Closing the Mushroom Production Loop: Evaluating Soil Microbe Changes Following Field Application of Compost Inoculated with Spent Mushroom Substrate

Final report for ONE22-422

Project Type: Partnership
Funds awarded in 2022: $24,712.00
Projected End Date: 12/31/2023
Grant Recipient: NOFA/Mass
Region: Northeast
State: Massachusetts
Project Leader:
Expand All

Project Information


This project evaluated whether spent mushroom substrate (SMS), a fungal-rich byproduct of mushroom farming, could be effectively combined with mature compost to create a microbial-rich soil amendment for application on specialty crop production fields. Five farmers participated in this project: one mushroom farmer who supplied SMS, and four specialty crop farmers who combined the SMS with mature compost in various ratios to evaluate whether the compost could be effectively inoculated by SMS. SMS was combined with compost at three rates (10%, 25%, and 50% SMS) for 14d, during which time farmers performed daily monitoring for physical changes and moisture. After 14d microbial samples were taken to observe changes in fungi and bacteria as a result of the inoculation process. Microscopy results showed an increase in fungi, particularly predatory fungi, and the fungal:bacteria ratio, proportional to increasing levels of SMS. Despite findings that this could increase the microbial levels of production fields, farmers did not apply the SMS-Compost mixture to their fields. Future research is necessary to identify the impact of SMS-inoculated compost on the microbial composition, soil health, and plant growth and yield on production fields. If successful, SMS would make a valuable resource for improving fungal communities in production fields while using an existing mushroom farming byproduct.

Project Objectives:

This project seeks to accomplish the following objective:

  • Evaluate which ratio of compost:spent mushroom substrate (SMS) best increases the microbiological activity of finished compost over the duration of a 14d period

Positive findings from these objectives will provide the following benefits to farmers:

  • Provide mushroom farmers with a use for a production byproduct, sustainably closing the production loop
  • Offer vegetable farmers an opportunity to increase soil fungal activity and soil health characteristics, likely leading to improved crop growth and production without requiring much additional time or a change in management

If this project is successful, we envision developing partnerships between specialty mushroom and vegetable farms in the Northeast to create a continual cycle of SMS utilization in compost. The compost inoculation method is a straightforward and time-efficient way to increase microbial communities in an amendment vegetable farmers are already using, making it easy for this to be widely adopted and successful within the farming community.


Nationally, the mushroom industry was responsible for over $1.09 billion in sales in 2019-20. Specialty mushrooms, or all mushrooms except the ubiquitous Agaricus mushrooms (which include the button, portobello, and crimini varieties), make up just a fraction of total mushroom sales nationally. However, their consumption has been growing since the introduction of shiitakes to supermarkets in the 1980’s and is predicted to continue to increase as consumers find more uses for them and consume them as meat alternatives.

Over recent years, specialty mushroom producers have been falling short of demand in the Northeastern United States. While the Agaricus production industry is dominated by larger-scale farms primarily in Pennsylvania, California, and Florida, specialty mushrooms are typically produced by geographically-scattered small-scale farms producing for local markets. In 2014 there were 57 specialty mushroom growers in the Northeast, and there has been a recent push to increase the number of growers to meet increasing consumer demand.

Mushrooms are considered to be one of the most environmentally-friendly foods to produce, yet their proliferating production has required increased secondary outlets for the substrate that results after mushrooms are harvested. Specialty mushrooms are grown on mushroom substrates: grain, sawdust, or plug spawn that is typically used for 1-3 production cycles, or flushes. Following the final flush, the mushroom substrate is considered “spent” and is then discarded, creating waste as a byproduct. Despite being unusable for further mushroom production, spent mushroom substrate (SMS) is nutritionally rich and abundant in fungal spores. While it can be used as a soil amendment, as compost, and for animal feedstock, among other uses, the mushroom industry’s growth has created more SMS than can be consumed, leading to a surplus of SMS that threatens the sustainability of mushroom production. Developing new outlets for SMS that pair the mushroom industry with vegetable farming can create a closed-loop synergy that benefits both the environment and farmers.

