Background to our problem

Concerns have been raised worldwide concerning the production and use of conventional chemical fertilisers (Quaik et al, 2012). These issues include:
• The challenges associated with meeting the increased demand for these fertilisers
• The decreased land availability for agriculture and food production
• Environmental contamination and degradation
• Concerns for human health as a result of consuming synthetically fertilised crops that haven’t been prepared appropriately

Commercially available chemical fertilisers can be inappropriate for a long term nutrient management solutions to increase crop yields because they can cause soil pollution and pose a health threats to humans if the subsequent produce is not prepared appropriately (Quaik et al, 2012).

Worm farming is an organic, waste management approach that uses worms to decompose organic waste, forming a compost material in addition to a natural liquid fertiliser enriched with humus (Carlos et al, 2008).

These products are produced through the process of Vermicomposting. Vermicomposting is a biotechnological process that transforms energy-rich and complex organic substances into stablised humus-like product (Suthar, 2007). The process takes semi-decayed organic wastes and transforms it into biologically organic manure by passing it through the digestive tract of earthworms, impregnating it with gastrointestinal mucosa, vitamins and enzymes (Abduli et al, 2013). Vermicompost leachate (VCL) is the liquid released by the earthworms and microorganisms during the decomposition process (Kandari et al, 2011). VCL, also known as ‘worm tea’, stimulates plant nutrient uptake and supports plant development due to the presence of humic acids, fluvic acids and plant growth regulators (Carlos et al, 2008). As Worm farming has become an increasingly popular organic farming waste management technique on a domestic scale(Kandara et al, 2011) there is the potential to explore the outputs of these farms, by analysing both the chemical composition of this output and thus its suitability as an alternative source of nutrients for plant growth. Furthermore a comparison of the growth implications of VCL and liquid fertilisers can provide a measure of its effectiveness for plant growth.

The popularity of organic fertilisers has increased significantly in recent years. (Webster and Taylor, 2009) report that the sale of vermiliquids has grown by 38% from 1997 to 2009. Although there is raised interest in VCL due to its ease of production and use, particularly on the local scale, currently there are no standards or guidelines for the production of consistent vermicompost leachates. Furthermore there is a lack of studies that provide analysis for appropriate application rates of VCL and how it should be packaged and stored(Webster and Buckerfield, 2010).

When using VCL to assist plant growth, there are two key factors to take into account. The VCL nutrient content varies depending on the initial substrate for the vermicomposting process (Quaik and Ibrahim, 2013).

This may be an issue for commercial potential for VCL in which controlling the inputs is difficult. The concentration of the leachate being applied also has a significant impact on plant growth. At high concentrations, VCL can inhibit seed germination and growth and cause leaf burning (Carlos et al, 2008, Quaik et al, 2012., Kandari et al, 2011). The majority of plant species have varied nutrient requirements for optimum plant growth. As a result, different plants may benefit from the addition of VCL formed from varied substrates and with varied concentrations. These issues create an added complexity in how to determine an optimal method for application of VCL on varying plant species.

An important issue for the use of VCL as a commercial biofertiliser is that the end product is strongly dependent on the substrates used (Quaik and Ibrahim, 2013). Due to the heavy dependence on the inputs of the vermicomposting, the effectiveness of the produced VCL to assist plant growth is highly dependent on the substrate for the process. The resultant inconsistency in product performance due to varied substrates presents an issue for VCL’s commercial application because industry relies on producing and supplying consumers with a product that has guaranteed effective and consistent performance.

Previous studies have shown that VCL offers strong potential for assisting plant growth. This is primarly because, due to its formation process, the nutrients present are completely soluble in water (Quaik and Ibrahim, 2013). Its solubility allows its nutrients to be easily diluted, which is why VCL may be considered a good foliar fertiliser. Furthermore, using VCL as a foliar fertiliser
helps to compensate for the loss of nutrients through leaching by adding excess nutrients to the soil (Quaik and Ibrahim, 2013).

Additionally, VCL alone may improve plant growth, however it is most beneficial when used to supplement traditional chemical fertilisers (Carlos et al, 2008., Quaike et al, 2013, Quaik and Ibrahim, 2013). As shown by Arthur et al (2012), using VCL on tomato plants found the application of VCL to be effective in improving plant growth in plants deficient in phosphorus or potassium. However, it was not very effective for plants deficient in nitrogen. This study found that plants fertilised with VCL may require supplementary use of conventional chemical fertilisers to provide additional nitrogen to ensure optimal plant growth.

It is important to note the drawbacks of VCL as alternative fertiliser. (Sherman and Appelhoff, 2011) critised the use of VCL commercially because VCL is liquid that has passed through undigested organic material, and thus it may contain pathogens or excess nutrients that may cause the application of VCL to be harmful to plants. Sherman and Appelhof (2011) states that VCL does not have potential as an alternative to commercial liquid fertilisers for this reason alone.

Our method aims to assess the plant growth of soybean and lettuce when fertilised with VCL compared to commercial Aquasol. Liquid feeding makes nutrients more readily available to plants, as opposed to solid fertiliser, which requires the breakdown and solvation of nutrients before it can be taken up by plants.
Furthermore, because VCL is formed as the by-product of an organic process, it may benefit plant growth due to its microbial activity. Thus when exploring VCL's effectiveness as a fertiliser both its chemical composition and biological activity will need to be considered.

Currently, the main ways to obtain information about the benefits and issues associated with worm farming and how to set up and use worm farms and the subsequent leachate produce are in the form of internet podcasts and television shows, council brochures and workshops, in schools, and advice at nurseries or gardening centers. These resources lack a scientific backing for the claims they make about the process and the benefits of the VCL. Additionally, as current scientific literature cannot entirely explain the vermicompost process, this further prevents worm farming from being embraced as an alternative for the improvement and enhancement of plant growth.

Thus it is evident that there is a large potential in this area for research to provide better understanding about the outputs from the wormfarming process. In addition, educational activities and programs with scientific backing are required to inform and justify the effectiveness of vermicomposting and the use of vermicompost leachate to the public, businesses and the agricultural sector if it is to be utilised more commonly on both a local scale and potentially a commercial scale.