On-farm production of mycorrhizal fungus inocula

Final Report for LNE03-179

Project Type: Research and Education
Funds awarded in 2003: $129,849.00
Projected End Date: 12/31/2007
Matching Federal Funds: $53,043.00
Region: Northeast
State: Pennsylvania
Project Leader:
David Douds, Jr.
USDA/ARS Eastern Regional Research Center
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Project Information


The goal of this project was to develop, refine, and transfer to farmers a new technology for “on-farm” production of arbuscular mycorrhizal [AM] fungus inocula in temperate climates. Briefly described, 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 agreed to participate in this project. Inoculum of AM fungi was successfully produced at each site. We conducted bioassays of each inoculum each year of production, and results ranged from 4.7 to 1200 infective propagules per cm3 of compost and vermiculite mixture. The inocula were utilized with varying degrees of success. The inoculum was demonstrated to increase the yield of strawberries, potatoes, and carrots. Tomato and pepper seedlings were produced under the routine nutrient regimes at each farm. Most trials with tomato and pepper plants showed a neutral effect of the inoculation which was hard to evaluate due to lack of good establishment of the mycorrhizas prior to outplanting. Those trials demonstrated the need for proper cultural conditions in the greenhouse for mycorrhiza establishment. A positive correlation with tomato was noted between yield response to inoculation and extent of colonization at outplanting.

Major technology transfer/outreach efforts were conducted at field days at The Rodale Institute. In addition, the method for on-farm production was presented at two meetings of the Pennsylvania Association of Sustainable Agriculture and several other venues.


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- each step with its associated cost.

Production of AM fungus inocula on-the-farm eliminates many of these costs. The system requires materials that are readily available or easily purchased: compost, vermiculite, grow bags, and weed barrier cloth. The bags are filled with a compost and vermiculite mixture. The vermiculite is used as a fairly inert ingredient to dilute the nutrient rich compost. Growth media that are too high in nutrients are inhibitory to the growth and reproduction of AM fungi. Development of prediction formulae for dilution ratios, using nutrient analyses of the compost as input variables, was one of the objectives of this work. Seedlings of bahiagrass (Paspalum notatum Flugge), precolonized by AM fungi, are transplanted into the mixture and tended for one growing season during which both the fungi and the host plant proliferate. The bahiagrass is then winter killed, and the AM fungi over winter in place. The following spring the inoculum (i.e. the compost and vermiculite mixture with root pieces) is ready to be mixed into horticultural potting media for the production of vegetable seedlings for outplanting.

The production of inoculum and growth of plants with AM fungi was considered a large, initial step for farmers to make. Taking full advantage of the symbiosis, however, requires several more changes in farm management which, in the initial stages of the project at least, were considered a complication likely to limit participation. One of the changes is a decrease in nutrients, notably P, applied to seedlings during the greenhouse production/ mycorrhiza development phase. Too high of P level, and the mycorrhizas do not develop. Adoption of this practice was difficult because: 1) controls required the higher level of P, 2) many other plants, not part of the experiments, were also grown in the same greenhouse at these farms and required the full P level, and 3) the time constraints of the normal work day of growers prohibited mixing several special nutrient solutions for different applications. The second change is application of less fertilizer P to the field. This can only be partially addressed since many agricultural soils in the eastern US, and all the farms in this study, are already very high in P due to decades of fertilizer and manure applications. Growth responses to inoculation with AM fungi are most often seen in low P soils. Nonetheless, we have observed responses to inoculation as part of this project (see below).

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.

We fell short of our performance target. Only two of the cooperating farmers continue to produce inoculum. In addition, we presented field workshops about the method without the aid of any cooperating farmers.


Materials and methods:

A. Production of colonized bahiagrass plants

Bahiagrass seedlings were transplanted into 66 cm3 conical plastic pots (RLC 4 ‘Pine Cell,’ Stuewe and Sons, Corvallis, OR 97333) containing a 0.75:1:1:0.75 [v/v/v/v] mixture of field soil, sand, vermiculite, and calcined clay (‘Turface,’ Applied Industrial Materials Corp., Deerfield, IL 60015) and grown in a greenhouse for 3-5 months prior to outplanting into the on-farm inoculum production systems. Inoculation treatments included the AM fungi: Glomus mosseae, Glomus claroideum, Glomus etunicatum, and Glomus geosporum originally isolated from the Farming Systems Trial at The Rodale Institute Experimental Farm; Glomus intraradices; and Gigaspora rosea. Plants typically were inoculated by placing a band of pot culture inoculum, including colonized roots, in the center of the column of media mix in each conical pot. Plants received Hoagland’s nutrient solution minus P (Hoagland and Arnon, 1938) biweekly while in the greenhouse.

