Introduction

Quality manure can help to heal up the degraded soil health and vermicompost is one of the good options for that. Vermicomposting is a bio-oxidative process in which detritivorous earthworms interact with some microorganisms and other fauna within the decomposer community, accelerating the stabilization of organic matter and greatly modifying its physical and biochemical process (Domínguez 2004). It is very effective, cheap, environment friendly, and easy method of recycling biodegradable waste using selected species of earthworms. Through eating, burrowing, and casting, earthworms modify the physical, chemical, and biological properties of organic matter and soil.

The epigeics among the three ecological categories of earthworms is used in vermicomposting. The biochemical decomposition of organic matter is primarily accomplished by the microbes; however, earthworms are the crucial drivers of the process by fragmenting and conditioning the substrate, and by increasing the surface area of organic substance available for microbial attack after comminution (Domínguez et al. 2010). In vermicomposting process, earthworms add various intestinal microflora in matrix; moreover, gut enzymes play dominant role in this process (Whiston and Seal 1988). They also change pH and organic matter dynamics in terms of quality and quantity, microbial and invertebrate activity, and the abundance, biomass, species composition, and diversity of the microflora and fauna (Lavelle et al. 1998).

Different organic substances have different palatability, nutrient content, and constituents which may influence the growth and performances of earthworms (Suthar 2007). These factors may also affect the quantity and quality of vermicompost produced. Yan et al. (2013) found that nutrients in initial organic waste material affects the nutrient contents of vermicompost and there was a positive correlations between nutrient contents in raw plant residues and vermicompost for N, K, and Ca. Vermicompost is proving to be highly nutritive organic fertilizer and more powerful growth promoter against the destructive chemical fertilizers which has destroyed the soil properties and decreased its natural fertility over the years. Higher content of nutrients in vermicompost have been reported by numerous researchers (Lourduraj and Yadav 2005; Gurav and Pathade 2011; Abdelmonem et al. 2016).

Among the commonly used feeding materials, water hyacinth is an important one. It is a hydrophyte that uptakes heavy metals and stores in its biomass. These plants are called bio-accumulators as they accumulate the contaminants in their tissues (Boyd 1970). Water hyacinth has high tolerance against contaminants like heavy metals and is able to absorb large quantities. Heavy metal content of cow dung and poultry manure depends on the feed stuffs supplied for those cattle and poultry. Again, source materials which used as poultry litter have effects on the heavy metal content of that poultry litter. During vemicomposting, the heavy metal content decreases to some extent that resulted reduced content of those metals in vermicompost. Numerous research findings supported the issue (Kagi and Kojima 1987; Jain et al. 2004; Pattnaik and Reddy 2011; Singh and Kalamdhad 2013; Suthar et al. 2014). On the other hand, some researchers have reported the increased total heavy metal concentrations in vermicomposts than the feeding substances (Khwairakpam and Bhargava 2009; Suthar 2010; Hait and Tare 2012).

Soil health is one of the key factors for sustainable farming and food security. In some cases, degraded soil quality is hampering crop cultivation seriously. Application of vermicompost can be a good option to heal up the soil health when these vermicomposts would be quality assured, i.e., rich in plant nutrients, level of toxic element, and/or heavy metal lies within the tolerable range. The variations in quality of vermicompost produced from the different organic substances offer an insight into the effect of initial feeding materials on the nutrient content of vermicompost produced. Research is needed to assess productivity and quality of vermicompost produced from different sources using various earthworm species. Hence, the present study was undertaken to evaluate the performance of earthworm species to produce quality vermicompost as well as suitability of feeding materials used in vermicomposting.

Materials and methods

Experimental location

The experiment was carried out in the vermicompost shed of the Department of Soil Science, Sylhet Agricultural University (SAU) of Bangladesh. The chemical analysis was done in the departmental laboratory at SAU and partially in the regional laboratory, Soil Resource Development institute (SRDI), Sylhet.

Experimental design

The study was carried out using chari (cement-made bowl shaped jar) following factorial CRD with three replications. A total of 24 chari was used and kept in 3 sets; 12 chari for E. fetida and 12 for E. eugeniae.

Treatments

Eight treatment combinations using the following two factors were tested.

