Is your compost moisture on target?
We’ve said it before, but mushrooms are basically water in fancy packaging. With water making up at least 90% of what you’re selling, it’s important to get substrate moisture levels right.
Approximately two-thirds of the water in first flush mushrooms has come from the compost. As the crop cycle continues, water is increasingly drawn from the casing. Yet the underlying compost remains a vital source of water as well as nutrients.
MushroomLink recently spoke to Robert Tolson of Premier Mushrooms about the importance of getting compost moisture right. He also provided some practical tips on how to measure moisture in compost.
Identifying bacteriophages in mushroom compost
Bacteriophages may not be alive, but they are the most abundant biological agents on earth.
Bacteriophages are viruses that attack bacteria. The classic image of a bacteriophage looks a bit like a lunar landing module, with a capsid 'head' containing genetic material, collar and sheath, and a set of “legs” that attach to the bacterium’s surface. These (larger) phages have double stranded DNA genomes. However, others are simply a single, filamentous strand of coated DNA or RNA, or a tiny capsule.
Despite their abundance, bacteriophages are little studied. This is most likely because it is very difficult!
University of Sydney PhD candidate Rebecca Martin has taken on the considerable challenge of isolating and identifying bacteriophages present in mushroom compost.
Exploring the effects of fatty acids in mushroom compost
Just as for humans, in mushrooms fatty acids are precursors to hormones, involved in membrane function and many other purposes.
While mushrooms are low in fat, they contain many essential fatty acids, including relatively high levels of PUFAs. There is evidence from more than 50 years ago that adding oilseeds rich in fatty acids to compost increases mycelium vigour and yield.
Sarah Faulina, originally from Indonesia, is now one year into a PhD examining the effects of fatty acid supplements in mushroom compost. She aims to discover the mechanism by which fatty acids increase growth of the Agaricus mycelium. The overall objective is to achieve the same increases in yield as from oilseed supplementation, but at less expense.
Growing beyond peat: the PEATLESS consortium
A new European consortium has launched the PEATLESS project, aimed at accelerating the transition to sustainable growing media with significantly reduced peat content. With the tagline #lesspeat, the initiative will develop, test and promote low-peat blends tailored for three key horticultural sectors: mushrooms, seedlings, and ornamentals.
Coordinated by the Technological Research Centre for Mushrooms of La Rioja (CTICH), the project brings together 12 partners from four countries — including research institutes, universities, industry players and policy makers.
Backed by €4.2 million from Horizon Europe and the Swiss State Secretariat for Education, Research and Innovation (SERI), the consortium will run from 2025– 2028.
Final report summary: Alternate casing substrate – providing review of research to date and an expert forum for future R&D investment (MU22009)
We've pulled together a concise two-page summary of the Alternative casing substrate - review of research to date and expert forum for future R&D investment project to make key insights from the full Hort Innovation final report easier to access.
The summary highlights the objectives, methodology, key findings, and recommendations to help the Australian mushroom industry respond proactively to a deep dug casing phase-out, giving growers a clear pathway toward sustainable, locally sourced casing alternatives.
This summary also includes a link to the full final report.
Fact sheet: Air porosity and moisture in compost
Balancing air and moisture in compost is crucial for optimal mushroom growth. This fact sheet explores how air-filled porosity (AFP) and bulk density impact compost quality, mycelium development, and water availability. Learn about the key factors influencing AFP, the role of different straw types, and how compost structure affects yield throughout cropping.
Studying the microscopic metropolis
Dr Michael Kertesz and Dr Meghann Thai, together with Honours project students, have been studying the microbiological goings-on inside mushroom compost, seeking to understand species diversity and richness, nutrient pathways, nutrient inputs/losses and a whole lot more. These comprehensive investigations have yielded a wealth of data that provides valuable insights into the diverse, rich, and varied processes taking place in compost. By understanding processes that are invisible to the naked eye, this research opens a window into their complexity and significance.
The Future of Casing
As the future of imported casing material is uncertain, a recent Hort Innovation levy-funded project reviewed the viability of existing alternatives and new research into future materials.
As the future of imported casing material is uncertain, a recent Hort Innovation levy-funded project reviewed the viability of existing alternatives and new research into future materials.
