18 MISC. PUB. 528, U. S. DEPT. OF AGRICULTURE 
trouble are liver flukes and Bang’s disease. In localities where either 
of these occur, ponds fertilized with manure should not be used for 
stock water. 
The use of hay for fertilization is also experimental. Legume hays 
decay more rapidly in water than grass hay and, therefore, should be 
applied in small amounts at frequent intervals. 
In the light of present knowledge, the following trials may be made 
for the use of organic fertilizers on a per acre basis. 
Manures. Horse and cow manure at 2 to 3 tons per season, in appli- 
cations of 500 pounds at monthly intervals. Sheep and hen manure 
are higher in percentages of nitrogen and phosphorus and these 
manures may be used at the rate of 1 or 2 tons per season. 
Seed Meals. A mixture of either soybean or cottonseed meal and 
superphosphate at the ratio of 3 to 1, by weight; 800 to 1,000 pounds 
or more per season; in applications of 100 pounds per week until a 
water bloom is established. The use of lime with cottonseed meal may 
be beneficial in soft waters. 
Hay. One to three tons per season in applications of 500 pounds a 
monthly intervals. 
All these materials should be well scattered over the surface of the 
pond where the depth is 6 feet or less. The frequency of application 
can be determined by the growth of filamentous algae. When it ap- 
pears, fertilizing should be terminated. It should be remembered that 
all of these organic materials are low in phosphoric acid; therefore, 
their action can be improved by the addition of superphosphate. 
COMPARATIVE EFFECTIVENESS OF FERTILIZERS 
A proportionate relationship between plankton production and car- 
rying capacity 1s not found when a comparison is made between the re- 
sults obtained with commercial and organic fertilizers (72) (table 5). 
With organic fertilization, the fish production may be doubled but the 
plankton production is increased only shghtly. This difference is 
partly explained by three factors: (1) A considerable portion of the 
fertilizing elements is not available until after slow bacterial decom- 
position of the organic material. (2) Organic material is eaten by 
insect larvae and zooplankton organisms and the phytoplankton stage 
is eliminated. (8) Seed meals are eaten in small quantity by fish and 
that part which is eaten increases fish production but does not fertilize 
the water. The plankton and insect larvae are thus eliminated as 
stages in the food chain leading to fish. 
Taste 5.—Plankton production and fish-carrying capacity in ponds fertilized 
with organic and inorganic fertilizers (12)* 
3 Fish-car- 
Pond No. Fertilizer pane rying 
E capacity 
Parts per 
million Pounds 
Bi a cle INONO =e nos ee eee Be oe ee ee ee aya 92. 7 
As eis Ee ihe, Dn ee iil Cottonseedimoeal.2_ 222203) faa ae eee eee 7.8 295. 4 
6 a eee Weaving Mash es = yee es eee oe ee ee ae ee eee 10.6 451.8 
ASS Soe eee anaes Cottonseed meal--superphosphate_-_------------------------ 15. 4 578. 8 
Lbs fae eee Superphosphate+-ammonium sulfate--basic slag-_----------- 31.0 588. 0 
1 Experiment conducted from May 22 to November 18, 
