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 pH
5
. This may
enhance phytoplankton productivity and substantially increase
fish yields in limed fertilised ponds relative to unlimed fertilised
controls
4
.
Agricultural limestone cannot be applied simultaneously with
phosphate fertilisers as this will cause phosphorus to precipitate
12
.
This is due to the high calcium concentrations from the limestone
reacting with phosphate to form tricalcium phosphate
18
. It is
therefore desirable to add liming materials well in advance of
fertilisers.
Liming is not usually considered to be a form of fertilisation
13
.
However, liming increases the concentration of calcium and/or
magnesium,which can be limiting nutrients, for phytoplankton,
at low concentrations
5
. 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 years
3
. The effective period of an
application, as indicated by water hardness, is determined by
the rate of water loss to seepage and overflow from ponds
3
.
Liming has been reported to be ineffective in a pond with a water
retention time of less than three weeks