A subsample of plants was withheld from outplanting each year and used to quantify the status of mycorrhizas at time zero. Roots were cleared and stained (Phillips and Hayman, 1970) and assayed for percentage root length colonized by AM fungi via the gridline intersect method (Newman, 1966).

B. Vermiculite and compost dilution ratio study

Two experiments were conducted at The Rodale Institute Experimental Farm in Kutztown, PA over the 2003 and 2004 growing seasons. Each utilized a complete factorial experimental design with three factors: 1) compost (three types); 2) mixture ratio with vermiculite (4 levels); and 3) AM fungus (3 types), with three replications per treatment combination.

The first experiment was initiated on May 29, 2003. Twelve nine-compartment enclosures were constructed with silt fence walls (1 m X 1 m; 0.3 m tall) supported by wooden stakes. Each had a weed barrier cloth floor and was divided into nine 0.11 m2 sections using black plastic sheeting. Each enclosure was filled to a depth of 20 cm with one compost and vermiculite dilution. Three composts were used: yard clippings compost [YCC], dairy manure + leaf compost [DMLC], and controlled microbial compost [CMC]. The YCC was produced in windrows by the Lehigh County Compost Facility, Allentown, PA. The DMLC was made on site with a 1:4 [v/v] mixture of manure and leaves, respectively. The manure component contained shredded newspaper bedding. The CMC was purchased, and consisted of animal manure, bedding, clay loam, rock powder inoculant, and finished compost. The mixture was composted for 10-14 weeks with frequent aeration. Analyses of the composts indicated that CMC had the highest level of P and the lowest C:N ratio (Table 1). Each compost was diluted with vermiculite at the following ratios (v/v, compost: vermiculite): 1:2, 1:4, 1:9, and 1:49. Three sections of each enclosure then received seven plants of one of the following inoculation treatments: G. mosseae, G. rosea, or uninoculated.

Compost and vermiculite mixtures were sampled on December 4, after death of the bahiagrass, for quantification of colonization of roots and inoculum production. Colonization of roots was assayed as above. AM fungus spore production was quantified under a dissecting microscope after isolation of spores from 50 cm3 samples of mixture, one from each enclosure section, by wet sieving and centrifugation (Gerdemann & Nicolson, 1963; Jenkins, 1964).

The second experiment was initiated on May 21, 2004 with the same experimental design and sampling regime as the first except YCC and DMLC were diluted 1:1, 1:2, 1:4, and 1:9 [v/v] with vermiculite and the CMC was diluted 1:9, 1:19, 1:49, and 1:99. Inoculation treatments included G. mosseae, G. rosea, and G. intraradices. In addition, seven gallon black plastic bags (‘Grow Bags,’ Worm’s Way, Bloomington, IN 47404) were used instead of the silt fence enclosures. Each was filled with 18.2 L of compost and vermiculite mixture. Three bags were filled for each compost X dilution X AM fungus treatment combination.

Equations to predict the optimal compost: vermiculite ratio were developed in a two step process using linear regression via SAS (Statistical Analysis System, Cary, NC). First, equations of the form y= a+a1x+a2x2 or y= a+a1x+a2x2+a3x3 were developed where y= spore population, x= fraction of compost in the growth mixture, and a and an are the intercept and slope regression coefficients, respectively, of the quadratic or cubic equations. These equations were generated for each AM fungus x compost combination of each experiment. They were then solved to yield the fraction of compost giving the maximal sporulation within the range of compost and vermiculite mixtures studied. Finally, those optimal compost fractions for a given AM fungus were used as the dependent variable for regression against compost nutrient analyses as the independent variables (Table 1) using the FORWARD selection procedure of SAS linear regression. This generated three equations, one for each AM fungus studied, predicting optimal fraction of compost as a function of one or more characters of compost chemistry.