Despite known soil health benefits derived from SMS application to farm fields, SMS produced in the Northeastern U.S. is underused by farmers and many small-scale mushroom producers do not have an outlet for their SMS. Particularly in organic agriculture, compost is a popular soil amendment that offers nutrient and soil-building benefits, similar to SMS. However, it is frequently devoid of beneficial fungi that can help improve both soil health and vegetable growth. As a fungus-rich substrate, combining SMS with finished compost offers a method of inoculating compost with fungi to improve the microbial diversity of the compost farmers are presently using. Simultaneously, it can increase the utilization of SMS by vegetable farmers who are already familiar with applying compost as a part of their production while gaining additional benefits as conferred by the SMS and creating a demand for the waste product that hampers mushroom production.

Proposed Work
In an effort to close the production cycle of specialty mushroom farmers in Massachusetts, this project will evaluate the ability of fungal populations in SMS to inoculate finished compost and measure the effects of applying combined compost and SMS on vegetable production systems and soil health. Fat Moon Farm, a certified organic mushroom farm, will provide SMS to a total of five farms and community gardens throughout Massachusetts for this use.

The goals of this project are to evaluate whether finished compost can be inoculated by SMS over the duration of a 14d period, and whether the resultant amendment induces any changes in soil physical and biological properties following application in a manner typically used by small-scale vegetable growers. It is expected that the findings from this project will reveal the capacity for SMS to inoculate compost, increasing its overall fungal communities to enrich the microbial biodiversity of compost and benefit soil biological and physical properties. Our preliminary trials have shown SMS to effectively increase fungal communities within compost, yet we have not yet evaluated its impacts when applied to a vegetable production system. Positive results from this study can demonstrate a use for the SMS waste produced by specialty mushroom farmers, helping to alleviate the disposal issues created by this burgeoning industry while offering vegetable farmers an abundant, locally-produced source of soil-benefitting microbes and carbon. Farmers will be able to use these findings to create a consumption cycle of SMS, offering an outlet for the mushroom production byproduct that benefits vegetable production soils.

To address these goals, this project will be divided into two phases. Phase 1 will evaluate the effects of SMS on finished compost by evaluating the change in microbial communities following a 14d incubation period. Phase 2 is a field trial, wherein farmers will apply the amendments resulting from Phase 1 onto their production fields to evaluate physical and biological changes.

NOFA/Mass acknowledges the historic marginalization of Black, Indigenous, and People of Color (BIPOC) farmers both in Massachusetts and throughout the U.S., and deliberately strives to address these issues in all of our work and outreach. The outcomes of this project will be relevant to all individuals regardless of color, but BIPOC individuals will be directly involved throughout this project, including with essential NOFA/Mass staff and three of the five farmer participants. Furthermore, the community garden partner, Home City Housing (HCH) in Springfield, MA, gives us the unique opportunity to work directly with BIPOC youth. HCH youth volunteers are integral to the HCH production staff and will be directly involved in this project’s farmer responsibilities. This project will provide youth volunteers with the opportunity to implement and oversee the proposed experimental design, rendering an immersive learning opportunity while also potentially benefiting their soils and vegetable production. Finally, BIPOC staff from NOFA/Mass will be closely involved in several aspects of this project at HCH, giving the youth an opportunity to see them as role models for potential knowledge and personal growth.

This project will contribute to Northeast SARE’s outcome statement by increasing mushroom production sustainability, diversifying value-added compost products, and improving the health of soils essential to environmentally low-impact and regenerative farming while providing healthful products to consumers.  


Click linked name(s) to expand/collapse or show everyone's info
  • Elizabeth Almeida - Producer
  • UlumPixan Atho'hil Sukil - Producer
  • Anna Gilbert-Muhammad - Producer
  • Dalia Marzuca - Producer
  • Brittany Overshiner - Producer
  • Jen Salinetti - Producer


Materials and methods:

This project evaluated microbial biomass in compost inoculated with spent mushroom substrate (SMS) . Five farmers participated in the trials using the SMS provided by Fat Moon Farm.

