Compositional Evaluation of Vermicompost Prepared from Different Types of Organic Wastes using Eisenia fetida and Studying its Effect on Crop Growth

Vermicomposting is a process in which earthworms and the associated microorganisms stabilize the organic materials in the soil and convert them to nutrient-rich humus. Earthworms consume most organic materials such as scrap paper, food preparation leftovers and residues, agricultural crop residues, animal manure, yard trimmings and organic byproducts from industries. Vermicompost is the product of vermicomposting, while vermiculture is the rearing of worms for this purpose. Economic benefits include biowastes conversion that reduces waste flow to landfills, elimination of biowastes from the waste stream, reducing the contamination of other recyclables, creation of low-skill jobs at the local level and using relatively cheap and simple technologies that make vermicomposting useful for under-developed agricultural areas (Appelhof, 1993). The three main classes of organic wastes suitable for vermicomposting are generated from animal, plant and urban settlements (Thomas et al., 2012).

Vermicomposting can be added to deprived soils as earthworms convert the soil nutrients into forms which are more readily available to plants such as soluble nitrates, calcium, exchangeable phosphorus, potassium, ammonium nitrogen and magnesium (Edwards and Bohlen, 1996). The vermicompost also has emissions of earthworms and enzymes that improve growth and yield of crops (Kale et al., 1992; Singh et al., 2013).

Recycling organic wastes to vermicompost using earthworms provides a mean to not only produce organic manure locally but also treat organic waste in an eco-friendly manner (Geetanjali, 2007). Vermicompost improves soil health and fertility as they add major and micro nutrients, organic matter and plant growth promoting substances besides improving the soil structure (Gopal et al., 2013).  Vermicompost contains reduced contaminant levels and increased nutrient saturation than the original organic materials (Ndegwa et al., 2000; Laxmi et al., 2014). It consists of water-soluble nutrients and is a very good soil conditioner and organic fertilizer. It is also relatively easier for plants to absorb (Coyne and Knutzen, 2010). The earthworms grind the minerals and uniformly mix them in simpler forms, making nutrients readily available for plants. The digestive systems of the worms create niches for certain species of microbes, thus creating a “living” soil environment (Edwards, 2004). Vermicompost also contains worm mucus that does not let nutrients wash away on watering the plants (Nancarrow and Taylor, 2012).

In small scale system, garden and kitchen wastes are used along with earthworms to digest the organic wastes, such as fruits and vegetables, vegetable and fruit peels and ends, coffee grounds and filters, tea bags, grains such as bread, cracker and cereal, eggshells, leaves and grass clippings, newspapers, paper toweling etc. (Selden et al., 2005). Large scale systems require large quantities of food from reliable sources like dairy manure, sewage sludge, brewery and cotton mill waste, agricultural waste, food processing waste, grass clippings and wood chips (Sherman-Huntoon, 2000; Singh et al., 2013).

The species of earthworms most commonly used for vermicomposting include Eisenia foetida (the red wiggler), Eudrilus eugeniae (African Nightcrawlers), Eisenia hortensis (European nightcrawlers), Perionyx excavatus (Blueworms) and Lumbricus rubellus (Selden et al., 2005). These species can be found in soil rich in organic matter throughout North America and Europe. They live in compost, rotting vegetation and manure piles (Hale, 2008). Since they feed on wastes and are shallow- dwelling, they can easily adapt to living in the confines of a worm bin. However, Lumbricus terrestris are not recommended as they burrow much deeper than can be accommodated by most compost bins (Domínguez and Gómez-Brandón, 2012).
 
The present study was undertaken with the objectives of :
 
1. Analyzing and comparing nutrient contents of vermicompost prepared from different organic wastes locally available using red worm Eisenia fetida.
2. Assessing the growth enhancing ability of vermicompost samples obtained on the selected plants.

All the five vermicompost types produced using different substrates (neem leaves, sugarcane bagasse, orange peels, wheat straw, rice straw and sawdust) in the small scale experiment in pots on trial basis and then grown in tanks, the Vermicompost samples obtained were analyzed for their composition and their effect on plant growth. The vermicompost were prepared during monsoon season from late June to mid September 2018 in the premises of Institute of Home Economics, Hauz Khas, New Delhi, India (Mean temp 30-35°C, humidity 70-75%). The steps were as follows:
 
Collection of Organic Wastes
 
The locally available organic wastes selected for this study were grass, saw dust, wheat straw, bagasse and neem leaves.
 
