Composition variability of spent mushroom substrates during continuous cultivation, composting process and their effects on mineral nitrogen transformation in soil

Spent mushroom substrates (SMSs) are a typical by-product of mushroom production, which is rich in nutrient like nitrogen. The reuse of SMSs as soil amendments has become the focus of attention. Due to its nutrient content, SMSs could contribute to reduce the use of non-renewable resources, such as peat. Recently, a SMSs recycling strategy was adopted in an edible mushroom industry Ltd., China. The waste materials experienced a continuous cultivation, composting process which sequentially includes the cultivation of Pleurotus etyngii, the cultivation of Pleurotus ostreatus, the composting process, and were finally used as soil amendments. The main objective of this study was to investigate the composition variability of SMSs during continuous cultivation, composting process and their effects on mineral nitrogen transformation in amended soil. The components analysis suggested the relative moisture and polysaccharide content of SMSs decreased by 33.6% and 17.1%, respectively, during the continuous cultivation, while protein increased by 29.5%. Moreover, relative humic acid content of SMSs increased by 18.6% during composting process while biodegradable matter (BDM), polysaccharide and protein decreased by 38.6%, 79.4% and 50.0%, respectively. The results of a 42-day incubation experiment suggested that addition of spent mushroom composts (SMCs) can significantly enhance the mineral nitrogen contained in soil. With the amendment of SMCs, 39.4% of input nitrogen was converted into mineral nitrogen within day 42. Combined application of SMCs/urea was considered to be a better strategy, since it provided soil with more mineral nitrogen than SMCs alone throughout the whole incubation.