Evaluation of Compost + Spent Mushroom Substrate Mixture Fungal Development
Setup – To evaluate the effects of inoculating compost with SMS, compost and SMS were mixed at Compost:SMS (C+SMS) rates of 10% SMS, 25% SMS, and 50% SMS. The evaluation included controls of compost without SMS and SMS without compost. All piles had a total volume of 0.5 cubic yards. Five piles were created: two controls (compost, no SMS; SMS, no compost), and three piles with the different C+SMS ratios.

Designated volumes of compost and fresh SMS were evenly mixed by hand with a shovel. SMS was easier to break apart when fresh, whereas the mycelium in dried SMS formed into a leather-like material that made the block more difficult to break apart. All amendments were watered to 50% moisture capacity, as evaluated using a soil moisture meter, and covered with a tarp to maintain moisture content. Control piles were watered and covered with a tarp using the same procedure as for the C+SMS amendment piles. Tarps were anchored at each corner to keep in place. Piles were watered with tap water. Water-derived chlorine may have a potentially deleterious effect on fungal populations, yet the study deliberately did not control for chlorine in water to make procedures easier for farmers to replicate independently.

A quart-size volume of representative sample was collected from all treatment and control piles to be used for baseline electrical conductivity (EC), pH, and fungal activity measurements. Samples were preserved in quart-size plastic zipper bags and analyzed for all three parameters within 24 hours of collection.

EC and pH were measured using a hand-held Groline Hydroponic Waterproof pH/EC/TDS/Temperature meter according to manufacturer instructions. The probe was calibrated prior to use at each farm using the procedure found in this document pH and EC Equipment and Procedure. For both EC and pH measurements, a soil slurry was made by thoroughly mixing soil in deionized water at a 1:2 ratio. The slurry rested for 15 minutes before sampling per meter instructions. The probe was rinsed with deionized water when switching between amendment types to minimize any potential contamination.

Microbial activity was evaluated using the Microscope Assessment Procedure established by Dr. Elaine Ingham as a part of the Soil Food Web evaluation practice. These techniques are based upon peer-reviewed soil microscopy methods and are effective means for identifying soil microbial activity. Microscopy was performed using a biological compound microscope with 40X-400X total magnification to identify microorganisms by morphological groups and obtain a biomass count. Fungal counts were evaluated by length, width, and a description of melanin. Fungi and bacteria were  reported in µg/g of soil. Assessed organisms were: bacteria (including actinobacteria as a separate sub group), fungi (including oomycetes as a separate sub group), protozoa (flagellates, amoeba, ciliates), nematodes (bacteria, fungal, root feeders and omnivores).

Monitoring – During setup, NOFA/Mass staff trained farmers on evaluation protocols for assessing the piles and adding water. Farmers were instructed to monitor the piles every other day for two weeks for moisture, temperature, and physical changes to the piles, including changes in color, odor, and mycelial growth. Moisture was  measured using a pre-calibrated soil moisture meter; tap water was added using a 5-gallon bucket demarcated in 2.5-gallon increments to maintain 50% moisture on all piles. Temperature was evaluated using a soil thermometer. Farmers were trained on evaluating physical changes to the piles during pile setup and were instructed to record all observations and water additions throughout the two-week period on the data sheet provided.

Final Evaluation – After two weeks, the fungal inoculation process terminated and a final microbiological, EC, and pH sample was collected from each pile and was evaluated using the same procedure described in the pile setup.

This project originally intended to include a field trial evaluating compost + spent mushroom substrate impacts on soil health, yet these activities ultimately were not performed. Soil samples were collected from each farm to identify the baseline soil microbial composition at each farm and application site. 

Replication over Time
The trial initially occurred in fall 2022 and was repeated in spring 2023 to determine any seasonality impacts.

