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The Power of Spent Mushroom Substrate: A Preliminary Study on SMS and Closing the Waste Loop with Fungi for Regenerative Urban Agriculture
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The Power of Spent Mushroom Substrate: A Preliminary Study on SMS and Closing the Waste Loop with Fungi for Regenerative Urban Agriculture


Sydney Gibson

Dr. Hong Wang

University of Arkansas at Little Rock

Date: August 5, 2025

Table of Contents

1.        Abstract

2.        Key Findings

3.         Introduction

4.         Background

5.         Methods

6.        Results & Visual Data

7.        Conclusion

8.        References

9.        Acknowledgments

Abstract

Spent mushroom substrate (SMS), the soil-like material left over after growing mushrooms, is often viewed as agricultural waste. This white paper explores its potential as a regenerative soil amendment in permaculture and small-scale agriculture. In a preliminary study using blue oyster mushroom SMS, I compared SMS-amended soil to unamended control soil to examine effects on soil health indicators: microbial carbon dioxide (CO₂) output, nitrogen levels (nitrate and ammonia), and pH. The SMS-treated soil showed enhanced microbial activity, nutrient cycling, and slight pH moderation, suggesting that what was once “waste” can become a valuable resource for soil regeneration. These findings align with the ethos of sustainable, circular systems (turning organic waste into soil wealth) and offer a low-cost alternative to synthetic fertilizers. Further research, including field trials and longer-term studies, is encouraged to validate and expand upon these results.

Key Findings:

•        Boosted Microbial Activity: SMS-amended soil released significantly more CO₂ (an indicator of microbial respiration) than control soil in the initial days, pointing to heightened microbial and fungal activity.

•        Enhanced Nitrogen Cycling: Soil with SMS showed a steady rise in nitrate levels over two weeks, with minimal ammonia buildup. This suggests that SMS promotes nitrification (conversion of ammonia to plant-available nitrate) and improved nitrogen availability.

•        pH Stabilization: SMS caused a slight acidification of the soil (down to ~6.4 from neutral 7.0), which remained stable and within healthy bounds. This moderate pH shift may benefit nutrient availability and reflect active organic matter decomposition.

•        Improved Soil Structure: Visually, SMS-treated soil retained moisture better and developed a more friable, crumbly texture with visible fungal mycelium, indicating improved soil structure and biology. These physical improvements can aid water retention and root growth.

Introduction

Soil health degradation is a critical challenge for global agriculture, especially under climate stress and decades of intensive farming. Conventional practices heavily rely on synthetic fertilizers, which are energy-intensive to produce and can degrade soil life over time. At the same time, agriculture and food production generate immense amounts of organic waste. A prime example is mushroom farming: for every 1 kg of mushrooms harvested, about 5 kg of spent mushroom substrate (SMS) is generated. Disposing of this nutrient-rich material represents a lost opportunity and an environmental burden.(Medina et al., 2009)

As interest grows in permaculture and regenerative agriculture, a key principle is closing the waste loop and finding ways to turn today’s waste into tomorrow’s resource. Spent mushroom substrate, the leftover medium from mushroom cultivation, is one such underutilized resource. Often treated as waste, SMS contains a wealth of partially decomposed organic matter, fungal mycelium, and beneficial microbes(Uzun, 2004; Medina et al., 2009) This raises an exciting question: “what if we could reclaim this “dirt” to rejuvenate our soils?”. By repurposing SMS as a soil amendment, we not only reduce waste hauling but also potentially enrich the soil with organic carbon and nutrients in a slow-release form.

Early evidence and anecdotal reports suggest that incorporating SMS into soil could improve its fertility and structure. (Uzun, 2004; Ahlawat et al., 2006; Zied et al., 2011). Gardeners and researchers have noted that SMS can increase soil organic matter and water-holding capacity, foster microbial life, and even boost crop yields. In fact, heavy applications of SMS in field trials have produced yield increases up to 50% in certain crops, matching the performance of commercial fertilizers. SMS slowly releases nutrients and improves soil texture, water retention, and microbial activity: traits that align perfectly with sustainable farming goals. Given these promising attributes, exploring SMS in a small-scale, urban gardening context is a logical next step.