C. Production of AM fungus inoculum on the cooperating farms

Inoculum was produced in enclosures for the first two years of the project. Walls of the enclosures consisted of silt fence (Mutual Industries, Philadelphia, PA 19120) held in place with wooden stakes. The floor was weed barrier cloth (American Agrifabrics, Alpharetta, GA 33003), and sectional dividers were made of black plastic sheeting (Warp Bros., Chicago, IL 60651). The enclosures at each site were 3 m x 0.61m x 0.41 m (10 ft long x 2 ft wide x 16 in tall), with each subdivided into five 0.61 x 0.61 m sections. The enclosures were replaced with 7 gallon black plastic “grow bags” in 2005 and subsequent years (12 to 20 per site). Typically, the compost and vermiculite mixture used was the same at each site, a 1:4 [v/v] mixture of yard clippings compost, produced in windrows by the Lehigh County Compost Facility, Allentown, PA, and vermiculite.

Each enclosure section, or grouping of 3-4 bags, received bahiagrass seedlings colonized with an AM fungus (see above). Four to five different AM fungi were typically grown at each site. The installation was maintained by both the farmers and the research team by weeding and watering through the growing season. After frost killed the bahiagrass, the inoculum media remained in place throughout the winter for use the following spring.

D. Quantifying the inoculum produced

The medium from a subsample of compost and vermiculite mixture, pooled across all bags/ enclosure sections on a given farm, was used to conduct most probable number (MPN) bioassays to estimate the number of AM fungus propagules per cm3 of inoculum (Alexander, 1965). The samples were diluted 10-1 through 10-5 with a soil, sand, vermiculite, and calcined clay potting mixture, and potted in conical plastic pots with bahiagrass seedlings. Plants were grown for 4 weeks in a controlled environment growth chamber after which root systems were examined to detect AM fungi.

E. Vegetable seedling production and inoculation

Vegetable seeds were germinated at the individual farms according to the practices of that farm. Inoculation with AM fungi occurred by adding a mix of inocula of all species produced at that site to the peat based horticultural potting media. Rate of addition was 1:19 inoculum:media [v/v] the first year and seedlings received the routine nutrient regime while in the greenhouse. When this produced sparsely colonized seedlings, the inoculum addition was increased to 1:3 or 1:4 in subsequent years.

Potatoes and carrots were inoculated in the field. Seed potatoes were inoculated by placing 15 cm3 of inoculum directly beneath each. Controls were mock-inoculated by placing an equivalent volume of a freshly prepared compost and vermiculite mixture below the seed potato to account for the effect of those inoculum constituents. Carrots were inoculated by raking inoculum into the freshly prepared bed prior to seedling. Control beds were likewise mock-inoculated.

F. Outplanting, field experiments, and sampling

Plants were typically outplanted by alternating runs of the different treatments, e.g. alternating 24 inoculated with 24 uninoculated seedlings, down the row to yield 7-10 runs of each experimental treatment per cultivar. Sampling for peppers and strawberries was conducted on 10 plant sections, and for tomatoes on 4 plant sections, within each run of an inoculation x cultivar treatment combination. Therefore, the experimental unit for these trials was the 10 or 4 plant sampling unit. Potatoes and carrots were harvested by unearthing entire replicate plots/beds by hand with shovels and weighing the harvest of each bed as a unit.

G. Communicating with the target audience

Each cooperating farmer was visited before the project began and given an introduction to the project and mycorrhizae in general and an opportunity to observe AM fungus spores and colonized roots through the microscope. They were consulted as to the best location for the inoculum production system and were advised on its care and maintenance. We did find it best to visit the sites several times throughout the summers to help catch up on the weeding and site maintenance. In addition, since outplanting a statistically valid experiment required more labor and care than normal outplanting, it was best for us to be present and assist with outplanting. As far as harvesting and weighing, those farms experimenting with only one cultivar were able to handle the extra workload of record keeping for sequential harvests, but we felt it best if we handled the harvesting and data collection on those farms with numerous cultivars. Final results were shared with each farmer at individual meetings after the growing season.

Literature Cited

Alexander, M. 1965. Most-probable-number method for microbial populations, p. 1467-1472. In C.A. Black (ed.), Methods in Soil Analysis. Amer. Soc. of Agronomy, Madison, WI.

Gerdemann, J.W. and T.H. Nicolson. 1963. Spores of mycorrhizal Endogone species extracted by wet sieving and decanting. Transactions of the Brritish Mycological Society, 46: 235-244.

Hoagland, D.R. and D. I. Arnon. 1938. The water-culture method for growing plants without soil. University of California College of Agriculture, Agriculture Experiment Station Circular 347. Berkeley, CA, U.S.A.

