Fertilization

Fertilizing Ponds

The decision of whether to fertilize a fishing pond should be considered very carefully. Proper fertilization significantly increases the total weight of fish produced in a pond, often by as much as three times. But there are many reasons not to fertilize, including potential water quality issues, high expense, and the fact that it is a long-term commitment. Consider the following when making your decisions.

Fertilizer stimulates growth of microscopic plants, called phytoplankton. Phytoplankton forms the base of the food chain, and small animals eat these small plants and serve as food for bream, which in turn are eaten by bass. Phytoplankton makes the water turn green, or “bloom,” which also shades the bottom and discourages growth of troublesome aquatic weeds.

Most ponds should not be fertilized. If only a few people fish a larger pond, it does not necessarily need fertilization to have good fishing. However, in a heavily fished pond, proper fertilization produces the best fishing. Fertilization significantly increases the total weight of fish produced in a pond, increasing the number of fish that need to be harvested.

Many Mississippi ponds should not be fertilized. Here are some cases where this is true:

• Ponds not fished heavily. Fertilizing a large pond is a waste of time and money if you fish it only occasionally. You just produce more fish that aren’t caught, increasing the possibility of crowding and slow growth.
• Muddy ponds. Mud keeps sunlight from passing through the water and binds up phosphorus from fertilizer. This prevents good plankton growth. If a pond stays muddy most of the time, do not fertilize the pond until the mud problem is corrected.
• Undesirable fish populations. If undesirable species dominate the pond, renovate the pond, restock, and then begin fertilizing. Similarly, if desirable species are out-of-balance and are small, fertilizing just makes more small fish. Fix the balance first.
• Ponds infested with weeds. During warm months, pond weeds use up the fertilizer the microscopic plants should get. The pond stays clear even after repeated fertilizer applications, and you gain more weeds.
• Ponds that are fed commercial feed. It is not necessary to fertilize ponds if you follow a feeding program. Commercial feed adds nutrients to the water, and adding fertilizer can degrade water quality.
• Too much water flow. In some spring-fed ponds, too much water flows through the pond to maintain plankton blooms. In this case, fertilizer constantly being diluted has little positive effect.

Some Mississippi ponds benefit from fertilizer. Here are some cases where this is true:

• Ponds that are heavily fished. Ponds that receive heavy fishing pressure may be at risk of overharvest or poor fishing. Fertilization can increase the abundance of fish to compensate for heavy fishing.
• Ponds managed for trophy fish. To produce big bass, you need overabundant prey and low bass density. Using a fertilization program and removing small bass can achieve good results.

Type, Rate, and Application of Fertilizer

Fertilizer is always marked with three numbers separated by dashes. These numbers indicate the percentage of the fertilizer product that is made of nitrogen (N), phosphorus (P), and potassium (K), respectively.

A fertilizer with an N-P-K of 13-37-0 is 13 percent nitrogen, 37 percent phosphorus, and 0 percent potassium. The key ingredient for most ponds is phosphorus (middle number), so select a fertilizer with high phosphorus content.

Several types of fertilizer can be used, and all can be effective if the pond soil pH and water chemistry are in the correct ranges. Pond fertilizers are available in liquid, granular, or powdered forms. Liquid fertilizers dissolve most readily, followed by powders, and then granular types.

Liquid fertilizer

Use of liquid fertilizers has declined in recent years, but they are still available. Typical formulations for liquid fertilizers include 10-34-0 and 13-37-0. Apply these fertilizers at the rate of ½ to 1 gallon per surface acre, depending on pond location and soil fertility.

Dilute liquid fertilizer with at least two parts water to one part fertilizer before application. In small ponds, you can spray liquids effectively from the bank with hand-held sprayers. Boats make application easy in larger ponds. You can spray the diluted fertilizer over the water surface or let it flow into the prop-wash of an outboard motor. You can pour or broadcast powdered formulations directly on the water surface.

Powdered fertilizer

Powdered, highly water-soluble fertilizers, such as 12-49-6 or 10-52-0, are available and have proven to be effective and convenient. For these reasons, they have grown in popularity. Formulations are typically applied at the rate of 2 to 8 pounds per surface acre, again depending on pond location and soil fertility. Powdered fertilizer can be easily broadcast over open water, as it dissolves rapidly before sinking too deep.

Granular fertilizer

Granular fertilizers are less expensive and are available in many formulations. Most older ponds respond well to a phosphorous-only fertilizer such as Triple Super Phosphate (0-46-0), which is the most economical formulation. Rates range from 4 to 12 pounds per acre per application. In some areas, it may be difficult to buy 0-46-0, but 0-20-0 is usually available. If it is, use twice the amount recommended for 0-46-0.

If you use granular forms, apply them in a way that minimizes fertilizer-soil contact. You can do this by making fertilizer platforms—one for each 5 to 6 acres of water. Build the platforms so you can raise or lower them. Pour the right amount of fertilizer on the platforms so 4 inches of water covers them. Waves will distribute the fertilizer throughout the pond. Never spread granular fertilizer on the pond surface—it will simply sink to the bottom and be ineffective.

Building a platform can be difficult in existing ponds. An alternative method is make a floating basket. A plastic laundry basket can be floated in a PVC ring and anchored offshore to hold granular fertilizer at the right depth.

Make a Fertilization Schedule

Begin fertilization when water temperatures have stabilized at 60°F or higher. Usually this temperature occurs around March 15 in south Mississippi and April 1 in central and north Mississippi. Early fertilization shades the pond bottom and helps control filamentous algae, a common problem in Mississippi ponds in spring.

Make the first three applications of fertilizer 2 weeks apart. This should establish a good bloom. The ideal bloom makes the water green and results in a visibility of about 18 inches. Use a yardstick with a white tin can lid on the end to measure the bloom, or make or buy a Secchi disk.

When you can see the lid in 24 inches of water, it is time to fertilize again. This is usually about every 2 to 4 weeks. When water temperature drops below 60°F in the fall, stop fertilizing for the year. New ponds, or those that have never been fertilized, sometimes fail to respond to fertilizer, and it can be difficult to start up a plankton bloom. If your first efforts to produce a bloom with 0-46-0 or other low-nitrogen fertilizer don’t work, even after liming the winter before, use a more complete (high-nitrogen) fertilizer, such as 20-20-5, at a rate of 40 pounds per acre on the specified schedule until the pond gets a green bloom. Continue with a normal application rate of high-phosphorus pond fertilizers after that.

Important Points on Fertilization

• Once you start fertilizing, you must continue fertilization from year to year! Stopping fertilization will leave the pond with too many fish for the food produced, and fish will starve and crowd quickly, resulting in poor condition and growth.
• Improper fertilization is worse than no fertilization. Follow the fertilization recommendations provided here, and maintain the recommended bloom density for the entire growing season.
• Do not try to kill aquatic plants by applying fertilizer. Although fertilization can shade the bottom and prevent weed growth, fertilization after weeds are established usually just makes more weeds.
• A bloom should develop after two to three applications. Many Mississippi fish ponds do not develop a satisfactory phytoplankton “bloom” when fertilized at recommended rates because of low soil pH and water alkalinity. Lime can increase fish production in ponds with acid bottom mud and soft water by altering the soil pH and alkalinity of the water. If a bloom does not develop after four applications of fertilizer, check for lime requirements, too much water outflow, too many weeds, or muddy water.