  • Factor-A: 2 (Earthworm species)

    • Two species of earthworms: Eisenia fetida and Eudrilus eugeniae

  • Factor-B: 4 (Feeding materials/substrate)

The feeding materials used in the experiments were cow dung, cow dung + water hyacinth, cow dung + poultry litter, and poultry litter + water hyacinth. The ratio of substrate is presented in Table 1. The treatment combinations were as follows:

  • T1: E. fetida-cow dung, (ECD)

  • T2: E. fetida-cow dung + water hyacinth, (ECDWH)

  • T3: E. fetida-cow dung + poultry litter, (ECDPL)

  • T4: E. fetida-poultry litter + water hyacinth, (EPLWH)

  • T5: E. eugeniae-cow dung, (EuCD)

  • T6: E. eugeniae-cow dung + water hyacinth, (EuCDWH)

  • T7: E. eugeniae-cow dung + poultry litter, (EuCDPL)

  • T8: E. eugeniae-poultry litter + water hyacinth, (EuPLWH)

Table 1 Substrate (feeding materials) ratio used for different treatment combinations
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Collection of earthworm species

Eisenia fetida

The earthworm species E. fetida was collected from “Mon Vermicompost” of South Surma upazila (sub-district) under Sylhet district of Bangladesh. It is commonly known as redworm or red wiggler worm. They are epigeic and rarely found in soil. They are actually native to Europe, but have been introduced to every other continent except Antarctica.

Eudrilus eugeniae

This species was collected form “Annopurna Agro Service” of Domar, Nilphamari district of Bangladesh. E. eugeniae popularly known as the “African Night Crawler” is a large, rapidly growing, prolific, and ideal epigeic vermicomposting worm under tropical conditions.

Collection and thermophilic pre-composting of feeding materials

Among the feeding materials, cow dung and poultry litter were collected from nearby commercial dairy and poultry farm, respectively. In those farms, cattle and poultry are fed with controlled supply of fixed feed stuff. The main feed stuff used in the respective dairy farm is rice straw, green grasses collected from surrounding fields, mustard oilcake, etc. Again, sawdust is the bedding material used in the poultry farm from where the poultry litter was collected. Fresh water hyacinth was collected from a canal beside BSCIC (Bangladesh Small and Cottage Industries Corporation) industrial area at Khadimnagar, Sylhet. Each of the feeding stuff was allowed for 21 days of pre-composting. The materials were placed in the form of heaps under shady place. Watering was done regularly twice in a day in order to maintain the optimum temperature and moisture. Following pre-composting, respective amounts of the feeding materials were collected randomly for each treatment and mixed thoroughly for use in the experiment. Each of the feeding materials was sampled at the starting and at end of the pre-composting process for chemical analysis.

Processing and chemical analysis of feeding material sample

The collected feeding material samples were air-dried first in a shady place followed by oven drying for 24 h at 65 °C. To obtain homogenous powder, the samples were finely ground by using a grinding mill to pass through a 60-mesh sieve. Such processed samples were analyzed chemically to determine cadmium and lead contents using the methods described in Table 2.

Table 2 Methods used for chemical analyses of feeding materials and vermicompost
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Acclimatization of earthworms

The collected earthworms of both species were kept first in earthen chari for a period of 21 days, in order to allow them to adapt to the weather of the experimental site. During this period of acclimatization, the worms were fed with cow dung. After that, sufficient amount of the worm species was transferred for a short period of 10 days in the respective pre-composted feeding materials or mixture of feeding materials as stated in the treatment section of this manuscript. This was done for adapting themselves to the experimental feeding materials prior to starting actual experiment.

Experimental set up

Earthworms of similar sizes were carefully selected from the earthen pots for further studies. A total of 100 g earthworms were introduced in each of the chari. The chari was covered with wet gunny bags to maintain the optimal moisture. Distilled water was sprinkled on the materials when necessary, to maintain moisture level of 70% (wet weight basis). The experiment was set in shed to avoid direct sunlight. Each of the chari was monitored every day. Three replicates were maintained for each of the treatments.

All the chari were maintained in the shed for an incubation period of 45 days. The appearance of black granular powder on top of feeding stuff indicates harvest stage of compost. Watering was stopped for at least 5 days before this stage. After completion of the incubation period, all of the earthworms were removed from the chari manually by hand sorting. Following separation from vermicompost, the total number and biomass of live earthworms were measured through quantification and weighing scale. Then the materials in each chari were made to pass through a bamboo made sieve to separate vermicompost from other residual debris. All the sieved samples were gently mixed to achieve homogeneity. The samples were spread on a brown paper in the laboratory for air-drying. The processed samples were kept in polythene bags for subsequent chemical analysis.

Data collected

  1. 1.

