4.1 Introduction – Paddy rice is typically cultivated in level basins (Figure 17) that are inundated with water for the majority of the growing season. Figure 17. In level basins, various growth stages of paddy rice are cultivated. Most rice varieties maintain better growth and produce higher yields when grown in flooded soils than in dry soils, which is the primary reason for flooding the rice fields.
Why is it necessary to flood rice?
What is inundated rice? A type of paddy rice, flooded rice systems are irrigated, rainfed, or deep-water rice production systems with a growing cycle between 105 and 150 days, depending on the variety. Each year, flooded rice is grown for up to two or three seasons.
- Inundating rice fields improves the growth of the majority of rice varieties, reduces their susceptibility to erratic precipitation, and increases yields relative to dry soils by reducing pests and weeds.
- China, India, Indonesia, Bangladesh, Vietnam, Thailand, Myanmar, and Japan produce the majority of the world’s flooded rice.
Diverse water regimes exist in flooded rice fields, but they can be broken down into four categories: I permanent flooding, (ii) shortened flooding, (iii) intermittent flooding, and (iv) periodic moistening. The environment (through climate and natural flooding) and humans determine water regimes (through water management).
Natural or environmental flooding is determined by the biophysical environment (e.g., extreme rainfall during the monsoon season). Farmers decide how much and for how long to flood, or existing collective irrigation structures determine flooding periods (e.g., the government opens a levy, and all farmers’ fields are flooded without individual control).
Sometimes, these influences even vary by season. Flooded rice systems can include nutrient management, water management, agroforestry, open burning, livestock, and energy use for irrigation or processing, and can be affected by these factors. To expand flooded rice areas, land-use change may occur.
Current annual rice crop losses exceed $1 billion, primarily due to the fact that the highest yielding varieties have no resistance to flooding. However, by introducing the gene into strains that lacked it previously, researchers improved submersion tolerance without diminishing yield or grain quality.
How can we prevent flooding of rice fields?
How to administer water
- Rice is typically cultivated in fields that are continuously flooded for seven to ten days prior to harvest.
- Continuous flooding aids in ensuring adequate water and weed control.
- The cultivation of lowland rice requires a great deal of water.
In an irrigated lowland production system, 1 kilogram of rice requires 1,432 liters of water on average. Total seasonal water input to rice fields ranges from as little as 400 millimeters in heavy clay soils with shallow groundwater tables to more than 2,000 millimeters in coarse-textured (sandy or loamy) soils with deep groundwater tables.
- The typical amount of water required to irrigate rice in Asia is 13001500 mm.
- Rice is irrigated with an estimated 3443% of the world’s total irrigation water, or 2430% of the world’s developed fresh water resources.
- Water for agriculture is becoming increasingly scarce worldwide.
- Rice is highly susceptible to water shortages due to its semi-aquatic ancestry.
To maximize rice yields and maximize water use efficiency, the following good water management practices can be implemented: 
- With field channels, water can be delivered separately to each seed bed, and the main field need not be irrigated until it is time to plant in the main field.
- In addition, the ability to control water on your field is essential when you need to retain water (especially after applying fertilizer to prevent nutrient loss) or drain the field for harvest.
- In every type of irrigation system, the construction of individual field channels is recommended.
Large and deep cracks can cause significant water loss during land soaking prior to puddling, as water drains down the cracks and beyond the root zone. Turn the soil to fill voids. Using puddles to reduce water loss 
- For clayey soils that develop fissures during the fallow period, puddling produces a dense, compacted pan.
- For sandy soils with a coarse texture, puddling may not be effective.
- Due to the low infiltration rate of heavy clay soils, puddling may not be required to reduce water losses
- however, puddling may still be required if the soil was cracked prior to primary tillage, if weeds are present prior to transplanting, or if the soil is too hard or cloddy for transplanting after soaking.
Despite reducing water loss, puddling itself is water-consuming. There is a trade-off between the amount of water used for puddling and the amount of water “saved” by a compact hard pan during the crop growth period. Wet land preparation can consume up to one-third of the total water necessary for rice cultivation in an irrigated system.
- Erect field channels
- Utilize shared/community seed beds
- plant adjacent fields simultaneously, or
- Implement direct wet seeding
Most fields require two plowings before they can be leveled. In wet land preparation, the second plowing should be performed with standing water in the field in order to distinguish high and low areas. Read: | Good bunds are required to restrict water loss.
To reduce water loss, bunds should be well compacted and cracks or rat holes should be filled with mud at the start of the growing season. Bunds must be sufficiently high (at least 20 cm) to prevent flooding during heavy rainfall. Lower levees of 510 cm in height can be utilized to maintain the ponded water depth at that level.
When additional water storage is necessary, these levees can be augmented with soil. Read: Different crop establishment techniques necessitate distinct water management strategies: Initial water levels after transplanting should be around 3 centimeters, increasing gradually to 510 centimeters (with increasing plant height) and remaining there until the field is drained 710 days prior to harvest. 
- When there are numerous weeds, AWD should be postponed for two to three weeks to aid in the suppression of weeds by ponded water and to increase the effectiveness of herbicide.
- Policy brief:
- Direct-sown rice
Keep the soil moist, but not saturated, from the time of sowing until emergence to prevent seed rot. If there is no rainfall after sowing, apply a flush irrigation to wet the soil. When plants have three leaves, saturate the soil and then follow the safe Alternate Wetting and Drying practices described above.
- Read:
- In the event of water scarcity, implement water-saving technologies such as and consider switching from puddled to non-puddled transplanting or.
: Water management