Reusing spent mushroom substrate (SMS) to grow new oyster mushrooms supports the circular economy idea, but without rebalancing nutrients—especially nitrogen—it leads to lower yields, showing that smarter substrate recycling methods are needed for sustainable mushroom farming.
Imagine growing delicious oyster mushrooms 🍽️ — and then using the “leftovers” from that process to grow the next batch! That’s exactly what researchers from Brazil and Spain explored in their study “Evaluation of Reuse of Spent Mushroom Substrate for New Pleurotus ostreatus Crop Cycle”.
This research dives deep into one of today’s most exciting sustainability challenges: how to turn agricultural waste into valuable inputs — a core principle of the circular economy. 🌍♻️
But the question is… can we really reuse Spent Mushroom Substrate (SMS) — the used material left after mushroom harvest — to grow new crops effectively?
Let’s dig into what they found 👇
When mushrooms like Pleurotus ostreatus grow, they feed on a mixture of sawdust, straw, and bran — all rich in nutrients and organic carbon. After the harvest, that material (now called Spent Mushroom Substrate) still contains a lot of organic matter: lignin, cellulose, proteins, and minerals.
In theory, this “waste” could be recycled as fertilizer, animal feed, bioenergy material, or — even better — reused as new mushroom substrate. This would close the production loop and reduce both waste and production costs. 🌱
However, the big question remains — can oyster mushrooms grow again using their own leftovers? 🍄🔁
The scientists carried out their experiments at São Paulo State University (UNESP). They tested how adding different amounts of reused SMS (5%, 10%, and 20%) would affect the next mushroom crops over three growth cycles.
They used two substrate types:
Each mixture was carefully prepared, sterilized, and inoculated with the oyster mushroom strain P. ostreatus POS 22/03. They then measured how well the mushrooms grew — looking at factors like:
🍄 Yield (% of mushrooms harvested)
⚖️ Average mushroom weight
🌿 Number of mushrooms
🌸 Number of clusters
They also checked the substrate’s chemical properties: nitrogen (N), carbon (C), carbon-to-nitrogen ratio (C/N), pH, and electrical conductivity — all key factors for fungal growth.
In the first experiment, mushrooms grown on high-nitrogen substrates produced 22% more yield than those on low-nitrogen ones. The high-N mix gave heavier mushrooms too 🍄💪.
However, once harvested, the spent substrate showed less nitrogen, lower pH, and higher electrical conductivity, meaning nutrients had been used up and salts accumulated.
So right away, the team knew — the nutrient balance would be crucial in the next cycles.
The team mixed 5%, 10%, and 20% of the spent material back into new substrate recipes.
💡 The result?
Adding more SMS did not improve yields — in fact, yields decreased as more SMS was added.
Why?
Because replacing fresh bran and grains (the nitrogen-rich ingredients) with SMS diluted the nutrient content. The C/N ratio (carbon-to-nitrogen) went up, making it harder for the fungus to grow efficiently.
However, there were some silver linings 🌤️:
For the final test, the team reused SMS a third time — meaning they grew mushrooms using material that had already been reused twice!
Unsurprisingly, performance dropped again. Mushroom yields and numbers fell, especially in low-N substrates. The more SMS added, the fewer mushrooms produced.
Still, even after multiple reuses, Pleurotus ostreatus managed to fruit — proving this fungus’s legendary adaptability. 🍄🔥
Chemical analysis confirmed a trend:
This shows that with every reuse, the substrate becomes “tired” — too carbon-heavy and nutrient-poor for optimal yields.
Fungi like P. ostreatus need a balanced C/N ratio to thrive. Too much carbon (like cellulose and lignin) and too little nitrogen (from bran and protein sources) leads to slower growth.
In this study, the C/N ratios climbed well above 50:1 — far beyond the ideal range (15:1 to 40:1) for healthy mushroom growth. That imbalance explains the reduced yields.
Other factors also played roles:
Despite these challenges, the mushrooms didn’t completely fail — a good sign that SMS could still be part of a sustainable cultivation mix, just not as a full replacement for fresh substrate yet.
Globally, the mushroom industry produces over 44 million tons annually 🍄🌎 — and with it, massive amounts of SMS waste. Improper disposal can pollute soil and water or release greenhouse gases.
