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FARMER TO FARMER Sept. / Oct.
1996 No. 16
PLANT NUTRITION FROM THE SEA
Marine Products Can Be Used To Supplement Soil Nutrients
By Brian Baker
Marine products can provide
an important supplement for soil-building and crop nutrition. Fish emulsion,
kelp and kelp extracts, and shellfish wastes are sources of key plant
nutrients and vitamins. Fish products can be used as a sidedress, foliar or
irrigation feed to supplement soil nutrients, particularly nitrogen. Most of
the nitrogen in the these products is in the form of enzymatically digested
protein, making it less prone to leaching than more soluble forms, but more
available than the nitrogen in compost and cover crops. Each of these fish
products has advantages and disadvantages that should be considered.
Fish Meal
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.
Fish Emulsion
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.
Fish Hydrolysate
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 liquefies 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.
Shellfish Waste
Several sources of shellfish waste have a beneficial effect on soils. Oyster
shell 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.
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