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Straw from two cereal crops and two legumes was used in the experiment: maize (Zea mays, variety Saludo), wheat (Triticum aestivum, variety Faustus), soy bean (Glycine max, a mix of varieties Merlin, GL Melanie, Marquise, Aurelina, ES Favor, RGT Sphinxa, ES Comandor, Amarok, and Arcadia) and faba bean (Vicia faba, variety Tiffany). All straws were produced with certified organic farming practices[15], which ensures that there are no remains of fungicides on the material, which could influence mushroom growth. Maize, faba bean, and wheat were cultivated in 2019 under scientifically controlled conditions at the experimental station of the Thünen-Institute of Organic Farming in northern Germany. To get a nutrient-poor maize straw despite using a feed variety of this crop (sweet maize varieties cannot be cultivated in cold, northern German climate), the maize was left standing in the field for four months after harvest season before cutting it, allowing nutrients to leach back into the soil. Soy was grown at the organic experimental station Gladbacher Hof of the University Giessen in central Germany. The different straws included all the above-ground parts of the plant, except the grain, and the cobs in the case of maize. All the straws were chopped (< 2 cm) and dried for 5 d at 40 °C for storage.
Grain spawns with the mycelium of P. ostreatus ((Jacq.: Fr.) P. Kumm, strain number: P10001, type of grain: wheat) was used to inoculate the straws for mushroom cultivation.
Experimental design
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The experiment consisted of four treatments (wheat, maize, soy, and faba) with eight replicates. Each replicate consisted of a polypropylene mushroom grow bag with a micropore filter (50 cm × 8 cm × 0.1 cm, Hemoton brand®) filled with 800 g of moist, pasteurized substrate (200 g dry matter and 600 g water) and 20 g of mushroom grain spawn (6.6 g dry matter). Hot air pasteurization at 100 °C for 3 h was used to pasteurize the substrate. Grain spawn was added to the substrate after letting it cool down, ensuring that the spawn was well distributed by twisting and shaking the bags. The mushrooms were cultivated under controlled conditions in the laboratories of the Thünen-Institute, at 21 °C and 90% humidity in a grow-box (HOMEbox Vista Medium), as depicted in Fig. 1.
Figure 1.
Different substrates are used for mushroom cultivation in a random replication approach in a grow chamber.
Since it was intended to use the same amount of dry matter and water in the different treatments, but the straws had different water-holding capacities, the replicates were hung in a way that allowed excess water to drip from a small opening at the bottom.
Data collection
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Up to three flushes were harvested from each replicate. The fresh weight of the harvested mushrooms was determined immediately after harvest. The dry yield was determined after drying at 105 °C for 24 h. From this data, the biological efficiency (BE, percentage of dry matter of substrate converted to fresh matter of mushrooms[2] and the biomass conversion rate (BCR, percentage of dry matter of substrate converted to dry matter of mushroom) were calculated. The visually discernible occurrence of bacteria or molds in each replicate was checked and the mycelial growth (from 0% of substrate colonized to 100%) was estimated weekly during the first three weeks of the experiment. After the cultivation period, the substrate was removed from the bags, crushed, and dried at 105 °C for 24 h, to determine the dry weight of each replicate and to take samples for chemical analyses. All raw data on mushroom yield and the composition of SMS is made available in the Supplemental Table S1 to be published with this study.
Chemical analyses, estimations of protein content and carbon emissions
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The nitrogen (N) and carbon (C) content of the spawn, straw, SMS and mushrooms were analyzed with the DUMAS-method[16]. The protein content (XP) of the straw and mushroom was estimated by multiplying the nitrogen content with the factor 6.25, which is commonly used in the analyses of feed[17]. Carbon emissions through respiration of the fungal mycelium are estimated by subtracting the amount of carbon found in the SMS and the mushrooms from the amount present in the straw before cultivation. The crude fiber (XF) of the straw was determined with the Weender-van Soest analysis[18]. The number of analyses were focused on SMS. While only one collective sample from the straw, spawn and mushrooms were taken, a separate sample from the SMS of each replicate was analyzed. To assess whether the type of straw influences the protein composition of the harvested mushrooms, three more samples from mushrooms cultivated on the same straw under the same conditions were analyzed a year later and are included in the results of this study. All analyses were carried out in the laboratory of the Thünen-Institute of Organic Farming.
Estimations of feed quality
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To calculate the metabolizable energy (ME) of the different straws for ruminants, the following formula was used[19]:
ME (MJ) = 0.0312 * digestible fat (g) + 0.0136 * digestible fiber (g) + 0.0147 * (digestible organic matter (g) – digestible fat (g) – digestible fiber (g)) + 0.00234 * raw protein (g)
The data on the digestibility of the different fractions of the maize and wheat straw were taken from the publications of the German association for agriculture[19], while the data on faba bean straw was taken from the Dutch central feedstuff databank[20]. For soy bean straw, only incomplete data could be found. Information for the digestibility of organic matter and of protein of soy straw was found on the Feedipedia database[21]. To fill in the missing values on the digestibility of lipids and fibers in soy straw, we used the data on straw from a similar legume, namely the pea, Pisum sativum, from the DLG[19]. The compiled digestibility data can be found in Table 1.
