Fertilization of ponds

Fertilization is the use of fertilizers to increase the production of natural food for fish. Considerable quantities of nutrient elements are regularly removed from the pond ecosystem through the harvested fish/shrimp crops and thus for retaining the pond fertility, the required amount of fertilizers need to be replenished.

Fertilization is necessary step in extensive and semi-intensive methods of farming operations.

Importance of fertilization

The fertilizers are used to increase fish production in ponds. The pond fertilization improves fertility in the following way:

Ø    It increases the production of the natural food organisms to be eaten by the fish. These organisms include phytoplankton, zooplankton and insects.

Ø    It does not cause dietary diseases.

Ø    It improves the hygienic condition of the pond by speeding up the decomposition of food residues and excreta.

Classification of fertilizers

Fertilizers are classified into two categories:

1.                  Inorganic or mineral fertilizers

2.                  Organic fertilizers or manures of plant and animal origin

1. Inorganic fertilizers: Commercially produced inorganic compounds containing major nutrients- nitrogen, phosphorus and potassium are known as inorganic fertilizers. Due to their high solubility in water the nutrients become readily available soon after their application, which helps to increase the primary productivity.

Inorganic fertilizers are-

a. Nitrogenous fertilizers: Sodium nitrate, ammonium nitrate, ammonium phosphate, ammonium sulphate, calcium ammonium nitrate, urea, ammonia liquor, etc., are the important nitrogenous fertilizers used in fish ponds.

Generally dose of nitrogenous fertilizer is 50 kg/ha. Generally 40-80 kg of urea are distributed per hectare every 15-20 days has been recommended for rearing ponds. Most of the nitrogenous fertilizers deplete reserves of bases and make soil acid.

b. Phosphate fertilizers: The most commonly used phosphatic fertilizers are the orthophosphates, superphosphates, dicalcium phosphate, triple super phosphate.    

Generally dose of phosphate fertilizers is 40 kg/ha. The optimum quantity seems to be 30-60 kg P₂O₅ per hectare.

c. Potassium fertilizers: Muriate of potash (KCl) and sulphate of potash (K₂SO₄) are the two commonly used fertilizers as a source of potassium. The favourable action of potassic fertilizers can be seen in ponds with low alkalinity, with peaty bottoms.

Generally dose of potash is 50 kg/ha. 

d. Calcium fertilizers: Calcium is usually applied in the form of lime, which is widely available as ground lime stone, slaked lime and quick lime.

Some of the actions of calcium fertilizers are to increase the pH of the tank, increase alkalinity and to precipitate organic matter.

The recommended application rate is 210 kg/ha annually.  

Above mentioned major nutrients are expressed on a percentage by weight basis. Nitrogen is expressed as %N and phosphorous as % P₂O₅. Commercially available inorganic fertilizers are usually sold with such trade names as 16-20-0 (16% N- 20% P₂O₅- 0%K), 45-0-0 (urea).

2. Organic fertilizers: The organic fertilizers are definitely of animal or plant origin and the nutrients present in them are either made available directly or after decomposition and transformation by the microbes.

The organic manures are generally recognized on the basis of the following criteria:

a. Organic manures with little or no carbohydrates: It has been found that the ponds treated with liquid manure a procured from the stables and byres (cow sheds) impart fertility for good fish yield. It is applied in small doses once or twice every 8 days in deeper parts of the pond. Stimulated growth of phytoplankton, filamentous algae and zooplankton has been noticed in ponds treated with liquid manures.

Increased yield through the use of guano and blood meal has also been reported.

b. Organic manures containing mainly carbohydrates: In this category, the manures made out of mustard oil cake, mahua oil cake, cotton seed meal, soyabean meal, etc.

Green manuring is used in fish ponds in many countries. In this method undecomposed green plant tissue is turned into soil by sowing a nitrogenous or other crop on dry pond bottom.   

c. Organic manures having considerable amount of carbohydrates with nitrogenous matter: They are available in a variety of forms such as farmyard manure (dung of cattle, sheep, pig and goal), poultry manure (poultry droppings), sewage (only diluted and pre-treated sewage can be used as a fertilizer), sludge (mud-like deposits or mixtures).

The rate of application for shrimp ponds ranges from 500 to 2000 kg/ha.

Advantages of organic fertilizers

1.                  It encourages bacterial growth, in turn favours better production of the zooplankton. It also stimulated growth of phytoplankton and filamentous algae.

2.                  It improves the bottom mud.

3.                  It increases the effectiveness of many inorganic fertilizers by providing the necessary organic matter base.

4.                  Organic fertilizers act as fish feed, i.e., organic fertilizers directly feed by fish.

5.                  They provide substrate for micro benthos attachment.

Disadvantages of organic fertilizers

1.                  There is a risk it might cause an oxygen deficit.

2.                  It favours certain diseases (gill rot).

Ref.

Gupta, S. K., and Gupta, P. C., (2006), General and applied ichthyology.

Marcel Huet, 1979. Textbook of fish culture Breeding and cultivation of fish.