Pond preparation
In any earthen pond culture system the bottom soil play
important role infish production. High organic matter content in neutral soil
often promotes higher primary productivity and hence higher fish yield. Natural
food organisms are one of the most important food sources in ponds. It is rich
in protein, vitamins, minerals and other essential growth elements that simple
supplementary feed cannot complete. Fish yield in pond can also be affected by
the presence of predators, deteriorating water quality and improper pond
management. Hence, pond preparation is a first step towards ensuring higher
fish production. It includes pre-stocking and post stocking management
practices. Pre-stocking pond preparation includes soil sampling , drying,
manuring and fertilization, weed control, insect control , predatory and
weed fish control. Post stocking pond
management includes the other steps which support a good yield like natural
plankton production, disease free aquatic environment, weed control, management
of various pond structures application of inputs as and when necessary and
regular monitoring of growth.
A brief description of pond preparations steps are given
below.
13.1. Soil sampling:- Prior to pond preparation,
soil samples are collected from the pond bottom, dikes for pH, organic matter
and important nutrient contents analysis. 12 soil samples from 0-15 cm top soil
are collected from one ha pond area in S- shaped pattern. Soil in sieved to
remove stones, wooden material and coarse particles. All the samples are dried
in air and labeled after mixing sub samples properly. The dried soil is then
packed in labeled plastic bag and analysis for its composition. Soil pH
analysis is generally conducted to determine nature of the soil if acidic or
basic. For newly developed ponds where acid sulphate soils are found lime
application rate can be calculated based on pH of soil. When acidic soil
condition is detected, corrective measures can be incorporated in the pond
preparation activities. Calcium sulfate (CaSO4.2H2O) are
used in soil having alkaline pH.
13.2. Leaching :-If
the soil is acidic it is flushed with freshwater to dissolve the acids, salts
undesirable metallic compounds like aluminum, iron and excess sulfur ions are
washed out.
13.3. Pond drying:-The
pond bottom is exposed to sun light and air to eradicate undesirable fish
species, insects and disease causing agents. Soil exposure to air and light
also fasten the mineralization of organic matter. Harmful gases trapped in the
bottom soil are also released. The pond is dried until the soil cracks or when
it is firm enough to hold one's weight without sinking more than 5 cm on
walking over the surface. While drying other activities like repair of dikes
and inlet and outlet gates, leveling, installation of screens and substrates
installation if required are undertaken.
13.4. Tilling:-Tilling or ploughing of
bottom soil improves soil quality by exposing subsoil to the atmosphere thereby
speeding up the oxidation process. It also helps to turn the sub surface soil
nutrients and their subsequent utilization to improve the pond productivity.
13.5. Liming:-Lime are the materials
which contain calcium and magnesium compounds and are capable of neutralizing
acidity. Most common liming materials are oxides, hydroxides and carbonates of
calcium and magnesium having higher percentage of calcium compared to
magnesium. (a) CaO - Calcium oxide or Quick lime (b) Ca(OH)2 Calcium hydroxide or slacked lime, (c)
CaCO3- Calcium carbonate agricultural lime are the commonly
occurring forms of limes. Calcium
carbonate is most widely used lime in aquaculture.
13.6.
Liming substances:- Liming
substances are the following:
(a) Calcium oxide (CaO):- Calcium oxide is
variously known as unslaked lime, burnt lime and quicklime. It is manufactured
by roasting calcitic limestone in a furnace. Calcium oxide is caustic and
hygroscopic and is sold commercially in powder and granular forms.
(b) Calcium hydroxide (Ca(OH)2):-Calcium
hydroxide is referred as flaked lime, hydrated lime, slaked lime or builder's
lime. It is prepared by hydrating calcium oxide. It sold commercially in powder
or granular forms.
(c) Calcium carbonate ( CaCO3) and
mixed calcium-magnesium carbonate, [CaMg (CO3)2]:-The
carbonates occur widely in nature. Among the common forms that can be utilized
as liming substances are calcitic limestone which is a pure calcium carbonate
and dolomitic limestone which is a calcium-magnesium carbonate with varying
proportions of calcium and magnesium. Commercial calcium carbonate is known as
agricultural lime. The carbonates are the least reactive of the three liming
substances.
13.7.
Action of liming:- The
favorable actions of liming are: (a) kills most micro-organisms especially
parasites due to its caustic reaction, (b) raised pH of acidic water to neutral
or slightly alkaline value, (c) increases the alkaline reserve in water and mud
which prevents sudden fluctuation in pH, (d) neutralizes the harmful action of
sulfides and acids, (e) promotes biological productivity since it enhances the
breakdown and degradation of organic substances by bacteria creating a more
favorable oxygen and carbon reserves, (f) precipitates suspended or soluble
organic materials, decreases biological oxygen demand (BOD), increases light
penetration, enhances nitrification due to the requirement of calcium by
nitrifying organisms. Excessive liming, however, can be damaging because it
decreases phosphorus availability through precipitation of insoluble calcium or
magnesium phosphate.
