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 was scheduled to occur in year three at a field day at The Rodale Institute.

PERFORMANCE TARGET
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.

PROGRESS ON THE MILESTONES
All of the seven milestones listed in the proposal have been addressed in the first two years of work.

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, six 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 was conducted at The Rodale Institute in 2003 and repeated in 2004. Results of the first experiment are presented (see outcomes, below). The current replicate of the experiment will not be terminated until December, 2004 and data collection not completed until January, 2005.
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. The results of inoculum production efforts in 2003 are presented (see outcomes below). Research effort on this Milestone was repeated in 2004, but results will not be available until January, 2005.
5. “Four to five of the farmers successfully produce inoculum, as verified by most probable number assays conducted by the investigators.” All five farms with enclosures successfully produced inoculum in 2003. This Milestone was repeated in 2004.
6. “All farmers successfully complete field experiments utilizing the inoculum the following year.” This Milestone was addressed in 2004, one year ahead of schedule, and exposed several unforeseen problems in conducting research on-the-farm (see outcomes, below).
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.” A workshop on this topic was conducted at a Field Day at The Rodale Institute. One hundred sixty four farmers, academics, extension agents, and media people (including 56 members of the Quebec Ridge Tillage Club) attended the Field Day demonstrations and lectures.

OUTCOMES
1. (Milestones 4 and 5) Inoculum production enclosures were constructed at five farms in 2003 and all farms in 2004. Results of inoculum production in 2003 are shown below:
John Shenk, Lititz, PA: 75 propagules per cm3
Steve Groff, Holtwood, PA: 4.65 propagules per cm3
Joseph Griffin, Oley, PA: 21.5 propagules per cm3
Matt Zoschke, Fond du Lac, WI: 7.5 propagules per cm3
Nicole Shelly, Philadelphia, PA: 20 propagules per cm3

These values were significantly lower than those seen in preliminary research in the Philadelphia area in 2001 and 2002. Potential reasons for this were addressed in 2004: enclosures were initiated 2 weeks earlier and the number of nurse plants was increased from 10 to 13 per enclosure section.

2. (Milestone 3) 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. Experiments were conducted at The Rodale Institute to predict the optimal dilution ratio for composts with differing chemical analyses. The experiment in 2003 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. Results indicated that the optimal ratios for inoculum production and development of mycorrhizas (Figs. 1 and 2) were correlated to the P concentration and N:P ratios of the composts (Table 1). Better results were achieved with the yard clippings and dairy manure composts (low P and low N:P ratios) in the 1:2 and1:4 dilution ratios for G. rosea and G. mosseae, respectively (Figs. 1 and 2) than in more dilute mixtures. The controlled microbial compost had the highest P concentration and lowest N:P ratio (Table 1), and both fungi responded better in the 1:49 dilution ratio than in more concentrated mixtures (Figs. 1 and 2).

The ratio experiment was repeated in 2004, with some modifications based upon the results of 2003. The yard clippings and dairy manure composts were diluted with vermiculite 1:1, 1:2, 1:4, and 1:9 [v/v] since the more concentrated mixtures yielded better results in 2003. In contrast, the controlled microbial compost was diluted 1:9, 1:19, 1:49, and 1:99 in 2004 to see if sporulation and colonization were enhanced by diluting the compost even further.

3. (Milestone 6) As mentioned above, inoculum produced in 2003 at four farms was used to grow seedlings for outplanting at those farms, and another two farms received inoculum for use, in 2004. This occurred one year ahead of the grant schedule and turned out to be fortuitous because it exposed various problems in on-farm research which will be corrected in the 2005 growing season. Among these problems were:
a. Farmers’ normally busy lives are even busier during the planting season. Research personnel should be present while inoculum is utilized and plants are out planted, to ensure the experiment is run as planned.
b. Communicate even minor details to the growers. (One farmer’s greenhouse man didn’t keep track of which plants received the inoculum and which did not.)
c. Visit sites regularly to assist with plot maintenance if necessary. (Plots at one farm became completely overgrown with weeds.)
d. Communicate frequently to stay abreast of harvesting schedules. (Vegetables at one farm were harvested without collecting data on inoculated vs. uninoculated plots.)
e. Mix the inoculum into the potting media at a greater rate than the Most Probable Number bioassays would recommend, i.e. instead of using enough inoculum to provide a calculated 100 propagules per plant, increase to 300-500 propagules. The small volume needed for the minimal 100 propagules is difficult to mix properly. (The two experiments with the best chance for success were hampered because the green pepper and strawberry plants were only sparsely colonized at the time of outplanting.)