Can you reuse spent mushroom substrate? (2024)

For every kilogram of mushrooms produced, there will be 5 – 6 kg of by-product[1]. As worldwide, around 12.74 million tons (MT) of mushrooms were consumed (2018)[2] we will end up with 38.22 to 63.7 million tons of spent mushroom substrate each year.

How do youdeal with that?

To answerthis question, I will talk first about what spent mushroom substrate is, thenwhat you can use it for, and finally, show you how to apply it to your mushroomfarm.

Soundsgood? Then let’s start!

What isspent mushroom substrate?

Spent mushroom substrate (SMS) is the leftover substrate (compost in case of button mushroom) after the termination of the entire mushroom crop, after which mushroom cultivation becomes unremunerative[3].

The term „spent mushroom compost” (SMC) is used interchangeably with “spent mushroom substrate” (SMS)[4]. During my article, I will use the term spent mushroom substrate or the abbreviation SMS.

The top 3 mushroom producers are China 5,150,000; Italy 785,000; USA produces 388,450 MT of mushrooms[5] (all numbers are metric tons).

What to do with spent mushroom substrate?

There aremany exciting areas SMS can be applied[6].

Bioremediation (Air, water, soil, pesticides)
Crop production (greenhouse crops, field crops, general soil amendment/fertilizer, nursery, and landscape)
Cultivation of mushrooms (casing material, cultivation substrate)
Food for animals and fish
Disease management
Renewable energy
Enzyme recovery (e.g. α-Amylase, Laccase, Xylanase)[7]

For thepurpose of this article, I will only focus on the cultivation of mushrooms. Iwill show you how to use it as a substrate source.

But thereis no free lunch.

SMS possesses some agronomic disadvantages to its possible further use in horticulture or agriculture. Principally, it has high salt content, and if incorporated into land at high application rates or utilized in too high a quantity in a growing medium, it inhibits plant growth[8].

A study on the mean composition of SMC from Ireland, the Netherlands, and the United States reported that the content of nitrogen is considerably high; however, the amount of readily available nitrogen in the form of nitrate and ammonium is small.

In contrast to nitrogen, phosphorus is water-soluble, is readily available to plants, and is the main determining factor in applying SMC to land.

With thatin mind, we can now think about how to reuse mushroom substrate.

How toprepare spent mushroom substrate

Before youcan use SMS, you have to prepare it. But what is the right way to do it?

During myresearch, I found the following process, which is used for Pleurotus spp.:

Process for Pleurotus spp.

Mechanical shredding
Drying
Adding substrate
Adding supplements
Mixing
Bagging
Sterilization
Cooling
Inoculation
Incubation
Fruiting

If you aregrowing Agaricus and you want to use SMS as part of your casing layer than thisprocess can guide you:

Process for Agaricus spp.[9]

Mechanicalshredding
Pilingfor 14 weeks
Turnoverevery 14 days for 10 weeks
Addingsubstrate
Mixing

Is it possible to grow mushrooms on spent substrate?

By now, you should know the answer. Absolutely. SMS is considered a nutrient-rich source for mushrooms[10].

If so, whatresults can you expect if you are using SMS?

In thefollowing section, I will show you examples from several studies obtained fromapplying spent mushroom substrate. We first take a look at Pleurotus spp. andthen Agaricus spp.

Growing Pleurotus on spent mushroom substrate

In the first study done back in 2012, the researcher mixed spent mushroom substrate (from Pleurotus) with wheat straw (1:1), calcium sulfate, and calcium carbonate. They pasteurized the mixture at 60-65°C for 8 hours and applied either Calprozime®, Champfood®, or Promycel® 600 to it.

As the results (Fig. 1) are showing, adding one of the three supplements to the mixture helped to increase not only the overall biological efficiency but the biological efficiency for the 1st flush.

Second, the biological efficiency of all three mixtures was similar to commercial control. That’s not bad at all for reusing your current substrate.

Can you reuse spent mushroom substrate? (1)

Figure 1: Influenceof different supplements added to spent mushroom substrate on the biologicalefficiency of Pleurotus ostreatus[11]

In the next study, the author used spent shiitake mushroom substrate to cultivate Pleurotus sajor-caju (actuallyLentinula sajor-caju).

While doing the research, the author found out that “85% of the original hemicellulose, 44% of the original cellulose and 77% of the original lignin was not consumed during the production of a full crop (78% biological efficiency) of shiitake[12]”.

With thesenumbers in mind, we now can understand why reusing spent mushroom substrate isa good strategy. To work, you don’t need that much additional substrate orsupplementation.

For this study, the author used 14,528 g SMS (45 % moisture), 785 g white millet (12 % moisture), 785 g wheat bran (12 % moisture). He then added soybean (12 % or 24 %) and or calcium carbonate (1 % or 2 %) to the mixture.

The results are speaking for themselves (Fig. 2). To get the most out of your SMS, you have to add supplements to it. The best result was achieved by adding 12 % soybean and 1 % calcium carbonate.

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Figure 2: Effect of different substrate types of spentShiitake substrate mixture with white millet and wheat bran supplemented withsoybean and calcium carbonate on the biological efficiency of Pleurotussajor-caju[13]

Growing Agaricus on spent mushroom substrate

Thefollowing study used SMS as part of the casing layer[14]. This layer is needed toinitiate pinhead formation.

The authors mixed the SMS either with vermicompost, sunflower seed hulls, peat Sphagnum peat moss, or brewery residues.

According to figure 3, the best result was achieved by adding sunflower seed hulls and brewery residues (70:30) to the spent mushroom substrate.