Commonly occurring chemical reaction in pond
water are as follows
CO2 in water is mainly produced as
a result of respiration and degradation of organic matter. CO2 is
three times more soluble in water than oxygen. It reacts with water
and form carbonic acid (H2CO3) which is a weak acid and
breaks up into H++ HCO3- ions. In presence
of carbon dioxide CaCO3
dissolve in water and form calcium bi carbonate Ca(HCO3).This is
stable product present in excess of CO2. In Presence of Acid and
base different reaction occurs.
13.8.
Methods of liming
Liming can be done in three
different ways:
·
Broadcast
over dried pond which includes the dike walls.
·
Mixing
with water and spraying over the pond, and
·
Liming
the flowing water into the pond.
In general, any one of
these methods may be employed. When we are using the first two methods, lime
should be spread as uniformly as possible over the complete surface of the pond
or pond water. The third method is uncommonly practices although it saves the
labor in spreading.
Agricultural wastes like
basic slag, cement factory wastes, paper mill sludge have also been found to be
suitable for use as liming materials as they contain good amount of CaO. Rock
phosphate containing calcium besides phosphorous may be used as a source of
phosphorous in acid soils but only to a
limited extent due to its effectiveness under moderately acid condition which
is rather undesirable for fish ponds.
13.9. Fertilization:-One
usual way of increasing carrying capacity of a pond is to improve its natural
fertility through the addition of organic or inorganic fertilizers. Pond
fertilization is an important and necessary step in extensive and
semi-intensive methods of farming operations.
(a)
Organic manures
Proximate nutrient content
of certain oil cakes are as follows
|
Oil cake |
Nitrogen % |
Phosphorous% |
Potash% |
|
Ground nut oil cake |
6.0-6.5 |
0.8-1.0 |
0.8-1.0 |
|
Mustard oil cake |
4.0-4.5 |
1.0-1.6 |
1.0-1.5 |
|
Madhuka seed cake |
2.0-2.5 |
0.5-0.8 |
1.5-1.9 |
|
Neem cake |
4.5-5..0 |
0.8-1.0 |
1.0-1.5 |
Animal wastes also
strengthen the food chain ensuring easy availability of natural fish food
organisms that support the fish growth. The nutrient content in the different
animal waste are as follows
|
Animal wastes |
Nitrogen % |
Phosphorous% |
Potash% |
|
Cattle dung |
0.4-0.5 |
0.2-0.4 |
0.1-0.2 |
|
Pig dung |
0.4-0.6 |
0.3-0.6 |
0.2-0.4 |
|
Duck droppings |
0.6-0.9 |
0.3-0.6 |
0.4-0.6 |
|
Vermicompost |
0.4-1.4 |
0.1-0.25 |
|
(b)
Inorganic
fertilizers
Inorganic fertilizers are
synthetic fertilizers containing pure form of nutrient. When inorganic
fertilizers are applied in pond immediately they are dissolved in water to
release contained nutrient. Nitrogen,
phosphorus, potash calcium, magnesium, sulphur are macronutrients while copper,
iron, iodine, selenium, zinc, cobalt, chromium are some of the micronutrients.
Nitrogen is required for the synthesis of
protein in living beings. In soil and water it can be supplemented by
application of urea, calcium ammonium nitrate, potassium nitrate, ammonium
sulfate, ammonium nitrate, sodium nitrate and liquid nitrogen. In pond average
amount of urea applied is 20.0 kg/ha/month.
Nitrogen content present in
some of the inorganic fertilizers are
|
Inorganic fertilizers |
Formula |
Nitrogen content |
|
Urea |
CO(NH2) |
44-46% |
|
Calcium nitrate |
Ca(NO3)2 |
15% |
|
Ammonium nitrate |
(NH4)2NO3 |
33 |
|
Ammonium sulfate |
(NH4)2SO4 |
21 |
|
Sodium nitrate |
NaNO3 |
16 |
|
Potassium nitrate |
KNO3 |
13 |
Phosphorous in fresh water
ponds affect pond productivity.
Phosphorous is useful in the synthesis of cell wall of plant and animal
cells and tissues. The main form of inorganic phosphate fertilizers are as
follows
Phosphorous is also
released in water as a result of degradation of plant and animal remains. The
availability of phosphorous to a large extent depends on the soil pH. It is
more available at neutral pH. If the pH is acidic it combines with the Aluminum
present in the water and form Aluminium phosphate. Under alkaline conditions it
combines with calcium and form calcium phosphate. These complexes make
phosphorus unavailable minimizing the phytoplankton production. Mostly in pond
single super phosphate is used in pond water the normal rate is 25 kg/ha/yr.
|
Name of fertilizer |
Formula |
Phosphorous
content in % |
|
Single super phosphate |
|
|
|
Diammonium phosphate |
(NH4)2HPO4 |
20-23 |
|
Tripple super phosphate |
Ca(H2PO4)2 |
7-22 |
|
Rock phosphate |
|
12-17 |
|
Nitrophosphate |
Ca(H2PO4)2H2O |
10-15 |
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