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?
Safe Mushroom – A new food safety code of practice designed for mushroom farms
Mushroom farms that are supplying the major retailers are unavoidably familiar with food safety certification programs. They may be audited to Freshcare, or another base program, with HARPS on top, plus Sedex and – potentially – other retailer-based requirements.
Anyone implementing a food safety standard on farm will know that there are a large number of criteria which have no relevance to mushroom production. For example, DDT used years ago in the bottom paddock will not affect the mushrooms, nor is the crop likely to be contaminated by passing kangaroos or leaking septic systems. Mushroom production is not made unsafe by local flooding (unless there is major damage to infrastructure), and there is no ‘planting material’ to be considered.
Third party audited food safety and quality programs can be expensive to implement and audit, especially for small growers. They include issues which may be only tangentially related to food safety – such as labelling, the potential for food fraud and worker health and safety. Keeping the required records and ensuring compliance can be a full time job for many businesses. While a requirement for supply to some customers, they are beyond the reach of smaller, family based farms.
However, food safety is just as important for somebody growing a few blocks in a shipping container as for a large, high-tech shelf farm. To the consumer, mushrooms are a commodity; they don’t differentiate one farm from another. If a food safety outbreak was to occur, it would affect the whole industry, not just the individual grower.
To bridge this gap, the MU20000 team (Extension and adoption for food safety, quality and risk management) have developed the ‘Safe Mushroom’ standard.
Whereas a standard such as Freshcare includes more than 30 pages of compliance criteria, Safe Mushrooms is just over three. This is because it only includes elements that directly affect food safety of mushrooms.
The aim was to allow small farms to demonstrate that they are following safe practices, without the time and cost of higher-level programs. To do this, the requirements have been kept as simple as possible. Growers essentially need to show that they have:
a. considered potential sources of contamination
b. implemented strategies to reduce risk and
c. kept records where appropriate
Most of these are simply good management practice, so should not impose additional costs on the business.
The team have developed examples of the information required, including farm and production facility maps, a typical operations flow chart for mushroom production, work instructions and risk assessments for growing media and casing. There are also record sheets for activities like chemical application and staff training, as well as scheduling cleaning and pest management.
The next step is to trial the program to check how easy it is to implement, and whether additions or subtractions are needed.
Free training and assistance will be provided. A second party audit will be done remotely by another member of the project team, at no cost to the business.
It should be emphasised that this program does not meet the current supply requirements of the major retailers. However, it will provide a food safety foundation and evidence that a farm is following safe practices.
Note that microbial testing of mushrooms and irrigation water is also available through project MU20000. These test results meet all food safety certification requirements (e.g. Freshcare), not just those of Safe Mushroom.
If you are interested in trialling this new program at your farm, please contact Jenny Ekman jenny.ekman@ahr.com.au or 0407 384 285
Associated Resources:
Mushroom Farm Hygiene video
This video explains the steps of mushroom farm hygiene with special reference to the fungal disease Lecancillium or dry bubble
Poultry litter – more than just a nitrogen source
Poultry litter is surely proof that one person’s waste is another’s windfall. Poultry litter is a highly cost-effective source of nitrogen. It is also a great source of the microbes essential for good compost production.
By Jenny Ekman and Geoff Martin
Poultry litter suitable for compost production is entirely sourced from broiler sheds. Litter is not just manure, but contains bedding material, feathers, blood, and potentially dirt or other materials. Manure from caged birds is less suitable, tending to be wet, sloppy, and low in carbohydrate. Litter from barn-based egg production and turkey manure are not suitable for making compost as they are relatively low in nitrogen.
What goes in affects what comes out
Modern broiler chickens are incredibly efficient converters of feed to body mass – approximately 1.5kg of chicken food produces 1kg of chicken. High feed use efficiency equals less waste, especially of the carbohydrates which nourish microbes during composting.
Despite this efficiency, feed still accounts for up to 70% of the cost of raising chickens. What goes in affects what comes out, so the type of feed used is clearly going to affect the attributes of the manure.
For example, broiler chickens were once fed mixtures of maize and soya, meat meals, offal, feather meal and tallow. However, the outbreak of mad cow disease in the UK focussed consumer concern about feeding meat meal (offal and poultry waste) products to chickens. Modern mixes are predominantly grains (wheat, barley, and sorghum) plus vegetable proteins and oils, vitamins, calcium carbonate, and other minor ingredients. These include enzymes to help the birds break down non-starch polysaccharides in grain.
