Continuous flooding helps ensure sufficient water and control weeds.
Lowland rice requires a lot of water.
On average, it takes 1,432 liters of water to produce 1 kg of rice in an irrigated lowland production system. Totalto rice fields varies from as little as 400 mm in heavy clay soils with shallow groundwater tables to more than 2000 mm in coarse-textured (sandy or loamy) soils with deep groundwater tables.
Worldwide, water for agriculture is becoming increasingly scarce. Due to its semi-aquatic ancestry, rice is extremely sensitive to water shortages.
To effectively and efficiently use water and maximize rice yields, the following good water management practices can be done:
The construction of separate channels to move water to and from each field greatly improves the control of water by individual farmers.
Field channels allow water to be delivered to the individual seed beds separately and the main field does not need to be irrigated until it's time to plant in the main field.
In addition, the ability to control water to your field is important when you need to retain water (especially after applying fertilizer so nutrients are not lost) or when you need to drain the field for harvest.
Construction of individual field channels is the recommended practice in any type of irrigation system.
Large amounts of water can be lost during land soaking prior to puddling when large and deep cracks are present due to drainage of water down the cracks, beyond the root zone.
Till the soil to fill cracks
Perform shallow tillage operations before land soaking. This fills in the cracks and can greatly reduce the amount of water used in land preparation.
Puddle the field to reduce water loss
Despite reducing water loss, the action of puddling itself consumes water. There is a trade-off between the amount of water used for puddling and the amount of water “saved” during the crop growth period because of a compact hard pan.
Wet land preparation can consume up to a third of the total water required for growing rice in an irrigated production system.
If water cost or availability at the time of crop establishment is a concern, consider dry land preparation which uses considerably less water than wet land preparation.
Minimize time between operations to reduce water use
In some canal irrigation systems, the period of time between land soaking for land preparation and planting can be up to 40 days. To minimize time between operations:
A well-leveled field is crucial to good water management. An unleveled field requires an extra 80−100 mm of water to give complete water coverage. This is nearly an extra 10% of the total water requirement to grow the crop.
Most fields need to be plowed twice before you can level. In wet land preparation, the second plowing should be done with standing water in the field to define high and low areas.
Bunds should be high enough (at least 20 cm) to avoid overflowing during heavy rainfall.
Lower levees of 5−10 cm height in the bunds can be used to keep the ponded water depth at that height. These levees can be heightened with soil when more stored water is needed.
Different crop establishment methods require different water management practices:
Continuous flooding of water generally provides the best growth environment for rice.
After transplanting, water levels should be around 3 cm initially, and gradually increase to 5−10 cm (with increasing plant height) and remain there until the field is drained 7−10 days before harvest.
For direct wet seeded rice, field should be flooded only once the plants are large enough to withstand shallow flooding (3-4 leaf stage).
Alternate Wetting and Drying (AWD) can be started a few weeks (1-2) after transplanting. Irrigate and then allow the water depth to drop to 15 cm below the surface using a field water tube (pictured to the right) to monitor the water level depth. Once the water level has dropped to 15 cm below the surface, re-flood the field to a depth of 5 cm above the surface and repeat. From one week before to one week after flowering, the field should remain flooded. After flowering, during grain filling and ripening, the water level can drop to 15 cm below the surface before re-flooding.
When many weeds are present, AWD should be post-poned for 2-3 weeks to assist suppression of weeds by ponded water and to improve the efficacy of herbicide.
Policy brief: AWD reduces green house gas emissions and saves water
Direct seeded rice
Keep the soil moist but not saturated from sowing till emergence, to avoid seeds from rotting in the soil.
After sowing, apply a flush irrigation to wet the soil, if there is no rainfall.
Saturate the soil when plants have developed three leaves, and then follow the safe Alternate Wetting and Drying practices as described above.
Read: Direct seeding
Lowland rice is extremely sensitive to water shortage (below saturation) at the flowering stage. Drought at flowering results in yield loss from increased spikelet sterility, thus fewer grains.
Keep the water level in the fields at 5 cm at all times from heading to the end of flowering.
In case of water scarcity, apply water-saving technologies such as Alternate Wetting and Drying (AWD) and consider changing planting method from puddled transplanting to non-puddled transplanting or dry-direct seeding.