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Figure 3:Effect of Pleurotus spent mushroom substrate with different amendments on thebiological efficiency of Agaricus blazei[15]

Many studies “have shown that it is possible to produce A. bisporus on NCS and that yields may be equal to or exceed those on traditional Phase II compost[16].”

The authors continue, “however, to date, A. bisporus is not produced commercially on NCS. The economic feasibility of producing A. bisporus on sterilized NCS remains to be determined, and the most economical and productive processes for producing mushrooms on this substrate are still evolving.”

What do the authors mean by NCS? NCS stands for non-composted substrate.

In their study, the authors used the following formulafor the casing layer:

Oak sawdust (28 %), millet (29 %), rye (8 %), peat (8 %), ground alfalfa (4 %), ground soybean (4 %), wheat bran (9 %), and CaCO3 (10 %).

Supplements: Target® (T) or soybean meal (SM)

But they varied not only the type of the substrate butalso the time of supplementation. To understand the next chart (Fig. 4) here isthe legend:

Substrate: SMC (S), NCS (N); PIIC (P)

Timing: Spawning (S), Casing (C)

Supplement: SM (S), Target®(T)

Therefore, SCT stands for SMC + Casing + Target®.

Interestingly the combination PSS (PIIC, Spawning, SM) didn’t produce any mushrooms. On the other side, the combination NCT (NCS/SMC, Casing, Target®) produced with 144 % the highest biological efficiency.

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Figure 4: Impact of non-composted substrate &spent mushroom compost on the biological efficiency of Agaricus bisporus (1^st.letter: substrate, 2^nd letter: timing, 3^rd letter:supplement)[17]

To understand the influence of the timing better, let’s take a look at figure 5. The best time to add the supplement is at the casing phase. Doing so will increase the B.E. by 25 %

Can you reuse spent mushroom substrate? (5)

Figure 5: Influence of the timing of thesupplementation on the biological efficiency of Agaricus bisporus grown ondifferent substrate (SMC, NCS, PIIC).[18]

Besides the timing, we see a difference between the two supplements. The supplement Target® increases the B.E. by 25 % in comparison to the SM supplement (Fig. 6).

Can you reuse spent mushroom substrate? (6)

Figure 6: Influence of the supplement on the biological efficiency of Agaricus bisporus grown on different substrates (SMC, NCS, PIIC).[19]

The nextstudy helps us understand the influence of various parameters of the casinglayer on biological efficiency. The authors mixed spent mushroom substrate withcoconut fiber pith in different ratios (Fig. 7). They also added calciumcarbonate (100 g/L) to the mixture.

As figure 7 indicates, not all combinations could get close to the control batch, but some did.

The second thing that stands out is that only one mixture with spent mushroom substrate reached a similar B.E. than the control.

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Figure 7: Impactof different casing materials of SMS on the biological efficiency of Agaricusbisporus[20]

Tounderstand these results, let’s take a closer look at figure 8. In this figure,we see the correlation of different parameters of the casing layer and thebiological efficiency (B.E.).

This chart underlines what I wrote in the beginning. Spent mushroom substrate (SMS) contains a lot of salt, which will lead to a higher electrical conductivity (EC).

As the EC has a negative correlation with the B.E. adding to much SMS to the casing layer will reduce the B.E.

With that inmind, we now understand the results of figure 7 better. While the firstmixtures with SMS (5:0 and 4:1) are still leading to a high B.E., the nextmixture with a ratio of 3:1 resulted already in a lower B.E.

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Figure 8: Correlationbetween different parameters and the biological efficiency of Agaricus bisporus[21]

Regulationsconcerning spent mushroom substrate

As I showedyou in the last two chapters reusing of spent mushroom substrate (SMS) ispossible.

When it comes to SMS itself, there are several things, especially regulations concerning this topic. In the next short paragraph, I will give you some head start. Still, please check your national and regional legislation to avoid any negative consequences as this article is only for educational purposes only and not legal advice. Especially because there are too many different regulations (Fig. 9) out there and I by no means a lawyer.

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Figure 9: Summary of controls and regulations concerning spent mushroom compost (SMC) disposal in the United States, the Netherlands, the United Kingdom, Canada, and Ireland.

The authorof this study[22]mentioned the following aspects:

SMC management policies

Except for the US, none of the studied countries [US, Canada, Netherlands, UK, and Ireland] has special or standard legislations that are specifically enforced for the correct management of SMC immediately after cropping.

Disinfection before disposal

Recommendeddisinfectants for disease control following cropping are [..] variableworldwide and, in some cases, are not applied and/or not legislated.

Storage of SMC

Formushroom growers who organize SMC removal as soon as it is produced, permanentstorage facilities are not mandatory on the farm. However, for the majority ofproduction units, temporary or permanent SMC storage facilities are required asthe land-spreading of waste materials is generally prohibited for the wintermonths.

Utilization of SMC

Utilization confines exist for diverse end-uses of SMC. The factors that determine the further use of SMC in agriculture or horticulture include nutrient and salt content, substrate maturity, water-holding capacity and the presence of weed seeds, insects or pesticides (Anonymous, 2004a).

As I saidearlier, please check if any regulations concerning these points or others areapplying to you. To do so, you can, for example, use the next figure 10, whichillustrates the handling of spent mushroom compost (or substrate) within onecountry as a guide. But it doesn’t replace talking to a lawyer.

Can you reuse spent mushroom substrate? (10)

Figure 10: Authorizedsituations for spent mushroom compost (SMC) under residual waste regulations(adapted from Anonymous, 1997b) (MFEMP, mushroom farm environmental managementplan)[23].

Now I want to hear from you:

What do youdo right now with your spent mushroom substrate?

And did youget excited reusing your spent mushroom substrate while reading my article?

Let me know by leaving a quick comment.