Effects of Increased Nitrogen Fertilization on Water Quality and Yield of Nile Tilapia, Oreochromis niloticus, and Common Carp, Cyprinus carpio, in Earthen Ponds in Egypt

Abstract

This study investigated the effects of increased nitrogen fertilization on water quality and yield of Nile tilapia, Oreochromis niloticus, and common carp, Cyprinus carpio, in earthen ponds in Egypt. Nine 0.1-ha ponds were filled with water from the Nile River and fertilized once every two weeks with urea and triple super phosphate. Three fertilization regimens were evaluated: (1) no fertilizer (control); (2) low nitrogen treatment in which ponds received 30.9 kg urea/ha plus 30.9 kg triple super phosphate/ha (daily equivalent to 1.0 kgN/ha and 0.4 kg P/ha); and (3) high nitrogen treatment in which ponds received 92.7 kg urea/ha plus 30.9 kg triple super phosphate/ha (daily equivalent to 3.1 kg N/ha and 0.4 kg P/ha). There was a significant increase in total ammonia-nitrogen, nitrate-nitrogen, pH, and chlorophyll awith increased nitrogen in fertilizers; but alkalinity, hardness, total phosphorous, secchi disk visibility, and dissolved oxygen (at 0600 and 1400) were similar. Temperature and secchi disk visibility were the only water quality variables that changed significantly (P<0.05) with season; temperature increased during the summer, but secchi disk visibility decreased. There was no significant difference (P> 0.05) in final body weight, net yield, and reproduction of Nile tilapia among the three treatments. Final body weight and yield of common carp were also similar, regardless of fertilization treatment. It appears that nitrogen did not limit primary production. Low density of tilapia, enhanced turbidity by common carp that affected algal growth and reproduction, and phosphorous limitation may have combined to lower yield in this study.