Preparation of Tank for rearing Eisenia fetida
 
The tank was prepared in the dimensions of 100x40x40cm in length, width and height using concrete, cement, stones as materials for construction on sides and it was filled with grass leaves mixed with cowdung so as to rear maximum number of worms (Eisenia fetida).
 
Experimental Setup for the preparation of Vermicompost
 
Pot experiment
 
In this, cemented pots of sizes 16 inch height x 14 inch diameter, each of capacity 10kg, with small holes at the bottom were used. Small pebbles were placed in these pots followed by spreading a shallow layer of sand of approximately 1 cm. On this layer, 1 kg cow dung was added and then 40 earthworms were introduced in each pot. After adding 5 kg of following substrates separately: grass, wheat straw, saw dust, neem leaves, bagasse in these pots the mixture was covered with big dried leaves and wire mesh. The experiment was set up in duplicate for each substrate. The composting mixture was allowed to stand for 15 days by sprinkling water every 2-3 days. After turning, further incubation was allowed till another 15 days. A set up without earthworms was taken as control. After successful trial run in pots the experiments were set up in pits for the production of vermicompost.
 
Pit experiment
 
Pits of sizes 1m length x 80cm width x 20cm depth, made of bricks, concrete and cement on four sides but not on floors were constructed. The vermicomposting setup was prepared by putting one inch layer of pebble at the bottom and then a shallow layer of sand, 4 kg cow dung layer, earthworm 2 kg over cow dung layer and finally 20kg of organic waste. The five substrates were used in duplicates namely grass, wheat straw, saw dust, neem leaves and bagasse. The contents were covered with a framed wire mesh cover. Turning was done after 2 weeks and water was added regularly to avoid drying up of the biomass.
 
Harvesting Compost
 
Vermicompost was ready after two months (60 days). When the vermicompost was ready, worms were harvested and compost samples were processed for different parameters. The vermicompost samples were allowed to dry in pits/pots for 3-4 days. The samples were collected, sieved and packed inside airtight plastic bags. Samples were stored at refrigeration temperature and analysed for chemical composition and effect on plant growth.
 
C, H, N and S Analysis
 
The contents of carbon, hydrogen, nitrogen and sulphur present in the dried and finely powdered vermicompost samples were analyzed using CHNS analyzer (at Delhi University Instrumentation Center). The samples were homogenized, weighed in tin containers and introduced into the combustion reactor via the Autosampler together with oxygen. After combustion, the resultant gases were separated via GC column and percentage of C H N S was finally detected by a Thermal Conductivity Detector.

Potassium estimation
 
Atomic Absorbance Spectrophotometer (at Delhi University Instrumentation Center) was used for the analysis of potassium element in the vermicompost samples.
 
Phosphorus and humic acid
 
The phosphorus content of vermicompost samples were estimated by acid digestion of sample followed by the use of molybdate reagent (Jackson,1973). Vermicompost samples were examined for humic Acid content using the methods reported in the literature (Page, 1982).
 
Effect of vermicompost on plant growth
 
Tomato, brinjal and capsicum plants were grown for two months in the soil supplemented with the vermicompost samples and in the soil without vermicompost (control). Fresh and Dry Weights were measured in all the vermicompost samples.
 
Statistical analysis
 
Two-way analysis of variance (ANOVA) was computed using SPSS (version No. 10) to  test the level of significance of difference between the vermicompost samples produced by the Eisenia fetida during vermicomposting of different organic wastes samples with respect to nutrient parameters and effect of vermicompost on plant growth.

Vermicomposting has been proven to be a very efficient method of increasing crop production and yield, due to high nutritional content and better water percolation and aeration of soil. It also improves plant growth by enhancing germination and crop yield, improving root growth and structure and enriching the soil with microbes. In this study, we try to understand the various aspects of vermicomposting when earthworm Eisenia fetida (red-worms) are grown on different organic waste materials such as grass, saw dust, wheat straw, sugarcane bagasse, neem leaves, etc. We have quantified the nutrient quality of the various vermicompost samples obtained from these locally available organic wastes and studied the effect of the obtained vermicompost samples on the growth of some crops such as tomato, brinjal and capsicum.

The results confirmed the ability of E. fetida to convert these organic wastes into nutritious vermicompost. The major nutrient and the organic carbon contents in the vermicompost produced using these wastes are given in Table 1 and 2.



