TECHNIQUES OF FISHPOND MANAGEMENT 11 
FERTILIZING 
Pure water will not sustain living organisms; to do so water must 
contain in solution certain gases and mineral salts, mainly oxygen, 
carbon dioxide, nitrogen, phosphorus, calcium, and potassium. Pond 
waters contain nitrogen, phosphorus, calcium, and potassium in vary- 
ing amounts depending upon the fertility of the soils over which they 
have flowed or through which they percolated. Most of the.carbon 
dioxide results from decomposition of organic matter, although some 
oxygen and carbon dioxide are absorbed from the atmosphere. During 
growth processes, plants use carbon dioxide and release oxygen, and 
animals consume oxygen and release carbon dioxide. In pond water, 
the balance of these gases depends to some extent upon this exchange 
between plants and animals. 
In addition to dissolved substances, there are suspended inorganic 
and organic solids in pond water. Most suspended inorganic solids 
are insoluble and do not contribute to the fertility of the water. Silt 
reduces the productivity by diminishing the light that may enter the 
water and by smothering the organisms living on the bottom of the 
pond. Some dead organic solids are eaten by. fish and insect larvae, 
but if these solids are to go into solution they must decay through 
bacterial action. Algae can convert into living tissue only the dis- 
solved substances in the water. 
In Alabama, it was found that nonfertilized ponds supported from 
40 to 200 pounds of pan and game fish per acre (25). This produc- 
tivity was directly related to the fertility of the soil in the pond drain- 
age; in poor soil the productivity was low, in good soil it was high. 
Tllinois lakes with a mixed fish population had an average standing 
crop of 600 pounds per acre (26). ‘Ten percent of this total was game 
and pan fish. In lakes supporting only game and pan fish the stand- 
ing crop was 200 to 800 pounds per acre. In Michigan, glacial lakes 
with low fertility had a standing crop of 92 pounds per acre, of which 
84 pounds were game and pan fish (26). Soil fertility varies in dif- 
ferent parts of the country and so also does water fertility. Poor soil 
will produce a poor crop, whether it be corn or fish. 
To increase the productivity of a poor soil, a farmer applies fertilizer 
in the form of barnyard manures, crop residues, or commercial ferti- 
lizers. Similarly, the productivity of a pond may be increased by 
adding fertilizer to the water (fig. 3). The use of fertilizer in ponds 
to increase fish production is an established practice in Europe and the 
Orient. Many different organic substances have been used—bone, 
fish, cottonseed and soybean meals, grain and grain threshings, sewage 
and sewage sludge, tankage, hay, and manure are a few of them. A 
large number of commercial fertilizers and combinations of commercial 
fertilizers with manures and other organic materials have also been 
used. 
A review of European experience shows increases in production of 
28 to 300 percent resulting from the use of various kinds of fertilizers 
~ (3). In many of the European experiments, the best results were 
obtained when nitrogen, phosphorus, and potassium were all added 
rather than only one or two. Elements other than these, and possibly 
calcium, are ordinarily present in sufficient quantities for plant growth. 