This study was born from both scientific curiosity and personal experience. As a mushroom cultivator and avid urban gardener, I often found myself with piles of “used” mushroom substrate exuding an earthy, mushroom smell and threaded with white mycelium. Its rich appearance and fungal aroma made me wonder: “Could this spent substrate invigorate soil life instead of heading to the landfill?  Might SMS serve as a low-cost alternative to synthetic fertilizers, feeding soil organisms and plants alike? And could a fungi-based solution help build a circular, regenerative system in our gardens by returning fungal biomass to the earth?”.

To begin answering these questions, I conducted a controlled 15-day experiment, tracking how partially spent mushroom substrate affects soil CO₂ respiration, nitrogen levels, pH, and physical condition. The goal was to gather data on whether SMS can boost microbial activity and improve soil health metrics in the short term. The following sections detail the background of SMS, the methods of the trial, results observed, and implications for sustainable agriculture.

Background
 Mushroom cultivation is typically done on a prepared substrate of organic materials, for example, a blend of straw, sawdust or wood pellets, soy or cottonseed hulls, and other agricultural byproducts. After one or more harvest cycles (called “flushes”) of mushrooms, the remaining substrate is considered “spent.” In commercial operations, this spent mushroom substrate is often removed to make way for fresh substrate. Despite being called “spent,” SMS is far from lifeless. It is a soil-like, organic-rich material containing the remnants of the growing medium along with fungal mycelium (the root-like network of the fungus) and various microorganisms. In essence, SMS is a partially decomposed compost that still holds nutrients (like carbon and nitrogen compounds) and active enzymes from the mushroom growth process.

Researchers and growers are increasingly exploring ways to use SMS rather than dispose of it. Early studies and trials have reported several potential benefits of adding SMS to soil: it can improve soil structure and aggregation, increase moisture retention, and boost microbial populations. (Ahlawat et al., 2006; Zied et al., 2011) The presence of fungal matter and partially broken-down organics means SMS continues to decompose in soil, releasing nutrients more gradually than synthetic fertilizers and supporting beneficial soil biota. For example, one study found that SMS amendments significantly increased soil microorganism counts and enzyme activities in various farming systems, highlighting its ability to stimulate soil life (Ahlawat et al., 2006) Another noted that SMS additions led to higher soil organic carbon and nutrient levels, translating into improved crop performance. (Zied et al., 2011) These properties make SMS an attractive candidate for regenerative agriculture; it contributes to soil fertility and health while recycling a waste product.

Despite these promising aspects, SMS as a direct soil amendment (without full composting) remains underexplored, especially in small-scale and urban garden settings. Much of the SMS produced commercially is piled outdoors to weather into a form of compost or used in large quantities on farmland. Small growers and mushroom hobbyists, however, often produce smaller batches of SMS. In many cases, this ends up in the trash or compost heap. Permaculture principles urge us to find uses for such “waste” streams on-site if possible. That provided the inspiration for this project: applying fresh or partially spent mushroom substrate straight into garden soil and observing the effects. This approach aligns with circular farming practices and could reduce reliance on external inputs like chemical fertilizers.

Given SMS’s composition and known benefits, the hypothesis was that mixing spent mushroom substrate into soil would stimulate microbial activity, enhance nutrient cycling (particularly increasing nitrate through microbial nitrification), and lead to subtle improvements in soil chemistry (such as pH and organic matter). I anticipated an initial surge in microbial respiration (as microbes feast on the new organic inputs) and gradual improvements in nitrogen availability. Additionally, I expected the SMS-amended soil to retain moisture better and perhaps exhibit visible signs of mycelial growth, indicating an active soil food web. This study represents a preliminary test of these ideas, undertaken with simple tools and a curious mind, aiming to spark further exploration into fungi-based solutions for sustainable agriculture.

