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°C
for 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.
 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/