Abstract
Spent mushroom substrate (SMS) has been employed in recent years for different applications. However, most of these applications have been unable to solve the problem of its disposal completely, except its agricultural use. Because of this, it is important to identify the variability in the organic composition of SMS to evaluate its capacity as a soil amendment. Therefore, a study was carried out involving the analysis of different organic matter (OM) fractions in the two types of SMS obtained from 19 mushroom industries in Spain. In this experiment, 40 different types of SMS [19 spent substrates of Agaricus bisporus (SMS‐AB) and 21 spent substrates of Pleurotus (SMS‐P)] were evaluated for OM; soluble polyphenols; organic nitrogen (Norg); total organic carbon (Corg); water‐soluble carbon (Cw); cation exchange capacity (CEC); Corg/Nt, Cw/Norg, and CEC/Corg ratios; humic acid‐like carbon (Cha); fulvic acid‐like carbon (Cfa); 0.1 M sodium hydroxide (NaOH)–extractable organic carbon (Cex); humification ratio (HR) (Cex / Corg × 100); humification index (HI) (Cha / Corg × 100), percentage of humic acid–like carbon (Pha) (Cha / Cex × 100) and Cha/Cfa ratio. In comparison with the limits set by the Spanish legislation for organic fertilizers, SMS‐AB and SMS‐P had suitable and high Corg/Nt ratios, respectively, and both of them showed high OM contents. The study of the different fractions of OM showed that SMS‐P had higher contents of Corg, Cw, and soluble polyphenols than SMS‐AB. However, the fraction of organic N was significantly higher in SMS‐AB than in SMS‐P. The study also showed that only SMS‐AB had a percentage of humic acid–like C greater than that of the fulvic acid–like C. Moreover, in most cases, the values of the humification parameters of this waste were higher than those of SMS‐P, indicating a greater OM humification in the SMS‐AB compared to SMS‐P. Regarding the parameters related to the OM stability and its maturity, it has been observed that only SMS‐AB had values of these parameters higher or close to the established limits for mature organic materials. The origin influenced in the parameters related to OM (OM, Corg, Norg, and Cw) in SMS‐AB, whereas SMS‐P only showed significant differences in the humification parameters (Cex, Cha, HR, HI, Pha, CEC, and Cha/Cfa and CEC/Corg ratios) related to the origin. The heterogeneity in OM composition of the studied SMS did not allow the formulation of simple equations for the complete evaluation of the composition of these wastes from easily determined parameters.
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