    Amount of vermicompost produced: The separated vermicompost were air-dried and weighed to get the amount of vermicompost produced in each of the treatments.

  2. 2.

    Collection and chemical analysis of vermicompost samples: Vermicompost samples were collected replication wise for each of the treatments randomly from the freshly harvested vermicompost heap. The collected samples were then air-dried and preserved for chemical analysis. Chemical analysis was done to determine the chemical properties of vermicomposts using the methods cited in Table 2. Vermiremoval of cadmium and lead from the feeding materials was calculated using the contents of these metals in feeding materials and vermicomposts. The total content of heavy metals (cadmium and lead) in organic materials before and after pre-composting was found almost the same. Hence, vermiremoval of cadmium and lead from the feeding materials was thus calculated using the contents of these metals in feeding materials (pre-composted) and vermicomposts.

  3. 3.

    Change in weight of earthworm populations: After the completion of the experiment, earthworms in each chari were separated from vermicompost carefully and were weighed to get their live weight. The differences between initial and final weights of the earthworm were calculated to estimate the changes in weight of earthworm populations.

  4. 4.

    Change in number of earthworm populations: At the start of experimentation, the number of earthworms comprising in 100 g of weight for each chari was counted. Accordingly, at the end of the study, the final numbers were counted to find out the changes taking place in the number of earthworm population during experimentation.

Statistical analysis

Data recorded on different parameters were subjected to statistical analysis through computer-based statistical program R following the basic principles, as outlined by Gomez and Gomez (1984). Significant effects of treatments were determined by analysis of variance (ANOVA) and treatment means were compared at 5% level of significance by Duncan’s Multiple Range Test (DMRT).

Results

Effect of earthworm species and feeding materials on vermicompost productivity and earthworm biomass

Vermicompost productivity

The vermicompost productivity was affected significantly by the earthworm species used in the study (Table 3). The highest amount of vermicompost was produced by E. fetida (456.7 g kg−1) and the lowest amount (414.9 g kg−1) was produced by E. eugeniae. Feeding materials used in the study had significant role in vermicompost productivity. The highest productivity was recorded by using cow dung (512.9 g kg−1) followed by cow dung–poultry litter (484.1 g kg−1), and the lowest productivity was found from using poultry litter–water hyacinth (387.2 g kg−1) as feeding materials. Accordingly, interactions of earthworm species and feeding materials were found to affect significantly the vermicompost productivity. The highest productivity was observed from the interaction of E. fetida–cow dung (534.4 g kg−1) followed by E. eugeniae–cow dung (491.4 g kg−1), and E. eugeniae–cow dung + poultry litter (487.0 g kg−1) interactions.

Table 3 Effects of earthworm species, feeding materials, and their interactions on vermicompost production and dimension of earthworm population
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Increase in earthworm biomass

During the incubation period, the weight of earthworm population increased at different rates in different treatments (Table 3). Earthworm species affected significantly the rate of such increase in biomass. The highest increase in biomass was found for E. eugeniae (20.17%) and the lowest was in E. fetida (12.00%). Earthworm biomass was also significantly increased by the feeding materials used. Among the feeding materials, cow dung influenced for the highest biomass (28.83%) and cow dung–water hyacinth helped for the lowest biomass of earthworm (10.00%). Cow dung + poultry litter (13.00%) and poultry litter + water hyacinth (12.50%) had statistically similar role in biomass production. Interaction of earthworm species and feeding materials affected earthworm biomass significantly during the experiment. The highest role in earthworm biomass production (31.67%) was played by E. fetida when the feeding material was cow dung and it was followed by E. eugeniae (26.00%). The lowest biomass was produced by E. fetida when fed with poultry litter + water hyacinth (2.67%).

Increase in earthworm number

Like earthworm biomass, earthworm number was also significantly increased by earthworm species, feeding materials, and also by their interaction (Table 3). E. fetida and E. eugeniae influenced for the highest and lowest increase in earthworm number (16.67 and 5.24%, respectively). Cow dung influenced for the highest increase in earthworm number (14.38%) followed by cow dung + water hyacinth (10.70%) and the lowest increase was in poultry litter–water hyacinth (9.13%) as feeding materials. E. fetida–cow dung interaction showed the highest increase in earthworm number (23.23%) followed by E. fetida–cow dung + water hyacinth (17.48%). E. fetida–cow dung + poultry litter and E. fetida–poultry litter + water hyacinth had statistically similar effects on earthworm number (13.27 and 12.73%, respectively).

