Stress Tolerant Rice Varieties

The high yielding long-duration varieties such as Swarna-Sub1, Ranjit-Sub1 and Bahadur-Sub1, are able to tolerate complete submergence for two weeks. Depending on flood-water quality, the submergence-tolerance period may vary. Turbidity of water hinders radiation to reach plants, thereby impacting the photosynthesis process in plants. BINA Dhan 11, a medium-duration submergence-tolerant rice variety could be grown in all the districts of Assam including the areas having low rainfall, and under delayed post-flood sowing conditions mostly prevalent in upper Brahmaputra valley zone. The varieties for different growing situations are listed below along with their brief characteristics description.

Seed quality and treatment

• Seed quality:Quality seed is clean (contains no pebbles, soil particles, weed seeds), genetically pure (contains only grains of one variety) and healthy (well filled, of the same color, without cracks, and no obvious disease- or pest-damage).
• Seed selection: :Seeds are immersed in plain water and stirred well. Seeds, those sink down are selected, and those floats are rejected.
• Seed treatment: Adopt seed treatment with recommended fungicides only. Once the selection process is done, the seeds should be soaked directly in one of the following fungicidal suspensions for 12 hours. One liter of fungicidal solution is required to treat one kg of seed. Treated seeds should be kept in incubation for 48-72 hours.

• Safety precaution: Plastic gloves should be used while handling chemicals to avoid ill- effect on health

Nursery raising

• Time of sowing :Last week of May to the first week of June is the most appropriate time for raising a nursery.
• Seed rate :40 kg per hectare
• Nursery size: For one hectare of the main field, the nursery seedbed size should vary between 750 and 1000 m², but should not be more than 1/10thof the main field size. Land is thoroughly puddled and seedbeds of 10 m length, 15 cm height and 1.5 m breadth are prepared keeping a 60-cm gap in between the beds. The length of the bed may vary according to convenience and availability of space.
• Irrigation:Irrigate to maintain saturated condition in the surface soil of the seedbeds. Maintain 2-3-cm standing water 2-3 days prior to uprooting.
• Plant protection: Adopt plant protection measures in the standing nursery as per standard package of practices.
• Seedling priming against insects: As protective measure against stem borer, gall midge and hoppers, the uprooted seedlings are washed and the root portion is dipped in 0.02% solution of Chlorpyriphos (2 ml/lit of water) along with 1% urea (10g/liter of water) for 3 hours. Alternatively, spray Chlorpyriphos 20 EC @ 0.02% in the standing nursery 5-7 days before uprooting.
• Nursery fertilizer: Use 3-1-2 g N-P₂O₅-K₂O + 2 kg manure per m² i.e., equivalent to 3-1-2 kg N-P₂O₅-K₂O + 2 tons manure in 1000 m² of nursery area for one-hectare main field.

Field preparation

For preparation of the main plot, the following points should be kept in mind -

• Field should be prepared thoroughly by ploughing with desi plough 4 times, followed by harrowing and laddering.
• Ploughing should be started at least 2-3 weeks ahead of transplanting so that weeds are dried-up/decayed.
• Alternatively, one pass of mouldboard plough followed by one or two passes of modified helical blade puddler are sufficient for obtaining good quality puddled soil.
• The ploughing intervals should be spaced such that the weeds germinated after the first round of ploughing are knocked down in the next round.
• If available, apply compost or manure uniformly prior to field preparation, and mix it well with the soil.
• Repair the bunds to reduce water losses from the field during the cropping season.
• Level the fields, best by maintaining a shallow water layer in the field.
• The basal fertilizer dose is applied to the field (see fertilizer section below).

Transplanting

• Seedling age: 30-35-day old seedlings for long-duration, 25-30-day old seedlings for medium-duration, and 20-25-day old seedlings for short-duration varieties, are transplanted in a thoroughly prepared main field.
• Spacing: 20-25cm x 15cm (8-10 x 6 inches)
• Seedling density: 2-3 seedlings per hill.
• Depth of seedling: 4-5cm

Fertilizer management

For transplanted rice, fertilizer recommendation per hectare is 60-20-40-5kg of N-P₂O₅-K₂O-Zn. The nitrogen dose is split into 3 applications - approximately 1/3rd as basal, 1/3rd at tillering, and 1/3rd at panicle initiation. Under submerged conditions, additional 20 kg N and 20kg K₂O is applied 5-7 days after recession of flood to facilitate regeneration, and boost recovery from flood-shock. The detailed schedule and method of applying all nutrients is given in the table below:

DAT= Days After Transplanting

Note:

• Stop urea broadcast, in case Bacterial Leaf Blight symptoms appear.
• Apply ZnSO4 in soils deficient in zinc, once in three years.
• As far as practicable, drain out standing water before fertilizer application.

Weed management:

Keep the field weed-free, especially during the early phase of crop growth. Weeds cause maximum damage in the early phase of the crop growth. But the later control is also important to prevent seed-setting by the weeds. Two weeding are done manually or mechanically (using paddy weeder or power weeder ); first at 3 weeks after, and second at 6 weeks after transplanting.

Herbicides:Herbicides should be selected based on presence of weed flora, and considering even previous weed pressure in the field.

Herbicide application

• Equipment:Given their superior effectiveness, herbicides should only be applied using multi-nozzle boom fitted with flat-fan nozzles. While spraying, the new spray-swath should always overlap 25 % of the previous spray-swath margin to ensure uniform application.
• Pre-emergence (PE) Herbicides: Most PE herbicides require moisture at the soil surface at the time of application. Without sufficient moisture, the PE herbicide will not be that effective.
• Pre-emergence herbicides can be used by splash method in 3-5cm standing water in the field, preferably within 2-3 days after transplanting.
• Pre-emergence herbicides supplemented with one hand-weeding will be more effective to take care of the germinated weeds, and the weeds emerging later in the season.
• Post-emergence (PoE) Herbicides: PoE herbicides, if required, should be applied between 20-25 DAT when weeds attain 2-4-leaf stage. Ensure that there is no standing water in the field; however, the field should have moisture at the time of PoE application.
• Spray volume: Use spray volume of 300 liters/ha in all herbicide applications.

Herbicide safety:

• Read the label prior to use to understand both the toxicity level and the safety measures required.
• Plastic gloves, goggles or face-shield, and full clothing should be worn by the person while mixing, and during application of the herbicides.
• Post-application, all clothes need to be washed separately from the family laundry.

Select suitable and need based herbicide (s) from the table given below

DAT= Days after transplanting.

Given below are some of the recommended herbicide-combinations. Depending on weed flora, follow the application timing and doses as per above table

• Pretilachlor (PE) followed by bispyribac-sodium (PoE)
• Pretilachlor (PE) followed by bispyribac-sodium (PoE) + pyrazosulfuronBispyribac sodium (POE) +pyrazosulfuron

Irrigation:

In Sali season, in the absence of rain, application of 5 cm irrigation water 3 days after disappearance of ponding water is recommended in medium and heavy soils.

Plant protection measures:

It is applied, if threshold levels of pests are present in the field. Follow plant protection measures as per state recommendations.

Harvest and post-harvest

• Harvest when 80-85% of the grains attain physiological maturity i.e. visually straw-colored.
• Minimize the time during which the harvested plants remain in the field and avoid field drying. Make sure that the panicles stay dry.
• Thresh and dry within two days after harvesting. It is advised to adopt mechanised drying using a solar bubble dryer. In the absence of mechanised drying, alternatively follow Sun drying on a mat or plastic sheet, keeping the thickness of the grain layer at 3 to 5 cm
• Clean thoroughly by winnowing. Store the rice in a cool, dry, and clean area.