A fertilization program can greatly increase fish production in fishing ponds.
Adding nutrients stimulates the growth of the microscopic plants, or algae, that feed the small animals that feed the fish. Fertilization can increase fish production by three to four times, resulting in more fish, bigger fish or both in properly managed ponds. Also, these tiny plants can shade the bottom and prevent aquatic weeds from taking over.
However, fertilizing carries significant risks, so it's important to consider carefully whether or not your pond would benefit from a fertilization program.
Once you start fertilizing your pond, you should continue fertilizing each year because the total weight of fish in the pond will increase, and the fish will come to depend upon the additional food resulting from fertilization.
Likewise, if you choose to fertilize, you will need to increase fish harvest to remove surplus production and prevent stunting. A typical pond requires removal of about 15 pounds of bass and 30-40 pounds of bream per acre per year to maintain balanced predator-prey populations. Fertilization may double or triple the amount of fish that need to be removed, so do not fertilize if your fishing effort and harvest are light.
Ponds that already receive nutrients from the watershed, such as nutrients from cattle or from the application of poultry litter, usually do not need additional nutrients. Ponds should not be fertilized if a commercial feed is provided to fish, or if they are muddy, weedy, have existing dense plankton blooms, have a fish population that is out of balance, or have excessive water flow.
Also, fertilized ponds are green, so don't fertilize if you don't want a green pond.
Before fertilizing a pond, it is important to test the alkalinity of the water to see if the pond would benefit from the addition of agricultural limestone. Alkalinity test kits are available at most pool and spa stores. A pond may have enough nutrients to be productive, but the nutrients are not available because alkalinity is too low.
Adding lime may provide a boost in productivity without fertilization. A soil sample will be needed to determine if and how much lime will be required. For small ponds, collect 10 to 20 samples from the pond bottom, mix them together, let the mixture dry, and then submit the mixture as one sample to MSU for analysis. Larger ponds will require submission of two or more samples created the same way. Your local Extension agent can assist with this process.
You should also test the hardness of the water. Hardness is a measure of the concentration of calcium and magnesium. Phosphorus is less soluble in hard water, so fertilization rates must be adjusted accordingly.
If you decide to fertilize, begin applications in the spring when the water warms above 60 degrees Fahrenheit, usually in early March. This timing promotes the growth of algae before rooted aquatic weeds can become established.
Once you start a fertilization program, maintain it throughout the growing season. Fertilization is effective only during warmer temperatures and should be discontinued when water temperatures fall below 60 F, usually in October.
The required number of applications during the growing season will vary from one to 10 or more, depending upon the pond's response to fertilization.
Choose a fertilizer high in phosphorus, as it is the most important nutrient in ponds.
Fertilizer comes in three forms: liquid, powdered and granular. Granular fertilizers are small pellets and are the easiest type to find in stores. Granular fertilizers must be kept off the bottom mud until the pellets dissolve. Granules can be placed on a wooden platform set at 4" to 12" below the water surface, or the fertilizer bag can be slit open on top in an "X" and carefully sunk in shallow water.
After the initial fertilizer application, see how the pond responds to the added nutrients. The water should develop a greenish or green-brown color within a week or so. Allow at least one week, and preferably two, between applications in order to monitor the results of each addition.
A good way to measure bloom density is to use a pie tin nailed to the bottom of a yardstick. Lower your pie tin or disk into the water until the disk just disappears from view, then raise the disk until the disk can just be seen again, and measure the depth by noting the water line on the yard stick. In farm ponds, a depth between 18 inches and 24 inches is ideal. If the bloom is thicker than this (depth reading less than 18 inches), don't fertilize. If it is greater than 24 inches, apply fertilizer.
For additional information on pond fertilization, contact the local Extension Service office and request Publication 1428, "Managing Mississippi Ponds and Small Lakes."