On-farm production of mycorrhizal fungus inocula

On-farm production of mycorrhizal fungus inocula

Summary

Arbuscular mycorrhizal [AM] fungi are soil fungi that form a mutualistic symbiosis with the majority of crop and horticultural plants. Among the benefits to the host plant are enhanced: nutrient uptake, disease resistance, and water relations. Given these benefits, utilization of AM fungi should be an integral part of farming systems that seek to minimize chemical inputs. Commercial production of these fungi currently is done in greenhouse pots with plants or in the laboratory in Petri dishes with root organ cultures. These methods then require isolation and purification of the fungus, mixing it with a carrier, and/or transport of bulky pot culture inocula to the farmer. This has limited the utilization of AM fungus inocula to plant production systems requiring only small volumes of inoculum.

The goal of this project is to develop, refine, and transfer to farmers a new technology for “on-farm” production of AM fungus inocula. The farmer would purchase or grow host plants pre-colonized with individual species of AM fungi and transplant them into enclosures filled with compost diluted with vermiculite. The plants grow for one growing season during which the fungi proliferate as the roots grow throughout the media. The farmer utilizes the inoculum the following spring by mixing it into potting media used for growing vegetable seedlings for transplant to the field.

A core group of farmers have agreed to participate in this project. The plan was for inoculum production to occur at the farms in year two and utilization of this inoculum in year three. A major technology transfer/outreach effort will occur in year three when a field day is held at The Rodale Institute.

Objectives/Performance Targets

Four of the participant farmers will produce and utilize inoculum of arbuscular mycorrhizal fungi, thereby increasing profits and environmental quality by increasing yields and decreasing synthetic inputs, and two will be present at a field workshop to transfer technology to other farmers.

Accomplishments/Milestones

Of the seven milestones listed in the proposal, three were scheduled to be met in year one. We are on schedule with those three, and are ahead of schedule with the next two.

1. “Ten-20 farmers read a letter describing the project, its needs, and potential benefits.” It was unnecessary to contact that many farmers. All six farmers initially contacted consented to be part of the experiment. A seventh, the Sommerton Tanks Farm in Philadelphia, was added later.
2. “After face-to-face meetings, at least six farmers decide to be part of the project. These farmers become the core group.” As mentioned above, the core group is seven farmers, five of whom received an introduction to mycorrhizal fungi and observed them through a microscope when the investigator visited their farms.
3. “A formula that predicts the optimal dilution of compost with vermiculite for production of AM fungus inoculum is developed.” The experiment outlined in the proposal to address this Milestone has been conducted at The Rodale Institute. The final sampling was conducted December 4, 2003 (see outcomes, below). Data collection includes set up of 36 Most Probable Number [MPN] bioassays that entail four weeks of growth of plants. These assays will not be complete until February.
4. “All 6 farmers of the core group have their composts analyzed. The investigators visit and supervise construction of the enclosures, filling with compost-vermiculite mixtures, and transplant of the precolonized bahiagrass plants.” All were interested in starting immediately. As a result, inoculum production enclosures were set up at five farms and two received inoculum produced in 2002 for inoculation of vegetable plants. This Milestone will be repeated in 2004.
5. “Four to five of the farmers successfully produce inoculum, as verified by most probable number assays conducted by the investigators.” Enclosures at four of the five farms have been sampled. At present, spores of AM fungi have been counted but the four-week MPN bioassays are still growing at the time of this report (see outcomes, below). This Milestone will be repeated in 2004.
6. “All farmers successfully complete field experiments utilizing the inoculum the following year.” This Milestone will be addressed in 2004, one year ahead of schedule.
7. “Four of the participant farmers continue to produce and utilize inoculum of arbuscular mycorrhizal fungi, thereby increasing profits and environmental quality by increasing yields and decreasing synthetic inputs. Twenty to 30 farmers will attend a workshop on this technology.” (no work was done on this Milestone)

Impacts and Contributions/Outcomes

I. Enclosures 10 ft long, 2 ft wide, and 1 ft high were constructed at five farms and filled to a depth of 8 inches with a 1:4 [v/v] mixture of yard clippings compost and vermiculite. The enclosures were constructed of silt fence (walls), weed barrier cloth (floor), and black plastic sheeting (sectional dividers). Bahiagrass seedlings precolonized with AM fungi were transplanted into the enclosures, one AM fungus species in each of the five enclosure sections. Samples collected in November 2003 indicated AM fungus spores indeed were produced at each site, though not in the quantities observed in prior research in 2001 and 2002. This may have been due to the cooler, wetter summer in 2003 vs. past years, or conducting these experiments further from the warmer, metropolitan Philadelphia area where initial experiments were located. A final conclusion on inoculum production cannot be drawn, however, until results of the MPN bioassays are ready in late December to early January. Spores are only one component of the inoculum of AM fungi, so the compost-vermiculite mixtures may be very infective nonetheless.

II. Since host plants do not allow growth of AM fungi within their root systems when grown in high nutrient media, dilution of the composts with an inert ingredient such as vermiculite is essential for the proliferation of AM fungi. An experiment was conducted at The Rodale Institute to predict the optimal dilution ratio for composts with differing chemical analyses. The experiment was a complete factorial design, with three factors. The first factor, compost type, had three levels: yard clippings compost, dairy manure+ leaf compost, and controlled microbial compost. The second factor, dilution ratio, had four levels: 1:2, 1:4, 1:9, and 1:49 [v/v]; compost: vermiculite. The third factor, AM fungus inoculation, had three levels: Gigaspora rosea, Glomus mosseae, and non-inoculated controls. Twelve enclosures, 3 ft x 3 ft x 1 ft tall, were constructed, each divided into 9 sections. Each enclosure contained one of the compost X ratio treatment combinations, and three replicate sections of each AM fungus inoculation treatment. The enclosures were weeded and watered, as needed, throughout the growing season. As noted above (Milestone 3), results of this experiment will not be available until later in the winter. (I will gladly provide a report at that time.)

III. Lastly, the efficacy of the inoculum produced by this technique was tested in a field experiment at The Rodale Institute. Potatoes were grown under two management regimes: conventional (chemical fertilizer and pest control) and organic (compost added for fertility). Seed potatoes were inoculated at the time of planting with 15 cm3 of one of four treatments: a fresh mixture of compost and vermiculite (control), a commercially-available AM fungus inoculum (“Myke” from Premier Tech), on-farm inoculum produced in 2002 using yard clippings compost, or on-farm inoculum produced in 2002 using dairy manure+leaf compost. On-farm inoculum treatments averaged 10.8% greater yield of tubers (g fresh wt per plant) than controls under organic management and 17.9% greater yield than controls in the conventionally managed plot. In each management, the on-farm inoculum slightly out-performed the commercial inoculum.