Methods

To evaluate the impact of SMS on soil health, a side-by-side trial was set up with two treatment groups: (1) Control – soil only, and (2) SMS-amended – soil mixed with spent mushroom substrate. The SMS used in this study came from blue oyster mushrooms (Pleurotus ostreatus) grown on a mixture of soy hull pellets, cottonseed hull pellets, and hardwood sawdust pellets. After two flushes of mushrooms, the remaining substrate was collected as the “spent” material for the experiment. This SMS was partially spent (not fully exhausted or composted), ensuring it still contained living fungal mycelium and undecomposed organic matter.

Both the control and SMS treatment used the same base soil (a garden topsoil mix) to allow a fair comparison. The SMS was mixed at a 1:1 ratio by volume with soil for the treatment group. In practice, this meant equal parts of soil and SMS were blended thoroughly. The control group soil was left unamended aside from moisture adjustments. Two identical containers (one for each treatment) were prepared and kept in the same indoor environment (room temperature) to avoid external variables like rain or temperature swings.

Key steps and measurements in the 15-day trial included:

•        Container Setup: Two 1-gallon plastic containers were filled. One with plain soil (control) and one with the soil+SMS mixture (treatment). The soil moisture in both was adjusted to a moderate dampness to simulate watered soil conditions.

•        CO₂ Monitoring: I measured CO₂ levels as an indicator of microbial respiration. Each day, a portable Temtop air quality meter (CO₂ sensor) was placed into each container, which was then sealed for a short interval to let CO₂ accumulate from soil respiration. After a fixed time (~3 minutes), the CO₂ concentration (in parts per million, ppm) was recorded. This process was repeated daily at roughly the same time, providing a time series of CO₂ output for each treatment.

•        Soil Nutrient and pH Tests: Basic soil testing kits were used to track nitrogen (N), phosphorus (P), potassium (K) levels and pH over the experiment. I focused on nitrogen in the form of ammonia (NH₄⁺, a product of decomposition) and nitrate (NO₃⁻, a product of nitrification). Soil samples from each container were tested on Days 1, 5, 9, and 13 for ammonia, nitrate, and pH. These intervals captured initial conditions and changes over roughly two-week span.

•        Qualitative Observations: We kept notes and photos of any visible changes in the soil. This included observing fungal growth (e.g. white mycelium threads), changes in soil texture (clumping, crumbliness), color, and moisture retention. Such observations provide context to the quantitative data.

All measurements were done with low-cost, accessible tools to mirror what a hobbyist or small-scale grower might use. While this means the data may be less precise than a laboratory analysis, the approach keeps the experiment replicable by citizen scientists. The relatively short 15-day duration was chosen to capture immediate effects of SMS integration; longer-term effects (and plant growth outcomes) were outside the scope of this initial study. Data from the CO₂ sensor and soil tests were logged and later graphed to visualize trends.

Results

Over the 15-day period, the SMS-amended soil showed distinct differences from the control in terms of microbial CO₂ output, nitrogen dynamics, and pH trends. In the SMS-treated container, we observed an early burst of microbial respiration, a sustained increase in nitrate (indicating active nitrogen cycling), and a slight but persistent drop in pH relative to the control. By contrast, the control soil exhibited lower microbial activity and more erratic nutrient changes. Additionally, physical observations suggested that the SMS-treated soil maintained moisture longer and had a fluffier structure. Below we detail these findings with accompanying graphs.

CO₂ Output

CO₂ output (ppm) in sealed soil chambers over 19 days for control (blue line) vs. SMS-amended soil (gray line). Higher CO₂ indicates greater microbial respiration.


 In terms of microbial respiration, measured as CO₂ release, the SMS-amended soil consistently produced more CO₂ than the control, especially in the early and late stages of the trial. As shown above, during the initial 3–4 days the SMS mix generated elevated CO₂ concentrations (~2,600 ppm) compared to the control (~1,600 ppm). This early CO₂ surge suggests that microbes (and possibly the oyster mushroom mycelium) in the SMS-treated soil rapidly began decomposing the fresh organic matter, releasing carbon dioxide as a byproduct of their respiration. After this initial peak, the SMS container saw a sharp drop in CO₂ by Day 5, even dipping briefly below the control’s CO₂ level. One likely explanation is that the burst of microbial activity depleted available oxygen in the sealed container or exhausted the most easily digestible substrate, causing a temporary slow-down in respiration. In this same period, the control soil’s CO₂ output remained relatively low and steady (~1,000–1,500 ppm).