Jenkins, W.R. 1964. A rapid centrifugal-flotation technique for operating nematodes from soil. Plant Disease Reporter, 73: 288-300.

Linderman, R.G. and E.A. Davis. 2003. Soil amendment with different peat mosses affects mycorrhizae of onion. HortTechnology, 13: 285-289.

Newman, E.I. 1966. A method of estimating the total length of root in a sample. Journal of Applied Ecology, 3: 139-145.

Phillips, J.M. and D.S. Hayman. 1970. Improved procedures for clearing roots and staining parasitic and vesicular-arbuscular mycorrhizal fungi for rapid assessment of infection. Transactions of the British Mycological Society, 55: 158-160.

Research results and discussion:

5. Results and Discussion/ Milestones
All seven milestones have been addressed.

1. “Ten-20 farmers read a letter describing the project, its needs, and potential benefits.” All six farmers initially contacted consented to be part of the experiment. A seventh 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.” The core group was seven farmers; six received an introduction to AM fungi and observed them through a microscope.

3. “A formula that predicts the optimal dilution of compost with vermiculite for production of AM fungus inoculum is developed.” The experiments to address this Milestone were conducted at The Rodale Institute in 2003 and 2004. Results of these experiments were presented in a research publication (#3 in section 8).

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.” Inoculum production enclosures were set up at five farms and two received inoculum in 2003, ahead of schedule, in the first year of the study. Inoculum was produced the next three years at each farm and at two farms in 2007.

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.” Experiments were conducted in 2005 with potatoes, tomatoes, peppers, carrots, and strawberries; in 2006 with potatoes, tomatoes, peppers, and carrots; and in 2007 using peppers, tomatoes, and leeks.

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 first aspect of this milestone was not met. We continued to produce inoculum past the original ending point of the grant at only two farms. (See section 10 for further discussion of the reasons behind this.) The outreach activities were 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 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 two workshops at the annual meeting of the Pennsylvania Association for Sustainable Agriculture in 2005 and 2007 (see report section #8 for more outreach activities).

The actual agronomic results of this project can be divided into three sections: i) inoculum production, ii) production of colonized seedlings, and iii) harvest data.

i) Inoculum production

Inocula were produced on-farm successfully each time it was attempted. Propagule densities varied widely (Table 2). Low values occurred typically in the early years before we had experience working with different composts, so vermiculite dilutions may not have been optimal. Formulae to predict the optimal fraction of compost in compost and vermiculite mixtures were developed for three AM fungi (Table 3).

ii) Production of colonized seedlings

Colonization status of seedlings at the time of outplanting was measured whenever possible. Representative results are shown in Tables 4, 5, and 6 and demonstrate the complexity of coordinating and interpreting research at more than one site under varied management practices. The data presented in Table 4 for Eagle Point Farm are representative of conventional farms which, in addition to producing vegetables, have a very diversified growing operation (also included here is Meadow View Farm). In the first years of the project, inoculum : potting media mixture recommendations were given based upon density of propagules in the inoculum, size of the cell in which the seedlings were to be grown, and the need to achieve at least 100 propagules of AM fungi per seedling. After this recommendation initially produced sparsely, or uncolonized seedlings (data not shown), mixture recommendations were adjusted to drastically increase the amount inoculum per seedling, e.g. one part inoculum to two parts potting media (Table 4). This still resulted in unsatisfactory levels of colonization, particularly among peppers. Colonization was even lower in 2006 (data not shown). However, the results for Cedar Meadow Farm in which tomato seeds were germinated in 100% inoculum, conflict with these results. These seedlings became well colonized (Table 5). Though this is another conventional farm, the seedlings were produced off site and no information was available on cultural practices by the contractor. An organic farm, Covered Bridge Farm, also participated in the study. Tomato seedlings produced by them were well colonized (Table 6), but again, we have no information on how they were grown.

iii) Harvest data

Yield of tomatoes and peppers in early experiments appeared to be largely independent of mycorrhizal fungus inoculation, especially when colonization was sparsely developed at outplanting (2003 and 2004, data not shown). Closer inspection indicates first, a possible cultivar effect in response to inoculation with AM fungi (see Table 4) and second, a positive correlation between the development of colonization at the time of outplanting and the degree of response to inoculation (compare Tables 4, 5, and 6). Addressing the problem of insufficient colonization of peppers and tomatoes prior to outplanting was the objective of the one year extension of the project (see below).

