Nitrogen fractions in spent mushroom substrate

Abstract

In the last decade, Poland has become the leader in mushroom production in Europe. Mushroom cultivation generates large amounts of spent substrate, which is a waste material and must be recycled. The substantial content of macroelements, including nitrogen, prompts using this organic material as a soil fertilizer. The objective of the paper was to determine the proportion of nitrogen in different forms extracted from spent mushroom substrates. The studies were aimed at determining the potential for the rational use of spent mushroom substrate in soil fertilization. The sequential extraction of nitrogen compounds was performed with a 0.25 M KCl solution (for the extraction of mineral nitrogen forms and the most labile organic nitrogen compounds) and with 0.25 M and 0.25 M H 2 SO 4 (hot hydrolysis for sequencing of organic nitrogen linkage that are easily hydrolysing and difficult to hydrolyse). The prepared solutions were tested for the total content of nitrogen with the method by Kjeldahl and for carbon with the oxidative-potentiometric method. The samples were also subjected to extraction of nitrogen bound to humic substances. It was found that spent mushroom substrate had a substantial potential for enriching fertilized soil with organic nitrogen compounds, which are, to a large extent, potentially liable to degradation. In summary, approximately 2/3 of the total nitrogen pool in the organic complexes and about 1/3 of the carbon pool were extracted using sequential extraction with a neutral salt solution and acid hydrolysis at different concentrations of hydrogen ions. The calculated C/N values suggest that the extracted organic compounds are vulnerable to degradation and indicate the resistance of compounds present in post-extraction residues. While fractioning organic matter, it was found that a relatively large amount of nitrogen was sequenced at the stage of decalcification of the samples, and the proportion of humic substances equalled about 1/5 of the total content of this element.