Moreover, the life of a broiler chicken may be as little as six weeks, compared to 10 weeks a few decades ago. This factor, combined with dietary changes, has reduced nitrogen levels in manure from approximately 5.7% to 3.5%. Modern litter has 30% less phosphorus, as well as lower levels of fats, carbohydrates, uric acid, and enzymes than it once did. In particular, the decline in the enzymes uricase and urease, which break down uric acid, has reduced ammonia levels during Phase I – vital to kick start the breakdown of straw in the first 48 hours of composting1.
While the use of antibiotics in chicken feed as growth promoters and therapeutic agents has been declining, they may still be used by some producers. Such products are not fully metabolised within the bird. They may even be designed to be excreted to avoid contaminating the flesh. Presence of such products in manure could also potentially affect microbial activity during composting.
Bedding materials matter
The type of bedding material used will depend on what is cheap and locally available. For example, rice hulls make an effective bedding material, but availability depends on how much rice is grown, which is largely determined by the cost of water. During the drought rice production fell close to zero, so there were no rice hulls to be had. Sawdust and wood shavings are also used as bedding, however the prices of these materials have increased. The last two years of good rainfall have seen many chicken producers change to wheat straw, which is now readily available.
A 2019 study by AgriFutures Australia2 found that more than 65% of chicken meat producers were looking for alternative sources of bedding materials due to cost and supply issues. For example, wood shavings can cost $22-$40/m3 compared to $10-$15/m3 for straw. The study identified several other alternative litter materials including nut husks, oat hulls, stubble pellets, miscanthus grass, and tree-litter.
The type of bedding material used is likely to significantly alter the C:N balance in the waste product. For example, litter from wood shavings has much lower nitrogen content than that from rice hulls, with clear implications for composting.
Another change due to increased cost/reduced availability of bedding materials is the more frequent recycling of the litter by re-use, layering or mixing. In the past, about 70% of Australian broiler chickens were grown on new bedding, with the remaining farms practicing partial re-use3
In the US, litter may be re-used for up to 2 years before the sheds are fully cleared out. The bedding is windrowed inside the shed, allowing it to partially compost, before re-spreading for the next batch of birds4
Australian growers appear to be also recycling litter, altering both the volume and composition of material available for compost production. This material may have higher nitrogen than single use litter, but also lacks bulk. The result is an increased requirement for straw, which is more expensive than poultry manure.
In conclusion, compost producers need to maintain good communication with their poultry manure suppliers. They need to know if production methods change. The way the chickens are grown will affect not just nitrogen in the litter, but also moisture levels, density, and a multitude of other factors. And that in turn affects the quality of compost produced.
References
1 Martin G. 2022. Poultry manure in mushroom compost production. Dr Mush Advisory
2 Watson K, Wiedemann SG. 2019. Review of fresh litter supply, management and spent litter utilisation. AgriFutures Australia. 128pp.
3 Chinavasagam HN, Tran T, Blackall PJ. 2012. Impact of the Australian litter re-use practice on Salmonella in the broiler farming environment. Food Res. Int. 45:891-896..
4 LeBlanc B. et al. 2005. Poultry production best management practices. Louisiana Ag Centre.
A COMPLEX WEB OF LIFE: BACTERIAL-FUNGAL INTERACTIONS
honours student Shivagami Shamugam
In his book Entangled Life, Merlin Sheldrake imagines the soil as a “horizonless external gut – digestion and salvage everywhere, with flocks of bacteria surfing waves of electrical charge... like the Wild West with all those bandits, brigands, loners, crap shooters… and the seething intimate contact on all sides by fungal hyphae.”
Getting up close and personal to the community of biota within compost reveals a hustle and bustle that could rival Tokyo central station at peak hour. Mushroom compost thrums with life and activity.
The fermented and pasteurised substrates that support mushrooms are home to countless microorganisms, interacting with each other in a series of physiological and biochemical reactions to create ideal growing conditions for the Agaricus mycelia.
Understanding these bacterial interactions in mushroom compost will likely underpin future developments in the industry as it searches for more sustainable sources of substrates.
University of Sydney honours student Shivagami Shamugam has been investigating the status of current research, and opportunities to exploit bacterial interactions, as part of a levy-supported research project with Dr Michael Kertesz. Her review has been accepted (with minor changes) for publication in the Journal of Applied Microbiology – a significant achievement for an honours student. The following attempts to summarise this review.
Review - Improving mushroom whiteness (MU19005)
Surveys of consumers consistently indicate that they prefer mushrooms to have white colour, firm texture, consistent maturity and good flavour. Of these, colour is clearly the top priority, and often the only one that can be easily considered at retail. Presenting clean, white mushrooms to consumers at retail is a proven method of increasing sales. For mushrooms, whiteness signals quality. It may also be assumed to indicate storage life, flavour and freshness.
This review discusses the information available about improving mushroom whiteness. Produced as part of the MU19005 project, funded by Hort Innovation.