Aquaculture CRSP 21st Annual Technical Report
Reaction of Liming Materials in Pond Bottom Soils
Tenth Work Plan, Effluents and Pollution Research 1 (10ER1)
Claude E. Boyd
Department of Fisheries and Allied Aquacultures
C. Wesley Wood
Department of Agronomy and Soils
Embrapa Meio Ambiente
Division of Aquaculture
University of Stellenbosch
Stellenbosch, South Africa
Three techniques for treating fish ponds with agricultural limestone were evaluated in ponds with clayey soils in Brazil and in ponds with sandy soils in South Africa. Amounts of agricultural limestone equal to the lime requirement of bottom soils were applied by the following methods to each of three ponds: (1) direct application over the pond surface; (2) spread uniformly over the bottom of the empty pond; (3) spread uniformly over the bottom of the empty pond followed by tilling of the bottom. The effectiveness of agricultural limestone applications did not differ among treatment methods. Agricultural limestone also reacted quickly to increase total alkalinity and total hardness of pond water to acceptable concentrations within two weeks after application. Data on soil pH and exchangeable acidity suggested that the reaction of liming material to increase soil pH was essentially complete after one to two months. In the clayey soil, agricultural limestone had no effect below a depth of 8 cm. Agricultural limestone reacted to a depth of at least 20 cm in the sandy soil. This research suggests that full ponds can be limed effectively. Aquaculture methods that allow ponds to be operated for several years without draining are highly desirable from standpoints of water conservation and environmental protection. Moreover, findings suggest that tilling of pond bottoms to incorporate liming materials is unnecessary, considering that tilling consumes time and is an expensive practice.
Acidic bottom soil is a common problem in pond aquaculture, and fish farmers often apply agricultural limestone to ponds as a remedy. Aquaculture ponds are usually limed after they have been drained for harvest and before they are refilled for the next crop (Boyd and Tucker, 1998). However, sport fish ponds usually are not drained for liming, and agricultural limestone is spread over the water surface from a boat (Boyd, 1982).
The objective of liming is to neutralize acidity in the upper
layer of bottom soil and to increase the concentrations of total alkalinity and total hardness in the water (Thomaston and Zeller, 1961). There have been several studies that showed positive responses in phytoplankton productivity and fish production following liming of acidic ponds, and methods for determining the lime requirements of bottom soils have been developed (Boyd, 1995). Nevertheless, liming often is applied to ponds indiscriminately without concern for bottom soil pH or total alkalinity and total hardness concentrations.
It is doubtful that liming has a large influence where soil