Initial characteristics of raw materials and different growth media
It is evident from Table 1, the pH of HSW and CD was alkaline (7.6 ± 0.17 and 8.2 ± 0.12, respectively). The EC of HSW was higher than CD. The ash content of HSW was lesser than CD; as a result, HSW contained more OM content (86 ± 0.75 %) than CD (78 ± 1.33 %). The TKN content in raw HSW was 11.2 ± 0.40 g/kg, and in CD, it was 8.1 ± 0.23 g/kg. The TP content of HSW was very low, i.e., 2.06 ± 0.05 g/kg as compared to CD, i.e., 7.45 ± 0.30 g/kg. The TK content was 9.48 ± 0.42 and 10.5 ± 0.23 g/kg in CD and HSW, respectively. The C: N ratio of HSW and CD was high, i.e., 44.5 ± 1.85 and 55.8 ± 2.4, respectively. The trace elements content (Cu, Fe, Mn and Zn,) in CD was comparatively higher than HSW.
Vermicomposting process significantly changed the physico-chemical properties of different waste mixtures (Table 2). The vermicompost was much darker in color, had good esthetics and processed into a homogeneous mixture after earthworm activity. The total amount of waste mixture was reduced 1.4–2.5 times after vermicomposting. This clearly indicated that the vermicomposting process significantly helps in abatement of organic matter pollution load in the environment. The physico-chemical characteristics and nutrient status of different substrates used as growing media in this study are given in Table 2.
The NPK content of both the vermicomposts was almost same but significantly higher than soil. The sandy-loam soil used in study was deficit in nitrogen and phosphorus (Table 2). Electrical conductivity (EC) of vermicompost was higher than soil, which may be due to the presence of more salts in the feed of cattle (Sangwan et al. 2010). The micronutrients content was significantly higher in vermicomposts than soil but was within permissible limits as recommended by European and American limits of micronutrients in the compost (Brinton 2000). The C:N ratios of the vermicomposts were 17.3 (V1) and 20.9 (V2). It was in range of a stabilized product for all types of growing media. It is reported that if C:N ratio is >20 plants cannot assimilate mineral nitrogen (Edwards and Bohlen 1996) and may affect the growth and flowering of marigolds in different growing media.
Effect of vermicomposts on marigold plant
Figure 1 represents the heights of marigold plants in different treatments with time. The minimum height was observed in control (soil) and maximum was observed in T4 (at the end of the experiment). It was 2.3 times greater than control. In all the treatments, plant height increased with the percentage of the vermicompost in the soil. In cow dung vermicompost-containing treatments, maximum plant height was observed in treatment T4 (Fig. 1). Similarly, in treatments containing HSW + cow dung vermicompost-containing potting media(T5, T6 and T7), maximum plant height was observed in treatment T7. Similar results of higher plant height with the use of pig manure vermicompost-amended potting media on tomatoes plants were observed by Atiyeh et al. (2000). The results revealed that the plants grown in potting media containing 20 % cow dung vermicompost had highest plant height followed by HSW + cow dung vermicompost. It may be due to more nutrient availability for plant growth in vermicomposts. Raviv et al. (1998) have attributed it to slow release of nutrients for absorption with additional nutrients like gibberellins, cytokinins and auxins, by the application of organic inputs like vermicompost in combination with vermin-wash. Arancon et al. (2008) have reported that different vermicompost dosages have different effects on plant growth. At higher vermicompost dosages in the potting media plant growth may be adversely affected due to higher salt content or excessive nutrient levels. Production of flower buds in different treatments at 30, 45 and 60 day is given in Fig. 2. The bud formation was started in first 30 days in all treatments except control (T1). It was started after 40 days in T1. After 60 days, total no. of buds was same in plants grown in cow dung vermicompost and HSW + cow dung vermicompost-containing potting media (Fig. 2). The flowering first sets in the potting media containing cow dung vermicompost (V1), followed by HSW + cow dung vermicompost (V2), and in last in the control (T1) (Fig. 3). Maximum number of flowers was produced in treatments T4 and T7, i.e., 20 % cow dung vermicompost and 20 % HSW + cow dung vermicomposts, respectively. The diameters of the biggest flower in different treatments are given in Fig. 4. The diameter of the flowers was higher in vermicompost-containing potting media than control. The largest diameter was recorded in treatment T4 followed by treatment T7 and smallest diameter of plants was recorded in control (T1). In control, the lesser growth of the plants resulted in production of smaller-sized flowers. The diameter of the flowers was 8.0 and 7.0 times more than control in treatment T4 and T7, respectively. The diameter of biggest flower increased with vermicomposts content in the potting media except in treatment T3 (Fig. 4).
These results indicate that addition of vermicomposts enhanced the growth and productivity of marigold plants. Atiyeh et al. (2000) have reported that after amendments of 10–20 % vermicompost in potting media, the tomato fruit yields increased significantly. Subler et al. (1998) reported that optimum plant growth responses occurred when 10–20 % vermicompost was amended with potting media which may be due to enhanced micronutrient availability, the presence of plant growth regulators, or the activity of beneficial microorganisms in the vermicompost. But when vermicompost concentration was >40 % in the potting media then the number and diameter of the flowers reduced than control. These antagonistic effects at higher vermicomposts dosage may be due to reduction in aeration and porosity and increased salt concentrations (Tucker 2005). In the present study, potting media was amended up to 20 % with vermicomposts and no adverse effect of vermicomposts was recorded on any studied parameters.
The fresh shoot biomass, fresh root biomass and shoot root ratio are given in Figs. 5, 6 and 7, respectively. The fresh shoot biomass was highest in treatment T4 followed by treatment T7 and T6, i.e., 14.7, 13.5 and 12.1 times higher than control, respectively (Fig. 5). Shoot biomass of the plants was directly influenced by the vermicompost content in the potting media. Maximum shoot biomass was recorded in the 20 % vermicompost-containing potting media (Fig. 5). Similar trend was observed for root biomass (Fig. 6). Lowest root biomass was recorded in control (T1) and highest root biomass was recorded in T4 (20 % cow dung vermicompost). The root biomass increased with the percentage of amendment in the potting media in different treatments. Maximum shoot root ratio was observed in treatment T1 (Fig. 7). Keeling et al. (2003) reported that applying vermicompost tea to oilseed rape plants at the initial stage of growth increased both root development and plant growth.