Table 1. Digestibility of the different macronutrient fraction in the different straw types: Digestible organic matter (DOM), digestible protein (DP), digestible lipids (DL) and digestible fiber (DF).
Straw type DOM (%) DP (%) DL (%) DF (%) Wheat 47 20 49 53 Faba bean 52 46 53 42 Maize 72 50 64 68 Soy bean 52 54 55 42 Statistical analyses
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For statistical analysis, Microsoft Excel and the freeware R-studio (version 4.0.3) were used. One-way analysis of variance (ANOVA) and the posthoc Tukey's test were used to compare different treatments and show significant differences. To test for the assumptions of normal distribution of the data and the residuals, histograms, and qq-plots were assessed and the Shapiro-Wilk test was used.
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The chemical analysis (Table 2) showed large differences between the types of straw with regard to the nitrogen content, while the carbon content was almost the same. The wheat straw contained the least nitrogen and faba bean contained the most. The carbon/nitrogen-ratio (C/N-ratio) of the straws varied from 45 to 130. The content of crude fiber content (XF) was lowest in maize straw followed by soy bean, wheat, and faba bean. The mushroom spawn had a notably higher nitrogen content than the straws with a C/N-ratio of 15.6.
Table 2. Chemical composition of the dry matter (DM) of different straws and mushroom spawn used for oyster mushroom cultivation.
Sample C (% DM) N (% DM) C/N-ratio XF (% DM) Wheat straw 47.12 0.36 130.37 47.97 Faba bean straw 47.12 1.05 44.75 49.86 Maize straw 47.07 0.68 69.72 38.03 Soy bean straw 47.18 0.59 79.91 43.86 Mushroom spawn 46.33 2.96 15.63 x In combination with the data in Table 1, the digestible protein and metabolizable energy were calculated. As Table 3 shows, wheat straw had the least digestible protein, while faba bean had the most. Maize straw, according to these calculations, had the most metabolizable energy.
Table 3. Protein, digestible protein (DP) and metabolic energy (ME) of the different straws for 1 kg dry matter and 1.4 kg dry matter (estimated daily feed intake of a goat).
Sample Protein DP ME g/kg
DMg/kg
DMg/1.4 kg
DMMJ/kg
DMMJ/1.4 kg
DMWheat straw 19.4 3.9 5.4 6.3 8.8 Faba bean straw 63.0 29 40.5 7 9.8 Maize straw 38.9 19.5 27.2 9.8 13.7 Soy bean straw 33.7 18.2 27.4 7.2 10.1 Mushroom production
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In the 56 days of the experiments, most replicates produced two mushroom harvests, with a few replicates producing only one or even three harvests. No clear pattern was discernible between treatments in terms of number of harvests. The occurrence of green mold was limited to one replicate of the wheat straw treatment and two replicates of the maize straw treatment. Since these replicates failed to produce mushrooms, they were taken out of the experiment, reducing the number of replicates in wheat straw to seven and in maize straw to six. Mycelial growth was the fastest in the soy bean straw treatment, where all replicates were fully colonized after 13 d, while the replicates in other treatments were fully colonized after 21 d.
Wheat straw produced significantly lower yields than all other treatments, both in terms of fresh matter (BE) and dry matter (BCR). Maize straw produced significantly more mushrooms than all other treatments in terms of fresh yield but not significantly more than soy straw in terms of dry yield (Table 4).
Table 4. Fresh and dry yield.
Treatment Fresh matter BE (%) Dry matter BCR (%) Wheat straw 58b (12.5) 3.8c (0.8) Faba bean straw 76bc (17.3) 6.6b (1.4) Maize straw 114a (10.2) 9.2a (0.9) Soy bean straw 89.1b (14.7) 8.6a (1.3) Biological efficiency (BE) and biomass conversion rate (BCR) of the different treatments. Significant differences between treatments are marked by letters above the data. Standard deviation given in brackets behind the mean. While wheat, faba bean, and soy bean straw produced more than 75% of the total dry yield in the first harvest, maize straw on average produced more than 50% of the mushrooms in the second and third harvests (Fig. 2).
Figure 2.
Average dry yield per dry substrate distributed over different harvest flushes in the different treatments. Error bars show standard deviation.
The composition of mushrooms from the different treatments is presented in Table 5. Mushrooms cultivated on faba bean straw contained significantly more nitrogen and thus protein than mushrooms from the other treatment.
Table 5. Chemical composition of the mushrooms from different treatments.
