<figure><img src="image_1.png" /></figure>

# Advanced Vermicomposting Modality:
Microbial Acceleration to Improve
Micronutrient Profile of Agricultural
Residue Derived Compost

Aarush Lal a++, Sailajakumari M.S. b#*, Rani B. a†,
Chitra N. c‡ and Aparna B d^

## Authors' contributions

This work was carried out in collaboration among all authors. All authors read and approved the final
manuscript.

## Article Information

DOI: https://doi.org/10.9734/ijpss/2024/v36i95004

**Open Peer Review History:**

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**Original Research Article**

Received: 10/07/2024

Accepted: 12/09/2024

Published: 16/09/2024

**Cite as:** Lal, Aarush, Sailajakumari M.S., Rani B., Chitra N., and Aparna B. 2024. "Advanced Vermicomposting Modality: Microbial Acceleration to Improve Micronutrient Profile of Agricultural Residue Derived Compost". International Journal of Plant & Soil Science 36 (9):556-63. https://doi.org/10.9734/ijpss/2024/v36i95004.

<footnote>a Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani, Trivandrum, Kerala, India.</footnote>

<footnote>b Department of Soil Science and Agricultural Chemistry, Regional Agricultural Research Station, Kumarakom, Kottayam, Kerala, India.</footnote>

<footnote>c Department of Agricultural Microbiology, College of Agriculture, Vellayani, Trivandrum, Kerala, India.</footnote>

<footnote>d Department of Soil Science and Agricultural Chemistry, College of Agriculture, Ambalavayal, Wayanad, Kerala, India.</footnote>

<footnote>++ PG Scholar;</footnote>

<footnote># Associate Professor;</footnote>

<footnote>† Professor and Head;</footnote>

<footnote>‡ Assistant Professor;</footnote>

<footnote>^ Professor;</footnote>

<footnote>*Corresponding author: E-mail: sailaja.ms@kau.in;</footnote>
ABSTRACT

Advancing circular economies and self-reliant agricultural systems will critically depend on innovative strategies to optimize resource utilization and agro-waste recycling for the sustainability of food production. The present study is focused on the potential of vermitechnology with diverse substrate compositions in bioconverting lignocellulosic agricultural residues into nutrient-rich amendments. Trials of vermicomposting were carried out exploiting *Eudrilus eugeniae* and a fungal decomposer consortium, Pusa Decomposer. Treatments included T1: *Gliricidia sepium* leaves (GL), T2: Banana pseudostem (BP), T3: Rice straw (RS), T4: Rice husk (RH), T5 (RS + BP - 8:1 w/w), T6 (RH + BP - 8:1 w/w), T7 (RH + RS + BP - 4:4:1 w/w) and T8 (RH + RS + BP + GL - 4:4:0.5:0.5 w/w) with 3 replications in CRD. T2 expressed peak Mn, Zn and Cu values at 418.40 mg kg⁻¹, 247.50 mg kg⁻¹ and 55.12 mg kg⁻¹, respectively. T3 reported summit Fe and B at 8669.50 mg kg⁻¹ and 37.00 mg kg⁻¹, respectively. It was found that the combination of RS and BP reported excellent nutrient solubilization and enhanced EC, which ratiocinates the role of substrate mix in determining vermicompost quality. These findings emphasize the importance of substrate selection and microbial augmentation with fungal decomposer consortia such as Pusa decomposer, which optimize the vermicomposting process for nutrient recovery and improved soil health.

Keywords: Vermicompost; *Eudrilus eugeniae*; Pusa decomposer; sustainability; micronutrient; paddy stubble; organic farming.

