Rice-fish system in Guimba, Nueva Ecija, Philippines

by Catalino dela Cruz, Ruben C. Sevilleja and Jose Torres

Guimba, Nueva Ecija, Philippines, has rainfed and irrigated rice-based agriculture. In rainfed areas, rice is grown during the wet season and remains fallow during the rest of the year. In irrigated conditions, rice grown during the wet season is followed by another crop of rice during the dry season. Rice-fish culture is practiced by some farmers. In areas with extremely light soils, farmers plant vegetables (e.g. squash, cucumber, mungbean, stringbeans, onions, bitter gourd, etc.) and watermelon after wet season rice.

The rice-fish system practiced by farmers in Triala Village, Guimba, is concurrent rice-fish with pond refuge and is irrigation-based. This system is for growout of Nile tilapia. The operation is done as follows.

Rice-fish field design and construction

1. Site selection

• Abundant and dependable water supply. Irrigation water, ground water, spring and other water sources are used when they are not contaminated by pesticides.
• Clay soil is best. Clay holds water, prevents seepage and leaching of fertilizers.
• Choose site with good drainage and that is free from flooding.

2. Design and size of field

• Independent filling and draining of each rice-fish compartment is considered.
• Ease of fish movement into the ricefields during grazing and draining is also considered. The fish should be able to get quickly into the canals or refuge when water level is very low.
• Size of rice-fish plot considers the natural partitions of the field. Small plots are easy to manage, and fish survival is usually high.
• Dikes are made strong and big enough to withstand the pressure of water level in the flooded ricefield.

3. Fish refuge

Pond refuge, which holds more water and is less risky, is preferred over trench refuge. Refuge size is usually 10 percent of the ricefield area. Bigger refuge or a pond adjacent to the ricefield may also be connected to it through a canal.

To construct the refuge, the pond is excavated at one end, or two ends if the field is large, inside the ricefield or adjacent/alongside but connected to the field so that the fish can have access to the area planted to rice.

4. Inlet and outlet gates and screens

These are made of bamboo and other low-cost materials. Screens prevent the escape of stocked fish or entry of unwanted fish into the field.

Examples of fish refuge layout for small and large plots

Rice agronomy

1. Rice varieties - high-yielding varieties; maturity period of 120-130 days; resistant to insects and diseases.

2. Seedbed preparation and seeding rate

3. Land preparation - After ploughing once and harrowing thrice, the field is leveled evenly so that every part of it will be uniformly irrigated.

4. Rice transplanting method

Age of seedlings : 25-30 days
Planting distance :
    20-25 cm between rows
    15-20 cm between hills

Straight-row planting (optional), if mechanical weeding is done.

5. Weed control - Fish stocked in ricefields control certain weeds. Weeds are also controlled through:

• thorough land preparation;
• flooding the field at an effective water depth for 1-2 weeks immediately after transplanting; and
• manual weeding.

6. Water management - Water depth in the field when rice is newly transplanted is 3-5 cm. This is then gradually increased up to 20 cm to provide better living space for both rice and fish as they grow bigger. One week before the rice harvest, water is slowly drained so that fishes have enough time to move into the refuge.

7. Fertilizer application - The amount of fertilizer applied follows the recommended rate in the area. In Guimba, the rate applied during wet season is 200 kg/ha of ammonium phosphate and 50 kg/ha of urea for the first or basal application. The basal application is done immediately after the final leveling, which is followed by transplanting. The rate for the second application or top-dressing is 50 kg/ha. This is applied 30 days after transplanting. The amount for top-dressing may be split into two equal applications. In this case, a third application is applied 75 days after transplanting.

During dry season, the same amount for basal application is followed. For top-dressing, the rate is 100 kg/ha. As an example, the amount of fertilizer for a 400 m2 of rice-fish during wet season is 8 kg of ammonium phosphate and 2 kg of urea for basal application. For top-dressing, 2 kg of urea are needed.

8. Insect control - The use of insecticide is not recommended. Farmers, however, apply insecticides known to be less toxic to fish.

Raising Colocasia

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:
1. Obtain young tubers.
2. Cut old leaves but retain the young leaves and shoot.
3. Cut the tuber into half.
4. Plant the tuber at 50-70 cm intervals along the side of the dike, about 10 cm below the water surface.
5. Start harvesting after 4-5 months.

Fish culture

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 l: 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 density

• 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.

Activity calendar for rice-fish culture

Supplemental feeding

• 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

Harvesting

• 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.

Annual budget (in US$) for a 1 ha rice-fish farm with pond refuge

Partial budget (in US$) for integrating taro with rice-fish farming (1 000 m² area)

Note: Increase in net income: 31.70 - 10.95 = 20.75