Treatment C (%) N (%) C/N Protein (%) Wheat straw 44.7a (1.1) 2.7b (0.3) 16.8b 16.8 (1.6) Faba bean straw 45.4a (1.2) 3.7a (0.2) 12.2a 23.2 (1.3) Maize straw 45.1a (0.8) 3b (0.2) 14.9b 19 (1.4) Soy bean straw 45.6a (0.6) 2.8b (0.2) 16.2b 17.7 (1.6) Standard deviation given in brackets behind the mean. Significant differences between treatments are marked by letters above the data. By synthesizing the yield data and the chemical analysis, one can estimate the amount of protein produced per kg of straw. On wheat straw, 6.4 g protein were produced per kg of straw, on soy bean straw 15.2 g, on faba bean straw 15.4 g and on maize straw 17.4 g.
Nitrogen and carbon flow
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The change in nitrogen and carbon content of the straws after cultivation differed notably between the different treatments. While the C/N ratios of wheat, maize, and soy bean straw were decreased by mushroom cultivation, it slightly increased on faba bean straw (Table 6).
Table 6. Chemical composition of the spent mushroom substrate (SMS).
SMS type C (% DM) N (% DM) C/N C/N ratio change Wheat straw 45.5 (0.9) 0.4 (0) 106.0 −24.4 Faba bean straw 45.6 (0.4) 1 (0) 47.3 2.6 Maize straw 43.8 (0.4) 0.7 (0) 62.7 −7.0 Soy bean straw 43.9 (0.4) 0.6 (0) 71.7 −8.3 Standard deviation of carbon and nitrogen content given in brackets after the mean. C/N change is the difference in the C/N ratio in comparison to the ratio of the straw before mushroom cultivation. The amount of dry matter, carbon, and nitrogen from the straw that remained in the SMS after cultivation is presented in Table 7. Dry matter, carbon and nitrogen reduction was notably lower in wheat straw than in the other treatments. The strongest reduction in all these metrics occurred in the treatment with maize straw. In terms of emissions per unit of mushrooms, wheat straw emitted the most carbon, with 3.5 kg per 1 kg of dry mushrooms, while soy straw emitted the least, with 2.6 kg.
Table 7. Mass transfer from straw to spent mushroom substrate in the different treatments.
Treatment Dry matter (%) C (%) N (%) Wheat straw 82.2 (6.4) 79.5 (5.6) 79.3 (12.3) Faba bean straw 70.1 (5) 67.9 (4.6) 60.5 (3.9) Maize straw 63.4 (1.9) 59 (1.7) 59 (3.9) Soy bean straw 67.1 (1.9) 62.4 (1.6) 61.5 (4) Standard deviation given in brackets behind the mean. By subtracting the amount of dry matter in the SMS (Table 7) and in the mushrooms (Table 5) from the amount of dry matter in each replicate at the beginning of the experiment (200 g straw + 6.6 g spawn), the unaccounted rest was calculated. This rest is the amount of carbon that was lost to respiration by the mushroom. As can be seen in Fig. 3, in the wheat treatment, 17% of the dry matter are estimated to be carbon emissions, 25% in the faba bean treatment, 32% in the maize treatment and 29% in the soy treatment.
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The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.
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About this article
Cite this article
Grimm D, Sonntag E, Rahmann G. 2024. Oyster mushroom cultivation on cereal and legume straw of poor feed quality. Studies in Fungi 9: e010 doi: 10.48130/sif-0024-0010
Oyster mushroom cultivation on cereal and legume straw of poor feed quality
- Received: 31 May 2024
- Revised: 05 July 2024
- Accepted: 09 July 2024
- Published online: 12 August 2024
Abstract: This study explores the viability of cultivating oyster mushrooms on cereal and legume straw of poor feed quality, investigating oyster mushroom productivity, and the implications for mass-, nitrogen- and carbon flows within the agricultural system. Four types of straw (wheat, maize, faba bean, and soy bean) were utilized as substrates for mushroom cultivation. Fresh yields varied widely, from 114% biological efficiency on maize straw to 58% on wheat straw, while dry yields ranged from 9.2% biomass conversion rate on maize straw to 3.8% on wheat straw. The protein content of mushrooms varied between 16.8% on wheat straw and 23.2% on faba bean straw, correlating with the nitrogen content of the straw. Furthermore, results revealed significant variations in carbon emissions, ranging from an estimated 3.5 kg (on wheat straw) to 2.6 kg (on soy straw) emitted per kg of dry mushroom produced. These findings underscore the importance of substrate selection in mushroom cultivation, with implications for agricultural resource management and food production. Depending on the focus, different substrates may be considered as optimal. While maize straw produced most mushrooms in this study, soy bean straw emitted the least carbon in relation to yield, faba bean straw produced mushrooms with higher protein content, and wheat straw retained the most nitrogen in the spent mushroom substrate.
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Key words:
- Mushrooms /
- Straws /
- Cultivation /
- Cereals /
- Legumes /
- Circular Economy