By about Day 7, CO₂ levels in both treatments stabilized at a lower baseline, but interestingly, a second wave of activity occurred in the SMS-treated soil around Day 8–9. The SMS soil’s CO₂ began rising again, pointing to either a rebound as oxygen was reintroduced each day or the microbes accessing another tier of organic material to decompose. In contrast, the control soil maintained a flatter profile. The most dramatic divergence came toward the end of the observation window: between Day 11 and Day 15, the SMS-amended soil’s CO₂ concentration spiked sharply, reaching nearly 5,000 ppm on Day 15. The control soil also rose (peaking around 3,000 ppm on Day 15) but stayed considerably lower. Such a late spike in the SMS treatment suggests a renewed microbial flourish, possibly as the substrate underwent further breakdown or as microbial populations bloomed in response to the ongoing nutrient release. After Day 15, CO₂ levels in SMS soil fell again but stayed above the control through Day 19. Overall, the SMS-treated soil showed higher and more variable CO₂ respiration, indicating a more dynamic and active microbial ecosystem than the control. These CO₂ trends support the idea that adding SMS “feeds” the soil life, at least in the short term, leading to bursts of metabolic activity.

Nitrogen Cycling

Nitrogen dynamics over 13 days: Nitrate (NO₃⁻) and Ammonia (NH₄⁺) levels in control vs. SMS-amended soil.

Nitrogen cycling in the soil was tracked by measuring nitrate and ammonia concentrations. Both the SMS and control started with low available nitrogen in the soil (common for an unfertilized soil mix). Over the 13-day monitoring, ammonia (NH₄⁺) levels in both treatments remained low and relatively stable,  generally under 0.5 ppm. The SMS-treated soil showed slightly higher ammonia readings than the control at a few points (still under 0.5 ppm, which is minimal). This indicates there was no significant accumulation of ammonia in either case; any ammonia produced by decomposition was likely being converted to nitrate or was too low to detect. The low ammonia suggests that ammonification (the process of microbes breaking down organic nitrogen into ammonia) was limited or that ammonia was quickly being used by microbes.

The more telling difference was in nitrate (NO₃⁻). Nitrate is a form of nitrogen that plants can readily uptake, and it’s produced in soil via nitrifying bacteria that convert ammonia into nitrate. In the SMS-amended soil, nitrate levels steadily increased throughout the experiment. Starting near 0, nitrate in SMS soil began rising noticeably after the first week (around Day 7) and continued to climb through Day 13, ultimately reaching about 3.5 ppm. This roughly linear increase in nitrate suggests active nitrification was happening, likely fueled by the organic nitrogen and microbial communities introduced with the SMS. By comparison, the control soil saw a different pattern: it experienced a jump in nitrate around Day 9 (peaking near 3 ppm) but then a sharp drop-off before a minor rebound by Day 13. The control’s nitrate spike could be due to a delayed mineralization of whatever organic matter was in that soil (perhaps decomposition of native organic bits or die-off of microbes releasing a pulse of nutrients), followed by leaching or usage of that nitrate in the micro-ecosystem, leading to the decline.

The contrast is clear: SMS amendment led to a more sustained and higher nitrate production than the unamended soil. By Day 13, SMS soil had significantly more cumulative nitrate. The consistent rise in the SMS treatment implies that the presence of SMS supported a thriving nitrifier population (bacteria such as Nitrosomonas and Nitrobacter) that kept converting any generated ammonia into nitrate. This is a positive sign for soil fertility, as nitrate is a crucial nutrient for plants. Importantly, the fact that ammonia stayed low while nitrate climbed in SMS soil indicates a healthy progression of the nitrogen cycle: organic nitrogen → ammonia → nitrate, all within a short time frame. These findings support the notion that SMS can kickstart nutrient cycling, supplying a slow trickle of plant-available nitrogen. Other studies have likewise found that SMS-fertilized soils show enhanced nitrogen transformations without causing excessive harmful nitrous gases or leachate under controlled use.

pH Stability 

Soil pH over 15 days in control (blue) vs. SMS-amended soil (gray). Initial pH ~7 in both soils.

