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 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
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
||"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 costs."
||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
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 Experimental Farm 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
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 of fungi
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 Farming
Systems Trial," a side-by-side comparison of organic and
conventional production systems. Douds recognized it as a great
opportunity to study endomycorrhizal associations.
"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 phases:
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 depress—mycorrhizal
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
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
Build your own on-farm inoculum production system
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 spring.
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.