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By: John D. Atkins
Extension Agriculture/Livestock Agent
FERTILIZATION OF FRESH
WATER FISH PONDS
One can increase
the productivity of a pond by adding fertilizer. If a fish species which
consumes small natural foods is grown, such as the bluegill or golden shiner,
then pond fertilization can increase the production of these fish. Fertilizers
provide nutrients to microscopic plants known as algae. These algae are eaten
by microscopic animals (zooplankton) and insects, both of which serve as food
for small fish. With proper fishing, the pond will also produce greater numbers
of larger bluegill.
In freshwater
ponds, the most needed nutrient is usually phosphorus, and additions of phosphorus
alone will add to the production of the pond.
Fertilizer is
available in a liquid or granular form. Liquids are best for pond applications
because they promote rapid growth of algae and because smaller applications can
be used which may reduce the cost of pond fertilization.(
Note: If a pond has constant out-flow of water, liquid fertilizer may not be
the product of choice).
Liquid fertilizers
generally have a high percentage of phosphorus, and this phosphorus is in a
form that is immediately available to the algae. Effects on the algae
populations can be seen within days of application with a liquid fertilizer.
For these reasons, it is recommended to use liquid fertilizers whenever
possible.
Most liquid
fertilizers have a similar NPK value (see Table 1 ), so application rates
are the same. With granular fertilizers, the application rates will vary
depending on the NPK value of the fertilizer that you are using.
1. Application rates for some common grades of
fertilizer.
|
Type |
Grade |
Fertilizer
Name/Chemical Content |
Amount
to Apply/ |
|
|
Liquid |
9-32-0;
10-34-0; 11-37-0; 13-38-0 |
Either
ammoniated polyphosphate or orthophosphate |
1
gallon (all grades) |
|
|
Granular |
20-20-5
|
Fish
pond fertilizer |
40
pounds |
|
|
18-46-0
|
Diammonium phosphate |
18
pounds |
|
|
|
0-46-0
+ 34-0-0 |
Triple
super-phosphate together with (+) Ammonium nitrate |
18
pounds + 24 pounds (a total of 42 pounds |
||
1.
A simple rule of
thumb which you can use is to start fertilizing as soon as the water
temperature is above 65° Fahrenheit.
2.
Repeated
applications should be done on a monthly basis, or whenever the water clears
enough so that a white (or black and white) disk attached to a yardstick is
visible to a depth of 18 inches or more.
3.
Dividing the
monthly application into two smaller applications, every two weeks, will
produce better results.
4.
Continue
applications until the water temperature drops below 70° Fahrenheit
Liquid fertilizer is heavier than water
and will sink to the bottom of your pond unless first diluted with water.
Granular
fertilizers should be placed on a platform, positioned one foot below the
surface, and allowed to dissolve. If granular fertilizers are simply broadcast across
the pond's surface, they will sink to the bottom, where most of the phosphorus
will be tied up chemically in the mud.
Often it is
difficult to get a response from the algae with fertilization and the following
are a few possible reasons for this:
1.
Muddy water - If the water is too muddy, the sun's light cannot
penetrate into the water well enough to support the algae.
2.
Aquatic weeds - If the pond has an abundance of aquatic plants, do
not apply fertilizer.
3.
Water
exchange - Fertilizers will not work
in ponds which are continuously and excessively exchanging water.
4.
Low
alkalinity - The solubility of
phosphorus is lower at low alkalinities, and extremely acidic waters may not
respond to fertilization. For good results, the alkalinity should be at least
20 parts per million. Liming of ponds with lower alkalinities will usually
relieve this problem.
John Atkins is
Agriculture/Livestock Agent for
Extension Service programs
are open to all people without regard to race, color, sex, age, handicap or
national origin.