Research results and discussion:

Four rural farms and one urban farm performed tests of inoculated finished compost. Compost was either purchased commercially or done in-house. All compost was inoculated with spent mushroom substrate with the goal of increasing fungal activity, these were applied at the following rates: 10%, 25% and 50%. The piles were then allowed to incubate for a minimum of two weeks.  All piles were evaluated via direct microscopy using a compound microscope in brightfield mode. In addition to this test, background microscopy testing was also performed on the fields where the inoculated compost would be applied to. Following this incubation period pH and electrical conductivity were also performed on the compost to ensure that these values were within the recommended range for field application. Lastly background testing was also performed in the field for soil hardness, bulk density, infiltration rate, visual structure, and aggregate assessment, slake and active carbon. These background tests will be repeated following inoculated compost field applications to track any potential changes.

Findings from soil testing will be shared with farmers following full analysis of data during winter 2023. Preliminary findings show the following:

  • Initial microscopy results indicate that all background/baseline soil testing showed an imbalance of fungi and bacteria, with the fungal activity being the most suppressed i.e., low fungal biomass was observed in all background soils. The samples of compost also appeared to have lower fungal values that are expected of biological diverse compost.
  • Protozoan values were consistent with the classic predator prey interactions meaning that high bacterial counts were typically associated with high protozoan values as bacteria are the primary food source to these microorganisms. However, this was not consistent within all fields tested as some soil background/baseline samples were completely void of protozoan populations.   
  • Nematodes were also evaluated as part of the microscope assessment and were not present in significant values in the soil background/baseline samples. No trend was observed when looking at soil samples; however, one significant outcome was the increased values of nematodes present post compost inoculum.
  • In addition to the microorganisms mentioned above other microarthropods were noted if present to indicate higher trophic levels and diversity. These organisms are also used a proxy for nutrient cycling.  These organisms were not found in all samples background or compost and only represented a minor value in the overall biomass of the samples.
  •  Another visual note during the microscope assessment was the overall “density” of the samples, in other words density is referred to the amount of mineral and aggregates present during the assessment. These data will be used to compare any potential changes over time after the inoculated compost is applied to the field.
  • Initial results for pH seem to indicate that with increasing spent substrate inoculum a decreasing pH value was observed. This would be consistent with increases in fungal activity and their respective enzymes, as these enzymes tend to fall on the lower pH scale. Whereas in with electrical conductivity values a specific trend could not be determined.  
  • Initial background/baseline sampling for soil hardness, bulk density, infiltration rate, visual structure, and aggregate assessment, slake and active carbon in the field plots indicate that these soils are not highly compacted and that the soil can support life provided proper and continued management. This portion of the testing will be monitored throughout the period of this grant and hopefully beyond.

Building upon these findings at the project end, we found that overall fungal populations increased with increasing inoculum. The greatest increase in fungal populations was observed in the 50/50 SMS-compost mixtures, whereas meaningful changes were not seen at the 10% SMS rate. Increases were observed for all measured organisms except bacteria, whose populations were controlled by the increase in predatory organisms. Consistent with this, at the end of the two week inoculation period, the fungi:bacteria ratio increased with increasing inoculum. The targeted fungi to bacteria ratio range is between 0.4-0.6 fungi:1 bacteria, and the 50% SMS/50% Compost mixture resulted in an average fungi to bacteria ratio of 0.5:1. In contrast, microbiological analysis of the compost farmers provided as a part of this project (which is the same compost they were using for their typical management), showed the average fungal to bacterial ratio to be 0.03:1, significantly below the recommended range. 

These fungi to bacteria ratio findings are also supported by observations of total fungi and total bacteria: total fungi were greatest in the mixtures with the greatest amount of SMS, and lowest in the mixtures with the smallest amount of SMS. Along these lines, total bacteria were lowest in the mixtures with the greatest amount of SMS and highest in the mixtures with the smallest amount of SMS. Interestingly, the total number of bacteria between the three trial mixtures (10% SMS, 25% SMS, and 50% SMS) were fairly similar, suggesting that the changes in the fungi to bacteria ratio were more a function of an increase in fungi than a decrease in bacteria.

