|April 2, 2004:
Results are in from the 2003 field tests of a low-tech system for
cultivating mycorrhizal fungi (MF) to improve plant health and boost
In preliminary trials at The Rodale Institute Experimental Farm,
substantial differences were found in the response of MF populations
to different soil environments. Test plots designed to demonstrate
how farmers can produce their own MF inoculant—to use in a
greenhouse mix, for instance—showed that two key MF species
performed better when grown with a dairy manure-leaf compost or
a yard clippings compost than when grown with a controlled microbial
The different MF response may be attributable to the higher phosphorous
levels in the controlled microbial compost, since MF populations
are believed to be inhibited by high phosphorous conditions. The
2003 data will help researchers refine the MF inoculant production
system so that it can be passed on to farmers.
The inoculant production research is part of a multi-year project
led by Agricultural Research Service scientist Dr. David Douds.
A soil microbiologist who has dedicated his career to the study
of mycorrhizal fungi, Douds has been collaborating with Rodale Institute
researchers since 1989, studying the effects of conventional and
organic farming practices on MF populations and the effects of MF
populations on crop yields.
Previous years' field studies found higher and more diverse MF
levels in organically-farmed than in conventionally-farmed soils,
in part because of the use of over-wintering cover crops in organic
systems. Field experiments have also demonstrated dramatic yield
increases when crops were inoculated with MF: up to a 34 percent
yield gain in sweet peppers, and up to a 45 percent gain in potatoes.
The on-farm inoculant production system should enable farmers to
realize similar yield increases with minimal costs. "These
systems could become as common as a compost pile" for organic
and sustainable farms, notes Rodale research technician Matt Ryan.
Constructed out of landscape fabric, the yard-square planting enclosures
are simple to build and require little maintenance other than watering.
This season, Douds and the Rodale researchers will repeat the experiment
with a few adjustments based on the 2003 results. The yard clippings
compost and the dairy manure-leaf compost—which produced the
best results at higher concentrations—will be tested at compost:vermiculite
mixtures of 1:1, 1:2, 1:4, and 1:9. The controlled microbial compost—which
produced the best results at lower concentrations—will be
tested at dilutions of 1:9, 1:19, 1:49, and 1:99.
In addition, Douds plans to evaluate the feasibility of using native
soils, instead of host plants pre-inoculated with MF, in the production
system. Reasoning that undisturbed soils from a given farm—say
from a hedgerow or native prairie remnant—should contain the
MF species best suited to the local conditions of that farm, the
researchers will mix controlled amounts of native field soils into
sterilized compost:vermiculite mixtures, and then plant non-inoculated
host plants into the enclosures.
A final, more elementary possible refinement is the use of large
bags—either of woven polyethylene or of burlap—for the
propagation system, rather than having farmers construct the raised
beds out of sheets of landscape fabric and wooden stakes. In addition
to being simpler, using bags would enable farmers and growers to
start the MF propagation beds in the greenhouse in early spring,
and then move them outside when conditions permit. Last year's results
indicate that inoculant enclosures started earlier in the season
produced significantly more viable MF propagules.