A variety of results were achieved with other crops. The only complete experiment with strawberries was a success (Table 7). Inoculation with AM fungi produced on-farm at Shenk’s Berry Farm increased yield of strawberries 17% over uninoculated controls. In each of the next 2 years, however, young plants received for growth in flats prior to outplanting came from the supplier already heavily colonized by AM fungi due to previous growth in mycorrhizal fungus infested media, so no replicate experiments could be conducted.

Another crop grown with AM fungus inoculum was potatoes. These were grown at Somerton Tanks Farm and Covered Bridge Farm, as well as at The Rodale Institute. Definite cultivar differences in response to inoculation were seen (Table 8). Yukon gold potatoes were unresponsive while other cultivars largely were responsive to inoculation with AM fungi produced on-farm. Inoculation of potato cv Superior with AM fungi produced on-farm increased yields at The Rodale Institute 45% in 2002 and 10-15% in 2003 in both conventional and organic farming systems (see #2 of Section 8).

Carrots were inoculated when seeds were sown in the beds. Response to inoculation varied (Table 8). Cultivar Nelson responded positively one year but cv Yokum did not respond the next year. Lack of replication prohibits speculation as to whether this indicates differences in cultivar response or whether this was due to differences in rainfall or temperature. (We had no control over what cultivar was planted.)

Work done during the one year no-cost extension

A one year extension was requested to address the problem of insufficient colonization of tomato and pepper seedlings during the greenhouse production phase. Colonization of seedlings by AM fungi prior to outplanting was very low early in the project. We had two choices to address this issue: 1) ask the farmer to change his/her greenhouse nutrient regime in case over supply of P was the issue or 2) increase the proportion of inoculum in the growth medium to increase the number of propagules of AM fungi in case infectivity of the fungi in horticultural potting media was the issue (Linderman and Davis, 2003, see references at end of Methods section). We chose first to address option 2 by recommending an increased proportion of inoculum in the final growth medium. Early recommendations of 1:19 [v/v inoculum to potting media] were revised to 1:2 or 1:3 [v/v]. When this did not correct the problem, we returned to the laboratory to address option 1 and to studied the response of AM fungus colonization of tomato and pepper seedlings to increasing proportions of compost based inoculum in the potting media and to inorganic P application. Finally, we examined the cultivar dependence of colonization of roots of pepper and tomato by AM fungi. Several experiments were conducted.

In an initial experiment, tomato and pepper seeds were germinated in 100% inoculum produced on-farm in a 1:4 [v/v] mixture of compost and vermiculite. Seedlings were only sparsely colonized 4 weeks later (data not shown). This contradicted the results at Cedar Meadow Farm (Table 5), likely because in our germination system, the pots are watered from below yielding much less leaching of P from the substrate than germination in flats watered from above. This result prompted two questions: 1) What dilution of compost based on-farm inoculum is necessary to result in colonization by AM fungi? and 2) Since bahiagrass roots become well colonized and AM fungi proliferate heavily in 1:3 [v/v] mixes of compost and vermiculite, while tomato is not colonized at all under those conditions, are bahiagrass and peppers/tomatoes fundamentally different in sensitivity to P level re colonization by AM fungi?

The first line of thought was addressed by a serial dilution experiment. Bahiagrass and two cultivars of tomato seedlings were transplanted into conical plastic pots (165 cm3, super cell, Stuewe and Sons, Corvallis OR) containing 10-1, 10-2, 10-3, 10-4 and 10-5 dilutions of on-farm inoculum, produced in a 1:4 [v/v] mixture of YCC compost and vermiculite, with horticultural potting mix or soil based potting mixture. Results were markedly similar across plants and growth media and indicate a dilution of the inoculum between 10 to 100 fold would produce acceptable levels of colonization after 4 weeks of growth (Table 9).

Another experiment was conducted to examine the response of colonization to increasing fertilizer P application in tomato, pepper, and bahiagrass. Seedlings were transplanted into a peat based horticultural potting medium mixed with on-farm inoculum to yield a 10 fold dilution of the inoculum. A balanced nutrient solution (Hoagland and Arnon, 1938) was applied three times per week. The P level of the solution was adjusted to yield P concentrations from 0 to 62 ppm. After six weeks of growth there was nearly complete inhibition of colonization of tomato and pepper at 31 ppm P while bahiagrass had colonization levels of 20% of root length (Figure 1). This indicates that basing our recommendations for inoculum dilutions for growth of pepper and tomato upon many years of experience with bahiagrass was the cause of much frustration.

