acidic muds of ponds to pH 6.5 has been shown to increase
soluble phosphorus concentrations. This reflects the greater
solubility of phosphorus from muds at this pH5
. This may
enhance phytoplankton productivity and substantially increase
fish yields in limed fertilised ponds relative to unlimed fertilised
controls4
.
Agricultural limestone cannot be applied simultaneously with
phosphate fertilisers as this will cause phosphorus to precipitate12.
This is due to the high calcium concentrations from the limestone
reacting with phosphate to form tricalcium phosphate18. It is
therefore desirable to add liming materials well in advance of
fertilisers.
Liming is not usually considered to be a form of fertilisation13.
However, liming increases the concentration of calcium and/or
magnesium,which can be limiting nutrients, for phytoplankton,
at low concentrations5
. These nutrients are most likely to be
limiting in waters of low total hardness.
Lime must be periodically reapplied to remain effective.
Ponds treated with approximately 1000kg/ha agricultural
limestone or hydrated lime have been reported to show increased
productivity for two to four years3
. The effective period of an
application, as indicated by water hardness, is determined by
the rate of water loss to seepage and overflow from ponds3
.
Liming has been reported to be ineffective in a pond with a water
retention time of less than three weeks12.