Soil pH is an important factor for nutrient availability and microbial activity. In this study, both the control and SMS-amended soils began near neutral pH (≈7.0). However, the two treatments diverged over time. The SMS-amended soil showed a trend toward slightly acidic conditions, while the control soil stayed closer to neutral. By Day 5, the SMS-treated soil’s pH had dropped to about 6.5, whereas the control remained around 6.8–7.0. This early dip in pH for the SMS soil is likely due to organic acids being produced as the fresh substrate was broken down by microbes. Fungal and bacterial decomposition can release acids (like carbonic acid, organic acids), which will temporarily lower pH. From Day 6 to Day 11, the SMS soil’s pH partially rebounded, rising slightly to just above 6.5, before settling around 6.4 by Day 15. In contrast, the control soil showed only minor fluctuations: a small uptick around Day 6 (just over 7.0) and a gentle decline to about 6.9 at Day 15.

Throughout the test, the SMS-amended soil remained consistently about 0.3–0.5 pH units lower than the control. This indicates that incorporating SMS induces a modest acidification of the soil environment. It’s important to note that both soils stayed within a generally plant-friendly pH range (roughly 6.4 to 7.0). In fact, a pH in the mid-6s can be ideal for many plants because certain nutrients (like phosphorus and micronutrients) become more available in slightly acidic conditions. The persistent lower pH in SMS soil is a sign of ongoing microbial and chemical processes: as microbes decompose organic material, they produce CO₂ (which forms carbonic acid in water) and other organic acids, releasing hydrogen ions that acidify the soil. The stability of this effect suggests SMS can act as a pH buffer, preventing spikes to alkalinity, and might help stabilize pH in soils that would otherwise drift. For growers, this means SMS could gently adjust overly alkaline soils downward or at least maintain a stable pH as it breaks down. No extreme pH swings were observed, which is good. It implies SMS is unlikely to harm soil by making it too acidic; it just nudges it slightly more acidic than neutral.

Soil Physical Changes: Alongside the numbers, some qualitative differences were noted in the SMS-amended soil versus the control. Within a week, the SMS-treated soil developed visible white strands of fungal mycelium throughout, confirming that the mushroom’s fungal network was still active in the soil. By Day 9, the SMS soil appeared darker and more friable (crumbly) than the control soil, which remained a bit more cloddish. The improved crumb structure in the SMS mix likely results from the organic matter binding soil particles and the biological activity creating air pockets. We also observed that the SMS-amended soil tended to stay moist longer between waterings. This makes sense, as organic matter like spent substrate can significantly enhance a soil’s water retention and reduce surface evaporation. These observations echo broader findings that adding organic amendments (including SMS) can improve soil texture, aeration, and moisture-holding capacity.  By the end of the trial, the SMS-amended soil had a rich, earthy smell and plenty of visible fungal threads, whereas the control soil smelled more like plain dirt and showed little obvious biological growth.

In summary, the results support SMS as a beneficial soil amendment. SMS stimulated microbial respiration, accelerated the conversion of nitrogen to plant-available forms, and maintained a slightly more acidic (but stable) pH:  all indicators of active and healthy soil processes. Coupled with the physical improvements in soil structure, these data suggest that even a relatively short incorporation of SMS can boost soil vitality. The next section discusses what these findings mean in context and how they could be applied or investigated further.

