الفهرس 
Factors affecting fertilizationOnly 14 pages are availabe for public view
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Abstract
The present study was conducted in El-Khaslzaa fish farm, Kafi El-shelkh governorate to evaluate tlze different combiizations of chemical fertilizers on the productivity of fish in polyculture earthen1 ponds . The work was carried out in two experiments during two production seasons.The aim of tlze first experimeizt was to reach the best combination of nitrogenous and plzosplzorus fertilizers that produce the maximum fish yield , while the aim of the second experiment was to investigate the best application fkequency intervals of chemical fertilizers wlich realized the maximum development of the natural food in ponds and 111 tulm increases the productivity of these ponds . Six fertilization treatments were made in the first experiment by the combination of two levels of urea (5 and 10 kg 1 feddan) as a source of nitrogen and three levels of moizosuperphosplzate (1 5 ,20 and 25 kg / feddan)as a source of phosphorus in addition to the control whclz received no chemical fertilizers . The experiment was carried out in small ponds ranged between 140 and 520 m2 in area . Each treatment was applied in two replicates and the experiment was lasted for 160 days . Grey mullet and red tilapia were stocked in the experimental ponds at a rate of 4000 fingerlings / feddaiz ( 40 % grey mullet and 60 % red showed that : I- The plzysico - chemical properties of ponds water were in the acceptable range and were as follows : a - Dissolved oxygen values ranged from 4.06 to 4.30 mg / L and did not differ significantly ( P > 0 -05 ) . b- PH values were similar in the different experimental ponds and ranged between 7.16 and 7.27 . c- Average total ammonia concentration in tlze different ponds was 0.12 ppm with no significant differences (p > 0.05 ),while nitrite concentxation was 0.11 - 0.12 ppm.