Nitrogen Transfer in an Integrated System of Tilapia

Nitrogen transfer from aquaculture to agriculture in integrated systems has been difficult to quantify, and the contribution of fish effluent to nitrogen utilization by crop plants is poorly documented. Therefore, labeled nitrogen, 15N, was used in a small scale integrated system in a controlled environment greenhouse to determine nitrogen transfer from the fish system and its utilization by plants. Tilapia fish were grown in m3 tanks and fed a complete diet that was amended with 15N ammonium sulfate. Fish effluent amended with ingredients of a basic nutrient solution and 0%, 25%, 50 % and 100 % of the recommended mineral nitrogen was used to irrigate Summer Bibb lettuce in 5 gal lysimeters in two trials. In trial 1, percent 15N recovered by lettuce was significantly higher in effluent amended with 50 % mineral nitrogen as opposed to 0 % or 100%. Dry weight of lettuce was significantly lower only when irrigated with effluent only (no mineral nitrogen added). In trial 2, percent 15N recovered by lettuce was significantly higher in effluent amended with 25 % mineral nitrogen as opposed to 0 % or 50%. In treatments with the same amount of mineral nitrogen added, addition of effluent did not affect dry weight. Although 15N recovery demonstrated efficient nitrogen transfer from the fish feed to the plants, results indicate that effluent alone does not supply sufficient nitrogen for lettuce production