Discussion

The preliminary findings from this project paint an encouraging picture of SMS as a tool for soil regeneration. In essence, the spent mushroom substrate “woke up” the soil by injecting a dose of organic matter and microbes, which in turn led to measurable changes in soil chemistry and biology. Let’s interpret the results in a broader context:

Microbial Bloom: The significantly higher CO₂ emissions from SMS-amended soil indicate a microbial bloom: microbes (and possibly the residual fungus) rapidly consuming the new organic inputs. This is a clear sign of stimulated microbial activity. Soil life drives nutrient cycling and plant health, so an amendment that boosts microbes is generally positive for soil ecology. Notably, after the initial frenzy (and a brief lull), there were secondary increases in CO₂, suggesting a sustained or multi-phase decomposition process in the SMS soil. The control soil, lacking that extra food, showed a more subdued microbial response. These observations align with other research showing that SMS can increase microbial biomass and enzymatic activity in soil(Ahlawat et al., 2006). For gardeners and farmers, this means SMS could be a microbe-rich inoculant as well as a fertilizer, introducing beneficial fungi and bacteria that continue to work in the soil.

Enhanced Nitrogen Availability: One of the most valuable outcomes was the rise in nitrate in SMS-treated soil. Nitrate is crucial for plant growth, and seeing it climb steadily suggests that SMS is not just adding inert organic matter but actively fueling the nitrogen cycle. The microbes in the SMS likely include nitrifying bacteria, or they created conditions favorable for native nitrifiers, which converted organic nitrogen -> ammonia -> nitrate efficiently. The control soil’s erratic nitrate pattern (a spike then drop) might indicate it lacked a steady supply of degradable material or a robust microbial community, so it released a little nitrate and then tapered off. By contrast, the SMS kept breaking down and feeding the microbes, resulting in continuous nitrate production. Importantly, nitrate levels remained modest (peaking in the low single-digit ppm), which is expected in a small container without plants (most of the nitrogen is likely tied up in biomass or organic forms). The key point is the trend: SMS-treated soil was heading in the right direction for fertility, accumulating more plant-available nitrogen over time. Over a longer period or with plants growing, we might expect that SMS could significantly contribute to a plant’s nitrogen needs. This supports the idea of SMS as a biofertilizer substitute for synthetic N fertilizers. (Medina et al., 2009) It’s telling that in larger-scale studies, SMS amendments have matched synthetic fertilizers in boosting yields likely because of this nutrient release and improved soil condition.

pH Moderation: The slight acidification observed in SMS-amended soil is another piece of the puzzle. While on the surface a lower pH might seem negative, but the shift is small and likely beneficial. Many composts and organic amendments cause a gentle lowering of pH as they decompose, which can help unlock phosphorus and micronutrients that are less available in alkaline soils. The SMS kept the soil pH around 6.4–6.5 after the initial drop, which is well within an optimal range for most crops. The control soil hovering near 6.8–7.0 is fine, but the stability of the SMS’s pH despite ongoing decomposition suggests a buffering effect. Essentially, SMS may help stabilize pH by countering the natural tendency of some soils to become too alkaline (especially if, say, the water or parent material is alkaline). Moreover, certain beneficial microbes thrive in slightly acidic conditions, so SMS could be indirectly promoting a more microbially friendly pH environment. From a regenerative agriculture standpoint, avoiding extreme pH swings and keeping soils in a biologically active pH range is a good thing and SMS appears to contribute to that.

Soil Structure and Moisture: Though harder to quantify, the physical improvements in the SMS-treated soil are worth highlighting. By the end of the study, the SMS-amended soil was visibly healthier looking. It had a crumbly texture, retained moisture, and was teeming with fungal life. This contrasts with the control, which started as the same base soil but ended up comparatively drier and lifeless in appearance. This outcome underscores a major advantage of organic amendments: they improve soil structure, meaning better aeration for roots and microbes, improved water infiltration and retention, and reduced risk of compaction. The fact that SMS did this in just over two weeks is impressive and speaks to the high organic matter content and conditioning effect of the substrate. Extrapolating that over a growing season, periodic additions of SMS could significantly build soil tilth (the workability and health of soil). Gardeners often pay for peat, coco coir, or compost to enrich their soil, yet SMS could potentially provide similar benefits at little or no cost if sourced from local mushroom farms or personal grows. This ties back to the theme of sustainable, circular systems: a waste product becomes a soil conditioner that reduces the need for imported peat or chemical soil additives.