1. INTRODUCTION

Developing circular economies and self-relying
systems that focus on resource utilization
optimization and recycling is crucial for creating
sustainable ecosystems in terms of food
production endeavours. Sustainability can be
achieved with proficiency when the direct
dependence on conventional nutrient sources
can be reduced to certain degrees by exploiting
other feasible opportunities for crop growth.
Efficient and maximum utilization of agri-waste
via bio-conversion to nutrient-rich amendments is
one of the best modes of mitigating multiple
issues simultaneously. Human health, climate
and ecosystems are in progressing state of
threat of deterioration as higher demands for
agricultural products necessitate rapid growth of
the agriculture sector health [1,2]. Recent
surveys depict that 1 billion tonnes of agricultural
waste is produced globally, each year,
contributing to 1/5th of total greenhouse gas
emissions [3]. Out of which global rice production
yields over 750 million tons annually, generating
substantial biomass waste like straw, husk, and
bran [4]. While, approximately 114.08 million
metric tons of banana cultivation residues are
globally produced [5]. Lignocellulose forms a
major proportion of the structural component of
agricultural wastes such paddy stubble.
Lignocellulose components primarily consist of
cellulose, hemicellulose and lignin. Lignin is
strongly attached to hemicellulose molecules via
covalent and hydrogen bonding, making it highly
resistant to enzymatic hydrolysis [6]. Hence, a

need for microbial colonies capable of
degradation of lignocellulytic polymers efficiently,
that can be exploited on a practical scale
persists. Morphologically, three distinct fungal
species phyla are able to degrade lignin
complexes (brown-rot fungi, white-rot fungi, and
soft-rot fungi). Other fungi, such as coprophilic
fungi growing on dung and litter-degrading fungi,
are also effective lignin degraders [7,8]. Among
the entire roster of viable biomass conversion
methods, implementation of vermitechnology is
the most dynamic one. Earthworms aerate,
crush, mix, chemically degrade and biologically
stimulate the decomposition of organic matter.
Moreover, conjoint action of earthworm foraging
and nutrient metabolization along with the
hydrolytic action of microbial decomposer
consortiums, especially against structurally non-
reactive derivatives can allow enrichment of VC
with nutrients on a larger magnitude and with
nutrients possessing lower solubility.

**2. MATERIALS AND METHODS**

**2.1 Experimental Setup**

It was ascertained that the vermicomposting as
an activity is carried out in complete adherence
to the 2016 Kerala Agricultural University's
protocol. Specialized vermicomposting reactors
(VR) were constructed. Every VR had a gravel
bottom, covered with plastic mesh and a coconut
fibre layer. The reactors were loaded with 5 kg
pre-decayed biomass which included GL, BP,
RS, and RH in varying ratios with 100 g
bonemeal and 1 litre cow dung in (2:1 v/v). Adult *Eudrilus eugeniae* along with fungal decomposer consortium, Pusa decomposer (developed at the Indian Agricultural Research Institute) consisting of seven fungal strains, served as the primary composting agents of the study. The pattern of the experiment was completely randomized in design with eight treatments replicated three times to make up a total of twenty four VR units. Optimal moisture conditions were maintained during the study.

### Treatment details:

* T1: *Gliricidia sepium* leaves

* T2: Banana pseudostem

* T3: Rice straw

* T4: Rice husk

* T5: Rice straw + Banana pseudostem (ratio - 8:1 w/w)

* T6: Rice husk + Banana pseudostem (ratio - 8:1 w/w)

* T7: Rice straw + Rice husk + Banana pseudostem (4:4:1 w/w)

* T8: Rice straw + Rice husk + Banana pseudostem + *Gliricidia sepium* leaves (4:4:0.5:0.5 w/w)

## 2.2 Physico-chemical Analysis of Substrates and Vermiwash

pH and EC of the samples were noted by glass electrode [9] and graphite electrode [10] method respectively. Boron concentration was determined using a UV-1800 UV-Spectrophotometer by Shimadzu using the techniques described by Wolf [11]. Concentrations of iron, zinc, manganese, and copper were determined using an atomic absorption spectrophotometer, novAA-350 from Analytik Jena, described by Piper [12].

## 2.3 Statistical Analysis

All statistical analysis was carried under the KAU-GRAPES "R-package" ecosystem [13]. In which, significant difference was determined at 95% confidence level by analysis of variance followed by Least Significant Difference test.

## 3. RESULTS AND DISCUSSION

pH value, electrical conductivity, and micronutrient composition of VC are essential in determining the effectiveness of the material as an amendment. Accordingly, the pH was

recorded to understand its role in the solubility and bioavailability of other nutrients. The electrical conductivity was assessed to find out the ionic nature or possible salinity levels which could affect the soil adversely. Finally, the concentration of trace elements within the vermicompost was analysed in order to determine the extent to which vermicompost would be able to provide the required micronutrients for adequate plant growth. Such thorough understanding brings forward detailed information on the extent to which the use of vermicompost would help in enhancing soil fertility.