Effect of earthworm species and feeding materials on vermiremoval of cadmium and lead from organic feeding materials

Vermiremoval of cadmium from feeding materials

Significant reduction in cadmium content of different vermicomposts as compared with that of respective feeding materials was recorded due to earthworm species used in the study (Table 4). Lower cadmium content was recorded for vermicompost produced by using E. fetida (0.135 ppm) than E. eugeniae (0.310 ppm). While comparing with the cadmium content of feeding materials, significantly higher removal was found in using E. fetida (60.43%) than E. eugeniae (8.18%). Cadmium content of vermicompost and its vermiremoval, both parameters varied markedly with the feeding materials used in the experiment. The lowest content (0.198 ppm) was recorded in vermicompost produced from poultry litter–water hyacinth while the highest content (0.267 ppm) was found in case of cow dung + water hyacinth substrate. Again, the highest removal of cadmium was observed in vermicompost from cow dung + poultry litter (41.41%) followed by poultry litter–water hyacinth (34.39%) and cow dung (32.86%) as feeding materials. The interaction effects of earthworm species and feeding materials (substrate) on cadmium content and its vermiremoval varied significantly (Table 3). The lowest cadmium content (0.107 ppm) as well as the highest vermiremoval (65.12%) was recorded for vermicompost produced from the interaction effect of E. fetida and poultry litter + water hyacinth. On the other hand, the highest content (0.367 ppm) as well as the lowest vermiremoval of cadmium (1.62%) was found from E. eugeniae and cow dung + water hyacinth interaction.

Table 4 Effects of earthworm species, feeding materials, and their interactions on the content of cadmium and lead in vermicomposts, and their vermiremoval from feeding materials
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Vermiremoval of lead from feeding materials

Earthworm species had significant role on the removal of lead from organic substrate through vermicomposting process (Table 4). E. fetida was found to be more efficient in removing lead (48.18%) through vermicomposting which produced vermicompost having less content of lead (4.31 ppm) than E. eugeniae that showed 22.33% of lead removal from the feeding materials and a content of 6.38 ppm lead in vermicompost. Different feeding materials were found to have significant role on the vermiremoval of lead. The use of cow dung has resulted in the highest removal of lead (67.31%) from the feeding materials and hence the lowest content of lead (2.42 ppm) in vermicompost was observed. Again, the lowest removal of lead (22.76%) and the highest content (7.76 ppm) was recorded while using cow dung + water hyacinth as feeding material. Significant variations were found in vermiremoval of lead from feeding materials and the content of lead in vermicomposts due to the interaction of earthworm species and feeding materials used. The highest removal was noticed in E. fetida–cow dung interaction (74.16%) followed by E. eugeniae–cow dung (60.46%), E. fetida–poultry litter + water hyacinth (43.44%), and E. fetida–cow dung + poultry litter (43.38%) interaction. Accordingly, the lowest content of lead in vermicompost was observed in E. fetida–cow dung interaction (1.92 ppm) followed by E. eugeniae–cow dung (2.93 ppm), E. fetida–cow dung + poultry litter (3.64 ppm), and E. fetida–poultry litter + water hyacinth (4.83 ppm) interaction.

Effect of earthworm species and feeding materials on pH and nutrient content of vermicompost

Measurement of pH of vermicompost

The pH values of vermicomposts varied significantly due to earthworm species, feeding materials, and their interactions in the study (Table 5). Slightly alkaline pH (7.39) was observed for E. fetida while slightly acidic pH was noticed for E. eugeniae. Due to the effect of feeding materials, pH of vermicomposts ranged from 6.81 to 7.31. The highest value of pH was recorded for cow dung + water hyacinth while the lowest value was found for poultry litter + water hyacinth feeding material. The interactions of earthworm species and feeding materials also affected for the highest pH value (7.65) by the E. fetida–cow dung interaction followed by E. fetida–cow dung (7.63) interaction. These two interactions had statistically similar effects on pH of vermicompost. Again, the lowest pH value (6.63) was found in the E. eugeniae–cow dung interaction. Vermicomposts derived from interactions of Eudrilus eugeniae and feeding materials have considerably lower pH value than vermicomposts from interactions of E. fetida and feeding materials.

