Vermicast as organic pond fertilizer can be a good option for pond manuring as they do not pose long term harm to the soil like chemical fertilizer. Organic pond fertilizers used in this study were cattle dung and goat manure vermicasts, raw cattle dung and raw goat manure. This work focused on evaluating the application of vermicast derived from cattle dung and goat manure as fertilizers in fish ponds apart from the correction of pH on Pangasius hypophthalmus aquaculture wastewater. The substrates had been dried and passed through a 2 mm sized sieve before treatment. The lowest C:N ratio and highest total phosphorus have been found in goat manure vermicast (8.9, 3390 mg/kg), followed by cattle dung vermicast (10.8, 2925 mg/kg). Five different doses of organic pond fertilizers varied around 2, 5, 10, 25 and 50 g/L. Based on the results, 25 g/L doses in all treatments did not differ significantly and they found fit in maintaining the electroconductivity and dissolved oxygen level (respectively at 1600-1700 µS and 4.36-4.48 mg/L) of Pangasius hypophthalmus wastewater. For pH parameter, at 25 g/L raw goat manure treatment significantly different with other treatments (cattle dung vermicast, goat manure vermicast and raw cattle dung). The mean values of pH at range 6.3-6.5 when 25 g/L doses of cattle dung vermicast, goat manure vermicast and raw cattle dung were applied. Meanwhile, application of 25 g/L dose of raw goat manure in aquaculture wastewater was at pH 8.2 which is higher than other treatment. As the application of raw goat manure in aquaculture wastewater increased, the pH and electroconductivity was increased until 9.2 and 3500 µS respectively.
Key words: Pond fertilizer, Vermicast, Goat manure, Cattle dung, Fertilizer dose
1. INTRODUCTION
For centuries fish farmers have increased fish yields in ponds by using inorganic or chemical fertilizers and organic fertilizers or "manures" (Bocek, 2009). The main objective to the application of fertilizers in fishponds is to enhance primary productivity in assuring an abundance of different fish food organisms within the aquatic environment (Boyd and Tucker, 1998; Steinberg et al., 2006; Wang, 2000).
This primary productivity in a fish pond indicates the rate of formation of organic matter due to photosynthesis, and is comprised of different groups of living communities, mainly phytoplankton, benthos, and periphyton (Chattopadhyay, 2004). Evaluation of fertilizer value of different organic manure (pig, cow, chicken and green manure) has been subject to research in aquaculture systems (Green, 1990; Wolhfarth and Hulata, 1987). Organic manures, if not decomposed completely before application in aquaculture ponds, may result in water quality deterioration as they utilize oxygen during decomposition (Kaur and Ansal, 2010). Therefore, the amount of organic manure to be added in the pond depends mainly upon its biological oxygen demand (BOD), as their excessive use may cause severe dissolved oxygen depletion in the pond which results in the production of toxic gases like CO2, H2S, NH3, etc.; this spreads parasitic diseases (Chakraborty and Jana, 1998).
Hence the need to minimize the harmful effects of organic manures on pond ecosystems; the best alternative is to utilize fully decomposed/digested organic manures in comparison to undigested or semi-digested organic manures (Kaur and Ansal, 2010). Among the decomposed manures, the vermicompost variant is rich in all types of major and minor nutrients, vitamins, enzymes, antibiotics, growth promoters, etc. (C. Bhusan, 2003; Mitra, 1997). It is a form of organic manure, which can be produced from variety of organic wastes (cow dung, poultry waste, piggery waste, agricultural waste, etc.) by earthworms and is made up of worm castings (faecal excretion) and other organic material (Reinecke and Alberts, 1987). Few studies have been carried out to determine the fertilizer dosage required in fish ponds for optimum pond productivity and fish production without adversely affecting pond ecology (Garg and Bhatnagar, 1999).
