF inoculum to
the field is a problem," acknowledges Douds. "Commercial
companies are working on this for their particular inocula."
He smiles. We can only hope that he will be too.