Inoculating compost with SMS also led to a proportional increase in beneficial nematodes, with the 50% SMS/50% compost mixture containing 4800 nematodes per gram, compared with the 10% SMS/90% compost amendment at 670 nematodes per gram, and unamended compost with 120 nematodes per gram. The total number of beneficial Protozoa were also evaluated, yet the results were somewhat inconclusive: the number of beneficial protozoa were greater in the amendments with SMS than only compost, yet the 10% and 25% SMS amendments had more protozoa than the 50% SMS amendments, suggesting that there may be other factors regulating the beneficial protozoa populations. 

The final methods deviated from the original project design as in the field application component of the methods were not completed. Following the Phase 1 - Fall 2022 inoculation period, farmers did not apply the SMS-Compost mixtures to their fields as designed. This may be attributed to farmers not having the time or interest in applying the mixture, or from concerns regarding the impact of the mixture on their production fields. Furthermore, NOFA/Mass underestimated the amount of effort that would be required on our part to ensure that farmers applied the mixture, and thus failed to adequately support farmers to make this component happen. Therefore, it was not possible to observe or quantify any changes to soil health as a result of the SMS-compost mixture amendment being applied in a production system.

In fall 2022, NOFA/Mass took soil samples from the farmers’ production fields for baseline data in anticipation of the SMS-Compost mixtures being applied to their production fields. While the second phase of the project did not occur as planned when the farmers did not apply the SMS-Compost mixture, the baseline soil samples still provide valuable insights into the baseline microbial levels within their production fields. As expected, the inoculated compost had greater overall microbial mass than the field samples. Properly composted materials are expected to hold greater microbial activity than soil as their populations increase during compost decomposition. Bacteria and fungi are the primary decomposers during the typical composting process, yet the compost samples inoculated with SMS displayed a greater microbial diversity of higher trophic levels, specifically predators, than ordinary compost. Baseline soil samples showed that most production soils to be absent of this diversity or the presence of predators needed for proper soil functions. The baseline soil samples that did not follow this trend were obtained from the community garden beds that participated in this project, which have been heavily amended for microbes prior to the commencement of this project. These beds had similar biomass counts to those of the inoculated compost. However, the microbes were not evenly distributed throughout the beds, as some had lower numbers of fungi and nematodes. 

In addition, all baseline soil samples exhibited a lower fungal:bacteria ratio when compared to the inoculated compost (10, 25 and 50%). This ratio has been linked to plant succession with very low ratios corresponding to bare soils and on the other end of this spectrum with high F:B ratios corresponding to old growth forests. 

Despite the positive results showing an increase in fungal populations from SMS, and the findings that the SMS-Compost mixture can increase their soil’s microbial diversity, it is clear that farmers have reservations about integrating SMS into their regular production practice. In addition to concerns over potential negative effects of the SMS on their soils, farmers also voiced logistical concerns with implementing SMS usage. One farmer, who is located in fairly close proximity to Fat Moon Farm, has tried using SMS from Fat Moon Farm previously and found that, through the use of their box truck, fuel, and time to get the SMS, clean out the truck after getting it, and delivering and incorporating it into their composting area, it was costing them approximately $25/yard in order to use. Thus, while the product is free, the farmer found actually using the product to cost nearly the same amount as what they’d pay for cow or chicken manure. The farmer, as well as likely many farmers, reported being less likely to use higher-cost products than lower-cost ones, or would want to ensure there was an appreciable benefit to something that was of higher cost. 

To create a more sustainable practice, the farmer expressed the goal of having mushroom substrate blocks being created from hardwood harvested from the forests surrounding a farm and local residences, having them inoculated at the farm, and then returned to the compost. Doing so would require additional logistical considerations for mushroom harvesting but could create a more centralized, sustainable production system. One farm participating in this project, Whitemartz, is currently growing their own mushrooms and using the spent blocks in their composting system. If farmers were to diversify their farms to include mushroom block production this can then be incorporated into the composting process with no additional costs other than some extra labor, which could be offset through mushroom sales.

