**5. Discussion**

*Emerging Contaminants*

*\*Bacterial isolates - B1, B2, B3 and B4.*

**Table 7.**

**Figure 1.**

**Bacterial isolate\* Inhibition zone (cm)**

*Antifungal activity of bacteria isolated from SMS in dual culture plate assay.*

B1 0.45 1.17 1.12 1.66 B2 0.77 1.4 1.00 1.51 B3 1.05 1.25 0.75 0.82 B4 0.95 1.02 0.69 1.05

*Fusarium* **sp***. Phytophthora* **sp.** *Alternaria* **sp.** *Aspergillus* **sp.**

**4.3 Isolation of microbial flora from SMS**

*F2 -* Alternaria *sp. F3 -* Phytophthora *sp. F4 -* Aspergillus *sp.*

In this study, four different bacteria were isolated from the fresh spent mushroom substrate after *Pleurotus* spp., cultivation. The colony morphological variations among the four bacterial isolates of the bacterial strain 1 (B1) were irregular in shape with a colony size of 1.2 cm dia. The colonies had eros type margin rough or dry texture and were white in color. Cells of bacterial isolate B2 showed a diameter of 0.7 cm. The margin of B2 colonies were entire with smooth texture, mucoid consistency and cream in color. Colony morphology of B3 isolate showed irregular shaped colonies of 0.5 cm dia. B3 isolate colonies showed serrated margin with smooth or glistening texture and cream color. The B4 bacterial isolate had circular shaped colonies of size 0.2 cm with entire margin and yellow in color. The cellular morphology of B1, B2 and B3 isolates was observed as rods while B4 isolate had

*Antifungal activity of bacteria isolated from SMS in dual culture plate assay. F1 -* Fusarium *sp.* 

The biochemical properties of four bacterial strains isolated from the SMS obtained after *P. eous* cultivation showed significant variations in the biochemical characteristics studied. Based on the observations and results obtained by subjecting the bacterial colonies in different identification techniques, bacterial isolate B1 was identified as *Bacillus* sp., isolate B2 was identified as *Clostridium* sp., isolate B3 as *Pseudomonas* sp. and B4 as *Escherichia coli*. The findings on antifungal activity of four bacterial strains isolated from SMS are shown in **Table 7**

**258**

and **Figure 1**.

short rod shaped cells.

Mushroom growing is an ecofriendly activity as it utilizes the waste from agriculture, horticulture, poultry, brewery etc. for its cultivation. However, piling up of "spent mushroom substrate" released after mushroom crop harvesting may cause various environmental problems, including ground water contamination and nuisance [20, 36].

Production of 1 kg of mushrooms will generate 5 kg of spent residual material called spent mushroom substrate (SMS). An average farm discards about 24 t of SMS per month [37]. In Ireland, approximately 254,000 t of SMS is generated each year [38] and in The Netherlands, more than 800,000 t of SMS is produced per year [39].

In some countries, waste management of SMS is a major problem faced by farmers. Apparently, the obvious solution is to increase the demand for SMS through exploration of new applications for utilization. It would be more economical and favorable if SMS is to be recycled and reused. Considering the high organic matter of SMS, rapid advances have been made and the number of scientific research has increased in the past few years.

#### **5.1 Composition of spent mushroom substrate (SMS)**

Potting medium is an important factor for the production of crop in containers, and component and properties of the potting media are very crucial for higher and quality yields of potted plants. Chemical properties of growth media are very crucial from the point of view of nutrient availability to the plants. SMS used in our study in **Tables 1** and **2** showed that pH range 6.10 and EC range 1.75 dsm−1 are suitable for normal growth of plant. The average moisture content of SMS in our study has been measured as 72% which was also reported. [40].

Ability to provide essential nutrients to plants is one of the most fundamental criteria while judging the suitability of a growth medium [41]. Primary nutrients like nitrogen, phosphorus, and potassium are more available at pH 5.5–6.5 for substrates of organic and mineral origins [42]. Moreover, with the increasing pH, the solubility of many nutrients is reduced and some nutrients are precipitated as solid materials that plant cannot use [43]. In contrast many researchers reported high salinity of SMS, which is mostly responsible for the limited use of SMS as a potting media [9].

Results of our study showed that SMS had 0.87% nitrogen, 0.26% phosphorus content, 0.19% of potassium. SMS has been shown to increase the nutrient availability of growth media [44]. In general, most mushroom substrates have low N content, typically in the 1% to 3% range [45]. The overall nutrients of SMS were not enough to support normal plant growth without external fertilizer application. It is well known that physical properties of soil were directly related to crop yield [46]. SMS by maintaining high organic matter content in the soil and by providing the three primary nutrients e.g. nitrogen, phosphorus and potassium helps to provide soil fertility [41, 47].

#### **5.2 Effect of SMS on growth and biomass of selected plants**

Growth of root and shoot weight of the seedlings of green gram, black gram, tomato and chili were significantly higher when grown in 60% SMS mended soil than the control (**Tables 3**–**6**). Higher nutrient availability provided by SMS might have contributed to the better growth in 60% amended soil. Spent mushroom

compost (SMC) of *Pleurotus ostreatus* improved the agronomic characters and yield (pod no, fresh weight and dry weight) when it was added as soil conditioner to soybean at different levels of its concentrations [14].

Reason for poor root and shoot growth of the seedlings of the selected plants in 100% SMS may be that the paddy straw based. SMS may only be used as an amendment and not as a basic growth medium. While growth on straw, *Pleurotus* releases humic acids like fractions which when added to soil would increase its fertility. In addition, humic substances may affect the plant biochemical process [48]. Present findings confirm the efficacy of SMS in growth promotion in terms of seedling shoot and root weight.

SMS from *Agaricus bisporus, Hericium erinaceus* and *Pleurotus ostreatus* are effective to the growth promotions of pea, pepper and tomato plants respectively [29, 36].

The results of the present study revealed that the compost has a good impact in promoting better growth and yield. Further in order to promote growth and yield, it becomes imperative to optimize the usage of organic manure according to the crop requirement.
