FARMER TO FARMER Sept. / Oct. 1996 No. 16
Fish meals can contain as much as 12% nitrogen. There are several methods of transforming dried fish wastes into fertilizer. These are often stabilized with food and feed grade preservatives, and can spoil even with the preservative. Removal of the oil is an important step in both enhancing the nitrogen content and preventing rancidity. Fish meal, spray-dried fish and fish protein are less bulky and more concentrated than the other sources of nutrients. This is the most easily handled, shipped and stored of the fish products. The meal can be banded in or drop-slotted as a starter fertilizer, knifed in as a sidedress, or applied in solution as a foliar fertilizer. It is possible to use spray-dried fish protein in low-volume drip irrigation systems. When agitated with a drum beater, the fish protein easily goes into solution. Lines will not become clogged when they are properly flushed.
In the manufacture of fish emulsion, the by-products of cleaned fish, such as the heads, guts and bones are cooked at temperatures in excess of 180°F to kill most of the putrefaction bacteria. The resulting product is filtered and stabilized. In most cases, the stabilizers used are sulfuric or phosphoric acid. Fish emulsion is more difficult to store and transport than fish meal. It is lower in nutrients as well. It does have the advantage of going into solution more easily, requiring less attention and maintenance to apply as a foliar feed or to inject into a drip irrigation system.
The new technology that has increased fishing efficiency has also resulted in the taking of species or sizes not suitable for market, known as the by-catch. An increased catch of unsaleable whole fish has resulted from the increased by-catch of the fishing industry. These fish are often dumped overboard at sea, but are also brought into port in the holds of fishing boats. This has created an incentive to find a market for the by-catch in order to lower the cost of production.The liquid fish hydrolysate process minces the whole fish, then enzymatically digests, grinds and liqueifies the resulting product, known as gurry. Because it is a cold process, gurry putrefies more rapidly than fish emulsion and needs to be stabilized at a lower pH, requiring more acid. Researchers have tried formic acid, sulfuric acid, and others. Formic acid had phytotoxic effects on plants. Phosphoric acid is the preferred stabilizer. The hydrolysate process has substantially lower capital and production costs than fish emulsion production.
Kelp and Other Sea Plants
While most often used as a foliar spray, sea plants can also be used as a soil amendment, compost ingredient or irrigation feed. Wet seaweed gathered on the beach, washed and composted, can be a good biological source of potassium and trace elements. The colloids found in sea plants can improve soil filth. Kelp and other sea plants also contain relatively concentrated amounts of plant auxins, growth regulators and stimulants, such as indole-3-acetic acid (IAA), gibberellic acid and cytokinins. These can help promote rooting in transplants and cuttings, and also help to delay decay in mature crops. Kelp is a large underwater plant that accumulates a number of nutrients. Most commercial soluble aquatic plant products are based on the kelp species Ascophyllum nodosum, harvested from the North Atlantic off the coasts of Canada and Norway. These can be sold as meal, liquid extract or powder. Sea plants, particularly in liquid formulations, are often stabilized with food and feed grade preservatives to prevent decay. The powders, more heavily processed than the meals, contain lower amounts of nutrients and salts, but are easier to transport and store. According to some industry sources, the more heavily processed forms also contain lower concentrations of growth regulators.
Several sources of shellfish waste have a beneficial effect on soils. Oystershell lime provides approximately 40-50% calcium carbonate, and contains nitrogen in the form of protein from the muscles left on the shells. The material is faster acting than limestone. Crab waste contains 10-15% chitin, a substance that has demonstrated ability to suppress nematodes. Additional nitrogen is important to help suppress the nematodes, so some commercial products are fortified with urea. Both of these products have relatively limited distribution.
This article was developed under the sponsorship of the Organic Farming Research Foundation.