Uniformity of Spent Mushroom Substrate (SMS) and Factors in Applying Recommendations for Use

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Abstract
SMS may be obtained from a number of locations and from crops produced in different ways. Consequently such material may be variable in terms of physical structure and chemical analysis. This is important when choosing blends of material for subsequent reuse, including recomposting. Ranges for maximum and minimum values of plant nutrient properties of fresh SMS are outlined. In particular, pH (8.2-7.3), conductivity (2,380-1,410 μS cm−1) and C:N ratio (9-15:1) each vary from sample to sample. Nitrogen availability varies both in terms of organic- and inorganic-N and in the ratio of nitrate-N to ammonium-N. This appears to be a function of duration of cropping and subsequent storage conditions. Methods for determination and interpretation of plant nutrient content of SMS are discussed. The need for greater standardisation of salt extraction procedures and presentation of published data is discussed. Changes in composting procedures and Agaricus bisporus substrate recipes demand continuing research into the biology, potential uses and economics of SMS.