Pond fertilization through inorganic sources: an overview

Abstract

Input of nutrients through inorganic sources has long been a common practice
of pond fertilization. The state of the art of pond fertilization has been reviewed
in the present paper. Phosphorus through phosphate fertilizer is the most
important nutrient regulating the productivity offish ponds as 1 kg P2Os went
into 2.5 to 28.22 kg of carp production under different conditions. In most cases,
nitrogen is not considered as a limiting nutrient of pond productivity. Nitrogen
may be eliminated from fertilization programme in case of old well fertilised
ponds without reducing fish yields, however, there are differences of opinion
regarding the importance of nitrogen fertilizer in fish ponds. The ratio of N
and P seems to play an important role in limiting the efficacy of nitrogen
fertilizers. P limitation of phytoplankton occurs when the N : P ratio of the
nutrient supply is substantially higher than the mean atomic ratio of N to P
in phytoplan kton cells (15 : 1); an ambient ratio less than 15 : 1 results in
N limitation. The role of potassium as fertilizer in the pond culture system
has not been properly assessed. As fish pond soils exhibit higher amount of
organic mattsr than upland agricultural soils and as the pH of bottom soil
and water remains alkaline, availability of potassium in the pond sediment
is high. Thus, the concept of pond fertilization should be based on NPC rather
than NPK as practised in agricultural soil with less organic matter.
Generalised schedule of pond fertilization resulted in high variability of
productivity in different agroclimatic areas. Many interacting factors such as
soil type, wa;er depth, water retention time, species of culture, quality and
quantity of vegetation should be taken into consideration. More studies on
pond fertilization in the context of nutrient dynamics and fertilizer-microbial
interactions under different agroclimatic regions are necessary for an effective,
appropriate and economic fertilization programme. Also, the environmental
consequences of overfertilization resulting in pollution and subsequent hazards
in public health should be taken into account.