Technical instructions for water management in paddy fields
Good water management helps rice produce effective tillering, strong roots, less lodging and saves on irrigation costs. paddy fields do not need to be continuously flooded; In many stages, alternating wet and dry irrigation should be applied.
Summary: Rice plants need water, but keeping it submerged for the whole crop is not the best way. Continuous flooding weakens roots, increases pumping costs and can promote pests and diseases. Proper water management is to keep moisture in the early stages, add water when needed to control grass or raise paddy fields, and apply alternating flooding and drying in the remaining stages.
Applies to: paddy fields in the Mekong Delta and actively irrigated areas.
Duration: Throughout the season, from after sowing to before harvest.
Difficulty level: Medium. It is necessary to observe the field surface and water level regularly.
Estimated additional costs: Irrigation pumping costs are often reduced if the embankment and field surface are good.
Does rice need to be continuously flooded
No. Rice plants can withstand flooding better than many other plants, but that doesn't mean they have to be continuously flooded from beginning to end of the season.
Fields need water most clearly in two stages:
- First stage: keep moist and sometimes keep water shallow to limit weeds.
- Stage of flowering — flowering: needs enough water to grow flowers, reduce flatness and help seeds become firm.
In other stages, alternating wet and dry irrigation can be applied. When the soil has time to aerate, the roots grow deeper, the plants become stronger and the fields produce fewer toxins.
Benefits of correct water management
Water management is not just about saving water. It directly affects growth and pests.
Main benefits:
- Restricts ineffective branches, helping fields focus on cultivating effective branches.
- Roots grow deeper and stronger.
- The tree is hard, less likely to fall.
- Reduce irrigation pumping costs.
- Reduces some pests because the field is not constantly wet.
- Reduces black roots due to lack of oxygen in the soil.
- Creates conditions for beneficial microorganisms to function better.
Fields sown thickly and deeply flooded often look green quickly at first, but later the plants are easily weakened, have many pests, and are difficult to harvest.
Principle of alternating wet and dry irrigation
Alternating wet and dry irrigation means not keeping water permanently on the field surface. After watering, let the water drain naturally. When the water level in the soil drops to a level that requires watering again, add water.
Easy to apply threshold:
- When the water level drops to about 15 cm below the ground, you can water again.
- If you don't have a measuring tube, observe that the field surface has just cracked, then add water.
- Each time you water, you should only keep water at a maximum of about 5 cm.
Do not let the field dry out and crack deeply during the rice planting, flowering and firming stages. This is the period when lack of water can easily increase flatness and reduce productivity.
Phased water management schedule
| Phase | How to manage water |
|---|---|
| 1-7 days after recharging | Keep the field moist, avoid deep flooding, causing floating seeds or weak sprouts |
| 12-22 days after sowing | Water can be withdrawn to stimulate roots and limit useless branches |
| 28-40 days after sowing | Continue to withdraw water in a controlled manner, creating open fields |
| Making the field — flowering | Keep enough water 3-5 cm shallow to avoid drought |
| 7-15 days before harvest | Drain water to dry the field and make it easier to harvest |
This calendar needs to be adjusted according to soil, weather and variety. Light soils hold water poorly so don't let them dry for too long. You need to be careful when draining deep water from alum soil because it can cause strong alum activity.
How to use a water level monitoring tube
A simple way to know when to water again is to use PVC pipes placed in the field.
Preparation:
- PVC pipe about 15 cm in diameter.
- Tube length is about 30 cm.
- Punch a hole 20 cm below the tube.
- Holes are 0.5-1 cm in diameter, about 5 cm apart.
How to set:
- Plug the pipe into the field, the part with the hole is in the soil.
- Bury about 20 cm, leaving 10 cm above ground.
- Scoop out the mud from the tube to see the water level.
- Monitor the water level in the tube. When the water drops about 15 cm below the ground, water again.
Measuring tube helps avoid emotional watering. Looking at the surface of the field, it may seem dry, but the ground is still moist enough; On the contrary, sometimes the field surface is still moist but the root layer is lacking water.
Managing water in cold weather
When the temperature drops below 20 degrees Celsius, especially in the Winter-Spring crop, water should be kept 3-5 cm shallow to keep the rice plants warm. The shallow water layer helps reduce cold shock, especially during the seedling and early tillering stages.
Do not drain water too strongly during cold spells. When the weather warms again, you can return to the alternating wet and dry regime.
Conditions for effective water saving
If you want to manage water well, you need to prepare the field from the beginning of the season:
- The field surface is relatively flat.
- Strong seal, little leakage.
- There are sewers or active drainage lines.
- Do not let low places flood deeply and high places dry out.
- Have an irrigation pumping schedule suitable for the area or cooperative group.
If the field has a lot of unevenness, it should be improved gradually over each crop. Flattening the land helps sow evenly, fertilize evenly and manage water more accurately.
Water management checklist
- [ ] 1-7 days after sowing keep moist, do not submerge deeply.
- [ ] After the tree hardens, apply alternating wet and dry.
- [ ] Do not let the field lack water when planting and flowering.
- [ ] When it's cold below 20 degrees Celsius, keep the water 3-5 cm shallow.
- [ ] Drain water 7-15 days before harvest.
- [ ] Check embankments and drains regularly.
- [ ] Use PVC pipes if you want to monitor the water level more accurately.
Common mistakes
Keep deep water right after sowing: seeds float easily, sprouts are weak, plants grow unevenly.
Continuous flooding for the whole season: roots lack oxygen, plants become soft, susceptible to pests and diseases, and costly.
Withdrawing water when rice is growing and flowering: easily increases the rate of flatness and reduces productivity.
Draining water too deeply on alum soil: alum can rise, causing yellow rice and slow growth.
Not draining water before harvest: soft fields, difficult for harvesters to access, increased losses.