By Ruben Parrilla and Annie Sholar
Subhead: One man’s trash is another man’s treasure – or, in this case, one farmer’s trash is treasure for millions of soil microbes!
Note: this article was adapted from a November 2023 edition of NOFA/Mass’s Be a Better Grower newsletter.
Finding new ways of increasing your compost’s effectiveness is a clear win for your farm or garden. Finding a way that also reduces waste, costs little, and supports on-farm diversification? That’s a win-win-win!
NOFA/Mass is proud to present findings from a transformative project made possible through the Sustainable Agriculture Research and Education (SARE) grant program. We measured the impact of adding spent mushroom substrate, the medium used to grow mushrooms for one or more cycles, to compost – and were excited to see measurable benefits on pest control, nutrient cycling, and soil substructure in soil amended with this compost-substrate mix!
Soil biodiversity and microbial activity are important indicators of soil health for any farm. But measuring and improving soil microbes can be challenging for farmers; the tests and assessment tools are often costly and can be tricky to interpret the results.
NOFA/Mass is committed to finding and promoting simple ways for farmers to improve their soil health using accessible tools and techniques. This project with SARE was designed to find an easy change farmers can make to improve soil health with a simple compost amendment. For the next several years, NOFA will also work with the Massachusetts Department of Agricultural Resources (MDAR) to equip farmers with tools to help measure their soil microbe activity (including providing up to 30 farmers with free microBIOMETERs to use on their farms). If this article inspires you to monitor your soil health, please email info@nofamass.org to sign up to participate in the MDAR Microbes project!
Why are Soil Microbes Important?
Soil biodiversity can have a significant effect on how plants grow. Here are just a few examples of the fascinating interplay between soil biodiversity and agricultural ecosystems:
Pest Resistance: Soil teeming with beneficial microorganisms is a natural defense against pests. These microorganisms can outcompete harmful pathogens, reducing the need for chemical pesticides
Nutrient Cycling: Microbes break down organic matter and recycle nutrients, making them available to plants. This nutrient cycling ensures that plants receive the essential elements they need for growth and reduces nutrient leaching, minimizing environmental pollution.
Soil Structure: Well-structured soil offers aeration and proper water infiltration, providing the necessary living conditions for microbes. Microbial diversity encourages diversity in other soil-dwelling organisms, like earthworms and microarthropods. The burrows and channels they create enhance soil structure, contributing to a virtuous cycle of healthy soils.
Impact of Inoculating Compost with SMS: A Microbial Symphony Unveiled
Inoculating compost with spent mushroom substrate (SMS) is a simple way to build up the microbial diversity in your soil, supporting pest resistance, nutrient cycling, and soil structure.
Spent mushroom substrate from organic mushroom production is typically a blend of materials like sawdust and grain; some substrates include hay, manure, and other materials. After the fruiting bodies of the mushrooms are harvested, the rich mycelial networks produced by the fungus remain in the substrate.
Adding the SMS to your compost is an easy way to capture this abundant organic matter and add diversity-increasing fungal activity to your soil. During our trial period, we saw several indicators of increased soil biodiversity. While we did not directly measure crop outcomes, like yield or pest presence, we did see promising signs of healthier soils. Here are some of our observations:
1. Nematodes: Champions of Nutrient Cycling
The most significant population surge we observed post-inoculation was that of nematodes. These microscopic, worm-like organisms are pivotal in soil ecology, particularly nutrient cycling. As the nematode population booms, so does their ability to regulate the microbial community. Nematodes actively graze on bacteria, fungi, and other microorganisms, creating a dynamic balance in the soil. This predation controls microbial populations and facilitates the release of essential nutrients through the breakdown of organic matter. In this symbiotic dance, nematodes enhance nutrient availability, fostering a healthier and more vibrant soil ecosystem.
2. Trichoderma: The Beneficial Fungus
Mushroom substrate is prone to Trichoderma infection during mushroom cultivation. But while this fungus is potentially detrimental to mushroom production, it is an invaluable asset in agricultural soils. This fungus acts as a biocontrol agent, suppressing the growth of harmful pathogens. Its antagonistic nature makes it a natural ally against various soil-borne diseases. Furthermore, Trichoderma is renowned for its capacity to enhance plant growth by promoting root development and nutrient absorption. In the delicate balance of soil microbiota, Trichoderma emerges as a defender, contributing to the overall health and resilience of the agricultural ecosystem.
