TECHNIQUES OF FISHPOND MANAGEMENT 13 
From experiments conducted with distilled water inoculated with a 
plankton culture, it has been found (20) that the most efficient pro- 
duction of plankton is obtained when the water contains 4 parts per 
million of nitrogen (N), 1 part per million of phosphorus (P) and 1 
part per million of potassium (K). This is a ratio of 4:1:1.p. p. m. 
of nitrogen, phosphorus, and potassium (N—P-K). Ammonia nitro- 
gen is superior to nitrate nitrogen for plankton production, but in 
some waters excessive acidity develops when ammonium sulfate is 
used as the source of the nitrogen. ‘To neutralize this acidity, it is 
necessary to add lime (calcium carbonate—CaCO;). In distilled 
water cultures, maximum plankton production is obtained when the 
ratio of N-P-K-Ca is 4:1:1:8 p. p.m. A considerable quantity of 
the phosphorus is tied up by the soil of a pond bottom, and to com- 
pensate for this the amount of phosphorus shouid be doubled, making 
the ratio 4:2:1:8 p. p.m. In pond fertilization it was found that 
light applications of fertilizer at frequent intervals gave better plank- 
ton production than did heavy applications at less frequent intervals. 
Best plankton production was obtained when nitrogen, phosphorus, 
and potassium were added at the ratio of 1:14:14 p. p. m. at weekly 
intervals. The recommended amounts of commercial fertilizers will 
give this concentration in 1 acre of water 3 feet deep. 
It is customary to express the fertilizing value of fertilizers in 
terms of the percentages of available nitrogen (N), phosphoric acid 
(P,O;), and potash (K.O). <A fertilizer that contains 6 percent of 
nitrogen, 8 percent of phosphoric acid, and 4 percent of potash is 
known as a 6-84 fertilizer. Commercial mixed fertilizers are offered 
in many variations of these percentages. 
For fertilizing small ponds, it is more convenient to use a mixed 
fertilizer than to obtain separate ingredients and mix a fertilizer 
that will meet the requirements of plankton production. For plank- 
ton production, nitrogen, phosphorus, and potassium must be added 
at the rate of 1:14:14 p. p. m. of the elements. This ratio, expressed 
in whole numbers, is 8:4:2. Since the composition of fertilizers is 
usually given by stating the percentage of the oxides of P and K 
(conversion: PX2.3=P.,0;; KxX1.2=K.O), the desired ratio of the 
elements would be very nearly supplied by an 8-9-3 fertilizer. A com- 
mercial mixed fertilizer near to this ratio except that it is short on 
nitrogen is 6-8-4. By adding 10 pounds of sodium nitrate for every 
100 pounds of 6-8-4 mixture, the ratio is brought to approximately 
8-8-4, which supplies the elements N, P, and K in about the right 
proportion. 
Various mixtures of commercial fertilizers may be used to fer- 
tilize ponds (23). The following quantities are required for one 
application per surface acre: 
Commercial mixed fertilizer. 
Neutral or acid waters: 
100 pounds 6-8-4 mixture 
10 pounds nitrate of soda 
Apply separately or mixed. 
Alkaline waters (Above pH=8) : 
100 pounds 6-8-4 mixture 
10 pounds sulfate of ammonia 
Apply separately or mixed. 