In this study, the application of vermicast derived from cattle dung and goat manure as pH correctors in aquaculture wastewater and fish pond fertilizer was evaluated. There is as yet any litrature presented on vermicast products as pond fertilizer. Vermicast is organic material clustered, concentrated accumulation after passing through the worm stomach acting as a vermireactor. It contain microorganisms, enzymes, inorganic minerals and humic substance in a form available for plant (Ranganathan, 2006). Microfungi in earthworm guts of Perionyx millardi, Eudrilus eugeniae, Lampito mauritii and certain other earthworm species are available (Ghosh et al., 1989; Parthasarathi and Ranganathan, 1998; Tiwari and Mishra, 1993) in vermicasts. Some enzymes in vermicasts will continue to disintegrate organic matter even after they have been excreted (Edwards and Lofty, 1972). These cattle/ goat manure vermicasts were compared with the source of manure from cattle/goat. The mediums had been dried at 60 0C for 3 days, crushed and pass through a 2 mm sieve. Drying removes moisture from manure, which bring odors arising from anaerobic biological processes and reduces the pathogenic microorganisms (Berry and Miller, 2005).
2. MATERIALS AND METHODS
2.1. Source of aquaculture wastewater
The aquaculture wastewater that came from the Pangasius hypophthalmus culture had been found to be acidic; a sample was collected to be treated with organic pond fertilizers. The quality of this wastewater at pH 5 carried mean values of dissolved oxygen (DO) at 5.11 mg/L, electroconductivity (EC) around 500 µS and chemical oxygen demand (COD) at 274.7 mg/L.
2.2. Preparation of organic pond fertilizers
Four type of organic pond fertilizers (cattle dung vermicast, goat manure vermicast, raw cattle dung and raw goat manure) were used in this study. They were dried at 60 0C about 3 days, crushed and sieved at same size around 2 mm before being applied to aquaculture wastewater. Drying of manure at 50 0C or higher is recommended, as the drying effectiveness is improved and a greater degree of odor and pathogen removal is achieved (Berry and Miller, 2005).
2.3. Application of manure
The study was conducted at the School of Industrial Technology, Universiti Sains Malaysia. Organic pond fertilizers (cattle dung vermicast, goat manure vermicast, raw cattle dung and raw goat manure) were used with five different doses 2, 5, 10, 25 and 50 g/L employed on Pangasius hypophthalmus aquaculture wastewater. Each dose was mixed well in a 1 L beaker of Pangasius hypophthalmus aquaculture wastewater. After 15 minutes of stirring, the pH, dissolved oxygen (DO) and electroconductivity (EC) of the wastewater were taken. The chemical oxygen demand (COD) was taken at the initial and final stages of treatment, the later being with the highest doses of treatment. Wastewater parameters used (COD, pH, DO, and EC) conformed to Standard Methods for the Examination of Water and Wastewater (APHA, 1995). Data was analyzed using the Minitab 16 Statistical Software. Differences between different treatments were calculated using the one way ANOVA, while the Tukey's test was used to compare the data; the value of P < 0.05 was considered significant.
3. RESULTS AND DISCUSSION
3.1. Pond fertilizer nutrient quality
Nutrient compositions of the organic pond fertilizer are summarized in Table 1. Raw goat manure contains the highest value of pH, dry matter, potassium and C:N ratio, at 9.2, 94.8%, 456 mg/kg, 11 respectively. The lowest C:N ratio and the highest total phosphorus content have been found in goat manure vermicast (8.9, 3390 mg/kg), followed by cattle dung vermicast (10.8, 2925 mg/kg) make these both vermicast feasible as good organic pond fertilizer. Low C:N ratio indicates that the organic fertilizer would be effective sources of nitrogen through rapid nitrogen mineralization reactions (Havlin et al., 2005). Fertilizer with high C:N ratio make it slowly to be degrade by microorganisms as it contain high carbon matters (Wagner and Wolf, 1999).
