Introduction:
Coastal saline soil extends from the main sea coast to a few or even 50 km at places interior to the main land. The ground water table under these soils is generally present at a shallow depth and contains high amount of soluble salts. These salts accumulate on the surface of the soil due to capillary rise of saline groundwater during dry periods of the year rendering the soil highly saline. Almost the entire area of the rain fed coastal saline soil is mono cropped in nature. The major agricultural crop of kharif is rice, grown during monsoon period when soil salinity is low. During the rest of the year, the land usually remains fallow due to high salt content of the soil.
The kharif paddy varieties widely used in such areas are Mahsuri, Sadamota, Kalomota, Talmugur, Damodar, Dasal, Getu, Nona-patnai, Jaya, Ratna, Pankaj, Patnai-23, Luni, Cuttackdhandi, Pokkali, Vytilla, Bilikagga, CSR-4, CSR-6, Matla, Hamilton, Palman 579, BKN, RP-6, FR-46B, Arya, etc. Paddy cum brackish water fish/ shrimp culture aims at utilizing the summer fallow period of the coastal saline soil through a short term brackish water aquaculture without affecting the subsequent kharif paddy crop. This type of activity provides the farmers with a substantial subsidiary income during the fallow season.
In West Bengal, where the salinity is either low or lowered by fresh water discharge diluting the tidal water, the cultivation of fish is undertaken in paddy fields. In pokkali fields of Kerala, summer fallow months are utilized for brackish water aquaculture. The production of fish in such culture varies from 300 to 1000 kg/ha. The brackish water shrimp culture is introduced in a big way in such areas as the remuneration is very high. The species commonly cultured are Penaeusmonodon,Penaeusindicus,Metapenaeusdobsonii and Metapenaeusmonoceros.
Technical Parameters
The coastal area is mostly low lying, the elevation varying usually between sea level and 8 m above the MSL. Fields having elevation between low and high tide levels are desirable for water exchange during brackish water aquaculture and also for frequent draining of monsoon water during desalination process. The sluice in the embankment is essential for regulating the flow of tidal and drainage waters. The area having more than 1 m tidal amplitude is considered suitable for paddy cum shrimp culture.
Soil quality
Medium textured soils like silty clay or silty clay loam are most suitable for paddy cum fish/ shrimp culture.
Water quality
Heavy monsoon precipitation for the site is essential for desalination of the soil after brackish water aquaculture. Intake of brackish water must be suspended before the onset of monsoon. The cultured species is harvested and then the land is exposed to monsoon precipitation for the purpose of desalination.
Pond construction
The paddy plots should be renovated suitably for the purpose of paddy cum brackish water aquaculture. Construction of an earthen dyke surrounding the paddy plot is essential for retaining water and also for holding the fish and shrimp during aquaculture. The height of the dyke is required to be maintained between 50 and 100 cm depending upon the topography of the plot and tidal amplitude at the site. A perimeter canal is necessary on the inner periphery of the plot. For a one ha paddy plot, the width and depth of the canal may be about 2 m and 1 m respectively. The earth removed from excavating the canal may be utilized for constructing or strengthening the dyke. In addition to the perimeter canal, two cross trenches of about 1 m width should also be constructed at both the directions. The bottom of the trenches should be above the perimeter canal so that during the course of desalination, entire water can be easily removed to the canal. The area covered by the perimeter canal and the trenches will be about 12% of the total land area.
Water supply and drainage
The entry of tidal water during the culture is made through feeder canal and the flow of water into the field is regulated by a sluice gate fitted with wooden shutters and placed at about 30 cm height from the main plot. During high tide, water is taken into the plot after sieving through velon nets and split bamboo mats to prevent entry of any kind of fish/ shrimp and other undesirable species, especially carnivores. Another sluice is used for draining out water from the culture plot to the feeder canal at low tide periods for water exchange, desalination and drainage of excess water. On the entry and exit mouths of the slice gate, wooden shutters are provided to regulate the movement of water.
Pond management
The plots are prepared in two phases, once for brackish water aquaculture and again for paddy cultivation. For aquaculture crop, the plot is sun dried after the kharif harvest. If necessary, to rectify acidic soils, lime is applied depending on requirement of the soil. Usually no inorganic fertilization is done. However, urea may be used in extreme cases of nitrogen deficiency of soils @ 60 kg N/ha. Some shade zones are provided over the perimeter canal with twigs, hay, palm leaves etc., so that during summer the shrimp can take shelter and also hide themselves from predation.
Stocking
The paddy field is made ready for stocking and Penaeus monodon or Penaeus indicus are stocked @ 3 nos/sq.m
Feeding
Although natural food items have good conversion values but they are difficult to procure in large quantities and maintain a continuous supply.Hence only supplementary feed is given
Harvesting
Complete harvesting can be carried out by draining the pond water through a bag net and hand picking. The average culture period in paddy fields is around 100-120 days during which time the shrimps will grow to 35 gm size (depending on the species). Harvested shrimps can be kept between layers of crushed ice before transporting the consignment to market.
Production & Income
The expected production for an area of 0.5 ha. is around 350 kg. The income from 0.5 ha. has been assessed to be Rs.87500/-.
Marketing
Frozen shrimp contributes 70% by value and 30% by volume of our marine products exports. Japan, USA, European Union, South East Asia, China and the Middle East are the major markets for our shrimp. The shrimp catches from the wild are fast dwindling due to over exploitation and culture of shrimp is an alternative to increase shrimp production for export and also for local consumption.
Financial outlay
Details of the financial requirement for paddy cum shrimp culture in 0.5 ha. area have been indicated in Annexure I. The items and cost indicated under the model are indicative and not exhaustive. While preparing projects for financial assistance the costs have to be assessed taking into account actual field conditions. The projected capital cost for 0.5 ha. unit has been estimated to be Rs.67500 and operational cost for one crop to be Rs.51000.
Financial viability
The following assumptions have been made for working out the financial viability of the activity taking only aquaculture into account assuming that paddy cultivation was being done prior to taking up aquaculture and will also be continued after taking up aquaculture. The economics would remain unchanged for paddy, hence not taken into account for calculating economics and repayment. |