3. Snails: Architects of Soil Structure and Health
Snails played a distinctive role in our SMS-inoculated soils' physical and ecological structure. Their movements aid in soil aeration, which, in turn, promotes a favorable environment for microbial life. As they graze on organic matter, snails assist in breaking down plant residues, facilitating the decomposition process. Moreover, their excretions add valuable organic material to the soil, enriching its nutrient content. In this intricate web of interactions, snails emerge as architects of soil structure, contributing to a well-balanced and thriving soil ecosystem.
4. Earthworms: Soil Engineers and Nutrient Cyclers
The inoculation of compost with SMS also triggered a notable increase in earthworm populations. Earthworms, often called soil engineers, play a fundamental role in soil structure and nutrient cycling. Their burrowing activities create channels that enhance soil aeration and water infiltration. Earthworm castings, a byproduct of their feeding and burrowing, are nutrient-rich and contribute to improving soil fertility. Earthworms promote a healthy and well-structured soil environment conducive to microbial life and plant growth by tilling the soil.
In essence, the inoculation of compost with SMS orchestrates a diverse ensemble of soil-dwelling organisms, each playing a unique and vital role in promoting nutrient cycling, disease resistance, and overall soil health. This holistic perspective underscores the intricate connections within the soil ecosystem, showcasing the collaborative efforts of nematodes, Trichoderma, snails, and earthworms, to name a few, in fostering resilient and thriving soils.
We invite you to actively participate in the transformation of agricultural landscapes. We encourage farmers, gardeners, and advocates alike to experiment with SMS inoculation – join us in pursuing healthier soils, healthier communities, and a healthier planet!
BOX -
Using Spent Mushroom Substrate in your compost:
Start with finished compost. Finished compost has completed a “thermophilic,” or hot, phase and is transitioning to the maturation phase, stabilizing at a consistent temperature. The heat generated during the composting process has the potential to denature some organisms, diminishing biodiversity. For this reason, it is vital to use only finished compost when incorporating SMS.
Find your SMS blocks – contact a local organic grower about using their spent blocks.
Break down SMS black into the smallest possible size. This can be done by hand or with a shovel. Breaking down the SMS increases the surface area, consequently enhancing the number of inoculation points in the compost.
Use 5-gallon buckets to determine the volume of compost. Measure out the corresponding proportions of SMS to achieve the desired ratio of SMS to Compost.
The incorporation process involves volume measurements, employing ratios of 10%, 25%, or 50% SMS to compost.
For instance, if you have measured out 9 (5)-gallon buckets of compost, you must mix in 1 (5)-gallon SMS bucket to achieve a 10% SMS to Compost ratio. Mix thoroughly; the compost is now considered inoculated.
Monitor your compost pile for moisture.
Check if your pile has sufficient moisture – tightly squeeze a fistful of inoculated compost; if one or two drops of water come out of your fist, your pile is at optimum moisture!
Once at optimum moisture, use a relative moisture meter to check the moisture level every other day for the next two weeks.
Leave your pile to rest & incubate for at least two weeks – don’t turn your compost during this time. Turning the compost could disturb mycelial growth by breaking apart new hyphal connections (the growth points of soil fungi).
After the two-week incubation period, the inoculated compost is ready for application in the field!
Tips for successful implementation
This process is simple and should be adaptable to anyone using compost. Here are a few things we learned through this process. We hope you can learn from some of these tips, but feel free to experiment and develop a process that best fits your needs!
Keep in mind the time of year when performing this process. Spring and Fall are perhaps the best in our New England climate (temperate) as the height of the Summer may make it more difficult to control some of these conditions (temperature and humidity).
We used SMS mostly made up of sawdust and some grain. The SMS we tested only went through one “flush,” meaning it had only been used for one growing cycle of a mushroom.
We tested a two-week incubation period, but depending on your environmental conditions, you can leave the compost to incubate for longer to allow for greater potential biodiversity in your compost.
Look for macrofauna, such as earthworms and mollusks, as they can be an indicator of our microbial friends moving in. Or, use a microbial assessment tool like a microBIOMETER. (Massachusetts farmers can contact NOFA/Mass for information about an MDAR-sponsored project to provide some farmers with this tool at no cost.)
We broke up the SMS by hand; a mechanized approach would certainly save you some hard and messy work! Breaking up the SMS uniformly by hand can be difficult. If you intend to use the compost for direct seeding, which benefits from a uniform seed bed, a mechanized approach could be the right choice. If you are applying this to a bed with transplants or side dressing, then the size variation of the SMS is not as important to the bed preparation. Remember that the smaller the SMS pieces, the more inoculation points you’ll have – regardless of how the compost is applied.
Account for pH. We monitored the pH of the inoculated compost during our trial and found lower pH values in the inoculated compost after the incubation period. Certain crops may be sensitive to these lower pH values; be sure to monitor pH and proceed according to individual needs.
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