Rice management in rice-fish culture

by John Sollows and Catalino Dela Cruz

Rice-fish culture can be carried out under rainfed or irrigated conditions, in either direct seeded or transplanted fields. Timing of seeding and transplanting activities are affected by many factors (water availability, rice variety, etc.) but are not usually affected by the fish culture component.

Seedlings are best transplanted 25-30 days after seeding although the best age for traditional varieties may fall outside this. In practice, they often remain in the seedbed longer than this. Sometimes, droughts occur so that the fields are too dry to be transplanted and the farmer must wait for rain. In other cases, the family labour force is limited and the rice in the seedbed must «wait» until the family gets to it.

Most farmers find no problem in applying chemical fertilizers to their rice-fish systems. In some cases, it has been reported that fish die after exposure and when they are fed with pellets and may have ingested fertilizer granules for this reason.

The wide scale of rice-fish is still constrained by continued application of pesticides in rice-based farming. The use of pesticide is not recommended in rice-fish farming. In rice-fish culture, there are ways of controlling rice pests that do not need pesticide, such as:

• Quick submergence (for three hours) of rice plants in water. This makes the insects vulnerable to fish predation. Limitation: suitable only before plants are taller than the dikes.
• Two persons can drag a stretched rope (50-100 m) across the rice fields to knock off the insects into floodwater, after which they can be eaten by the fish. Limitation: suitable only before rice plants reach booting stage.

However, should a farmer insist on using pesticides, here are some helpful tips:

1. Considerations in applying pesticides:

• Choose and apply properly pesticides that have low toxicity to fish.
• Minimize the amount of pesticide getting mixed with water.
• Apply at suitable time.

2. Considerations in preventing fish poisoning:

• Drive the fish into the sump, draining the field slowly before spraying. Keep the fish in the sump until the toxicity in the sprayed field is gone.
• Increase water depth (+10 cm) to dilute the concentration of pesticides 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 second and third items above, 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 markets. Application of a toxic insecticide like Furadan or Curaterr ® can be made safe to fish if done properly through solid incorporation during the final harrowing. Furadan is a systems 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 are already in their full vegetative stage and the thick leaves will intercept most of liquid sprays, thus drastically reducing the concentration of pesticides reaching the water.

It is best to wait until the rice is well established before releasing seed fish, particularly if the fish are large. Fish can be stocked once two or three tillers have appeared for which the usual waiting period is 1-3 weeks after transplanting or 4-6 weeks after direct seeding depending on the state of the rice and the size of the fish.

Small fry (about 2.5 cm long) can be stocked immediately after transplanting, without harm to the rice. The authors have never seen a rice variety that does not work with fish, but some varieties are better than others. Deepwater-tolerant varieties are preferable to those which thrive in only very shallow water.

In some areas where rainfalls are highly unpredictable, farmers prefer to wait until very late in the rainy season to stock fish. At this time, surface water accumulation will be at its yearly peak and the chance of flooding from later rains is very slim. In such cases, long-lived, late-maturing rice varieties are best.

Rice varieties which tiller (i.e. produce new plant stems ) rapidly or under a wide range of water conditions will allow farmers to stock earlier in many cases.

Farmers have succeeded with early and late-maturing photoperiod-sensitive and nonsensitive, glutinous and nonglutinous varieties.

Effects on rice yield

The authors' experience indicates that rice yields rise on the average, by about 10 percent, in rice-fish situations. However, there is great variation from farm to farm so guarantees cannot be made.

Yields seem the most enhanced on farms with poor soil where fish are fed intensively. Possible mechanisms include:

• increasing availability of nutrients for increased floodwater productivity and uptake by rice; and
• reducing loss of ammonia through volatilization after fertilizer application by preventing floodwater pH to rise over 8.5.

The greatest danger to rice has already been indicated: big fish will damage very young rice; otherwise, some rice varieties do not tolerate deepwater. By using very sensible precautions farmers are not likely to harm their rice yields.