### 3.1 pH and EC

The pH of the final vermicompost did not differ significantly within treatments. It ranged between slightly acidic in some treatments to neutral in the majority treatments, which were well within the optimal range for earthworm survival [14]. Hence, the selected substrates and subsequent combinations were suitable for earthworm multiplication under controlled micro-climate. The initial reduction in pH during vermicomposting is due to increased microbial degradation action that is associated with release of organic acids, primarily humic acid. This acid production is further enhanced under the presence of secretions and vermicasts of *E. eugeniae* which act as foci of microbial proliferation [15]. Humic acid thus formed is stabilized by the presence of lignin decomposed derivatives during vermicomposting process [16]. It is during the later stages of composting that pH moves towards neutrality as microbial diversity improves allowing buffering action via multiple organic secretions. Similar results were interpreted by Xue-Jian et al., [17], Vinay and Charanjit, [18] and Syed et al., [19]. Victor et al., [20] linearly related the release of H⁺ ions to rate of nitrification during the composting of *Gliricidia sepium*. This could explain the lowest pH recorded in T1 (*Gliricidia* leaves) which possesses relatively higher nitrogen levels in *Gliricidia* leaves.

Substrate composition exerts influence on the EC of the vermicompost produced from the respective substrates. The water content of vermicomposts shows a positive correlation with EC. [21]. Furthermore, the process of vermicomposting itself impacts EC, as the microbial conversion of organic waste results in elevated levels of macronutrients and micronutrients, leading to changes in EC levels.
The improved catalytic action of fungal strains specializing in lignocellulose-derived compounds via Pusa decomposer incorporation further accelerates the dissolution of soluble nutrients. This may explain the relatively higher EC value in T5 (Table 2.) which could be a combined result

of high mineral solubilization and presence of highly succulent water banana pseudostem. Chen et al., [22] argued that an increase in EC of vermicompost samples can be due to high rate of carbon mineralization during degradation process.

<table><caption>Table 1. Physico-chemical characteristics of major substrates</caption><thead><tr><th>Characteristics</th><th>Rice straw</th><th>Banana pseudostem</th><th>Gliricidia sepium</th><th>Rice husk</th><th>FYM</th></tr></thead><tbody><tr><td>pH</td><td>7.2</td><td>7.81</td><td>6.87</td><td>7.65</td><td>6.20</td></tr><tr><td>EC (ds/m)</td><td>1.01</td><td>0.55</td><td>1.52</td><td>0.423</td><td>2.38</td></tr><tr><td>B (mg kg<sup>-1</sup>)</td><td>19.71</td><td>39.88</td><td>31.53</td><td>11.88</td><td>21.22</td></tr><tr><td>Fe (mg kg<sup>-1</sup>)</td><td>1125.76</td><td>457.65</td><td>197.26</td><td>174.98</td><td>1163.43</td></tr><tr><td>Cu (mg kg<sup>-1</sup>)</td><td>11.58</td><td>8.7</td><td>20.11</td><td>2.24</td><td>3.74</td></tr><tr><td>Mn (mg kg<sup>-1</sup>)</td><td>464.22</td><td>207.86</td><td>105.36</td><td>85.81</td><td>301.83</td></tr><tr><td>Zn (mg kg<sup>-1</sup>)</td><td>41.53</td><td>116.60</td><td>54.37</td><td>54.47</td><td>96.85</td></tr></tbody></table>

<table><caption>Table 2. pH and EC values of VC as influenced by varying substrate combinations</caption><thead><tr><th>Treatments</th><th>pH</th><th>EC (ds/m)</th></tr></thead><tbody><tr><td>T1</td><td>6.43</td><td>1.77<sup>b</sup></td></tr><tr><td>T2</td><td>6.96</td><td>0.71<sup>d</sup></td></tr><tr><td>T3</td><td>6.65</td><td>2.11<sup>ab</sup></td></tr><tr><td>T4</td><td>7.17</td><td>0.68<sup>d</sup></td></tr><tr><td>T5</td><td>6.68</td><td>2.61<sup>a</sup></td></tr><tr><td>T6</td><td>7.23</td><td>0.84<sup>cd</sup></td></tr><tr><td>T7</td><td>7.09</td><td>1.53<sup>bc</sup></td></tr><tr><td>T8</td><td>6.88</td><td>1.79<sup>b</sup></td></tr><tr><td>SEm (±)</td><td>0.228</td><td>0.231</td></tr><tr><td>CD (0.05)</td><td>0</td><td>0.692</td></tr></tbody></table>

