Inorganic-N release from spent mushroom compost under laboratory and field conditions

Abstract

Inorganic-N release from soil amended with spent mushroom compost (SMC), a by-product of mushroom production, was measured in three open laboratory incubations (25–30°C) and in field lysimeters. Rates of SMC application to the soil were up to 80 t ha −1 equivalent (0.84% dry weight in the laboratory). SMC contained 1.8% N of which 94% was organic, and had a C-to-N ratio of 17. Small amounts of inorganic-N were leached from SMC in the first incubation (3–18% of that applied). Trends in the data suggested that N in the SMC was initially immobilized in the 20 and 40 t ha −1 treatments, as shown by modelling using a negative first order exponential term; it was then slowly mineralized according to zero order kinetics. The laboratory optimized model of inorganic-N loss, when modified to account for field soil temperatures, estimated a similar amount of inorganic-N loss as was observed in the field. The century model overestimated inorganic-N leaching from SMC in the laboratory and underestimated inorganic-N leaching in the field. Fertilizer, containing N, P, K and S, reduced the net amount of inorganic-N recovered from SMC–soil mixtures. The rate of inorganic-N leaching from mushroom compost was considerably slower than from glycine or chicken litter applied at the same N rate. The sterilants applied to mushroom compost during mushroom production and compost sterilization had little effect on the rate of inorganic-N leached from the compost; however, hypochlorite and formaldehyde caused a small increase and decrease respectively in the cumulative amount of inorganic-N leached from mushroom-compost-amended soil. The slow rate of release of inorganic-N from SMC-amended soil is predominantly the result of the slow mineralization of recalcitrant organic-N in SMC.