Role of urea in fertilizing fish ponds | |
| Author | Pautong, Ambutong K. |
| Call Number | AIT Thesis no. AE-91-38 |
| Subject(s) | Urea as fertilizer Fish ponds |
| Note | A thesis presented in partial fulfillment of the requirements for the degree of Master of Science |
| Publisher | Asian Institute of Technology |
| Abstract | The objective of this study was to determine what happens to urea applied to ponds. To attain the objective of this study three experiments were conducted. Urea, dissolved in pond water at 4 mg urea-N/L initial concentration in 75-L aquariua and exposed to light in outdoor tanks, disappeared at rate of 249 ± 14 (1SE) ug urea- N/L/day. When covered from light, the bacterial decomposition was 90 ± 10 (1S.E.) ug urea-N/L. Chemical hydrolysis in distilled water exposed to light was insignificant. Urea, applied at fertilization rate of 21 kg N/L/week (approximately 2.1 mg urea- N/ L in water) in tanks, was gone after one week. Toxicity of urea was tested. The median lethal concentrations (LC50) of urea to sex- reversed male Nile tilapia (Oreochromis niloticus) fingerlings (mean wt. = 7.1 g) at 24-hr and 96-hr exposure were 19,700 and 16,800 mg urea/L, respectively. The 24-hr Lc50 for silver barb (Pontius gonionotus) fingerlings (mean wt. = 11.1 g) was 17,000 mg urea/L. The 24-hr LC50 of urea to tilapia and silver barb were significantly different (p>0.05). No mortality was recorded for both fish when exposed to 14, 000 mg urea/L or less. Urea was compared to three types of inorganic fertilizers (ammonium sulfate, potassium nitrate and NPK 14-14-14) as fertilizer inputs. After 90-day culture of sex-reversed male tilapia (mean 12.2g), the net fish yield of urea- fertilized tanks was 1.4±0.1 (S.E.) g / m2Lday which was higher than ammonium sulfate 1.2±0.1 (S.E.) g / m2 / day) and potassium nitrate- (0.8±0.4 (S.E.) g/m2/day), but lower than NPK- (2.0±0.1 (S.E.) g/m2 /day) fertilized tanks. Fertilization did not give significant difference in chlorophyll a concentration, as an estimate of phytoplankton abundance, between urea and inorganic fertilizers (p<0.05). Urea was slowly decomposed in ponds by bacteria and was utilized by plankton. The low decomposition rate of urea in water can provide nitrogen for plankton in pond for longer period because of this characteristic. It has low toxicity that normal fertilization rate should not effect fish kill. |
| Year | 1991 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Agricultural and Food Engineering (AE) |
| Chairperson(s) | Knud-Hansen, Christopher F.; |
| Examination Committee(s) | Edwards, Peter;Lin, Chang Kwei; |
| Scholarship Donor(s) | Government of The Netherlands; |
| Degree | Thesis (M.Sc.) - Asian Institute of Technology, 1991 |