Lignin Removal
Once upon a time, Agaricus mushrooms were just another fungi, albeit widely distributed. They grew from Alaska to the Congo, and from coastal grasslands to mountain forests. This adaptivity was due in part to their natural diet, which was based on partially degraded leaf litter and other organic materials in soil. Farmed Agaricus feeds primarily on wheat straw, degrading the tough celluloses, hemicelluloses (xylan) and lignin that together form plant cell walls. One key purpose of composting is to strip away straw’s waxy cuticle and start to break down the linkages between carbohydrates and lignin, making these materials easier for the mycelium to digest – as would have occurred in the natural environment.
Once upon a time, Agaricus mushrooms were just another fungi, albeit widely distributed. They grew from Alaska to the Congo, and from coastal grasslands to mountain forests. This adaptivity was due in part to their natural diet, which was based on partially degraded leaf litter and other organic materials in soil. Farmed Agaricus feeds primarily on wheat straw, degrading the tough celluloses, hemicelluloses (xylan) and lignin that together form plant cell walls. One key purpose of composting is to strip away straw’s waxy cuticle and start to break down the linkages between carbohydrates and lignin, making these materials easier for the mycelium to digest – as would have occurred in the natural environment.
Testing the effects of nitrogen
Project MU17004 (Optimising nitrogen transformations in mushroom production), led by Professor Michael Kertesz at the University of Sydney, aims to understand the influence of soil microbes on nitrogen transformations occurring in compost and casing during mushroom production. The objective of this ongoing project is to optimise nitrogen management, reducing losses from compost and improving yield and quality.
Project MU17004 (Optimising nitrogen transformations in mushroom production), led by Professor Michael Kertesz at the University of Sydney, aims to understand the influence of soil microbes on nitrogen transformations occurring in compost and casing during mushroom production. The objective of this ongoing project is to optimise nitrogen management, reducing losses from compost and improving yield and quality.
Balancing air and moisture within compost
What is the academic/technical knowledge around ventilation within the compost matrix during cropping and its effect on mycelium growth and mushroom yield? We know through experience that the 'right' structure and density of the compost in the growing containers is important, but we have no measures or even consistent data about the goals we are aiming for.
What is the academic/technical knowledge around ventilation within the compost matrix during cropping and its effect on mycelium growth and mushroom yield? We know through experience that the 'right' structure and density of the compost in the growing containers is important, but we have no measures or even consistent data about the goals we are aiming for.
MushroomLink fact sheet: Nitrogen and compost
What is the role of nitrogen in compost, how does it transform or ‘get lost’ from Phase I through to cropping, and what are the key considerations when adding compost to boost nitrogen in the substrate?
Alternative casings and a sustainable mushroom industry
Mushrooms are a low impact food. As vertical farms, their land footprint is small, and energy and water inputs into mushroom crops are much lower than comparable foods. Consequently, mushrooms have an excellent CO2eq rating. This ‘green’ image, coupled with great taste and an ever-growing list of health benefits, weaves a sweet narrative of mushrooms as a sustainable food source for a growing world population. There is just one little snag. Casing, or more specifically, peat casing.
Poultry litter - More than just a nitrogen source
The well-documented cholesterol-lowering effect of oats has been certified by nutritional regulators
globally since the late 1990s. Subsequent studies and clinical trials have shown consistent results that confirm, and even boost, the original claims. This high-level health claim has driven an increase in the consumption of oats globally1. Beta-glucan, the compound responsible for lowering cholesterol, is famously present in oat and barley grains. However, its presence in mushrooms is less well known.
Feeding mushrooms - The ‘ins’ and ‘outs’ of nitrogen in mushroom compost
While protein is a valuable portion of the dry matter (DM) in mushrooms, its content is quite variable, ranging from 14-30%. Dry matter itself ranges from a low as 7% up to 14%. High DM content and, therefore, high protein content, is associated with firmer mushrooms and improved shelf life.
MU17004 - Optimising nitrogen transformations in mushroom production
Key Delivery partner: The university of sydney
This project will ultimately help mushroom growers to optimise the rate and timing of nitrogen additions, to achieve maximum yield and nutritional value.
