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 of the 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 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 were presented in last year’s progress report. The results of the replicate experiment are presented here (see outcomes, below).

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 were presented in last year’s report. Inoculum production in 2004 is presented here (see outcomes below). Research effort on this Milestone was repeated in 2005. Instead of producing inocula in silt fence enclosures, we shifted all farms to using seven gallon plastic “grow bags” which make harvest of the inoculum easier. Results for inoculum production during the 2005 growing season will not be available until January, 2006 (samples have been collected, but the most probable number bioassays to determine density of propagules of AM fungi in the compost + vermiculite mixtures will not be completed for six weeks).

5. “Four to five of the farmers successfully produce inoculum, as verified by most probable number assays conducted by the investigators.” All seven farms with enclosures successfully produced inoculum in 2004. This Milestone was repeated in 2005.

6. “All farmers successfully complete field experiments utilizing the inoculum the following year.” This Milestone 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 last year’s report. Experiments were conducted in 2005 with potatoes, tomatoes, peppers, carrots, and strawberries (see outcomes, below) utilizing inoculum produced on-farm in 2004.

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. We believe most of the farmers wish to continue unofficial collaboration through the 2006 growing season. Most recognize the need for two years of yield data to draw firm conclusions about the efficacy of the inoculum.

Impacts and Contributions/Outcomes

1. (Milestones 4 and 5) Inoculum production enclosures were constructed at five farms in 2003 and all farms in 2004 and 2005. Results of inoculum production in 2003 and 2004 are shown in Table 1. The values for 2003 were significantly lower than those seen in developmental 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. The density of propagules of AM fungi in the compost + vermiculite mixtures typically increased in 2004 relative to 2003.

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. Results presented in last year’s report indicated that the optimal ratios for inoculum production and development of mycorrhizas were correlated to the P concentration and N:P ratios of the composts (Table 2). 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 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, 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. In addition, another fungus, Glomus intraradices, was added to the experiment. The results largely supported the conclusions of 2003 (Figures 1-4). 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. Glomus mosseae exhibited a broad optimum dilution ratio while the others required more narrow ranges of dilution of compost with vermiculite for optimal sporulation. A research publication containing these data will be prepared in 2006, and should also contain regressions enabling the prediction of the compost and vermiculite dilution ratio using input variables quantifying the nutrient composition of the compost.

3. (Milestone 6) Inoculum produced in 2004 at six farms was used to grow seedlings for outplanting at those farms in 2005. This year we attempted to avoid some common pitfalls of on-farm research by greater communication, increasing the amount of inoculum added per volume of horticultural potting mix for seedling production, and having personnel present at the time of outplanting and harvest.

Seedlings of tomato, pepper, and strawberry 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. Tomatoes for Cedar Meadow Farm were grown in flats containing 288 cells (10 cm3 volume) filled with 100% inoculum (1:4 compost:vermiculite). 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 8 to 10 sample blocks of four (tomato) or ten (pepper and strawberry) plants per treatment (inoculated vs control) for each cultivar at each farm. Experiments with potatoes were conducted with 3 to 6 beds per treatment. Bed dimensions varied with farm.

Crop response to inoculation with AM fungi varied with crop, and even among cultivars (Table 3). Peppers appeared to be fairly unresponsive to inoculation (Eagle Point Farm and Meadow View Farm). The response of tomatoes appears to be cultivar dependent. The cultivar “Florida” exhibited a positive response (Eagle Point Farm) while the response of cv. “Mountain Fresh” was nearly neutral at two farms (Shenk’s Berry Farm and Cedar Meadow Farm). Potatoes exhibited the most consistent positive response, with only the neutral response by cv. “Yukon Gold” among the five cultivars studied. This neutral response was consistent at both farms at which “Yukon Gold” was grown (Somerton Tanks and Covered Bridge Farms). Carrots (Somerton Tanks Farm) and strawberries (Shenk’s Berry Farm) also exhibited positive responses to inoculation.