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C, N, H and S estimation
 
It can be clearly seen that the vermicompost produced from neem leaves had the highest Organic Carbon content (31.40%) followed by sawdust based vermicompost (26.56%). The maximum total nitrogen content present in the vermicompost the samples was also observed in neem leaves vermicompost (2.147%) followed by wheat straw vermicompost (1.847%). Similarly, neem leaves vermicompost showed maximum hydrogen and sulphur content (Table 1). C/N ratio below 20 was observed in all the vermicompost samples which show increased availability of nitrogen to the growing plants when added to them. Similar results were reported for bagasse vermicompost by Thomas et al (2012). When the C/N ratio for an organic substrate ranges between 1 and 15, mineralization and release of Nitrogen occurs very rapidly, which can then be taken up by plants. The lower the C/N ratio, the more rapidly nitrogen will be released into the soil for immediate crop use (Brust 2019). In all the five organic wastes, vermicomposting resulted in lowering of C/N ratio, the most significant decrease was in sawdust from 325 to 18.16 followed by  bagasse vermicompost showing C/N ratio 16.19 as compared to control with C/N ratio of  110.  Vermicomposting also resulted in lowering C/N ratio for other organic waste indicating improved fertilizer quality of vermicomposts prepared from the organic wastes (Table 1).
 
Potassium, phosphorus and humic acid estimation

Analysis of Potassium, Phosphorus and Humic Acid content of different vermicompost samples show that these samples differ greatly in their composition (Table 2). Wheat straw based vermicompost show maximum potassium (17.2mg/g) followed by bagasse based vermicompost sample which also show comparatively high potassium content (16.3 mg/g). The phosphorous contents of all the vermicompost samples were found to be in the range of 14-20 mg/g). Increase in the content of N and P in vermicompost samples were also reported by Liu et al (2012). Humic Acid content of the vermicompost samples were in the range of  (0.034-0.089 g/g) with maximum content seen in wheat straw. Other researchers also reported that earthworm casts or vermicompost possess high contents of nitrogen (Bansal and Kapoor, 2000), phosphorus (Pramanik et al., 2010) and humic acids (Atiyeh et al., 2002; Arancon et al., 2006).
 
Effect on plant growth
 
Vermicomposting converts the unavailable forms of nutrients present in soil to the forms that are readily available to the plants, due to combined actions of earthworms and their respective microorganisms (Edwards and Fletcher, 1988). In all cases, better growth in terms of fresh weight and dry weight was observed in case of plants grown with vermicompost than control plants without vermicompost, as shown in Fig 1-3 and Table 3. The increase in plant growth in case of added vermicompost is attributed to high N, P, K, humic acid and plant growth hormones.



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Also, through this study it was possible to transform some agricultural wastes into useful products, which otherwise would have been dumped into a landfill or burnt, both of which would have been a waste, or resulted in pollution. Organic farming is sustainable farming, as it is environmental friendly. Vermicompost is nutritionally richer than manure and chemical fertilizers. It acts as a growth promoter and protects crop plants. Many reports talk about the improvements in growth, physiology and biochemistry of plants when treated with vermicompost (Sangeetha and Thevanathan, 2010; Illanjiam et al., 2019).

High organic carbon and high content of major nutrients N, P, K and Humic Acid in the vermicompost samples prepared from different organic wastes available locally establishes the ability of the Eisenia fetida to effectively recycle these wastes to valuable manure at farm level. In this paper, the role of vermicomposting in agriculture as well as in waste management has been emphasized, by showing better nutritional values of vermicompost and also the increased crop production in vermicompost treated soil. In all types of vermicomposts, growth of tomato, brinjal and capsicum were seen to be better than soil without vermicompost. All these observations strengthen our understanding of the role of vermicomposting in waste management and agriculture. Moreover, we also observed that the C/N ratio of the soil highly decreased on adding vermicompost, which indicates the increase in Nitrogen concentration, which is beneficial to plants. We successfully obtained better growth of plants while minimizing and utilizing agricultural wastes. Consequently, the observed results strongly suggest that vermicompost and its beneficial microbes might be explored as efficient for the enhanced growth of vegetable crops in the near future.

We would like to thank UGC (University Grants Commission) for their financial support in this major project.

All authors declare that they have no conflict of interest.