The project team are currently exploring the fate of nitrogen used in mushroom production and composting, including developing a better understanding the microorganisms that are involved in transforming the nitrogen that is added throughout the mushroom production process into other forms. They are also looking at ways and timings to maximise nitrogen use efficiency and promote nitrogen retention for composting, and more. A best practice guide for growers will be produced out of the project findings.
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This project explores the fate of nitrogen in mushroom compost and mushroom production, allowing growers to optimize the rate and timing of nitrogen additions to achieve maximum yield and crop nutritional value. Work in the current project period has focused on the timing of supplements added to compost during cropping, and on the efficacy of microbial inocula added during spawn run in promoting mycelial growth.
Supplementing crops with nitrogen immediately before each flush provided an increased yield of about 7 per cent, with much of this increase occurring in second flush. The nitrogen content of mushroom caps and stipes was found to be significantly enhanced in mushrooms from second and third flush, which contained 7-8 per cent N (dry wt) compared with 4-5 per cent N (dry wt) in first flush mushrooms. Similar results were found on a commercial farm, suggesting that late-flush mushrooms may be described as “high nitrogen” versions of the crop.
Test of mycelial growth promotion with combinations of abundant compost bacteria including Pseudoxanthomonas, Bacillus and Chelatococcus revealed that stimulation of mushroom growth was dependent on co-inoculation with the dominant fungus Mycothermus (formerly Scytalidium). Work is continuing to establish the effect of these treatments on crop yield.
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Since the last project update, work has focused on completing an overall nitrogen balance for mushroom composting and cropping, reviewing alternative nitrogen sources for Australian composters, and designing and testing microbial consortia for compost inoculation.
Detailed measurements taken during Phase 2 of composting showed nitrous oxide production much lower than expected, and ammonia released by the compost largely reabsorbed. Major loss of nitrogen during composting therefore occurs primarily during Phase 1, partly as leachate and partly as ammonia release.
Calculating an industry average for these losses is difficult because of variation in the proportion of recycled leachate used by different composters for straw wetting. Further limitations to nitrogen balance calculations were identified in the overall mass losses experienced by all composters.
Possible alternative nitrogen sources for the Australian mushroom industry were reviewed, focused on agricultural by-products already tested overseas. The need for an up-to-date inventory of the types, quantities, and localities of agricultural and food production by-products was highlighted. Local availability is particularly important in establishing test experiments for these feedstocks.
Ten bacterial taxa were identified as potential consortium for compost inoculation. The dominant genera are Pseudoxanthomonas, Chelatococcus, Chelatovorans, Thermus and Thermobacillus. These will be combined with Mycothermus, the dominant fungus in Phase 2 compost, for stability and functionality testing.
While some impact due to COVID-19 restrictions disrupted research progress, the team continues to work to mitigate any delays.
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Since the last project update, a survey of 10 Australian mushroom composting facilities across four States has been completed. It included a comparison of composting management processes and compost bacterial activity. The results delivered initial insights to inform the selection of compost yards for further nitrogen management analysis.
The survey revealed that an average of 10 per cent of input nitrogen is incorporated into the mushroom crop, and about 20 per cent of the total is lost as leachate or nitrogen-containing gases. Nitrogen losses also occur from the compost and casing during cropping. To better understand this process, two cropping trials have been established in the Marsh-Lawson Mushroom Unit. Analysis has unfortunately been delayed due to Covid-19 impacts.
The team have isolated specific microorganisms from high temperature composts, with the dominant strains identified by DNA sequencing and characterised. Interactions between the two main compost fungi (Mycothermus thermophilus and Agaricus bisporus) and the dominant Phase 2 bacterial taxa (Pseudoxanthomonas spp) have been examined in more detail. Due to the high relevance of these bacterial taxa, their entire genetic sequence has been determined, with analysis of their functional capabilities ongoing.
The compost isolate collection contains 175 isolates of 58 different species. This is now sufficient for the design of potential compost inoculation treatments aimed at optimising the composting process.
The reporting period coincided with Covid-19 related work and travel restrictions, resulting in considerable disruption to research progress. The team will continue to share results with industry as opportunities become available.
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The project team commenced work in January 2019 and have already isolated and characterised a substantial collection of bacterial strains taken from a range of Australian compost yards in New South Wales, Victoria, South Australia and Tasmania. These samples represent the dominant cultivable bacteria in composts and will underpin the rest of the project.
