Colocasia sp., an aquatic plant also known as taro, is an excellent food material. It can be grown as an added commodity in a rice-fish farm. Practically, all parts of the plant can be eaten (tubers, stalks and leaves). It can also be utilized as food for fish and animals, especially pigs. The culture requirement is simple, and there are no expensive inputs.
Here are steps in raising Colocasia:
- Obtain young tubers.
- Cut old leaves but retain the young leaves and shoot.
- Cut the tuber into half.
- Plant the tuber at 50-70 cm intervals along the side of the dike, about 10 cm below the water surface.
- Start harvesting after 4-5 months.
The species cultured are Nile tilapia (Oreochromis niloticus) and common carp (Cyprinus carpio). Large fingerlings, 15-25 g, are recommended as they reach harvestable size within one rice crop. If only small fingerlings (5-10 g) are available, fish culture is done in two stages:
- Stage 1: Raising 5-10 g fingerlings during one rice cropping (harvest size: mostly 50 g)
- Stage 2: Extending fish culture period after rice harvest for up to 2 months (harvest size: 50 g)
Stocking can be done before or during land preparation in the pond refuge; or 7-10 days after transplanting (DAT), if fish are released directly to the fields. If stocked in the pond refuge, animal manure should be applied into the refuge 4-5 days before fish stocking. About 15 kg may be applied in a 100 m² pond refuge.
The stocking rate for Stage 1, using either monoculture of Nile tilapla or polyculture of Nile tilapia and common carp is 5 000-7 500 fish/ha. For polyculture, the stocking ratio of Nile tilapia to common carp is 1:1 or 2:2, depending on which species is more important to farmers.
Ten days after transplanting, fish stocked in the pond refuge may be released to the field by making openings in the dividing dike. Fish will graze on natural food available in the ricefield.
Timetable for Rice-Fish Culture
Day – Activity
- 0 – Prepare and fertilize seedbed.
- 1 – Soak seeds (IR-36, 42, 52, 54, 64 and 74 as examples).
- 3 – Broadcast germinated seeds in seedbed.
- 7 – Prepare ricefield:
- Start of fish culture (STAGE I):
- Stock fish (Nile tilapia, 5-10 g in size) at 5,000- 7,500/ha. Insure water supply infields.
- 24 – Pull seedlings. Apply basal fertilizer. Use the kinds and rates of fertilizer recommended for the locality based on soil analysis.
- 25 – Transplant seedlings (wet bed method).
- 51 – Second application of fertilizer (top dressing). May split the amount into two applications hence the third application.
- 75 – Third application of fertilizer (top dressing)
- 100 – Drain water and harvest large/marketable fish.
- 120-125 – Harvest rice.
- 125 – Start of fish culture (STAGE Il): Prolong fish culture period after rice harvest for small-sized fish (30-40 9) stocked at 3,000-5,000/ha.
- 185 – Harvest second batch of fish.
This feeding is recommended at the middle culture period of rice (45-50 DAT), during which production of natural food in the fieldwater declines due to shading of rice leaves.
- Feeds: rice bran, kitchen refuse, ipil-ipil meal, etc. Animal manure may also be applied in the pond refuge.
- Feeding rate: 3-5 percent of fish biomass
Harvest fish by draining the water very slowly 1 week before rice harvest to avoid trapping the fish in the middle of the field.
Select large fish for consumption or disposal and confine the small fish (50 g) for stage 2 culture.
After harvesting rice, the field is immediately reflooded to about 30 cm deep, and the small fish in the refuge are released to allow them to grow for another 60 days before the dry season crop.
Benefits and Limitations of the System
1. Fish can contribute to increased rice yield by 10-15 percent by:
- Controlling certain weeds and insects such as stemborer and brown planthopper;
- Producing fish wastes, including uneaten feeds which add fertility to the soil;
- Increasing availability of nutrient for increased floodwater productivity and uptake by rice; and
- Reducing loss of ammonia through volatilization by preventing floodwater pH to rise over 8.5. During fertilizer application, increased plankton production tends to raise the value of pH beyond 8.5, the value at which ionized ammonia converts into an un-ionized form that is easily lost.
2. The increased size of dikes in the system offers opportunity to plant other crops, such as taro (Colocasia sp.), stringbeans, cowpea, wingbeans, eggplant and others.
3. The wide-scale adoption of rice-fish is still constrained by continued application of pesticide in rice-based farming. The use of pesticide is not recommended in rice-fish farming. There are ways of controlling rice pests that do not need pesticide, such as:
- Quick submergence (for 3 hours) of rice plants in water. This makes the insects vulnerable to fish predation. Limitation: suitable while rice plants are shorter than the dike.
- Two persons can drag a stretched rope (50-100 m) across the ricefields to knock off the insects into the floodwater, after which they can be eaten by the fish. Limitation: suitable before rice plants reach panicle initiation stage.
However, should a farmer insist on using pesticide, here are ways to apply it:
- Choose and apply pesticides that have low toxicity to fish properly.
- Minimize the amount of pesticide getting mixed with water.
- Apply at suitable time.
Preventing fish poisoning:
- Drive the fish into the refuge by draining the field before spraying. Keep the fish in the sump until toxicity in the sprayed field is gone.
- Increase water depth (+10 cm) to dilute the concentration of pesticide in the water.
- Flush water through the ricefield. Open the inlet and outlet of the field and allow irrigation water to flow freely, during spraying. Begin spraying from the outlet end of the field. When one-half of the field is already sprayed, stop for a while and allow the pesticides to flow out of the field. Then, continue spraying towards the inlet end of the field until it is finished.
To do the last two items above in applying pesticides, here are some examples: apply powder pesticides in the morning when dewdrops are still on the leaves; and apply liquid pesticides in the afternoon when leaves are dry.
There are a number of less toxic pesticides in the market Proper application of a toxic insecticide like Furadan or Curaterr can be made safe to fish if applied through soil incorporation during the final harrowing. Furadan is a systemic insecticide, the efficiency of which in controlling insect pests lasts about 50-55 days. Incidence of pests after this period can be controlled by spraying liquid pesticides. At this time, the rice plants have reached their full vegetative stage and the thick leaves will intercept most of the liquid sprays, thus, drastically reducing the concentration of pesticide reaching into the water.
source: www.nzdl.org, photo from china.org.cn