Development of fertilizer congealed with gelatin for seaweed culture

Abstract

Recently, discoloration of cultured nori Porphyra yezoensis and wakame Undaria pinnatifida has often occurred due to insu-cient dissolved inorganic nitrogen (DIN). Therefore, to supply the insufficient DIN in seaweed aquaculture areas, we attempted to develop a new nitrate fertilizer. This fertilizer was made of ammonium nitrate solution congealed with gelatin. Two types of fertilizer without a case (naked) and two types with a case were examined; the naked-type fertilizers had different amounts of gelatin, and the covered-type fertilizers were filled with ammonium nitrate solution and the cases had holes. The fertilizer cases had different diameters and numbers of holes. An experimental tank test was performed using an ultraviolet nitrate analyzer to measure the concentration of nitrate eluted into the water. 70% elution of ammonium nitrate from the naked-type fertilizer took approximately 5 days, but 60% elution of the covered-type fertilizer required about 20 days. The elution rate of the covered-type fertilizer with larger opening area of holes was more rapid. These results suggest that the elution rate of ammonium nitrate from the gelatin fertilizer could be regulated by changing the functional structure of the case.