Table 1: Characteristic of Dried Organic Pond Fertilizers
Fertilizers
pH
EC (µS)
Dry matter (%)
C:N Ratio
K (mg/kg)
Na (mg/kg)
P
(mg/kg)
Cattle Dung Vermicast
6.9
4600
93.7
10.8
265.0
585.0
2925
Goat Manure Vermicast
6.8
4000
78.5
8.9
422.5
622.5
3390
Cattle Dung
6.8
4300
73.3
13.4
297.5
257.0
1595
Goat Manure
9.2
3500
94.8
11.0
456.0
537.5
3130
3.2. Organic pond fertilizer dose-effect on water quality of Pangasius hypophthalmus aquaculture wastewater
Figure 1 below shows the effect of organic pond fertilizer on the pH for systems treated differently. The pH of aquaculture wastewater treated with raw goat manure differed significantly with other treatments (P<0.05). When the organic pond fertilizers doses were applied at 25 g/L, the pH of aquaculture wastewater stabalized; this did not apply to raw goat manure as the pH increased with the dosage to pH 9.2 which was the pH value of dried goat manure used in this study. This trend is depicted in Figure 1. Comparing all treatments, raw goat manure gave the highest increment in pH, which is pH 9 from an initial value of 5. The final pH surpassed other pond fertilizers, exceeding the standard aquaculture pH maximum of 8.5 (standard aquaculture water quality pH ranges around 6.5-8.5). Sudden changes in pH may stress and kill aquatic animals even when those changes occur within a pH range they normally tolerate (Tucker and D'Abramo, 2008). Meanwhile, the pH of aquaculture wastewater with goat manure and cattle dung vermicasts, as well as raw cattle dung treatments, did not vary significantly (P>0.05). The three treatments resulted in a stable pH range with a mean between 6.3-6.5 when organic pond fertilizers with a 25 g/L dosage was employed. This pH range recorded in this study did not fell below the standard aquaculture water quality pH recomended. Un-ionized ammonia is the toxic form can kill fish, predominates when pH is high and relatively nontoxic, predominates when pH is low (Hargreaves and Tucker, 2004). It has long been thought that liming ponds decreases ammonia concentrations but this could actually make a potentially bad situation much worse by causing an abrupt and large increase in pH (Hargreaves and Tucker, 2004).
Fig. 1. Change in pH of Aquaculture Wastewater with Doses of Organic Pond Fertilizer
Figure 2 shows the electroconductivity of aquaculture wastewater when applied with varying doses of organic pond fertilizers. Electroconductivity did not differ significantly in various treatments (P>0.05). Cattle dung vermicast had the highest electroconductivity when a 50 g/L dose was applied in aquculture wastewater at 2700 µS, followed by cattle dung at 2500 µS, goat manure vermicast and raw goat manure, both at 2300 µS. From this Figure 2, when the doses of organic pond fertilizers increase, the electroconductivity increases as well. Electroconductivity is a measure of how well a solution conducts electricity and is correlated with salt content. Freshwater fish generally thrive on a wide range of electrical conductivity. Some minimum salt content is desirable to help fish maintain their osmotic balance. Most freshwater in streams range between 20 to 1500 µS (Boyd and Tucker, 1998). 25g/L doses of organic pond fertilizers could give the water electroconductivity within the 1300-1700 µS range, which is ideal for freshwater fish. The vermicompost had been used for catfish ponds as Ghosh (2004) recorded that the Electroconductivity was at range 1300-1600 µS.
Fig. 2. Change in Electroconductivity (µS) of Aquaculture Wastewater with Doses of OrganicPond Fertilizer
The addition of some nutrients into the water will affect dissolved oxygen (DO) as shown in Figure 3. This data supports the findings of earlier researchers. Dissolved oxygen had proven give inverse relationship with the dose of manures applied in the production of Ceriodaphnia cornuta (Srivastava et al., 2006). Morris and Mischke (1999) suggest that organic fertilizers may cause dissolved oxygen problems during initial decomposition. Additionally, with high levels of organic fertilizers, the water turns dark and becomes dense with high concentrations of suspended organic particles, inhibiting light penetration and thus limiting primary productivity (Garg and Bhatnagar, 2002). A 4-7 mg/L range is good for many aquatic animals, while a 7-11 mg/L range is very good for most stream fish; dissolved oxygen below than 4 mg/L is classified as a bad lavel for aquatic animal (Boyd and Tucker, 1998).