Research conclusions:

By mixing spent mushroom substrate (SMS) with mature compost, the goal of this project was to inoculate compost with the fungal communities it is traditionally lacking to create a more microbially-rich soil amendment. When the compost was applied to production fields in a manner typically used by farmers, the SMS-compost mixture would then provide an additional microbial boost to the soils. Our project found that SMS effectively increased the fungal:bacteria ratio of finished compost, with fungal populations increasing proportionally to the amount of SMS added to the compost. 

Despite these positive findings, we were unable to evaluate the impact of SMS-compost mixture application onto production fields. Further testing to the effectiveness and safety of SMS in production systems would likely increase farmers’ adoption of SMS as a different amendment type. The utility of SMS as a soil amendment would also rely upon feasibility of SMS acquisition and incorporation. Based upon our findings, it is expected that a minimum of 25% SMS would sufficiently inoculate compost to have a positive impact on the total fungal biomass. Finally, having a mechanical way of breaking down the SMS blocks would make it easier for farmers to adopt this practice.

Based upon the findings of our project, SMS has good potential to increase the fungal populations of finished compost, yet more study is necessary to (1) identify the effects of the SMS-compost mixture as a soil amendment and (2) streamline the process of SMS acquisition and incorporation into compost. While small-scale production farmers may be too time or resource-limited to utilize SMS, commercial compost production facilities may be able to incorporate SMS into their finished compost to sell as a finished product with an additional fungal boost. These production facilities would presumably have the existing equipment to more easily create the “value added” SMS-compost product while creating both a sustainable outlet for SMS and a way for growers to increase their soil microbial diversity through compost.

Participation Summary
5 Farmers participating in research

Education & Outreach Activities and Participation Summary

2 On-farm demonstrations
2 Published press articles, newsletters
1 Webinars / talks / presentations
1 Other educational activities: 1 Podcast

Participation Summary:

6 Farmers participated
Education/outreach description:

The following education and outreach activities were developed as a part of this project:


Title: Adding Indoor Mushroom Production to Your Farm
Date: 3/21/23
Topic: Mushroom production and uses of spent mushroom substrate, microscopy table
Duration: 3 hours
Registrations: 12
Participants: 9
Promotional/Registration Page: Adding Indoor Mushroom Production to Your Farm _ NOFA_Mass


Title: Soil Testing at Woven Roots Farm October 2023
Date: 10/3/23
Topic: SARE MC discussion, SMS+Compost development, uses, project findings
Duration: 6 hours
Registrations: 32
Promotional Page: Building Soil Health with Mushroom Compost – NOFA_Mass


Summer Conference Workshop

Title: Spent Mushroom Substrate (SMS) as a Compost Inoculant for Vegetable Farming
Date: 7/26/23
Recording views: 41 (2/27/24)
Description: How can regenerative vegetable farmers in the Northeast tap into mushroom farmers' wastestream for mutual benefit? Spent Mushroom Substrate (SMS) is an abundant, nutrient-rich byproduct of mushroom farming. Hear from Elizabeth Almeida (Fat Moon Farms) and Rubén Parrilla (NOFA/Mass) about on-going research into the effectiveness of SMS as a fungal inoculant in finished compost and its impact on soil health parameters, including microbial activity, following application in production beds. We will learn about application ratios and benefits to soil microbiology and vegetable production, and hear from Elizabeth about Fat Moon Farms's current and planned operations and future learning opportunities for farmers and gardeners. This session aims to promote a continual cycle of SMS utilization in compost, and build partnerships between specialty mushroom and vegetable farms in the Northeast.
Description: Whova Agenda Webpage

Attendees at the Summer Conference workshop reported learning more than expected, and that the workshop content inspired them to seek out local sources of SMS to utilize in their own production. Attendees also expressed an interest in learning more about how plants respond to growth in the SMS+compost mixtures, suggesting opportunities for further study.



