The Influence on Yield of Mushrooms (Agaricus bisporus) of the Casing Layer Pore Space Volume and Ease of Water Uptake

Casing is the ‘soil’ layer applied to compost on which primordia known as pins form after airing, a proportion of which develop into mushrooms during several flushes or bursts of growth, usually occurring every six to ten days. Brown sphagnum moss peat casing (SP) was compared with black fen peat casing (BP) and gave significantly higher yields for each of five, potentially high-yielding composts, but a similar yield for a single potentially low-yielding compost. At the end of cropping, BP casing, which had poor structure, had permanently shrunk to a larger degree than SP casing. BP casing was also found more difficult to re-hydrate on the high-yielding composts and from the second flush onwards, these mushrooms had a progressively higher dry matter. This contrasted with those from the SP casing which had a progressively lower dry matter. In Northern Ireland, in the last decade, progressively more BP casing has been used. The likelihood that this has lowered potential yields is discussed.

In another experiment, eight casings were tested on a single compost, four contained 50% SP casing (as used for the control) plus 50% spent-mushroom-compost (SMC) the latter having been eluted with either water or citric acid and then either pasteurized or not. The three casings which comprised eluted SMC only were clay-like in consistency and mixing them with SP casing reduced pore-space. All casings initially contained a similar moisture percentage (v/v); however, during cropping they demonstrated a wide range of resistance to being re-hydrated at watering. This repellence was scored ‘blind’ and found to be inversely correlated with a measure of casing water uptake potential and with the percentage by volume of pore space contained within the casing, both measurements having been made at the start of the experiment. Water repellence was significantly, inversely correlated with mushroom moisture content and with yield. Casing water uptake potential and pore space were significantly correlated with mushroom moisture content and with yield. Yield was significantly correlated with mushroom moisture content and also with the number of primordia developing to pea size.