Fertilization in Aquaculture Ponds

Sachin O. KhairnarPh.D Scholar (Aquaculture Ecology)

Ocean University of China, Qingdao

Introduction

• Primary production of aquaculture ponds be augumented by increasing the availability of plant nutrients through fertilizer applications.

• Greater primary productivity leads to a higher abundance of natural food organisms.

• the primary producers of most ponds are microscopic, plantonic algae

• Plant require mineral nutrients for growth, and nitrogen and Phosphorus usually are the two nutrients present in the smallest quanties relative to plant requirement.

• Substances that increase nutrient concentrations to enhance plant growth are called fertilizers or manures.

• the term manure usually is reserved for animal excreta and agricultural by-products.

Chemical fertilizers• Primary Nutrients

1. Phosphorus: The most common phosphate compounds are ammonium phosphate, diammonium phosphate, potassium phosphate, dipotassium phosphate and phosphoric acid.

2. Nitrogen: ammonium nitrate, ammonium sulfate, urea(45%N).

3. Potassium: Potash is used for preparation of potassium sulfate and potassium nitrate

Chemical fertilizers• Secondary Nutrients

1. Calcium: Gypsum and liming material are source of Calcium.

2. Magnesium: Dolomite another liming material is source of Ca and Mg.

3. Sulfur: Elemental sulfur, mangnesium sulfate, potassium sulfate, super phosphate are source of sulfur

Form of fertilizers

• Solid fertilizers: • Liquid fertilizers

• Instantly soluble fertilizers

• Controlled release fertilizer

Solid fertilizers

1. Most familiar form of fertilizer, is dry, solid consisting of irregular shaped granules or spherical particles known as prills.

2. They must be stored in dry place to avoid to form cake in presence of moisture.

3. Fertilizer must be water soluble if nutrients contained in them are to be available for plants.

4. Solid fertilizers often are broadcast over pond surfaces in area is not more than 2m deep.

5. This type of fertilizer doesnot dissolve quickly and stand in water for 3 to4 hrs. before settling.

Liquid fertilizers• the most common liquid fertilizer for agriculture are solutions o

f ammonia and urea.

• Two liquid fertilizers, phosphoric acid and ammonium polyphosphate are considerable use in aquaculture.

• this fertilizers should be stored in mild steel containers.

• Liquid fertilizers are denser then water, if they are poured directly into the water, they will flow to pond bottom as a density current.

Instantly Soluble Fertilizers

• They are prepared by finely pulverising solid fertilizers, thus resulting powder will dissolve almost instantly in water.

• This fertilizers dissolves easily and quickly

Controlled-Release Fertilizers

• In this method fertilizer prills can be coated for slow, gradual release.

• The technology for producing controlled-release fertilizers involves coating a soluble fertilizer prill (core) with acopolymer shell of dicyclopentadine and a glycerol ester (linseed oil).

• The copolymer is applied in multiple layers and the shell thickness governs the nutrient release rate.

• Nutrient release rates depends upon temp.

Bulk blended fertilizer• Fertilizers with specific grades are made by mixing appropriat

e quantities of nitrogen, phosphorus and potassium compounds.

• If all three primary nutrients are included, then this bluk blended fertilizer is said to be complete fertilizer.

• A filler is added to make up the diff in weight.

• The filler is usually agricultural limestone

• This material is used becaus it will neutralise acidity.

Effects of nitrogen fertilizers on water quality

• Ammonium fertilizers and urea are considered as potenial sources of acidity in agricultural soils, because nitrification by Nitrosomonas, Nitrobacter and a few other species of bacteria produces acidity as follows:

NH4 + 2O2 ----> NO3 + H2O ..........(1)

• Hydrogen ions produced in nitrification neutralizes alkalinity in pond water

HCO3 + H -----> H2O + CO2 ...........(2)

• By above reaction we can calculated the amount of fertilizer (ammonium fertilizer) to neutralize the amount of alkalnity.

Manures• A wide variety of organic materials have been used as pond

manures.• Livestock dung, leaves, grass, weeds; • wastes from distilleries, tanneries, dairies and sugar refiner

ies;• cotton seed, peanut oilcake and sunflower oilcake• soyanbean and rice wastes• cottonseed meal • dry hay• many other agricultural wastes and by-products can be equ

ally useful

• The type of organic material obviously affects the nutrient composition of a manure.

• different batches of a particular kind of manure may also vary considerably in moisture and nutrient content.

• Animal dung will differ in composition, depending on the species of livestock, type of feed given to livestock, age of the dung and exposure of dung to the weather.

• Concentrations of fertilizer constituent in selected manures are much more lower then those of chemical fertilizers.

• Wastes from vegetable and fruit harvesting and processing usually are high in moisture and low in fertilizer value.

• Meals are much higher in quality than hay and wastes.

• Because of low fertilizer value, manure application rates are much higher than those for chemical fertilizers. eg. for 1 kg of DAP(18-46-0) contains as much as nitrogen as 36 kg of dairy cattle manure and for Phosphorus 230 kg.

The practice of pond fertilization

• Nutrient ratios ：

• Amount of nutrients

• Frequency of application

• Method of Application

Nutrient ratios• Lot of studies revealed that phosphorus-only can cause large increases in fish an

d shrimp production,but somehow greater results can achieved if nitrogen is also added to ponds.

• Fertilizer nitrogen requirement is less as compare to phosphorus, exception in case of diatoms.

• For general fertilization in fresh water ponds N:P Ratio is 1:1.3 to 1:1.7.

• Brackish water ponds need more nitrogen than fresh water ponds so the Ratio is 1:0.87. Potassium and other secondary nutrients have high concentration in seawater; Hence, fertilizers for brackish water ponds doesnt need this fertilizers.