<figure><img src="image_2.png" /><figcaption>Fig. 1. pH and EC characteristics of vermicompost as propagated by varying substrate combinations</figcaption></figure>
## 3.2 Micronutrient Content

Significant difference within treatments was observed for Fe, Zn, Cu, B and Mn. Complexing properties of organic matter plays a crucial role in determining the micronutrient availability. Micronutrient stability dictating availability follows the order: Cu²⁺ > Fe²⁺ > Zn²⁺ > Mn²⁺ and Cu²⁺ > Zn²⁺ > Fe²⁺ > Mn²⁺ for humic acid and fulvic acid, respectively [23]. Also, plant available micronutrient release could be due to high rate of mineralization of partially digested earthworm faecal matter by detritus microflora, which is further enhanced by the modification of the physical structure of the ingested material due to muscular action of the foregut which causes increased net surface area for microbial action [24]. T3 reported highest Fe and B readings at 8669.50 mg kg⁻¹ and 37.00 mg kg⁻¹, respectively, which were on par with T2. Similar results were obtained by Jusoh [25] and Shak et al., [26] via comparative studies. *T. harzanium* and *T. asperellum* which form a constituent of Pusa decomposer microbial load, are capable of efficient iron mineralization and further augmenting Fe concentration [27]. *T. asperellum* is efficient in iron mineralization by increasing available Fe levels via siderophore production [28]. Moreover, relatively higher Fe content reported in RS (Table 1), could further enhance

total soluble iron accumulation with the biomass matrix. Pusa decomposer also consists of *A. niger*, which has been reported to express high B mineralization capacities [29,30]. Increased activity of the aforementioned fungal strains can be attributed to increase in organic acid production via lignocellulolytic degradation processes occurring during RS decomposition. B content in T3 was in accordance with experiments conducted by Sharma and Garg [31] and Yan et al., [32]. Peak Mn, Zn and Cu concentrations were detected in T2 at 418.40 mg kg⁻¹, 247.50 mg kg⁻¹ and 55.12 mg kg⁻¹, respectively. This could be due to enhanced enzymatic activity, greater organic matter breakdown to simpler molecules allowing efficient solubilization and complexation of micronutrients via interaction with humic substances [33]. Microbial activity stimulated by earthworms along with biomass colonization by a diverse spectrum of microflora due to Pusa decomposer augmentation during vermicomposting leads to production of various organic acids, such as citric and acetic acids, which can solubilize micronutrients like Cu, Zn, and Mn, thereby, increasing bio-availability [34]. Similar results for Mn, Zn and Cu were obtained by Vidya et al., [35] by vermicomposting of BP via *E. eugeniae* vermiconversion.

