Leachate Chemistry of Field‐Weathered Spent Mushroom Substrate

ABSTRACT Passive leaching by rainfall and snowmelt is a popular method to treat piles of spent mushroom substrate (SMS) before its reuse. During this field weathering process, leachate percolates into the underlying soils. A field study was conducted to examine the chemistry of SMS leachate and effects of infiltration. Two SMS piles were deposited (90 and 150 cm in height) over a Typic Hapludult and weathered for 24 mo. Leachate was collected biweekly using passive capillary samplers. The SMS leachate contained high concentrations of dissolved organic carbon (DOC; 0.8–11.0 g L−1), dissolved organic nitrogen (DON; 0.1–2 g L−1), and inorganic salts. The pH, electrical conductivity, and acid neutralizing capacity were 6.6 to 9.0, 21 to 66 ds m−1, and 10 to 75 mmolc L−1, respectively. Inorganic chemistry of the leachate was dominated by K+, Cl−, and SO2−4 Leachate DOC was predominantly low molecular weight (