A third experiment was conducted to address the question: do cultivars of tomato and pepper differ in their susceptibility to colonization by AM fungi? Seedlings of eight cultivars of each were transplanted into three different inoculum/media treatments:
1) Berger peat based media amended 1:9 [v/v] with on-farm inoculum, 2) Berger media amended 1:19 [v/v] with on-farm inoculum, and 3) a commercially available potting media containing one propagule of the AM fungus Glomus intraradices per gram (Premier Promix BX with Mycorise, Premier Horticulture, Riviere-du-Loup, Quebec G5R 6C1 Canada). The on-farm inoculum used in this experiment was a mixture of four species produced in a 1:3 [v/v] mix of yard clippings compost and vermiculite, and contained 120 propagules per cm3. Therefore, the 70 cm3 volume of the individual cells contained 420 and 840 propagules of AM fungi in the on-farm treatments and less than 70 propagules in the commercial mix treatment. Plants were grown in a greenhouse for four weeks and received a balanced nutrient solution containing 0.31 ppm P three times per week. No colonization occurred in the commercially available pre-inoculated media, likely due to the small number of propagules and the short time frame of the experiment (Table 10). Both dilutions of the on-farm inoculum produced colonized seedlings, and the colonization level of the 1:19 dilution was satisfactory in many instances. ANOVA analyses showed significant cultivar and inoculation treatment differencess (Pr>F <0.0001). The final year’s experiments developed inoculation regimes and proper nutrient additions to achieve colonization of tomato and pepper seedlings by AM fungi. Optimal utilization of the technology for the on-farm production of AM fungus inoculum will depend upon the application of low P fertilizer solutions.

Participation Summary


Educational approach:

8. Publications/Outreach

A. Publications

1. Douds, D.D., G. Nagahashi, P.E. Pfeffer, C. Reider, and W.M. Kayser. (2006). On-farm production of AM fungus inoculum in mixtures of compost and vermiculite. Bioresource Technology, 97, 809-818.

2. Douds, D.D., G. Nagahashi, C. Reider, and P.R. Hepperly. (2007). Inoculation with arbuscular mycorrhizal fungi increases the yield of potatoes in a high P soil. Biological Agriculture and Horticulture, 25, 67-78.

3. Douds, D.D., G. Nagahashi, C. Reider, and P. R. Hepperly. (2007) Choosing a mixture ratio for the on-farm production of AM fungus inoculum in mixtures of compost and vermiculite. Compost Science and Utilization (in press).

4. Douds, D.D., J.E. Shenk, G. Nagahashi, and K. Demchak. Inoculation of strawberries with AM fungi produced on-farm increased yield. (submitted to Biological Agriculture and Horticulture)

B. Lectures and demonstrations:

1. Symposium presentation about on-farm production of inoculum at the Third International Conference on Mycorrhizas, Montreal, Quebec August, 2003.

2. Lecture presentation at the meeting of the Delaware Organic Food and Farming Assoc. Dec. 8, 2003.

3. Heart of Maine Conference, Bangor, ME (2/12/04)

4. Lecture/demonstration to interns of The Rodale Institute Experimental Farm, August 7, 2003; September 10, 2004.

5. The Rodale Institute Field Day July 16, 2004; July 22, 2005 (120 farmers and agr. professionals each year)

6. Northeast Organic Farming Assoc., Amherst, MA (8/13/04)

7. Soil Quality Workshop (Penn State/SARE): July 6, 2006.

8. Pennsylvania Association of Sustainable Agriculture: Feb, 2005; Feb 2007.

9. AM fungus lecture/demonstration to staff and interns of The Rodale Institute Experimental Farm and to the visiting students of the “Challenges for Innovative Agriculture” program, Gyeongsang Univ. South Korea, July 19, 2005; July 26, 2006; July 16, 2007.

