Sewage-fed fish

Sewage is a rich nutrient resource, cheaply available around big towns and cities. It can be well-utilized for fertilizing paddies, fish ponds and horticultural crops. Waste utilization through recycling also helps in maintaining a clean environment. This paper is based on existent practices in Eastern India.

Rice-fish/prawns

In areas where irrigation facilities are not available, a second crop of rice is possible by construction water storage structures within the field. These could be in the form of lateral, central or marginal trenches or unilateral/bilateral ponds which are also utilized for aquaculture. Based on the input requirements for a 0.4 ha field, the following methods are adopted:

Raise the peripheral dikes by digging a perimeter trench (3 m wide x 1.5 m deep) or a lateral pond. If necessary, inlets and outlets are provided and guarded with meshed screens.

Fill the trench with sewage water to a level of 1 5-20 cm

Deep water paddy (CN 570, 652; NC 487 or 492) is sown directly after the first monsoon shower.

When water level in the trench is- about 60-70 cm, stock about 400 mature (1.5-2 g) mole (Amblypharyngodon mole) together with 8,000 bata (Labeo bata) having an average weight of 2g. As soon as 3-4 g prawn (Macrobrachium rosenbergil) are available, 2000 juveniles are also stocked.

The fish and prawn move about the field when the water level in the trench rises and covers the paddy.

The water level in the field and the trench falls with the end of monsoon. The paddy ripens by November/December and about 560 kg are harvested from the field in 150 days. The fish and prawn continue to grow in the trench.

Utilize the water in the trench for raising a second crop of rice. Fertilize it by taking in sewage to a level of about 10 cm each month from December to February. A low-level dike Is constructed all around to maintain a 10-15 cm water level in the paddy field.

The field is fertilized with sewage and seedlings of high-yielding varieties (Ratna or IET 4094) are transplanted in January.

Sewage fertilization is repeated when the seedlings have taken roots and again during the flowering stage. The fields are irrigated regularly and the water level maintained until the rice is mature. Pesticides are used only when necessary.

A partial harvest of the prawns (50 g), bata (20 g), mole (20 9) is made.

The paddy is harvested by April with a yield of about 2.0- 2.4 t.

The fishes are finally harvested by the end of April or early May. The total fish harvest is about 112 kg bata, 50 kg prawns and 45-50 mole.

ADVANTAGES

1. The second rice crop contributes to additional food production,-- employment and income generation.
2. Fish crop provides a rich protein food of high market value and adds considerably to the farmer' income.

LIMITATIONS

1. Trench/pond construction is useful only in water-retentive soils.
2. Difficulties in fish seed transport, if away from the main road.

Rupee budget for rice-fish-prawn culture in a 0.4-ha unit.

1 US$ = 25.50 Rs

Horticulture-fish

The utilization of sewage for aquaculture and horticulture results in high yields and economizes on fertilizer and feed costs, resulting in higher profits. Based on the input requirements for a 0.4 ha pond, the following procedure is recommended:

Broadcast about 200 kg of quicklime over the entire pond surface after it Is drained and dried for about 10-15 days.

Load the pond with 30 cm of sewage in early June which gets diluted with rain water and filled up to a level of 1.2-1.3 m by early July.

Stock with 3000 fingerlings of six species (catla 15, silver carp 25, rohu 25, grass carp 5, mrigal 20 and common carp 10) or 2000 fingerlings of three species (catla 40, rohu 30, mrigal 30).

Use the dikes (500-1000 sq m of land around the pond bank) for growing vegetables, beginning with monsoon crops, followed by winter and then summer crops. Each crop is harvested as soon as it is ready. About 1500 kg of vegetables are harvested from 500 sq m of dikes.

A wide range of vegetables can be planted: okra, eggplant, cucurbit gourds, cabbage, cauliflowers, potato, radish, tomato, onion and leafy vegetables like Amaranthus, Ipomoea, fenugreek, spinach, etc., are raised in simple mixed or multiple cropping.

Load the pond with sewage effluence once a month to the extent of one-fourth or one-fifth of the water level.

Feed all waste leaves to the grass carp in the pond; 80 kg of leaves give about 1 kg of fish.

The pond is netted every 15 days and marketable fish is harvested. A total of 2400 kg of fish can be harvested from the pond.

ADVANTAGES

1. Waste utilization/recycling of domestic sewage brings about a reduction in biochemical oxygen demand/bacterial load before releasing in streams.

2. High-stocking densities and high-yield rates, especially of plankton feeders as well as detritus feeders, are possible.

3. Low-cost fish/vegetable production.

DISADVANTAGES

1. Cope pod parasites due to high organic load cause moralities
2. Sudden fall in oxygen level owing to cloudy weather or heavy intake also results in moralities.

Rupee budget for vegetable production on a 1000 sq m plot on the pond banks.

Note: About 25 different kinds of vegetables are grown in single/mixed or multiple cropping and an average production of 3,000 kg valued and Rs 7,260 obtained. The cost of production being Rs 5,400 a net profit of Rs 1,860 is taken by farmers. In small farms, the farmer himself works as labor which accounts for 60% of the total production costs; hence, he nets out an income of Rs 1,860 + Rs 3,240 = Rs 5,100 or US $ 204.00.

Prepared by: S.D. TRIPATHI & B.K. SHARMA

FARMER-PROVEN INTEGRATED AGRICULTURE-AQUACULTURE
A TECHNOLOGY INFORMATION KIT (IIRR-ICLARM)