Real-time matric potential dynamics in peat casings amended with wood fibre and bark, and their relationship to Agaricus bisporus yield and quality

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.