Closing the Loop with Fungi: Stepping back, the success of this trial, albeit small in scale, illustrates a powerful concept in permaculture and regenerative design: closing the nutrient loop. Fungi (the mushrooms) were used to break down raw materials into food; instead of discarding the “leftovers” (SMS), we cycled them back to the soil to continue the decomposition process. In doing so, we fed the next trophic level of soil microbes and enriched the soil for plants, creating a loop where waste is minimized. This approach can be especially meaningful in urban gardening or small-scale farming where resources are limited, and waste disposal can be problematic. An urban farmer can grow mushrooms on, say, coffee grounds or straw, harvest food, then use the spent substrate to improve their vegetable beds: a full-circle system that yields food and soil health together. Moreover, incorporating SMS into soil keeps carbon in the soil ecosystem longer (as opposed to landfilling it where it might anaerobically rot and emit methane). By stimulating microbial activity and potentially increasing soil organic carbon, SMS amendments might contribute to soil carbon sequestration efforts in a minor way (every bit helps in the face of climate change).

Limitations: It’s important to recognize the limitations of this preliminary study. The trial was short-term (15-19 days) and done in container conditions. Real-world soils and field conditions involve more complex interactions (e.g., plant roots, weather, varied microfauna). The measurements here: CO₂, nitrate, etc. capture a snapshot of soil processes without a plant using those nutrients. In a planted scenario, plants would likely take up some CO₂ (via roots) and nitrates, possibly muting the peaks we saw but directly benefiting growth. Also, the scale of this experiment was small, and results could differ with larger volumes of SMS or different soil types. For instance, adding a lot of SMS to a poorly drained soil could cause temporary waterlogging or other imbalances. We also did not measure phosphorus or potassium changes in detail; SMS likely contributes some of those too. Despite these caveats, the trends observed provide a proof of concept that merits further exploration.

Comparison to Other Studies: Interestingly, the outcomes here mirror findings from other research on SMS. The increase in microbial respiration and enzyme activity with SMS is well-documented, and improved nitrogen profiles have been reported in soils treated with composted SMS as well. Some large-scale studies even warn that heavy SMS use can lead to nutrient leaching if not managed (due to the flush of nitrates) highlighting the need to balance application rates. However, at the small scale and moderate rate used in this project (50% by volume in soil), we saw controlled, beneficial changes without any signs of nutrient overload (no extreme nitrates or ammonia accumulation). This suggests that SMS can be safely integrated in reasonable amounts for home gardens. It’s also worth noting that species matters: this study used blue oyster mushroom substrate. Different mushroom species’ substrates (e.g., button mushroom compost) have different compositions (often higher in manure content, salts, etc.  Oyster mushroom SMS is generally high in lignin/cellulose from wood and hulls and tends to have a neutral pH, which might make it particularly garden-friendly. So results might vary with other types of SMS, and that’s an avenue for further research.

Broader Impact: If the promise of SMS holds, it could reduce reliance on chemical fertilizers and peat-based soil amendments in sustainable agriculture. Synthetic nitrogen fertilizers are a major contributor to greenhouse gas emissions (both from their manufacture using natural gas and from field emissions). Utilizing SMS as a fertilizer alternative taps into a biological nutrient supply that is less prone to causing runoff or pollution if managed properly. It essentially repurposes existing biomass to nourish new biomass (crops), an elegant solution much needed in an era of high input costs and environmental constraints. Additionally, from a waste management perspective, mushroom farms and home growers often face challenges in disposing of tons of spent substrate. Creating partnerships between mushroom producers and local farmers/gardeners could be a win-win: farms get rid of their “waste” sustainably, and growers get a free or cheap soil amendment. This kind of synergy is at the heart of permaculture design, connecting one system’s output to another’s input.

In conclusion, the study’s findings support the hypothesis that spent mushroom substrate can enhance soil health in meaningful ways. We observed boosted microbial respiration, improved nitrogen availability, and stable pH in SMS-amended soil, along with better soil structure. These benefits underscore SMS’s potential as a regenerative agriculture input. While further research is needed to confirm long-term effects and optimal application methods, the evidence so far suggests that fungi’s leftovers hold real power in reclaiming the vitality of our dirt.

