A COMPARISON BETWEEN THE FIXED INPUT AND ON DEMAND METHODS FOR OPTIMIZING FERTILIZATION REQUIREMENTS, MINIMIZING COSTS AND INCREASING FISH PRODUCTION IN POLYCULTURE PONDS
Nabil A. Ibrahim; Gamal El-Naggar and Ahmad Nasr-Alla
WorldFish Center, Regional Center for Africa and West Asia,
Abbassa, Abou-Hammad, Sharkia, Egypt.
Received 23/ 6/ 2010 Accepted 29/ 7/ 2010
To determine the appropriate fertilization method that optimizes nutrient inputs, minimizes financial/environmental costs and ultimately maximizes fish production, this work was conducted in twenty earthen ponds of 2000 m2 each, at the WorldFish Center, Egypt, for 195 days. A polyculture of Nile tilapia (Oreochromis niloticus), silver carp (Hypophthalmichthys molitrix) and African catfish (clarias gariepinus) were used in this study. Urea (46% N) and chicken litter (3.4% N and 1.75% P) were used to achieve the concentration of the required nutrients through two fertilization methods, 1) fixed input method, (the use of 20 kg N and 5 kg P/ha/week) either for six months (Fixed-6) or three months (Fixed-3). 2) On demand method (quantities of fertilizers given to ponds were determined according to water analysis to maintain 2 mg N and 0.5 mg P/l level in pond water, for six months (Demand-6) or three months (Demand-3), the fifth treatment was control (without fertilization). All ponds were fed with the rate of 50% of satiation level after 3 months of stocking. Water quality parameters (DO, Temp., SD, pH, TAN, NO3-N, PO4, Chl. “a”, Alk. and TH) were measured weekly, they were at suitable levels for the growth of all cultured fish. Fixed-6 treatment had the highest fish production (4.8 ton/ha) and the highest tilapia class (size) followed by Fixed-3, Demand-6 and Demand-3 treatments, while control came the last, the revenue values were 57.54, 23.36, 21.25, 20.43 and 11.87 thousand LE/ha respectively. Fixed-6 treatment had also the highest production cost (20.05 thousand LE/ha) and control had the lowest (15.09 thousand LE/ha). There was no significant difference between both fixed treatments in either net profit (7.50 and 5.33 thousand LE/ha) or B/C ratio (0.37 and 0.29 for Fixed-6, and Fixed-3, treatments respectively). This study demonstrates that the use of fertilizers for six months could gain bigger fish and higher fish production than its use for three months but economically, it was not significantly different. While from water quality (environmental) point of view, the use of fertilizers for three months was better. Thus the final results of the present study recommended the method of fixed inputs for the first three months of the experiment with the use of fish feed at 50% of satiation level after three months of stocking (Fixed-3) treatment. This will save the loads of more than 4 ton chicken litter/ha and about 70 kg urea/ha, while achieving almost the same return and will may provide fish farmers a fertilization strategy that allow them to achieve higher economic returns with reducing nutrient inputs which also provide an environmentally-friendly fish culture.
Keywords: African catfish, Fertilization requirements Nile tilapia, and polyculture.