How Is Fish Fertilizer Made?

Fish have been used for centuries as source of nutrients for crops. In modern times, fish fertilizer has been especially valued as a natural nutrient source to be used in organic gardening and farming. Fish fertilizer contains nitrogen, phosphorus and many trace minerals. It can be applied either as a soil amendment or as a foliar application, where it is sprayed directly upon and absorbed through the leaves. Fish fertilizer is manufactured in two different forms: as a liquid emulsion and as a powder.

The Source

The first step in making fish fertilizer, of course, is catching the fish. Discarded fish parts left over from the process of canning edible fish are one source of raw material for the production of fish fertilizer. But the majority of fish fertilizer is made from a species of fish called menhaden. The menhaden is a smallish fish that is bony, oily and offers little as a food source for humans. It is fished exclusively for its value in the production of fertilizer, animal feed and other products.

After being cooked at a temperature of 210 degrees F, the liquids and oils are pressed out of the fish. The solids that remain are then ready to be ground into the powdered form of fish fertilizer. The liquid is used to make fish emulsion after first removing the pure fish oil. This is accomplished by placing the liquid in a centrifuge that separates the oil from the heavier soluble materials. The oil is used for other purposes, and the remaining soluble materials are sold as liquid fish emulsion.
Often, a small quantity of phosphoric acid is added to fish emulsion. The acid reduces the pH of the emulsion, which helps to prevent the decay of the enzymes in the fish emulsion. By preventing decay, the unpleasant odors associated with fish emulsion are reduced. Fish emulsion may also have synthetic nutrients such as urea added, which increase the nutritional potency of the fertilizer but which also render it unsuitable for sale as a pure organic fertilizer.
A smaller quantity of fish fertilizer is manufactured through a process of enzymatic deterioration. Using this alternative method of producing fertilizer, the fish parts are placed in a vat to which enzymes are added. The enzymes break down the fish solids into a liquid without the use of extreme heat. This process may preserve more of the natural amino acids, vitamins and other nutrients.