Finding productive ways to reuse SMS supports the circular economy — where waste becomes a resource. This approach can:
♻️ Reduce agricultural waste
💰 Lower production costs
🌱 Cut environmental impact
🔥 Decrease fossil fuel use from waste transport and disposal
Even though full SMS reuse didn’t boost yield, this study helps scientists fine-tune future strategies — such as:
The takeaway? Using spent mushroom substrate directly for new oyster mushroom cycles isn’t yet economically viable — but it’s a crucial first step toward zero-waste mushroom farming 🍄♻️.
Future research could explore:
Each of these options strengthens the circular economy in agriculture by keeping resources cycling instead of landfilled or burned. 🔄🔥
🌱 Goal: Test reusing Spent Mushroom Substrate (SMS) to grow new oyster mushrooms.
📊 Findings: Higher SMS reuse = lower yield, mostly due to nutrient imbalance.
🧫 Lesson: The C/N ratio and nitrogen content are vital for success.
💡 Future Path: Improve SMS reconditioning and mix with fresh biomass.
🌍 Impact: Supports circular economy goals by reducing agricultural waste.
This study shows that sustainability in mushroom cultivation is not just about what we grow — it’s about what we reuse. 🍄💚
Even though reusing Pleurotus ostreatus waste didn’t yield bumper crops, it marks a step toward smarter, more circular agriculture. The challenge now is to make that cycle nutrient-efficient and economically viable — transforming “waste” into the future of farming. 🌾♻️
Because in the circular economy, nothing truly goes to waste — not even a mushroom’s leftovers! 🍄🌎✨
🍄 Pleurotus ostreatus (Oyster Mushroom) - A popular edible mushroom known for its oyster-shaped cap. It’s easy to grow, rich in protein, and often used in sustainability research because it feeds on agricultural waste.
♻️ Circular Economy - A sustainable system where products and materials are reused, recycled, or repurposed instead of thrown away — like turning mushroom waste into new growing material! 🌍 - More about this concept in the article "Upcycling Copper for 3D Printing ✴️ Turning Scrap into Gold".
🌾 Agricultural Waste - Leftover plant materials (like straw, husks, or sawdust) from farming that can often be reused instead of discarded. In mushroom farming, it’s a key ingredient for growth substrates. - More about this concept in the article "Turning Agricultural Waste into Water Purification Gold 🌿 The Biochar Revolution".
🪴 Substrate - The “soil” for mushrooms — a mix of organic materials that provides nutrients for their growth. Common substrates include sawdust, straw, and bran.
🧫 Spent Mushroom Substrate (SMS) - The used-up substrate left after harvesting mushrooms. It still contains valuable organic matter and can be recycled for new crops or turned into compost or biofuel.
⚗️ Nitrogen (N) - An essential nutrient that helps mushrooms build proteins and grow faster. Too little nitrogen means slow growth; too much can cause imbalance.
🧮 Carbon-to-Nitrogen Ratio (C/N Ratio) - A measure of how much carbon and nitrogen are in the substrate. Think of it as the diet balance for mushrooms — too much carbon and they “starve,” too much nitrogen and they “burn out.” 🍽️ - More about this concept in the article "Boosting Biogas Yields: The Revolutionary Role of Corn Silage and Shredlage Technology 🌽⚡".
⚡ Electrical Conductivity (EC) - A way to measure how many dissolved salts or minerals are in the substrate. It tells growers if there are enough nutrients — but too much can stress the mushrooms. - More about this concept in the article "The Secret Life of Argan Trees: How Soil and Climate Shape Their Growth 🌳 🌧️".
🌡️ pH - A scale showing how acidic or basic the substrate is (from 0 to 14). Mushrooms like it slightly acidic — around 5.5 to 7 — for the best growth. - More about this concept in the article "Smart Hydrogel Tackles Methylene Blue Wastewater 🚰".
🌱 Biological Efficiency (Yield) - A measure of how efficiently mushrooms convert the substrate into edible fruit. It’s usually expressed as a percentage — higher yield = happier fungi! 🍄📈
Source: Vieira Junior, W.G.; da Silva Alves, L.; de Moura, J.B.; de Paula, A.T.C.; da Silva Freitas, M.A.; Orti, M.Á.; Alegría, F.J.G.; Zied, D.C. Evaluation of Reuse of Spent Mushroom Substrate for New Pleurotus ostreatus Crop Cycle. AgriEngineering 2025, 7, 342. https://doi.org/10.3390/agriengineering7100342
From: Universidade Estadual Paulista “Júlio de Mesquita Filho”; Universidade Evangélica de Goiás; Universidad de Castilla La-Mancha; Experimentación y Servicios del Champiñón (CIES).
