White button mushrooms are an important crop globally, and due to the role of peat in current cultivation practices, the industry is under increasing pressure to find suitable alternatives. Peat functions as “casing”, a surface layer that, amongst other functions, provides available water to the fungal mycelium and is considered essential for mushroom growth. This research aimed to determine the potential of bark as an alternative casing material and its suitability for commercial mushroom production. Two experiments were conducted, comparing two types of commercially available peat casing with bark-based casings. The bark casing in Experiment A was found to be statistically similar to the peat casing in terms of yield and quality. The two bark casings in Experiment B failed to produce a 1st flush of mushrooms, and total yields were significantly lower compared to the peat casings, highlighting the fact that the consistency of the bark material across both experiments was variable. There were several issues associated with the bark casing, which included water stress and cropping delays, all of which would be unacceptable from a commercial perspective. Further research is required to refine bark-based casing, focusing on a better consistency of the bark feedstock and reduction of contamination risk. This work contributes to ongoing research and development to address the dependency of mushroom production on peat.

Current mushroom (Agaricus bisporus) cultivation practices use peat, an environmentally costly resource. Peat functions as a water reservoir, supporting mycelial growth and mushroom formation. There is a knowledge gap in characterizing the physical attributes of alternative materials; conventional methods are destructive and often imprecise. This research aimed to determine, over time, the physical properties of peat and two bark-based alternative casing materials using X-ray computed tomography as a novel, high-resolution approach. A microcosm culturing technique was developed to facilitate scanning. A series of scans was taken at key growth stages to assess the dynamic changes that occur within the casing over the course of a mushroom production cycle. Measurements of porosity, pore surface area and pore size distribution revealed significant differences between peat and bark-based alternatives in addition to capturing the changes within each casing material over the mushroom production life cycle. Peat was found to have greater average pore size than bark-based treatments, and this divergence in pore size distribution increased significantly between treatments over the time frame of the experiment. A significant finding of the research is that relative increases in the air-filled porosity of different casing materials may be a useful predictor of casing media performance.

Wood fibre, uncomposted bark and windrow-composted bark were tested in two replicate experiments at amendment rates of 30, 50 and 70 % v/v with commercial peat-based mushroom casing. Their performance in terms of crop yield and mushroom quality was compared to an industry standard peat-based control. Hydro-physical behaviour (i.e. matric potential) between casing treatments was monitored during the crop by recording matric potential (Ψ_m) using solid-state tensiometers. Emerging and developing mushrooms utilised casing-contained water resulting in decreasing Ψ_m during a 'flush'. Differences in the magnitude and duration of Ψ_m evolution between treatments were correlated to mushroom cropping performance and quality metrics. Wood fibre treatments closely matched peat-based controls in water availability and crop timing, with Ψm values showing a similar rate of decrease over each flush (not exceeding -34.4 kPa). Class A mushrooms from these treatments were likewise indistinguishable from the controls in yield and quality. Conversely, bark-based casings diverged from peat-based control treatments with their timing and water dynamics strongly influenced by management conditions such as case-run length. Increasing rates of bark addition in some instances was correlated with incrementally delayed cropping (by as much as 4 days relative to control treatments). Additionally, the comparatively open pore-structure of bark containing treatments resulted in poor water retention, overpinning (during 1st flush) and pore-structure degradation over time, requiring careful crop management. A lack of available water occurred within these casing treatments (particularly in Trial 1, flush 2), was evidenced not only by the slow development of water-stressed mushrooms (e.g. premature opening, split stipes), but was also correlated with a pattern of stalling or halted Ψ_m evolution, as cropping progressed. Water stress in these casing treatments ultimately led to a higher relative proportion of Class B graded mushrooms. Averaged over two trials, Class B mushrooms constituted 53 % and 47 % of the total yield for uncomposted and composted bark respectively. Comparatively peat averaged just 24 %. In order to maintain yield, crop timing and stagger similar to that of commercial peat-based casing, peat-amended treatments must demonstrate similar expression of hydro-physical behaviour as well as an ability to retain structure over repeated flushing and watering cycles. Herein, it is demonstrated that sensor-monitored Ψ_m evolution coincides with substantial variation in the growth and progression of the crop and consequently in the yield of harvested mushrooms.