Many of the most prevalent strains identified were very similar, despite coming from different geographical areas, confirming the conserved biological nature of mushroom composting across Australia.
Analysis of the composts revealed that many of the dominant species have not yet been captured in the strain collection. These are now being targeted using specifically designed growth media and selective conditions.
A detailed survey regarding current nitrogen management by Australian composters was started, with field trips to facilities in Victoria, New South Wales and South Australia, and visits planned to Queensland. The results of this confidential survey will be used to identify composting yards that represent the diversity of processes in the Australian industry, informing the project’s detailed nitrogen balance studies.
ACT NOW
Read an overview of the project in this article, Optimisation of nitrogen use in mushroom production, published on pages 34-35 in the spring 2019 edition of the Australian Mushrooms Journal.
Project outputs:
Australian Mushrooms Journal, Spring 2019 edition page 30
MU17006 - Developing a database of bio-markers for compost quality control to maximise mushroom production yield
Key delivery partner: The University of Sydney
The quality and yield of button mushroom crops are critically dependent on the quality of compost used. Beginning in June 2019, this investment is exploring how microbial populations within compost can be used to understand, measure and manipulate compost quality.
The project team’s work involves investigating microbial populations across a range of mushroom composting facilities. This includes looking at the microbial population dynamics at different points along the composting timeline, how they align with other compost quality indicators and correlating everything back to mushroom crop yield and quality.
The research will culminate in a database of compost ‘bio-markers’ (microbe indicators) for the industry, which will be able to be used to assist in maximising productivity and crop outcomes.
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Progress in this project was severely impacted by the COVID-19 lockdown in the second half of 2021, and work in this period was therefore limited to software development and training.
Sample collection at participating compost yards for the feasibility study recommenced in December 2021, and was completed by April 2022.
These samples represent a time-course from three successive crops at four independent mushroom composting facilities across New South Wales, Victoria and South Australia. Analysis of chemical compost quality markers in these samples (pH, moisture, total C and N, soluble C and N, microbial biomass, humification index, nitrification index) is nearly complete, and the microbial community analysis of these samples has been completed.
The results indicate good reproducibility between compost crops at Phase II but considerable variability between individual crops at earlier stages of the composting process, and this will be used to inform the design of the full scale compost biomarkers study.
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Since project commencement, progress has been severely impacted by COVID-19 travel restrictions, leading to a temporary pause in research activites.
Restarting in January 2021, the team focused on developing effective and reproducible compost sampling strategies.
The initial phase worked to assess changes in microbial diversity and other compost quality parameters in three successive compost crops from yards in three different States. With sampling almost complete, the analytical methods required for analysis have been optimised.
The results from this study are now being used to prepare methods for a much larger one-year study.
Project outputs
Australian Mushrooms Journal, spring 2019 edition page 32
Australian Mushroom Industry - Can nitrogen be better managed in compost production
Button mushrooms contain high levels of minerals, vitamins and antioxidants, but are also an excellent source of protein. With 19 - 35% protein per gram of dry weight, they contain more protein than rice (7.3%), wheat (13 %) or milk (25%), and the high content of essential amino acids also means that button mushroom proteins are 90-98% as nutritious as most meat protein.
The nitrogen required to build these proteins comes from the compost, partly from raw materials such as manure, and partly from supplements added later in the process. The carbon:nitrogen ratio in the starting compost mix is usually set to between 30:1 and 35:1, which is optimal for growth of the microbes that convert the straw into productive compost, but only about 12-15% of this nitrogen finishes up in the mushroom crop that goes to market.
This webinar will discuss how nitrogen is transformed into mushroom protein during composting and cropping, where losses occur, and how changes in starting materials or composting processes might be used to increase compost productivity and the nutritional value of the mushroom crop.
Recycled organics as an alternative to peat in mushroom casing
The Australian mushroom industry uses approximately 25,000 tonnes of peat casing every year. Mostly imported from Europe or Canada at a cost of $300 per tonne, peat is both an expensive and limited resource.
Compost made from recycled organics is locally available and cheaper than peat.
Join Adam Goldwater from Applied Horticultural Research for a webinar where he will present the results of the recent trials of commercially viable white mushroom crops cased with blends of composted recycled organics and peat.
This is a Waste Less Recycle More initiative funded from the waste levy.