Call for Collaboration

This project is just a starting point, and it invites a broader community of gardeners, farmers, and researchers to build on the results. The spirit of this work is exploratory and collaborative, much like the open-source ethos, where ideas are shared and iterated upon. In that vein, I encourage fellow permaculturalists, mycologists, and curious growers to experiment with spent mushroom substrate in their own contexts and share their findings.

Here are a few ways to get involved or take this further:

•        Try it in Your Garden: If you grow mushrooms at home or have access to SMS from a local farm, try mixing some into a portion of your garden or potted plants. Observe over a season how it affects plant growth, soil moisture, and health. Even simple side-by-side trials (with and without SMS) can provide insights. Take notes or measurements if you can (even just plant height or yield).

•        Join the Discussion: Communities on Reddit (like r/Permaculture, r/Mycology, r/Gardening) are great places to discuss and compare experiences. I originally shared these findings in a Reddit post and was energized by the interest it received. If you have questions or results from your own SMS experiments, post them online: let’s learn from each other. The collective knowledge grows when we document successes and failures openly.

•        Collaborative Research: If you are a student or researcher, consider picking up this thread. There are many avenues to investigate: different types of SMS (from different mushroom species), effects on specific crops, long-term soil microbiome changes, optimal application rates, etc. There is room for more controlled studies as well as participatory research with citizen scientists. I’m happy to collaborate or provide my protocols to anyone interested in formally researching this. The data from this white paper could be expanded into a journal article or used as preliminary data for a larger grant on sustainable soil amendments.

•        Local Partnerships: Farmers and community gardens can partner with local mushroom growers or compost facilities to source SMS. Establishing a pipeline for SMS reuse can close the loop at a community level. If you are a mushroom farmer with excess substrate, reach out to gardening groups or community gardens to donate or sell it cheaply. Conversely, if you’re a grower, consider contacting local fungi farms. By reporting back on how these partnerships work (both agronomically and logistically), we can develop models for integrating SMS into local food systems.

•        Iterate and Innovate: Think creatively about how to improve the process. For instance, one could pre-inoculate soils with specific beneficial microbes to further enhance SMS breakdown or combine SMS with other amendments (like biochar or compost teas) to see if there’s a synergistic effect. Perhaps there are ways to fortify SMS (since it’s carbon-rich but relatively low in some nutrients) by co-composting it with kitchen scraps or manure to create a more balanced fertilizer. The possibilities are numerous, and every experiment is a chance to discover something new.

In the true spirit of permaculture and regenerative practice, collaboration and open knowledge-sharing will accelerate our understanding of fungi-based solutions. I invite you to take this knowledge and adapt it, test it, challenge it, and report back. This white paper is not an end, but rather a conversation starter. By contributing your experiences and data, we collectively move closer to sustainable, circular agriculture systems where waste is a resource, and humble mushrooms help drive renewal.

Citations

  1.         Ahlawat, O. P., Yadav, M. C., & Sagar, M. P. (2006). Utilization of spent mushroom substrate for vermicomposting. *Mushroom Research*, 15(1), 33–36.
  2.         Medina, E., Paredes, C., Pérez-Murcia, M. D., Bustamante, M. A., Moral, R., & Moreno-Caselles, J. (2009). Spent mushroom substrates as organic amendment: A review. *Bioresource Technology*, 100(18), 4227–4233.
  3.         Stamets, P. (2005). *Mycelium Running: How Mushrooms Can Help Save the World*. Berkeley, CA: Ten Speed Press.
  4.         Uzun, I. (2004). Use of spent mushroom compost in sustainable production of greenhouse vegetables. *Journal of Environmental Protection and Ecology*, 5(3), 608–614.
  5.         Zied, D. C., Pardo-Giménez, A., & Minhoni, M. T. (2011). Spent mushroom substrate as component of a potting media for lettuce. *Horticultura Brasileira*, 29(2), 174–178.

Acknowledgments

This research was made possible with the guidance of Dr. Hong Wang and the support of the University of Arkansas at Little Rock. Special thanks to the mycology community for their continued encouragement and inspiration.