Handbook of Vermicomposting by E.SREENIVASAN - HTML preview

CHAPTER 10

VERMICOMPOST: QUANTITY & APPLICATION

Vermicompost can be used for all crops: agricultural, horticultural, ornamental and vegetables at any stage of the crop and in any amount as it is ‘completely safe’ for soils and crops in all amounts.

• For general field crops: Around 2–3 t per ha vermicompost is used by mixing with seed at the time of sowing or by row application when the seedlings are 12–15 cm in height. Normal irrigation is followed.
• For fruit trees: The amount of vermicompost ranges from 5 to 10 kg per tree depending on the age of the plant. For efficient application, a ring (15–18 cm deep) is made around the plant. A thin layer of dry cow dung and bone meal is spread along with 2–5 kg of vermicompost and water is sprayed on the surface after covering with soil.
• For vegetables: For raising seedlings to be transplanted, vermicompost at 1 t per ha is applied in the nursery bed. This results in healthy and vigorous seedlings. But for transplants, vermicompost at the rate of 400–500g per plant is applied initially at the time of planting and 45 days after planting (before irrigation).
• For flowers: Vermicompost is applied at 750–1000 kg per ha.
• For vegetable and flower crops vermicompost is applied around the base of the plant. It is then covered with soil and watered regularly.

Scientists at the Central Research Institute for Dryland Agriculture, Hyderabad, India have recommended the quantity and time of application of vermicompost which is given in Table.7 (CRIDA, 2009)

The Value of Vermicompost

Vermicompost provides many benefits to agricultural soil, including increased ability to retain moisture, better nutrient-holding capacity, better soil structure, and higher levels of microbial activity. Literature survey shows that vermicompost is superior to conventional organic manures in a number of ways. These include:

• Rich in humic acids and enzymes: The growth responses of plants from vermicompost appears more like ‘hormone-induced activity’ associated with

Table.7: Recommended quantity and time of application of vermicompost in some crops

(Source: CRIDA (2009), Hyderabad, India)

the high levels of humic acids and humates in vermicompost rather than boosted by high levels of plant-available nutrients. Vermicompost is alsorich in enzymes like amylase, lipase, cellulase and chitinase, which break down organic matter, improving soil nutrients and fertility. (Chaoui,H.I, et al, 2003; Tiwari, S.C, et al, 1989) They also increase some important soilenzymes like dehydrogenase, acid and alkaline phosphatases and urease. Urease plays a key role in nitrogen cycle as it hydrolyses urea and phosphatase bioconvert soil phosphorus into bio-available form for plants.

• Free of pathogens and toxic chemicals: Several studies have indicated that vermicomposting leads to greater reduction of pathogens after 3 months upon storage. Whereas,the samples which were subjected to only thermophilic composting, retained higher levels of pathogens even after 3 months. Studies have also found that earthworms effectively bioaccumulate or biodegrade several organic and inorganic chemicals including heavy metals, organochlorine pesticide and polycyclic aromatic hydrocarbons (PAHs) residues in the medium in which it inhabits.

• Plant nutrient level: Vermicompost contains nutrients in plant-available forms such as nitrates (N), phosphates (P), soluble potassium (K), & magnesium (Mg) and exchangeable phosphorus (P) and calcium (Ca). Vermicomposts have large particulate surface areas that provide many micro-sites for microbial activities and for the strong retention of nutrients.

• Beneficial microbes: Vermicompost is rich in microbial populations particularly fungi, bacteria and actinomycetes. Suhane (2007) found that the total bacterial count was more than 1010 per gram of vermicompost. It included Actinomycetes, Azotobacter, Rhizobium, Nitrobacter and phosphate solubilizing bacteria (PSB) which ranged from 102-106 per gm of vermicompost. The PSB has very significant role in making the essential nutrient phosphorus (P) bio-available for plant growth promotion. The microbial population in vermicompost prepared from cow dung and municipal solid wastes as substrates was in highest abundance. Application of lime in the substrate enhanced the population of all above mentioned microbes irrespective of the substrates used for vermicomposting. Plant growth promoting bacteria (PGPB) directly stimulates growth by nitrogen (N) fixation, solubilisation of nutrients and production of growth hormones. There is also evidence to demonstrate that microbes, including bacteria, fungi, actinomycetes, yeasts and algae, produce plant growth regulators  (PGRs) such as auxins, gibberellins, cytokinins, ethylene and ascorbic acids in appreciable quantities.

• Stimulate plant growth: Vermicompost has consistently improved seed germination, enhanced seedling growth and development and increased plant productivity much more than would be possible from the mere conversion of mineral nutrients into plant-available forms. Vermicompost contains growth promoting hormone auxins, cytokinins and flowering hormone gibberellins secreted by earthworms. In 2006, Arancon, et al attributed the growth promoting effect of vermicompost to humic acids present in it. Vermicomposted organic wastes have beneficial effects on plant growth independent of nutritional transformations and availability. Whether they are used as soil additives or as components of horticultural soil less media, vermicomposts have consistently improved seed germination, enhanced seedling growth and development, and increased plant productivity much more than would be possible from the mere conversion of mineral nutrients into more plant-available forms. Paul and Metzger (2005) studied the impact of vermicompost on quality of vegetable transplants.

• Suppress disease: The ability of vermicompost to protect plants against various diseases comes from the high levels of beneficial microorganisms present in it. These microbes protect plants by out-competing pathogens for available resources, while also blocking their access to plant roots by occupying all the available sites. This analysis is based on the concept of the “soil food web”, a soil-ecology-based approach pioneered by Dr.Elaine Ingham of Corvallis, Oregon. This attribute of vermicompost was studied by Edwards and Arancon (2004) and reported that the effects of relatively small applications of commercially-produced vermicomposts suppressed the incidence of attacks by Pythium on cucumbers, Rhizoctonia on radishes in the greenhouse, and by Verticillium on strawberries and Phomopsis and Sphaerotheca fulginae on grapes in the field. The authors added that the pathogen suppression disappeared when the vermicompost was sterilized, indicating that the mechanism involved was microbial antagonism.

• Repel pests: Edwards and Arancon (2004) reported significant suppression of plant-parasitic nematodes in field trials with peppers, tomatoes, strawberries, and grapes. This is a relatively new area of research and further research is required, before vermicompost can be considered as an alternative to pesticides or alternative, non-toxic methods of pest control.