Earthworms play an important role in the turnover of organic matter in soil and maintaining a good soil structure (Lavelle, 1988). Physical properties in soils improved by earthworms include improved aggregation, stability, and porosity. The soil biological and chemical properties of soils that may be modified include nutrient cycling (mainly nitrogen and phosphorus), organic matter decomposition rates, and chemical forms of nutrients in soil and their availability to plants. They also change the soil pH, organic matter dynamics in terms of quality and quantity, microbial and invertebrate activity, and diversity of the microflora and fauna (Lavelle et al., 1998). Therefore, they are essential for plant growth especially in an extensive agricultural system, such as organic farming, which is based on nutrient release from turnover of organic matter.
Earthworms can also be used as a source of protein for animal feed which had been reported to increase the growth of fish, chicken and piglets (Guerro, 1983; Jin-you et al., 1982; Edwards and Niederer, 1988). The mean amounts of essential amino acids recorded in earthworms are found to be very adequate for a good animal feed. Moreover, earthworm tissues contain a preponderance of long-chain fatty acids, many of which cannot be synthesized by non-ruminant animals and an adequate mineral content (Edwards and Niederer, 1988). Recently, the enzymes derived by the earthworms, lumbrokinase or earthworm fibrinolytic enzymes (EFE) which has anticoagulant (blood thinner) property is extensively being used in pharmaceutical and cosmetic industries. Following these valuable application of earthworms, the management of earthworm communities provides a promising field for innovation in agricultural practises.
There are many factors affecting the growth and body mass of earthworms that need to be considered during cultivation of earthworms. The soil moisture obviously has an effect on the growth and activity of earthworms. Earthworms lose moisture through their cuticles, so they are very dependent on soil moisture. When soil moisture is optimum, earthworms increase in mass and in their activity if food sources are available (Lee, 1985; Edwards and Bohlen, 1996). Another important factor is the additions of organic matter in the form of farmyard manure which have been found to increase earthworm populations under favourable soil conditions (Lofs-Holmin, 1983a; Hansen, 1996).
Several studies found that the mass of earthworms were the highest in manured soil compared to unfertilized and mineral fertilized soils (Hansen and Engelstad,1999; Marhan and Scheu, 2005). The purpose of this study is therefore, was to identify the optimum soil moisture and level of fertilizer that can be used to increase the body mass of earthworms, Pheretima sp. during cultivation. The worms of the genus Pheretima are indigenous to Southeast Asia (Edwards and Lofty, 1972), and widely distributed in tropical rainforests with strongly acid soils. There were two treatments being tested in this experiment. In the moisture content treatments, four different levels of moisture level in soil were compared. As for the fertilizer treatment, the goat manure was added at two different levels and was compared with an unfertilized control.
The aim of this experiment was to investigate the effects of moisture content and fertilizers on the body mass of earthworms, Pheretima sp. under laboratory conditions. Any observed difference in body mass may then indicate the optimum soil moisture and fertilizer content which can improve the mass rearing of this species for commercial use. Materials and Methods
The study was carried out in the Animal House which is located at Level 8 of Building 3, Monash University, Sunway Campus commencing from 19th April 2010 to 10th May 2010 (22 days). The rearing conditions for Pheretima sp during the study consisted of containers (paper cup) held in continuous darkness at room temperature (25oC).
The earthworms, Pheretima sp. were obtained from a shop in Klang Valley. Each test container (paper cup) was inoculated with a sample size of five worms (n=5). Before the experiment commences, the initial body mass (Mi) of the worms in each containers was weighed using an analytical balance. Then, each container was added with 500 g of clay-brown soil which was obtained from the Green House of Monash University. Treatments used in this experiment are combinations of two factors, the level of fertilizer application and water application.
The treatments were within a Complete Randomized Design (CRD) with 3 replications. All replications of treatments are assigned completely at random to independent experimental subjects. The relationship between three different levels of fertilizer treatment and four different levels of moisture treatment as they relate to the changes in the body mass of earthworms was examined with a split-plot factorial ANOVA, where fertilizer was a between group factor, and moisture content was a within group factor. This resulted in 12 (4 treatment level x 3 replicates) moisture containers in each (three) groups of different level of fertilizer, which made a total of 36 experimental units.
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