The Influence of Spent Mushroom Substrate Fertilization on The Selected Properties of Arable Soil

In recent years, Poland has become a country with a very high Agaricus bisporus mushroom production. As a result, mushroom cultivation generates large amounts of spent mushroom substrate, which is a waste material and must be recycled. The annual quantity of waste is more than 1.500.000 t [Paredes et al., 2016; Zmarlicki, Brzozowski, 2018]. The spent mushroom substrate is a good material for fertilisation because of its high content of macroelements, including nitrogen. It is a valuable resource of organic matter as well [Jordan et al., 2008; Medina et al., 2009; Kalembasa, Majchrowska-Safaryan, 2009; Kalembasa et al., 2012; Majchrowska-Safaryan, Tkaczuk, 2013; Becher, Pakuła, 2014; Mohd Hanafi et al., 2018; Zied et al., 2020]. Uncontrolled disposal of spent substrate is a potential danger because of migration outside the prism of nitrogen and environment eutrophication. The application of the spent mushroom substrate as a soil fertiliser seems to be the most appropriate method for its utilization, as it improves the nitrogen balance in soil [Kalembasa et al., 2012; Becher, 2013; Majchrowska-Safaryan, Tkaczuk, 2013; Becher, Pakuła, 2014; Paredes et al., 2016]. This is especially important in light soils of lower humus content, where nitrogen is present at lower concentration to profitability of plant production.

More than 90% of the nitrogen content in the A horizons of soils occurs in the organic forms, 10% falls on the microbial mass of roots and mineral forms [Smith et al., 1997; Kalembasa, Kalembasa, 2016]. The special role in the accumulation of nitrogen in soils is attributed to natural and mineral fertilization and the cultivated plants [Meysner et al., 2006; Czekała, 2010; Sabienė et al., 2010]. The mineral forms of nitrogen (ammonium and nitrate) are mobile, therefore, these could be washed out from the soil. There is a danger of contaminating ground water. The highest loss of soil nitrogen is due to nitrate (NO₃⁻) leaching. In the terrestrial ecosystems of Central Europe, every year by an average of 15 kg NO₃⁻ ha⁻¹ is washed out from the soils [Haag, Kaupenjohann, 2001].

The aim of the study was to assess the effect of spent mushroom substrate fertilization on the A horizon properties of the Stagnic Luvisol, especially for the variation in the nitrogen fraction, in the two-year cultivation period.

Soil research was carried out in 2017 and 2018 on a production field in the Zając village (52°20′00″N 22°03′00″E) located in the Liw commune (east part of the Mazowieckie voivodeship) on the Siedlce Upland.

The experiment was designing in a randomized block with four replications 7×7 m plots on Stagnic Luvisol [IUSS Working Group WRB 2015, Polish soil classification 2019] developed from glacial till.

The experiment included the following 2 objects: control (without fertilisation) and fertilised with spent mushroom substrate (20 t ha⁻¹ SMS). Spent mushroom substrate obtained after 6-week cultivation of common mushroom Agaricus bisporus, originated from mushroom farm where mushrooms were cultivated on phase III substrate (after fermentation and inoculation with mycelium).

After harvesting the cultivation crop, samples of soil were collected from the A horizon (0–25 cm), air dried and sieved through 2 mm mesh. The following parameters were determined: soil texture with areometric method according to the Soil Science Society of Poland recommendation [2009], in soils – pH in 1 M KCl with potentiometric method; cation exchange capacity (CEC) calculated from hydrolytic acidity (Hh) and the sum of exchangeable base cations (S) determined witch the Kappen’s method; total organic carbon (Corg) with the oxidation-titration method [Kalembasa, Kalembasa, 1992], total nitrogen content (N-tot) determined by Kjeldahl’s method, on the basis of the obtained results, the C:N ratio was calculated. Degree of saturation of soils with alkaline cations (V) on the basis of the value of sum of exchangeable base cations (S) relative to the value cation exchange capacity (CEC) was also calculated.

In the spent mushroom substrate were determined: pH in deionized H₂O with potentiometric method, the content of dry matter (DM) with the drying-weighting method (at 105°C) and Corg, N-tot, C:N – by the methods as for soil samples.

In the spent mushroom substrate and soil samples, 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 2.5 M H₂SO₄ (hot hydrolysis for sequencing of organic nitrogen linkage that are easily hydrolysing and difficult to hydrolyse) [Kalembasa, 1995]. The obtained extracts, by acid hydrolysis, the nitrogen content determined by the Kjeldahl’s method. In the hydrolysate, it is part of the nitrogen occurring of non-replaceable forms (Table 1).

The statistical calculations were conducted with the STATISTICA 13 PL software. The relationships between the examined parameters were expressed as a simple correlation coefficient (r). Significant statistical differences were assumed at the level of p = 0.05.

Based on the soil texture in A horizons of the studied soils were classified as sandy loams (74% sand, 19% silt, 7% clay). In the studied A soil of particular objects of the experiment, differentiated pH values, sorption properties, organic carbon content, the total nitrogen content and the C:N ratio were found (Table 2). The application of spent mushroom substrate had an effect on differentiation of soil properties and an increase in their value in comparison to the control object. The differences were more marked after the first year of cultivation.

