The cost of buying sawdust is rising. A cheaper alternative would be sugarcane bagasse. **But can sawdust be replaced by sugarcane bagasse?**

How will sugarcane bagasse affect the number of days to spawn run, number of days to primordia formation, and number of days to harvest? How will it affect the number of fruiting bodies, yield, and biological efficiency?

To find out,** we have to run an experiment** in which we replace parts of sawdust with sugarcane bagasse and compare the results with each other.

The author of today’s research article used **100% sawdust** supplemented with **5% rice bran** amended with **1.5% calcium carbonate** for **control** (Fig. 1). He **replaced 25% and 50% of the sawdust** for the other mixtures **with sugarcane bagasse**. Supplementing with rice bran and calcium carbonate stayed the same.

To prepare those mixtures for sterilization, he bagged them. **The sterilization itself is done at 100°Cfor 8 hours**. After the cooldown, he inoculated the bags with 10g or 1,3% with a Pleurotus ostreatus strain and kept them in the dark.

The mycelium took **30 days to colonize the control substrate** (Fig. 2). Replacing **25% of the sawdust** with sugarcane bagasse reduced the time to **25 days**. But replacing a total of **50% increased** the number of days to spawn run **to 29 days**.

The bags were then transferred into the grow room to start the fruiting.

Unfortunately, the author did not provide any parameters for the cultivation phase. But he gives us the time to form the primordia and the time to the first harvest.

Regarding the **primordia formation**, it took **four days** if he used **100% sawdust** (Fig. 3). Replacing** 25%** of it with sugarcane bagasse **did not change the time**. But if he replaces** 50%** of it, it takes only **one day** for the primordia to form.

When it comes to the** time for the first harvest**, it takes another **four days** if we use **100% sawdust** (Fig. 4). This **time can be cut in half** if we replace **25%** with sugarcane bagasse. But replacing **50%** of it increases the time back to **four days**.

The **numbers for the first harvest** look like the following (Fig. 5). **100% sawdust 38 days**, **75% sawdust 31 days**, and **50% sawdust 34 days**.

Keep these time frames in mind, as we need them later.

Now that we understand the influence of the sugarcane bagasse on the cultivation cycle let us look at its effect on yield and biological efficiency.

Regarding the yield, we find that **100% sawdust produces 50g per bag** (Fig. 6), corresponding to a biological efficiency of 56.3%. Replacing **25%** of it decreases the yield to **41g per bag** or a biological efficiency of 45.1%. But replacing **50% **of the sawdust with sugarcane bagasse does not reduce the yield even further. So with a 50-to-50 mixture, we get **41g per bag** again.

Now the big question is, is it worth it?

The author concluded that rubber tree sawdust mixed with sugarcane could be an alternative substrate even though sawdust produces a higher yield.** The author did not provide evidence of the sawdust’s significance**. If there is no statistical difference, it does not matter which of the three substrate formulas you would use. All of them would give you a similar result.

Besides not mentioning any evidence, he did not say anything about the duration of the harvest and how many flushes each substrate formula produced. With this information missing, can we still find out if replacing sawdust with sugarcane bagasse is a good idea?

Yes, we can!

To do so, **we have to make the following assumptions**.

- There will be only one flush.
- We will extend the time frame from one harvest to a full year. Meaning we can cultivate mushrooms year-round.
- The cost of rubber tree sawdust is RM 690/ton, and
- sugarcane bagasse is RM 450/ton.
- The selling price is RM 4.5/200g.

With these assumptions, we can now calculate the profit and loss for each substrate formula (Fig. 7). Let us start with **100% sawdust**. It takes **38 days** for the first harvest. Leading to a total of roughly **10 harvests per year**. If each yields 50g per bag, **the total yield** comes down to **500g per year and bag**. The **total cost** for our 10 bags is **RM 3.38 ($0.75)**. If we can sell our mushrooms for RM 4.5 ($1) per 200 g, we can expect **total revenue of RM 11.25 ($2.5)**, giving us a **P&L of RM 7.87 ($1.75)**.

Using **75% sawdust** and 25% sugarcane bagasse gives us the following numbers. It takes **31 days** for the first harvest. Leading to a total of roughly **12 harvests per year**. If each yields 41g per bag, the **total yield**

comes down to **492g per year and bag**. **Total costs** are **RM 3.35 ($0.74)**. **Total revenue** is **RM 11.07 ($2.46)**. **P&L of RM 7.72 ($1.72)**.

Replacing 50% of the **sawdust **with sugarcane bagasse led to the following numbers. It takes 34 days for the first harvest. Leading to a total of roughly **11 harvests per year**. If each yields 41g per bag, the **total yield** comes down to **451g per year and bag**. **Total costs RM 3.40 ($0.76)**. **Total revenue RM 10.15 ($2.26)**. Given us a** P&L of RM 6.7 ($1.50)**.

With these numbers side by side, we can now better judge whether we should replace sawdust with sugarcane bagasse.

While replacing 50% seems to be fine, **replacing 25% is the way to go**.

**But to make the final decision, we must factor in more variables.**

**If we have shorter production cycles we have to run the sterilization unit more often.** Second, **the more harvests and sterilization, the more labor is needed**. These variables can change decision-making.

What also influences decision-making is improving in the following areas.

**For the author**, these were **particle size**, **C/N ratio**, **pH value**, and **moisture content**. **For me**, it comes down to the **sterilization method** and the **inoculation rate**. This means that while the author focuses on

the substrate, I focus on its treatment. Speaking of the treatment of sugarcane bagasse.

In this video, I talk about different sterilization methods (see recommended).

Catch you there.

**Recommended**

**Sources**

[1] F Ahmad Zakil et al 2020 IOP Conf. Ser.: Mater. Sci. Eng. 736 022021, DOI 10.1088/1757-899X/736/2/022021, https://creativecommons.org/licenses/by/3.0/