<figure><img src="image_3.png" /><figcaption>**Fig. 2.** Micronutrient profile of vermicompost as influenced by different substrate combinations</figcaption></figure>
<table><caption>Table 3. Micronutrient constituents of VC as propagated by different substrate combinations</caption><thead><tr><th>Treatments</th><th>Fe<br>(mg kg<sup>-1</sup>)</th><th>Mn<br>(mg kg<sup>-1</sup>)</th><th>Zn<br>(mg kg<sup>-1</sup>)</th><th>Cu<br>(mg kg<sup>-1</sup>)</th><th>B<br>(mg kg<sup>-1</sup>)</th></tr></thead><tbody><tr><td>T1</td><td>4052.50<sup>b</sup></td><td>280.85<sup>c</sup></td><td>155.50<sup>bc</sup></td><td>34.74<sup>b</sup></td><td>31.60<sup>a</sup></td></tr><tr><td>T2</td><td>7715.75<sup>a</sup></td><td>418.40<sup>a</sup></td><td>247.50<sup>a</sup></td><td>55.12<sup>a</sup></td><td>34.60<sup>a</sup></td></tr><tr><td>T3</td><td>8669.50<sup>a</sup></td><td>336.30<sup>b</sup></td><td>159.60<sup>b</sup></td><td>32.84<sup>bc</sup></td><td>37.00<sup>a</sup></td></tr><tr><td>T4</td><td>3315.00<sup>bc</sup></td><td>133.02<sup>ef</sup></td><td>94.92<sup>ef</sup></td><td>22.37<sup>de</sup></td><td>15.90<sup>b</sup></td></tr><tr><td>T5</td><td>2983.00<sup>bc</sup></td><td>295.12<sup>bc</sup></td><td>154.60<sup>bc</sup></td><td>27.70<sup>bcd</sup></td><td>18.65<sup>b</sup></td></tr><tr><td>T6</td><td>2065.25<sup>c</sup></td><td>84.81<sup>f</sup></td><td>89.60<sup>f</sup></td><td>20.46<sup>e</sup></td><td>16.55<sup>b</sup></td></tr><tr><td>T7</td><td>2768.00<sup>bc</sup></td><td>208.60<sup>d</sup></td><td>133.75<sup>cd</sup></td><td>23.32<sup>cde</sup></td><td>19.95<sup>b</sup></td></tr><tr><td>T8</td><td>2439.00<sup>bc</sup></td><td>163.25<sup>de</sup></td><td>114.89<sup>de</sup></td><td>31.47<sup>bcd</sup></td><td>16.45<sup>b</sup></td></tr><tr><td>SEm (±)</td><td>594.218</td><td>17.145</td><td>7.81</td><td>3.415</td><td>1.842</td></tr><tr><td>CD (0.05)</td><td>1781.463</td><td>51.4</td><td>23.413</td><td>10.239</td><td>5.524</td></tr></tbody></table>

## 4. CONCLUSIONS

In the present study, RS and BP proved to be exemplary substrates in vermicomposting, showing optimal improvement in nutritional profiles in vermicomposts. Thus, RS VC as a major substrate, increases the Fe and B content of the final vermicomposts similar to BP VC. While, BP is a very good substrate for maximum availability of Mn, Zn, and Cu. Innate nutrient rich constitution of RS and high rate of decomposition of BP under vermiconversion when subjected to the conjoined decomposing action of voracious *E. eugeniae* foraging and biomass breakdown via Pusa decomposer, yields VC with enhanced micronutrient dissipating capacity. The interaction of microbial activity with the digestion process of earthworms further enriched the vermicompost with nutrient elements essential for improving the agronomic value of vermicompost. Substrate composition had a significant influence electrical conductivity of the vermicompost. These findings suggest that the choice of substrate is a critical determinant of nutrient profile and quality of vermicompost. The acidic to neutral pH recorded in the vermicomposts represents the best condition for earthworm activities and microbial proliferation, hence enhanced decomposition and release of nutrients. Moreover, utilization of microbial decomposer consortium such as Pusa decomposer, further intensifies the composting process and allows for a wider microflora to colonize and proliferate within the composting micro-climate. Improved nutrient release in T2 and T3 proves potential to optimize nutrient content in vermicompost through modified allocation of substrates in various proportions. These findings provide valuable insights into the microbial augmentation of vermicomposting practices with respect to potent organic manure production with micronutrient fortification within

reduced maturity period while simultaneously managing exploitation of agricultural waste such as paddy stubble and banana pseudostem with an ecologically responsible approach. Thus, bolstering the practical possibilities for achieving sustainable food production systems.

## DISCLAIMER (ARTIFICIAL INTELLIGENCE)

Author(s) hereby declare that NO generative AI technologies such as Large Language Models (ChatGPT, COPILOT, etc.) and text-to-image generators have been used during the writing or editing of this manuscript.

## ACKNOWLEDGEMENTS

Authors are thankful to Department of Soil Science and Agricultural Chemistry, Regional Agricultural Research Station, Kumarakom, Kerala Agricultural University and College of Agriculture, Kerala Agricultural University, Vellayani, Trivandrum, India for providing all facilities required during course of study.

## COMPETING INTERESTS

Authors have declared that no competing interests exist.

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**Peer-review history:**

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