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.

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

All seven milestones listed in the proposal have been addressed.

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 Somerton 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 these experiments were presented in the annual reports for 2004 and 2005, respectively.

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 farmers enrolled in the project 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. Inoculum has been produced each year at each farm since then, with the results of inoculum production efforts in a given year detailed in the following year’s progress report. Inoculum production in 2005 is presented here (see outcomes below). Research effort on this Milestone was repeated in 2006. Also, we shifted all farms from silt fence enclosures to using seven gallon plastic “grow bags” for inoculum production in 2005 which made harvest of the inoculum easier.

5. “Four to five of the farmers successfully produce inoculum, as verified by most probable number assays conducted by the investigators.” All seven farms successfully produced inoculum each year.

6. “All farmers successfully complete field experiments utilizing the inoculum the following year.” This Milestone first was addressed in 2004, one year ahead of schedule, when plants were inoculated with AM fungi grown on-farm the previous year. Experiments that year exposed several unforeseen problems in conducting research on-the-farm and these were discussed in that year’s report. Experiments were conducted in 2005 with potatoes, tomatoes, peppers, carrots, and strawberries utilizing inoculum produced on-farm in 2004. The results of these experiments were presented in the 2005 annual report. Experiments were conducted in 2006 with potatoes, tomatoes, peppers, and carrots utilizing inoculum produced the previous year. These results are detailed 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.” The outreach activities have been completed. Workshops on this topic were conducted at the Field Days at The Rodale Institute in July of 2004 and 2005. 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 in 2004 and 120 attended in 2005. In addition, the on-farm inoculum production system and results of field trials were presented in a workshop at the annual meeting of the Pennsylvania Association for Sustainable Agriculture in 2005 and will be presented again in February 2007.

Other significant developments:

a) One cooperating farm experienced severe financial difficulties in 2006 and may not operate in 2007. In addition, the cooperating urban demonstration farm may not be in operation in 2007, and our collaborator at the Michael Fields Agriculture Institute has resigned.

b) Work completed to date has exposed a research need. Most of the work with peppers and tomatoes has shown no response to inoculation with the AM fungi. We believe this is largely due to poor establishment of the fungus during seedling growth in the greenhouse. Levels of inoculation which produce abundant colonization of bahiagrass, our test plant for the Most Probable Number bioassays, produce little colonization of pepper and tomato seedlings. Vegetable seedling culture conditions (media and nutrient regime) conducive to development of AM fungus colonization of roots must be developed first to properly demonstrate the efficacy of the inoculum produced on-the-farm. This is reason we requested, and were granted a no cost extension through Dec. 31, 2007.

Impacts and Contributions/Outcomes

1. (Milestones 4 and 5) Inoculum production enclosures were constructed at five farms in 2003 and all farms in 2004, 2005, and 2006. Results of inoculum production in 2005 are shown in Table 1. In general, inoculum production at the farms has improved over the course of the study.

2. (Milestone 3) Since host plants do not allow growth of AM fungi within their root systems when grown in high nutrient media (such as compost), dilution of the composts with an inert ingredient such as vermiculite is essential for the production of inoculum of AM fungi in this on-farm system. Experiments were conducted in 2003 and 2004 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 examining three composts (yard clippings compost, dairy manure+ leaf compost, and controlled microbial compost); each diluted 1:2, 1:4, 1:9, and 1:49 [v/v] with vermiculite; and used to grow the AM fungi Gigaspora rosea and Glomus mosseae. Optimal ratios for inoculum production and development of mycorrhizas were correlated to the P concentration and N:P ratios of the composts (see 2004 annual report). Better results were achieved with the yard clippings and dairy manure composts (low P and high N:P ratios) in the 1:2 and1:4 dilution ratios than in more dilute mixtures. The controlled microbial compost had the highest P concentration and lowest N:P ratio and both fungi responded better in the 1:49 dilution ratio than in more concentrated mixtures.

The ratio experiment was repeated in 2004. 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. In addition, another fungus, Glomus intraradices, was added to the experiment. The results largely supported the conclusions of 2003 (see 2005 annual report). Gigaspora rosea, Glomus mosseae, and Glomus intraradices sporulated best in yard clippings compost and dairy manure+leaf compost at the 1:4 and1:9 dilutions [v/v, compost:vermiculite] and in 1:19 and 1: 49 [v/v] dilutions of controlled microbial compost and vermiculite.

3. (Milestone 6) Inoculum produced in 2005 at six farms was used to grow seedlings for outplanting at those farms in 2006. No data was collected at one farm due to its rigorous harvesting schedule and distance from the laboratory.

Seedlings of tomato, pepper, and leek were produced on the various farms according to their routine practices, except that AM fungus inoculum was mixed into the potting media. Mixture ratios depended upon the volume of individual cells of seedling production flats. Flats containing 28 to 48 cells were filled with a 1:3 or 1:4 [v/v] mixture of inoculum and potting mix. Potatoes were inoculated by hand in the field by placing 15 cm3 of inoculum or the same volume of a fresh compost and vermiculite mixture (for the controls) directly under the seed potato. Carrots were inoculated in the field by spreading 6 L of inoculum (or freshly prepared 1:4 [v/v] mixture of compost:vermiculite for controls) over each 3.8 m long bed after it was roto-tilled. Each bed then received 6 rows of seeds.

Layout of field plots varied among farms due to differences in scale and bed arrangement for the different farms. Typically, however, there were 7 to 10 sample blocks of four (tomato) or ten (pepper) plants per treatment (inoculated vs control) for each cultivar at each farm. Experiments with potatoes were conducted with 4 to 8 rows per treatment.

As in past years, response to inoculation with AM fungi varied with crop, and even among cultivars (Table 2). Peppers appeared to be fairly unresponsive to inoculation, but as in 2005, cv Boynton Bell exhibited the best response. The response of tomatoes appears to be cultivar dependent. The most consistent response to inoculation of tomatoes was found at the Covered Bridge Farm. This was likely due to the fact that inoculated plants grown at this farm had the best percentage root length colonized by AM fungi at the time of outplanting among all farms studied (data not shown). Results this year confirmed previous results indicating that potato cv Yukon Gold is unresponsive to inoculation with AM fungi.