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 yields.
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 compost.
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
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
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.