Table 5 Effects of earthworm species, feeding materials, and their interactions on different parameters/nutrients in vermicompost
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Total nitrogen content of vermicompost

Different feeding materials used in the study significantly influenced the nitrogen content of vermicomposts where the highest content (1.91%) was found for using cow dung and the lowest (1.71%) was for poultry litter + water hyacinth as feeding material (Table 5). The earthworm species as well as the interaction between earthworm species and feeding materials did not affect the nitrogen content of vermicompost at all.

Available phosphorus content of vermicompost

Earthworm species had significant role on available phosphorus content of vermicompost (Table 5). The highest phosphorus content was observed with E. eugeniae (0.557%) where the lowest was found with E. fetida (0.474%). Again, the feeding materials also had significant effect on the available phosphorus content where it ranged from 0.365 to 0.622%. The highest content was measured for poultry litter + water hyacinth feeding materials and it was statistically similar with that of cow dung + poulty litter (0.580%). The lowest content of phosphorus was found in cow dung as feeding materials. The interactions between earthworm species and feeding materials have no significant role on the phosphorus content of vermicomposts where it ranged from 0.323 to 0.650%.

Exchangeable potassium content of vermicompost

Exchangeable potassium content of vermicomposts was not significantly varied with earthworm species where it ranged from 1.033 to 1.045% (Table 5). The feeding materials used in the experiment significantly affected the potassium content of vermicompost. The highest content was observed for cow dung + water hyacinth (1.289%) feeding materials followed by poultry litter + water hyacinth (1.013%) and cow dung + poultry litter (0.952%). The lowest content was observed for cow dung (0.902%) as feeding materials. The interaction between earthworm species and feeding materials did not affect significantly the potassium content of vermicompost where it varied from 0.877 to 1.350%.

Available sulfur content of vermicompost

Available sulfur content of vermicompost did not vary significantly by the earthworm species used in the study and it ranged from 0.209 to 0.217% (Table 5). On the other hand, it was significantly influenced by the use of different feeding materials. The highest sulfur content was recorded for cow dung + poultry litter (0.322%). The other three feeding materials have statistical at par effects on sulfur content of vermicomposts. The interactions between earthworm species and feeding materials did not play any significant role on the sulfur content of vermicomposts where it ranged from 0.141 to 0.337%.

Available zinc content of vermicompost

Earthworm species, those used in the experiment, did not influence significantly the zinc content of vermicomposts (Table 5). The highest zinc content was found 55.21 ppm while the lowest content was observed as 54.66 ppm. Accordingly, the interactions of earthworm species and feeding materials did not show any significant effect on zinc content of vermicomposts. On the other hand, different feeding materials used in the experiment affected significantly the zinc content of vermicomposts produced in the experiment. The highest zinc content was observed for poultry litter + water hyacinth (56.75 ppm) and similar effect was noticed for cow dung + water hyacinth (56.40 ppm) feeding materials. The lowest zinc content was observed for cow dung (52.88 ppm) which is followed by cow dung + poultry litter (53.73 ppm) as feeding materials.

Available boron content of vermicompost

Available boron concentration in produced vermicomposts varied significantly due to the feeding materials used in the study where it ranged from 56.2 to 61.3 ppm (Table 5). The highest content was noticed for using cow dung + poultry litter as feeding materials and it had statistical similarities with that of using only cow dung. Use of different earthworm species and their interaction with feeding materials had offered no significant role in the boron content of vermicomposts produced.

Discussion

Between the two earthworm species, E. fetida has performed better than E. eugeniae in terms of the amount of vermicompost produced. On the other hand, using only cow dung as feeding materials produced the highest amount of vermicompost comparing the other three combinations of feeding material. Accordingly, interaction of E. fetida–cow dung has also produced the highest amount of vermicompost among the interactions used in the study. Higher increase in earthworm biomass was found for E. eugeniae than for E. fetida. Larger body weight and voracious intake of food might be contributed to the issue. On the other hand, cow dung as feeding materials, has influenced for the highest number and biomass production of earthworm species. It might be due to the palatability of cow dung as feeding materials. Again, the interaction of E. fetida–cow dung had the highest role in earthworm biomass production. The influence of E. fetida as earthworm species was the highest increase in earthworm number. The interaction of E. fetida–cow dung showed the highest increase in earthworm number. Yadav and Garg (2011) described that the higher growth rate in a particular feeding substrate may be due to the more delectability and desirability of feed by worms. Suthar (2007) also realized that substrates that are easily decomposable and have excess nutrients will be more acceptable to earthworm. E. eugeniae escalated in total biomass much more rapidly than E. fetida, a species which grows relatively well in most organic wastes (Edwards 1988).