C. Effectiveness: It is difficult to assess the effectiveness of outreach efforts. Hundreds of farmers and agriculture professionals were exposed to the project. These included extension agents and interns beginning their careers in agriculture. One result of the outreach is the locations and agronomists that have requested information about on-farm production of inoculum and are starting their own projects. These include:

Frank Wertheim, U of Maine Cooperative Extension, Springvale, ME

Matt Steiman, Dickenson College organic farm, Boiling Springs, PA

Tim Griffin, USDA-ARS New England Plant, Soil, and Water Lab., Orono, ME

Chris Miller, USDA NRCS Cape May Plant Materials Center, Cape May Courthouse, NJ

Rod Stucker, R&M Enterprises, LLC, Boise, ID

No milestones

Additional Project Outcomes

Project outcomes:

Impacts of Results/Outcomes

All cooperating farmers as well as many other farmers, agriculture professionals, and students (see also list of outreach activities in section #8) now know much more about production, utilization, and management of AM fungi due to the funds made available by SARE for this project. These farmers and agriculture professionals now have a greater appreciation for soil biology.

Economic Analysis

The economics of this method for the on-farm production of inoculum can be calculated two ways: 1) comparing the cost of production with the cost of purchasing the same number of propagules of AM fungi commercially, and 2) comparing the cost of production vs. the income from enhanced yield.

The average number of propagules of AM fungi produced at all sites for 2004 and 2005 was 83 propagules cm-3 (Table 2). This translates to approximately 31 x 106 total propagules per inoculum production enclosure. These were produced at an approximate cost of $150 (not including the cost of the initial colonized bahiagrass seedlings). Purchase of that many propagules of AM fungi would cost from $2842 (AM120, Pawnee Buttes Seed Co., Greeley CO 80632) or $3565 (MycoApply Endo, Mycorrhizal Applications, info@mycorrhizae.com) on the low end to $11127 (AgBio- Endos, AgBio, Westminster, CO 80031) on the high end.

An example of the potential economic return of this technology can be demonstrated with the results with strawberry. One can estimate the economic benefit of inoculation of strawberries with the AM fungi produced on-farm in this experiment through a series of calculations. The planting scheme used here resulted in 28930 plants ha-1 (11760 ac-1). Inoculation resulted in an average increased yield of 78.3 g plant-1 over uninoculated controls, or 2265.2 kg ha-1 (Table 3). Fruit was sold per US quart (0.68 kg), for an average of $3.50 US, resulting in increased income of $11659 ha-1 ($4739 ac-1). The inoculation required 6 cm3 of inoculum per 120 cm3 planting cell. Therefore, the inoculum production enclosure yielded inoculum for a maximum of 62,016 plants, enough for 2.14 ha. The enclosure was produced at a cost of approximately $150 US. Therefore, the per ha cost was $70 for a potential return of $11659. These figures do not include the increased labor to harvest the extra fruit, the cost of the pre inoculated bahiagrass nurse plants, or any labor charge for maintenance of the inoculum production enclosure and mixing the inoculum into the potting media.

Farmer Adoption

Full adoption of the AM symbiosis in plant production can lead to many benefits to a farm in terms of economic and environmental sustainability. Seedlings could be grown with less fertilizer and pesticide application. Yields can be maintained or enhanced with less fertilizer input. Management practices that allow for better utilization of indigenous AM fungi, e.g. cover cropping, reduced tillage, and crop rotation (all discussed in outreach efforts); are also those that build soil carbon and soil quality in general, thereby enhancing overall sustainability. We have seen that even incorporating AM fungus inoculum into greenhouse practice is a large step not fully accomplished within the 4 growing seasons of this project, so the consideration of the symbiosis in the whole of farm operations is likely far off.

Assessment of Project Approach and Areas of Further Study:

Areas needing additional study

10. Areas Needing Additional Study

Several aspects of on-farm production and utilization of AM fungus inoculum require further study and other deficiencies in infrastructure hinder widespread utilization of the technology:

i) Currently, there is no commercial source of bahiagrass seedlings colonized by different AM fungi. We are examining modifications to the inoculum production system, such as seeding the compost and vermiculite mixture with field soil as starter inoculum of AM fungi, to get around this problem.

ii) We quantified the density of propagules in the inoculum produced at the cooperating farms ourselves. Ideally, there would be a commercial service that would do this at a reasonable price. However, the on-farm system has successfully produced inoculum each time it has been attempted, so we feel farmers can safely assume they have produced potent inoculum.

iii) Nutrient management issues are still a concern. We have developed a nutrient regime for conventional farmers to use to produce colonized seedlings in the greenhouse, but we have not explored options for the organic grower.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.