From Figure 3, dissolved oxygen went down drastically with the addition of 2 g/L to 10 g/L dosages. Dissolved oxygen did not differ significantly between all treatments (P>0.05). At 25 g/L of organic pond fertilizer, all treatments showed constant trends, maintaining dissolved oxygen around 4.36-4.48 mg/L. Goat manure vermicast demonstrated the higest dissolved oxygen at 4.48 mg/L when 50 g/L of organic pond fertilizer was employed. Kaur and Ansal (2010) also reported significantly higher dissolved oxygen in vermicompost manured pools as compared to cow dung, as observed in the present study. The vermicompost had been used for catfish ponds as Ghosh (2004) recorded better growth in catfish, Clarias batrachus and higher water retention capacity in vermicompost manured ponds as compared to inorganic fertilizer treated ponds in monoculture practice.
Fig. 3. Change in Dissolved Oxygen (mg/L) of Aquaculture Wastewater with Doses of Organic Pond Fertilizer
The addition of all organic pond fertilizers at doses of 25 g/L resulted in adherence to water quality requirements for aquaculture, since all treatments gave values of more than 4 mg/L of dissolved oxygen, a pH range between 6.5-8.5, and electroconductivity between 20 to 1500 µS (Boyd and Tucker, 1998).
3.3. Comparison between initial and final of treatments
The range of aquaculture wastewater parameters had been compared between samples during initial and final application stages of organic pond fertilizer at 50 g/L, as summarized in Table 5. Cattle dung vermicast gave the lowest value of chemical oxygen demand (COD) at 349.3 mg/L, followed by goat manure vermicast, raw cattle dung and raw goat manure (516, 497.7 and 1130.7 mg/L respectively). This result proved that both vermicast of cattle dung and goat manure were feasible as organic pond fertilizer instead of using raw source of animal manure. Vermicompost has also been reported to result in higher survival and growth of aquatic organisms including fish and prawn (Kumar et al., 2007). Direct pond fertilization using excessive manure can lead to water quality deterioration (Boyd, 1982), including severe depletion of dissolved oxygen and high chemical oxygen demand of water. But in this work the addition of all organic pond fertilizers at the highest doses of 50 g/L still resulted in a compliance to water quality requirements for aquaculture, since all the treatments gave mean values in the 4.43-4.48 mg/L range for dissolved oxygen, and pH 6.5-6.7 (except raw goat manure which was at pH 9). As for electroconductivity, salt content increased with organic pond fertilizer. Certain dose must be used to acheive the required electroconductivity of water which ranges at 20 to 1500 µS.
Table 5: Aquaculture Wastewater Parameters at Initial and Final (at 50 g/L)
Parameters
Treatments
Initial
Cattle Dung
Goat Manure
Cattle Dung Vermicast
Goat Manure Vermicast
Dose (g/L)
0
50
50
50
50
Temperature (0C)
28.8
28.8
28.8
28.8
28.8
pH
5.0c
6.7 ± 0.0577b
9.0 ± 0.0577a
6.5 ± 0.0577b
6.6 ± 0.0577b
DO (mg/L)
5.11a
4.43 ± 0.00577c
4.36 ± 0.00577e
4.41 ± 0.00577d
4.48b
COD (mg/L)
274.7±53.7b
497.7±111.0b
1130.7±213.5a
349.3±119.2b
516.0±75.3b
EC (µS)
500c
2466.7 ± 57.7b
2400b
2700a
2400b
+ Values with different superscripts in a row differ significantly (P < 0.05).
4. CONCLUSION
From this study, the correction of aquaculture wastewater pH employing cattle dung vermicast and goat manure vermicast is feasible. Both vermicasts are equaly suitable to be used as fish pond fertilizer. Application of these vermicasts resulted in water quality that complied to requirements for the freshwater aquaculture of Pangasius hypophthalmus.
