Leaflet 15: Liquid Fertilizer
Fisheries Leaflet No. 15
LIQUID FERTILIZER IN PONDS
Wildlife and Freshwater Fishieries Division
Department of Conservation and Natural Resources
Proper fertilization will significantly increase fish production in ponds. Research has proven that the use of liquid fertilizer will effectively and efficiently increase the abundance of plankton (green color), aquatic insects and other aquatic life available as feed for fish. Also, plankton (green color) shades the pond bottom and prevents the growth of rooted weeds. Fish do not eat fertilizer, therefore, it does not prevent fish from biting.
Phosphate in liquid fertilizer is more soluble in water than that in granular fertilizer. Less phosphate, therefore, is required to achieve the same results.
Liquid fertilizer can be purchased in three forms: One is clear green and is made from new acids. The second form is gray because clay has been added to suspend phosphate in the liquid. Either of these forms is suitable for use in ponds; however, the clear green form (Poly N) is preferable. The third form is brown-black, is formulated from used industrial acids and may contain undesirable metals and chemicals. Its use in ponds is not recommended.
How to Use Liquid Fertilizer:
1. Begin to fertilize the pond around February 15th of each year (or when the water temperature reaches 60oF)
2. Make the first three applications at 2-week intervals.
3. Make additional applications whenever a white object can be seen 16 to 18 inches below the surface of the water, or at monthly intervals (see the note at the end of this letter).
4. Discontinue fertilization when the water temperature falls below 60oF(around November 1).
5. By law, the label and/or the supplier must disclose the percentage of Nitrogen (N), Phosphate (P) and Potash (K) in a fertilizer. If the fertilizer has less than 30 percent phosphate, apply one gallon per surface acre per application. If it has 30 percent or more phosphate, apply 3 quarts per surface acre per application.
6. If the pond is less than two acres, the fertilizer may be applied with a garden sprayer or diluted 10 to 1 with water and broadcast from the bank. It should be sprayed or broadcast along at least 1/4 of the shoreline.
If the pond is larger, the fertilizer may be applied with a power sprayer if you can cover 1/4 of the surface area. If necessary, the fertilizer can be siphoned from a container in a boat into the prop-wash of a small outboard or electric motor. LIQUID FERTILIZER SHOULD NOT BE POURED DIRECTLY INTO THE POND. IT IS HEAVIER THAN WATER AND WILL SINK TO THE BOTTOM BEFORE IT CAN GO INTO SOLUTION.
The most economical way to obtain liquid fertilizer is to supply your own container(s) and to purchase a year's supply (10 applications) in or before February. Poly N may be stored in metal drums since it is relatively non-corrosive. Mound the drum horizontally. Screw a plastic valve into the 3/4-inch bung so that each application can be withdrawn easily. If the gray form of fertilizer is used, cut a hole in the upper side of the drum. Stir the fertilizer through this hole before an application is withdrawn.
NOTE: If your pond clears within two weeks following applications in the summer, fertilize more frequently (at two week intervals) with one-half the recommended rate. Liquid fertilizer is so soluble that it can be quickly consumed by the planktonic algae. Smaller, more frequent applications should solve the problem. If more frequent applications do not solve the problem, send samples of the pond bottom to the Agronomy and Soils Laboratory, Auburn University, Auburn, Alabama, to determine if the pond should be limed. Sample containers may be obtained from the County Extension Specialist in your county.