Liming is essential before most ponds can be effectively fertilized. Many times, ponds will not respond to fertilization if bottom muds are acidic. Under these conditions, agricultural limestone must be applied to correct the acidity. If the pond fails to develop a plankton bloom after repeated applications of fertilizer, mud samples should be taken from the pond’s bottom.
Mud samples should be taken from several different areas of the pond, then mixed together while wet to form a representative sample. The sample should then be spread on a piece of plastic on wood to dry. After drying, a soil test box (from the county extension office) should be filled with the dried mud and sent for analysis to: Soil Testing Laboratory, 961 S. Donahue Drive, Auburn University, AL 36849-5411; their telephone number is (334) 844-3958. The sample box should be labeled “fish pond.” A nominal fee will be charged for each analysis. (Note: Many ponds in Alabama’s Black Belt or those with limestone springs will not need lime. If in doubt, have a sample checked.)
If a representative mud sample cannot be taken, then a jar of pond water should be delivered to the local district fishery biologist for a check of the alkalinity. Alkalinity is a measure of the bases in water. Bases neutralize acidity. In general, if alkalinity is less then 20 ppm, lime is needed.
When lime is required, agricultural limestone (calcitic lime) should be applied. Do not use slaked lime or builders’ lime, which can be toxic to fish and dangerous to handle. Lime will have to be applied periodically (3-5 years) during the life of most ponds if effective fertilization is to be practiced. Lime must be applied evenly over the whole pond to make certain all of the bottom mud is covered.
If the pond is new, it should be limed heavily by spreader truck or tractor before filling, since liming is much more difficult after the pond collects water. Liming is labor intensive so many pond owners prefer to apply two to three times the recommended rate to increase the interval between applications. Some pond owners are physically unable to apply the weight of lime needed (tons); therefore, consultants are available that will apply the lime for a fee. A list of consultants is available from the district fisheries office.
The information above came from the Alabama Wildlife and Freshwater Fisheries Division's booklet Sportfish Management in Alabama Ponds, which is available as a PDF.