• A general fertlizer for brackish water ponds is 9-16-0 blended from sodium nitrate, triple super phosphate, trace nutrient package, and small amount of filler.

• Silicate fertilization may be beneficial to diatom production in B.W ponds, this fertilizer contains 15% of nitrogen, 3.5% of silicate and variety of trace elements.

Amounts of nutrients• Amount of Nitrogen ration depends upon the P2O5 (Phosporus pe

ntaoxide).

• the monthly application of the fertilizers varies in different ranges for e.g. 2 kg of P2O5 in case of liquid fertilizer and upto 25 kg of

P2O5 in case of solid fertilizers.

• In humid climate 2-1o kg/month of P2O5 is sufficent to achieve phytoplankton bloom and in case of arid climates its 2-3 times more.

• When fertiliztion is used at shorter interval, monthly dose should be divided into two or more smaller doses.

Frequency of Application• The ideal frequency of fertilizer application probably varies fr

om place to place, but 2-4 weeks of interval is adequate.

• the most critical and often most difficult aspect of pond preparation is initiation of phytoplankton bloom in the spring or at beginning of a crop.

• Larger or more frequent applications of fertilizers may be needed to initiate a phytoplankton bloom than to maintain an existing phtoplankton bloom.

Method of application• Broadcasting

• Platforms and bags

• Liquid fertilizers

Broadcasting Method• Solid, granular fertilizers often are broadcast over pond surfaces

• Fertilizers do not dissolve completely while settling through the water, but they finish dissolving while laying on the pond bottom.

• This favours adsorption of phosphate by the soil, and if water circulation in ponds is not good, nutrients that dissolve into the bottom water may not enter the illuminated upper layers for use by phytoplankton.

• Instantly soluble fertilizers can be braodcast over the entire surfaces of ponds. The particles will dissolve before settling out of the epilimnon.

Platforms and Bags • This method prevents phosphorus fertilizer from settling to the p

ond bottom,apparently decreasing the rate at which phophorus from the fertilizer is adsorbed by bottom muds.

• This method reduces fertilizer requirements by 20-40%.• Platforms should be about 30cm underwater and one platform wi

th an area of about 4m.sq. is adequate for 2-4 ha of pond area.• Fertilizer is poured onto the platform and water currents distribu

te nutrients as they dissolve.• Platforma also are sutaible for exposing controlled release fertili

zers to the water.• Fertilizers also have been placed in porous bags and suspended i

n pond water st different places in the pond.• The nutrients disslove and seep out of the bags to be mixed by w

ater currents.• Plastic bags of fertilizer can be laid on the pondbottom, and uppe

r surface of the bag cut away to expose the fertilizer to the water.• Platforms are superior to either of the bag techniques mentioned

above, but their construction requires more effort than the use of bags.

Secchi disc- A pond fertilization tool

Visibility Comments

< 20 cm Danger of DO problems every night

20-30 cm Plankton becoming too abundant

30-45 cm Ideal

45-60 cm Plankton becoming too scarce

> 60 cm Water too clear, inadequate plankton and danger of aquatic weed problem

Problems to consider when fertilizing

• Nutrients and Quantities 1.The faliure of the fertilization program may result from inadequate quantity of f

ertilizer or from the lack of a fertilizer nutrient. 2.As mention earlier phosporus is the nutrient most commonly limiting phytopla

nkton growth. 3. Nitrogen also is limitng in most brackish water and in some fresh water environ

ments. 4.The likelihood of other nutrients limiting phytoplankton is much less, but any e

ssential plant nutrient can be alimiting factor.• Acidic, Low-Alkalnity water Probably the most common resason in fresh water pond not to produce algal blo

omis low alkalinity water.• High Calcium Concentration 1. In waters with calcium concentrations of 50mg/l, or more and pH values of 8.0 a

nd above. So hard water should be treated with more amount of phosphate fertilizer than soft waters.

2.Standard dose is 60/kg/ha of superphosphate or abot 11 kg/ha of Phosphorus pentaoxide zt 2-week intervals.

• Turbid water: if pond water is turbid it will not respond to fertilizersas its visibility

will be less thsn 20 to 30 cm. • Macrophytes 1.Weed control must be effected in ponds which are chocked

with nacrophytes orfertilizer nutrients will stimulate macrophytes rather than plankton.

2.Application of fertilizer in late winter and early spring to weed infested pond will produce filamentous algae whcih grow over and shade weeds.

3.If pond contains more expanse of shallow waters, fertilization will not help to control the macrophytes.

4. to discourage the macrophytes, pond egdes should be deppened to 45-60 cm at time of construction.

• Excess Flow the detention time of water in apond should exceed 3 or 4wee

ks, otherwise fertilizer nutrients will be flushed out of the pond before they produce fish food.

• Ponds with feeding 1.Fish and crustaceans that are applied pelleted feed usually do not o

btain a larger % of their food from natural resources. 2.Metabolic wastes fertilize ponds and often cause heavy plankton bl

ooms, but early in the grow-out period when feeding rates are too low, two to three applications of fertilizer may be needed in some ponds to increse plankton turbidity and effect underwater weed control.

3. At other times, the use of fertilizer in fed ponds encourages excessive plankton blooms and increases the likelihood of oxygen depletion.

• Winter kill 1. A place with a long, cold winter, indicates that fertilization greatly

incresed plankton abundance and the growth of fish. 2.Unfortunately, organic matter accumulated in ponds as a result of

high rates of primary productivity during warm months, and the decomposition of this organic matter during the winter when ponds are covered with ice often result in oxygen depletion or winter kill of fish.

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