A chemical analysis of the spent mushroom substrate (SMS) used to fertilise the studied soils are presented in Table 3.

Over 90% of the nitrogen contained in the A horizons of the soils occurs as a part of organic compounds. Therefore, there is a close relation between the amount of organic compounds and the nitrogen content [Meysner et al., 2006; Spychaj-Fabisiak et al., 2007]. Kalembasa and Wiśniewska [2006] found the nitrogen content in soils to increase as an effect of fertilising with spent mushroom substrate (SMS). According to Mercik et al. [1995], a substantial increase in the N-tot content in soils may be obtained by increasing the amount of organic matter. In the second year of the experiment for the object fertilised with spent mushroom substrate, a decrease in the nitrogen content (by 20% compared to the first year) was noted. Duggan et al. [1998] found that in the first year of cultivation, after using spent mushroom substrate (SMS), the substrate should be supplemented with nitrogen fertilisation. Mineralisation of (or rather losses in) nitrogen in the soils of the objects fertilised with natural and organic fertilisers is less in the first year following their use than in later years.

The narrow C:N ratio of indicates its beneficial properties as a fertiliser. The ratio indicates mineralisation of organic nitrogen compounds to prevail over their synthesis, which results in releasing nutrients, which are available to plants [Kalembasa, Majchrowska-Safaryan, 2006; Jordan et al., 2008; Szulc et al., 2009; Rutkowska et al., 2009; Kalembasa, Becher, 2011; Becher, Pakuła, 2014].

In the studied spent mushroom substrate (SMS), more nitrogen was found in the mineral ammonium form (NNH₄) than in the nitrate form (N-NO₃ and N-NO₂) (Table 4). According to Mazur and Mokra [2009], the content of nitrogen in fresh biomass of the spent mushroom substrate approximates the content of this element in natural fertiliser. The nitrogen content of organic compounds of the studied fertiliser spent mushroom substrate formed the following series of decreasing amounts: N_ONH > N_ODH > N_OEH > N_OS (Table 5).

The content of mineral forms of nitrogen in the soil A horizons of particular objects was differentiated (Table 6). A greater amount of nitrogen in an ammonium form (NNH₄) (about 40% after the first year cultivation and about 50% – after second year) was found than in a nitrate form (N-NO₃ and N-NO₂). The share of ammonium nitrogen in the A horizons of soil fertilized with spent mushroom substrate was greater after the second year (3.13%) than after the first year of cultivation (2.22%). Using organic fertilisers often and in high doses results in slowing down the nitrification process, thus promoting the accumulation of the ammonium form of nitrogen in soils. Comparable contents of ammonium nitrogen in soils following were obtained by Wiater [2006] and Bednarek and Reszka [2008]. The greatest share of nitrate nitrogen form (N-NO₃ and N-NO₂) was noted in both years for the soil of control object (1.95% and 1.69%). The share of this form of nitrogen was greater about 16% after the second year than after the first year of cultivation. According to Wiater [2006], better soil aeration resulting from nurturing works done around root crops contributes to the improvement of their oxygenation and creates good conditions for the nitrification process.

As a result of acid hydrolysis, from the soil A horizons of particular experimental objects, 53% of soil organic nitrogen reserves (the average from 2 years) were isolated. In soil of particular objects, much more nitrogen was found in difficult-hydrolysing than in easily-hydrolysing compounds. The share (%) of organic nitrogen in N-tot, isolated from the studied soils, formed the following series of increasing amounts: N_OS (2.13–2.90%) < N_OEH (18.4–19.0%) < N_ODH (32.2–32.5%) < N_ONH (44.8–47.3%) (Table 7). The share of soluble organic nitrogen (N_OS) easily hydrolysing organic nitrogen (N_OEH), organic nitrogen difficult to hydrolyse (N_ODH) was lower after the first year of cultivation compared to the second year by 26.6%, 3.2% and 0.9%, respectively. While the share of not hydrolysing organic nitrogen (N_ONH) was greater by 5.6% after the first year of cultivation than after the second year.

According to Paul and Williams (2005), nitrogen in organic compounds, which can be extracted from soil with a neutral reagent at a low concentration, may represent the reserves of soil soluble organic nitrogen. Organic fertilization largely influenced the dynamics and content of easily hydrolysing nitrogen compounds in soil (Wiater, Dębicki 1993). The content of easily-hydrolysing nitrogen form in soil may be the basis for the inference about the nitrogen reserve for plants, especially because it is a form considered to be little changing over time (Wiater 2006).

A significant positive relation between the contents of soluble organic nitrogen (N_OS), easily hydrolysing organic nitrogen (N_OS), organic nitrogen difficult to hydrolyse (N_ODH) and the total content of nitrogen (N-tot) and value of cation exchange capacity (CEC) in the investigated soils was found (Table 8). Nitrogen strongly bound in organic compounds (non-hydrolysing) correlated significantly negatively with hydrolytic acidity (Hh) and degree of saturation of soils with alkaline cations (V). No significant correlation was found between the mineral forms of nitrogen and the properties of the studied soils, exception of the ammonium (N-NH₄), which significantly correlated with cation exchange capacity.