Season 6 Episode 2: Closing the Mushroom Production Loop
Date: November 26, 2023
Engagements (listens): 356 (through January 2024)
Description: Closing the Mushroom Production Loop: Evaluating Soil Microbe Changes Following Field Application of Compost Inoculated with Spent Mushroom Substrate with host, Tony Kennette, Ruben Parilla Soil Tech Coordinator and Education Dir NOFA MASS and Elizabeth Almeida of Fat Moon Farm. In this episode we discuss the use of compost inocullated with "spent" mushroom substrate, and the scientific discoveries found regarding increased fungal activity in the soil when applied. This podcast episode is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, through the Northeast Sustainable Agriculture Research and Education program under subaward number ONE20-378. 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.



Newsletter Articles (2)

Title: Can Mushroom Production Help Your Soil and Vegetable Production?
Date: March 2023 Be a Better Grower e-newsletter
Can Mushroom Production Help Your Soil and Vegetable Production_ – NOFA_Mass
E-newsletter opens: 1,205 subscribers
Online/website access: 186 views


Title: How and Why to Use a Mushroom Byproduct in Your Compost
Date: December 2023 Be a Better Grower e-newsletter
Nurturing a Vision of Sustainable Agriculture with Mushroom Substrate – NOFA_Mass
E-newsletter opens: 1,688 subscribers
Online/website Access: 118 views
Newsletter will be included in the March 2024 The Natural Farmer print publication The Natural Farmer - Spent Mushroom Substrate in Compost

Learning Outcomes

9 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

Farmers gained knowledge, skills, and awareness through the increased exposure to a new potential soil amendment, and the process of inoculating finished compost with Spent Mushroom Substrate (SMS). Through the inoculation process, farmers were directly observing and recording changes in the inoculated compost piles, giving them the opportunity to visually evaluate and understand the fungal growth and compositional changes that were occurring on a macro-scale. In addition, the participating produce farmers have been connected with a mushroom farmer, creating new connections for consumption of a mushroom production byproduct and use of a soil amendment. These skills were also taught to four youth participants at the Tapley Court community garden site who assisted in all parts of the measuring, mixing, and amendment evaluation and application process.

Project Outcomes

5 Farmers changed or adopted a practice
4 New working collaborations
Project outcomes:

As a consequence of farmers not applying the SMS+compost amendment to their production fields, no changes in behavior were reported. Thus, farmer benefits are more likely educational in nature, as opposed to practice and behavior-based. It is expected that, throughout this process, farmers gained knowledge on soil microbiology, microbial biomass levels in non-inoculated compost, and the impacts of microbial compost inoculations on microbial biomass and diversity. It is also expected that the participating farmers gained a greater appreciation of the fungal:bacterial ratio and the importance of fungi in controlling bacterial communities and supporting soil health and production. While these outcomes are purely content-based, it is our hope and expectation that this experience will positively inform farmers’ decision making processes in the future. Even if they do not ultimately utilize SMS as a microbial-rich soil amendment, we expect that the knowledge they gained through this project will lead them towards other microbial-supporting amendments and practices in the future.

Beyond the cohort of participating farmers, NOFA/Mass has received considerable external interest in this project and its outcomes. Less than 6 months into the project and as recently as last week we have been contacted by other organizations performing similar research who were interested in our outcomes and findings. Interested organizations include farmer-based research groups and mushroom producers, demonstrating a need for this work to continue, and to be disseminated, beyond this project. The need for this work is timely and well-demonstrated, and we hope it continues.

Assessment of Project Approach and Areas of Further Study:

Upon initiating this research, we were hoping to evaluate whether there was a way to increase the fungal populations and bacteria:fungi ratio in mature compost to have compost’s microbial composition better aligned with optimal crop production. We then hoped to identify whether any of the changes in microbial composition observed in the combined compost, after a period of 14d, could be conferred to soil, with commensurate soil health benefits, following compost application. Ultimately we were successful in identifying that SMS could increase the fungal communities within mature compost, yet we were unable to evaluate any field-based soil health changes were the mixture to be applied to production fields.