Vermiremoval of cadmium was found due to the use of both earthworm species and feeding materials as well as their interaction effects. In this context, the effect of earthworm species E. fetida, cow dung + poultry litter as feeding material and the interaction effects of E. fetida and poultry litter + water hyacinth were found promising. Again, E. fetida was found to be more efficient in removing lead from contaminated feeding materials. Accordingly, using cow dung as feeding materials and the effect of E. fetida–cow dung interaction have also resulted in the highest removal of lead from the feeding materials. It is assumed that earthworms’ gut has some mechanisms which bind different heavy metals like lead to form complexes or other unavailable forms. During vermicomposting, the heavy metals forms complex, aggregates with humic acids, and other polymerized organic fractions resulting in lower availability of these heavy metals to the plant, which are otherwise phytotoxic (Dominguez and Edwards 2004). The lower removal of those heavy metals from feeding materials, i.e., the higher content of those metals in vermicomposts might be contributed by the higher content of those metals in the feeding materials. Another reason might be contributed to the issue; several studies have shown that earthworms have a high potential for biological bioremediation of contaminated soils (Suthar et al. 2008; Nahmani et al. 2009; Li et al. 2010; Hirano and Tamae 2011). Although there are some contradictory reports available (Khwairakpam and Bhargava 2009; Hait and Tare 2012) but it is also reported that earthworms have some mechanisms to accumulate a high concentration of heavy metals like cadmium and lead in their body while the feeding material passes through their gut (Shahmansouri et al. 2005; Li et al. 2010; Brewer and Barrett 1995; Bamgbose et al. 2000). Again, some of the heavy metals are essential micronutrients for plants at lower doses, but in higher doses they may cause metabolic disorders and growth inhibition in most plant species (Sinha et al. 2005). Azizi et al. (2013) found that concentrations of heavy metals, namely Cr, Cd, and Pb in vermicompost were lower than initial concentrations in the raw materials while that of Cu and Zn were found to have increased compared with initial concentrations.

There was a reduced pH value observed in the vermicomposts than in the feeding materials used. It might be due to the different biochemical reactions occurred in the earthworms’ gut. Besides this, the pH values of vermicomposts were guided by that of the feeding materials used as the trend of pH in vermicomposts has similarities with that of the feeding materials. Regarding this issue, Ndegwa et al. (2000) opined that different substrate would result in the formation of a different intermediate; hence, there is a difference in pH of the vermicompost formed. Slightly alkaline pH was observed for E. fetida while slightly acidic pH was noticed for E. eugeniae. Vermicomposts derived from interactions of E. eugeniae and feeding materials have considerably lower pH value which lies in neutral or below neutral pH value. On the other hand, vermicomposts from interactions of E. fetida and feeding materials have pH that mostly lie in the upper ranges from neutral. Such findings indicate that E. eugeniae has some capability to reduce pH of alkaline substrate through composting.

The earthworm species E. eugeniae and poultry litter + water hyacinth as feeding material influenced for higher available phosphorus content. This feeding material, i.e., poultry litter + water hyacinth also showed the highest zinc content in vermicompost though cow dung + water hyacinth had the similar effect. This might be due to the nutrient content of feeding materials; in each case, there was an inclusion of water hyacinth which has higher content of P and Zn as found from the analytical results. It should be noted here that in most cases the Zn content in the vermicomposts is comparatively higher than that of the respective feeding materials. The findings of this study are in accordance with the study who found increased Zn content in the vermicompost (Sainz et al. 1998). For exchangeable potassium content of vermicomposts, cow dung + water hyacinth performed better as feeding materials while cow dung + poultry litter was found promising for sulfur and boron content of vermicompost. Here, it can also be assumed that the S and B content of feeding materials contributed for the higher content of those nutrient elements in vermicomposts. It is because the higher content of S and B was found in the chemical analysis of poultry litter which was one of the components of those higher S and B producing feeding materials. Yan et al. (2013) showed that nutrient in initial wastes material affects the nutrient contents of vermicompost. Vermicompost contains enzymes like amylase, lipase, cellulase, and chitinase, which can break down the organic matter in the soil to release the nutrients and make it available to the plant roots (Chaoui et al. 2003).

Conclusions

Both the earthworm species, i.e., E. fetida and E. eugeniae are promising in vermicomposting though there are some variability regarding quantity and quality of produced vermicompost. The choice of feeding materials used in vermicomposting is also important for quality concern of vermicompost.