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Workshop on composting technology

On the 7th and 8th of June, 2004, a workshop on composting technology was organized by Applied Plant Research and the Christiaens Group. In Vught, near Den Bosch, The Netherlands, eighty participants from all over the world discussed different approaches and processes for compost production.

During the workshop, several group discussions were held to elucidate and discuss the issues raised by the speakers. During the plenary forum discussions, all groups presented their thoughts and conclusions to be discussed by all participants.

Malting and composting

The first speaker, Johan Vissenaekens from Heineken Mouterij Albert (Belgium) gave a clear presentation about the effects of variations in ingredients on the malting process. He showed that malt is produced from barley by the malting process in the brewery by the following processes: steeping, germination and kilning.

Since the malting and composting processes are similar in several respects, the approaches applied in the malting process provided new view points for the composting process. Vissenaekens emphasized that the quality of malt is directly related to the quality of barley. Therefore, Heineken Mouterij characterizes before malting various parameters in malt such as protein content, moisture content and enzymatic potential. The strictly controlled process of malting is adapted to each barley variety. To ensure a homogenous quality of malt, products of the malting process can be mixed based on their physical and chemical characteristics.

Substitute raw materials

Ray Samp from the Agari-Culture Consulting Services (USA) gave a detailed description on his experiences on the use of substitute raw materials for Agaricus mushroom compost formulations.

When standard raw materials become unavailable or too expensive, these substitutes among which rye, oat or rice straw, orchard grass, turkey manure and brewer’s grain, can be applied. All regions may have their own cheap resources. Ray Samp showed that these resources require specific modification, pre-treatment, blending, and/or timing of addition depending on the nutritional, structural and economical characteristics.

Outdoor to indoor

David Tolson described the changes in processes when going from outdoor to indoor composting. He showed his experiences at the Tolson company, Elf farms, Australia.

Due to the shorter indoor process, he said, the physical manipulation of the compost is modified to make it homogenous. As a consequence, the scheduling of ingredient addition has been tightened, particularly in the biological phase. Keeping the heaps sufficiently cool is a big challenge in the hot summer conditions. According to their experiences, shorter straw is more easily tolerated with the shorter process. High enough ammonium levels can be reached by using less manure in total when it was dosed later in the process.

Moreover, Tolson stressed that quality control by intensive data analysis proved to be very important. He showed that compost and process parameters are related to the results achieved by mushroom growers. Based on the results, continuously review and selection of useful measurements are made at Elf Farms.


Bert Hamelers, Agrotechnology and Food Sciences, WageningenUniversity (The Netherlands), presented an extensive report on the fate of nitrogen during composting.

Nitrogen is a versatile component, which can undergo a wide series of microbial mediated redox reactions and can have several species with highly different physico-chemical characteristics. The amount of nitrogen should be sufficient in the compost, because it is an energy supply for the micro-organisms and a basic nutrient for mushroom growth.

As regards nitrogen forms, the ammonia levels must be low, while organically bound forms of nitrogen are highly preferred in the compost. Hamelers emphasized that good models are needed to better understand the nitrogen dynamics in order to optimise phase I process and reduce nitrogen emission.


Geert Lemmers (Sylvan, The Netherlands) was the first speaker of the second day of the workshop. He focused on the origin, role and losses of ammonia during composting.

Lemmers also highlighted, that we must understand the processes leading to the conversion of nitrogen to ammonium and ammonia to make cheap and consistent productive compost from batch to batch. Ammonia can originate from inorganic nitrogen sources (e.g. urea or ammonium salts) or organic sources which can undergo the ammonification process. Ammonia can increase pH, break down the wax coat on straw, increase the solubility of polysaccharides and it is also functions as a food for microbes.

The clearing profile of ammonia during composting is related to the raw materials used and their C/N ratio, as well as several chemical and physical characteristics of the process (temperature profile, anaerobia, moisture), the timing of additions and turning, not to mention the influence of microbes.

Finally, Lemmers selected a few points for further discussion wondering whether we can make consistently good producing compost without ammonia.

Microbiology and processing

Gerben Straatsma (Applied Plant Research, WageningenUniversity, The Netherlands) depicted an up to date overview on the latest results of compost microbiology and processing.

Thermophilic Scytalidium varieties possess the largest biomass and create selectivity in the compost. However, the numbers of micro-organisms decline with at least a factor of 100 after spawn run due to the dominating position of Agaricus, which produces inhibitory substances. Agaricus degrades much of the compost when the growing fruit bodies need the nutrients.

Straatsma pointed out the need of further research on many characteristics of the microbiology and physiology of the Agaricus mycelium, like effects of variability in mycelial coherence in Phase-III (after ‘shake up’) and control over primordium formation and patterns in numbers of fruit bodies and flushing. He also underlined our present lack of knowledge in the water absorption and retention characteristics and the effects of load on percolation and air circulation in compost.

Strains and compost

John Kidder from Amycel (USA) reviewed recent comparative analysis on different composts from Europe and the corresponding reaction of hybrid and non-hybrid mushroom strains to these composts. Kidder showed that Amycel aimed to determine a reliable method to easily evaluate the suitability of given compost to a particular mushroom strain.

To evaluate the rate of mycelial colonization of compost, 'race bottles' were successfully used. Cased composting plates can also be used all the way through fruiting to evaluate casing material as well as compost, but measuring growth was difficult in this case. Compost agar plates were hard to prepare and could dilute or remove some negative components of the compost (e.g. ammonia), but were easy to measure. Fusion agar showed the variation between hybrids and non-hybrids but was similar to compost agar in speed and uniformity of growth.

Research perspectives

Finally, Jacqueline Baar from Applied Plant Research (WageningenUniversity, The Netherlands) highlighted the main conclusions and the future research perspectives that appeared in the forum discussions. She underlined the still big lack of knowledge on the effects of the amounts of minerals and vitamins in compost. Diversity and quantities of microbes, in particular of actinomycetes and bacteria in general, are also mostly unknown, as well as the effect of aerobic-anaerobic conditions and other environmental factors on their populations, and the role of enzymes in the composting process. Baar stressed that novel molecular techniques enable us to study microbes in the compost to reconsider the temperature requirements. Since the assessment of the starting materials may result in optimal process, we must define what parameters we need to measure.

Baar initiated an international network of research institutions and companies to address and develop research issues in a consortium which, on the long term, will be more innovating and cheaper than individual actions.

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