Our success in evaluating the effects of combining SMS and compost is largely due to close connections between our Technical Services Manager, Rubén Parrilla, and Fat Moon Farm, who supplied the SMS. Also, as Fat Moon Farm was already producing the SMS and generally didn’t have to do much else in order to supply it, their overall time involvement in the research study was both minimal and straightforward: they didn’t need to learn new steps or generally alter their activities in support of it. Furthermore, the geographic proximity of Fat Moon Farm to Rubén facilitated frequent interactions and streamlined the SMS collection and distribution process.

In contrast to Fat Moon Farm’s streamlined involvement, the specialty crop farmers who were responsible for monitoring and spreading the SMS-compost mixtures had to alter their daily activities during busy periods in order to fulfill the needs of this project. At NOFA/Mass we overestimated the farmers’ capacity to accomplish these additional tasks. While we attempted to streamline the farmers’ component as much as possible, including simplifying the data sheet and instructions, setting up the SMS-compost mixture piles, and identifying where on their farm the SMS-compost should be applied, farmers ultimately did not follow through on what we needed in order to fully accomplish the field-based application component of this project’s goals. In addition, the farms were largely spread throughout Massachusetts, which made it harder for Rubén to visit the farms more frequently to answer questions and assist as needed.

In talking with other organizations, such as Farmland Trust, who have attempted similar farmer-based research projects, we have since learned that we need to be considerably more connected with the farmers to ensure that the requisite project activities are performed. For instance, we have learned that some farmers would benefit from daily or weekly texts reminding them to check on the compost piles, or reminders to spread the compost, rather than just assuming that the farmers were independent with this process after receiving instructions. We have learned that doing so, which, on the surface seems like an extraordinary amount of hand holding or micromanaging, may be necessary and essential to time and energy-strapped farmers who aren’t thinking about a research project in the middle of the afternoon.

Beyond the practical limitations, it is also possible that the farmers were reluctant to apply the SMS-compost mixture to their production fields because it was so new and experimental. While SMS has been used for landscaping and similar application purposes, its use in crop production is less documented. The farmers who agreed to participate in this project all showed a high level of initial enthusiasm for the project and its potential outcomes, yet it’s possible that production-related concerns may have overshined this enthusiasm once it was time to apply the mixtures. While these concerns have not been communicated to us directly, they would be reasonable and not unexpected given the experimental nature of this project.

Moving forward, we have received a great deal of interest in this project from both farmers and the community at large. We hope to continue this research and the field-application component of the project, but would apply some of the practical lessons we learned in future project design. From some of the feedback we received, it would also be useful to develop a plant trial to assess how plants responded to the inoculated substrate. Thus, we envision future projects could include a controlled plant growth-based study that evaluates crop performance in the SMS-compost mixture as compared with controls of all soil, all SMS, and all compost, which would likely be performed with plants in pots, and also a large-scale field-based study to evaluate changes in soil health characteristics, such as soil carbon sequestration, aggregation, compaction, and water infiltration. In contrast to the design we developed to this current project, the two proposed areas of future study don’t necessarily have to occur in tandem, which could make it more feasible if being performed on a farm (versus at a research institution) or by farmers. Furthermore, the studies could circumvent active production fields, which would ease any production-related concerns by the farmers: the potted study would be separate from production, and the field-based application could occur on a fallow or out of production field.

As this project presents a low-cost way to introduce new and expand existing microbial communities in a widely-used soil amendment, we believe that the findings will be of interest to specialty crop farmers, mushroom farmers, compost producers, researchers, and the general community at large. Of late, we have found farmers and the general community to be highly interested in soil microbiology, and approaches to increasing microbial communities in production. This project has shown that inoculating compost with SMS is an effective way to increase microbial communities in finished compost. WIth additional research showing that SMS-inoculated compost is not harmful to plant growth and soil health, and potentially even beneficial to soil health and crop production, this project opens the door to many new pathways for SMS use and compost modifications. We plan to continue to share the findings of this project with our community, in hopes that our findings will support use of SMS as a soil amendment and encourage further study and experimentation by farmers and researchers. We feel that SMS offers broad potential to create a sustainable outlet for SMS that can, hopefully, improve soil health and crop production, and are eager to contribute to future work that fully identifies the reality of this potential.

Information Products

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.