Better Management Practices in Pond Preparation

The main objective of pond preparation is to provide the shrimp with a clean rearing environment and optimum conditions for their growth and survival. Effective pond preparation is an integral part of successful shrimp farming. Poor preparation can result in deterioration of the soils during the crop, with release of nutrients and toxic compounds to the water column, creating stress for the shrimp and possible environmental problems with the discharge of effluents. Good pond preparation is also a proactive measure for disease control and should be a critical aspect of disease management strategy. Pond sludge that accumulates on the pond bottom may also need to be removed before the next crop; the on-farm disposal of sediments must be done responsibly. Intensive shrimp farming requires a considerable quantity of feed to be added to a pond over the course of a crop (approximately 10 tons for a 5 ton crop). This massive input of organic material has the potential to overload the organic load in sediments and cause deterioration of the pond soils for your next crop. Pond sludge can accumulate in the centre of the pond because of the action of aerators and water currents during the crop and will appear as a mound in the centre of the pond when it is drained.

Key Instructions for pond Preparation:

1. Completely drain out the water form pond. It helps in removing disease carrying crustaceans and other aquatic animals from previous crops of the pond.

Coordinate the same with neighboring farmers. Block the inlets and sluice pipes and other sources of water entry into ponds. Use pumps to remove any water logged inside the pond. Remove any snails, barnacles and gastropods manually.

2. Increase the water holding capacity of the pond. Bunds must be compacted well to prevent water seepage. If required, additional soil should be procured form outside to increase the bund height. Pond water depth must be maintained at a minimum water level OF 1.2 meter at the middle of the pond Fix a wooden depth scale to monitor the water depth. There should be a free board of 30cm from water surface to top of the bund.
3. Remove organic waste accumulated by the decay of unfed feed, dead and decaying plankton/algae and fecal matter of shrimp. This waste releases toxic gases like ammonia and hydrogen sulfide into the pond water and causes stress or death to shrimp.

Organic waste forms a black layer on the soil and its mostly accumulated at the feeding area, pond center and corners, and at the trenches Completely remove it by scraping when the soil is slightly wet. Dump the waste in the ditch created on the top of the bund and cover it with good soil. Make sure the dumped organic waste does not enter the pond through rain water. If it is difficult to remove the black soil completely, plough when If it is wet and wait till it dries.

4. Sundry the pond bottom till the soil loses its moisture. Sunlight and dryness kill algal spores, benthic algal mats, fish eggs and any predators potentially remaining in the soil. Coordinate to dry the neighboring ponds simultaneously to prevent water seepage form other ponds. The pond should dry in hot sun for 20 to 30 days or more till its soil cracks.
5. Plough the pond 2 to 3 times with the gap of 2 to 3days. It will help in oxidizing the organic matter and reducing gastropods. Tilling the pond bottom exposes more surface area of the soil, increases the effect of Oxidation, and encourages more aerobic bacteria. The tilling process also generally assists in the breakdown of organic residues and nutrients that are locked up in the soil, making them more biologically available for the next crop. After tilling, compact the pond bottom to reduce the turbidity and seepage.
6. Wet pond preparation can be done when the ponds cannot be dried. Apply tea seed cake of or chlorine (20ppm). Before ploughing, take out all dead animals. Use a tractor with gauge wheels to plough the pond with 15 to 20cm water. After Ploughing, drain out of the water from the pond.
7. Fertilization and liming of the pond bottom will help in improving mineral content of the pond bottom especially in ponds with low soil fertility and ponds which are in culture for more than 10 years. Apply dry vermicompost 250-1000 kg/ha or compost manure. Spread the vermincompost or compost manure all along the pond bottom. Do not use poultry manure or raw cow dung for fertilization.

Apply lime to maintain soil pH. Use a soil pH meter to test the soil pH. Soil should be wet while using the equipment. The levels of lime applications during pond preparation depend on the pH of the soil. Follow dosages given in the table below:

Spread the lime all along the pond bottom and along the slopes of the pond bund. A large proportion of the lime needs to be applied along the feeding areas and on the wet portions of the pond. When applying lime, farmers and workers should wear face mask. If the soil pH is more than 7, there is no need for lime application.

8. While installing aerators, follow a proper layout to achieve the maximum flow of pond water with the minimal energy input. Poor layout of aerators in the pond can lead erosion of the pond walls or bottom and significantly increase the amount of sediment in the sludge mound by the end of the crop. This can decrease the life span of ponds and increase maintenance costs.

Source : NaCSA