Rice requires ample water to grow and is usually cultivated with continuous flooding or intermittent flooding of rice fields. The total water requirement for rice is approximately 1,100-1,250 mm, with the critical growth stages being active tillering, panicle initiation, booting, heading, and flowering when water stress can severely impact yields. Proper water management through irrigation practices such as intermittent flooding, shallow and controlled flooding, and reducing percolation losses through soil management are important for optimizing rice production.

2.  Breif Intro:
Rice(Oryza sativa)
 Rice is the seed of the grass species Oryza sativa (Asian rice) or Oryza glaberrima
(African rice). As a cereal grain, it is the most widely consumed staple food for a
large part of the world's human population, especially in Asia. It is the agricultural
commodity with the third-highest worldwide production, after sugarcane and
maize, according to data of FAOSTAT 2012.
 Rice, a monocot, is normally grown as an annual plant, although in tropical areas
it can survive as a perennial and can produce a ratoon crop for up to 30 years.[6]
The rice plant can grow to 1–1.8 m (3.3–5.9 ft) tall, occasionally more depending
on the variety and soil fertility. It has long, slender leaves 50–100 cm (20–39 in)
long and 2–2.5 cm (0.79–0.98 in) broad.
 Rice cultivation is well-suited to countries and regions with low labor costs and
high rainfall, as it is labor-intensive to cultivate and requires ample water.
However, rice can be grown practically anywhere, even on a steep hill or mountain
area with the use of water-controlling terrace systems. Although its parent species
are native to Asia and certain parts of Africa, centuries of trade and exportation
have made it commonplace in many cultures worldwide.

3. Water Requirement:
 Crop water requirement is the water required by the plants for its survival,
growth, development and to produce economic parts. This requirement is
applied either naturally by precipitation or artificially by irrigation.
Average Water requirement – 1100 mm
Average Water requirement (SRI) – 700 mm
The daily consumptive use of rice varies from 6-10 mm and total water is
ranges from 1100 to 1250 mm depending upon the agro climatic situation,
duration of variety and characteristics of the soils.


4.  Stage-wise water requirement for
paddy
Stages of growth Water requirement
(mm)
Precentage of total
water requirement
Nursery 40 3.22
Main field preparation 200 16.12
Planting to panicle
initiation
458 37.0
Panicle initiation to
flowering
417 33.66
Flowering to maturity 125 10.00

6. Water Management for Different
Ecosystem
 System of Rice Intensification (SRI)
 Irrigation only to moist the soil in the early period of 10 days
 Restoring irrigation to a maximum depth of 2.5cm after development of hairline cracks in the soil until panicle initiation
 Increasing irrigation depth to 5.0 cm after PI one day after disappearance of ponded water.
 Transplanted lowland rice
 Puddling and leveling minimizes the water requirement
 Plough with tractor drawn cage wheel to reduce percolation losses and to save water requirement up to 20%.
 Maintain 2.5 cm water over the puddle and allow the green manure to decompose for a minimum of 7 days in the case of less
fibrous plants like sun hemp and 15 days for more fibrous green manure plants like Kolinchi (Tephrosia purpurea).
 At the time of transplanting, a shallow depth of 2 cm of water is adequate since high depth of water will lead to deep planting
resulting in reduction of tillering.
 Maintain 2 cm of water up to seven days of transplanting.
 After the establishment stage, cyclic submergence of water is the best practice for rice crop. This cyclic 5 cm submergence has
to be continued throughout the crop period.
 Moisture stress due to inadequate water at rooting and tillering stage causes poor root growth leading to reduction in tillering,
poor stand and low yield.

7.  Wet Seeded Puddled Lowland Rice
 During first one week just wet the soil by thin film of water.
 Depth of irrigation may be increased to 2.5cm progressively along the crop age.
 Provide adequate drainage facilities to drain excess water or strictly follow irrigation schedule of one
day after disappearance of ponded water. Last irrigation may be 15 days ahead of harvest.
 Dry Seeded Un-Puddled Rice
 As that of irrigated rice, canal water is used for irrigation
 For drill sown rice care should be taken to drain out excess rain water during first 10-15 DAS and the
water level in the field should not be more than 2.5cm height during tillering stage.
 In drill sown rice carry out hodta operation (Planking) in standing water at 40 DAS, and impound
sufficient rain water through the crop growth period.
 Semi-dry rice
The crop is irrigated from 30-35 days onwards, utilizing water impounded in the tanks.
 Irrigation may be to a depth of 2.5 -5.0cm only. Follow the schedule of one day after disappearance of
ponded water in order to save water and to bring additional area under this type of rice cultivation

8. Precautions for irrigation (common)
• The field plot can be 25 to 50 cents depending on the source of irrigation.
• Field to field irrigation should be avoided.
• Small bund may be formed parallel to the main bund of the field at a distance
of 30 to 45cm within the field to avoid leakages of water through main bund
crevices.
• To minimize percolation loss, the depth of stagnated water should be 5cm or
less.
• In water logged condition, form open drains, about 60cm in depth and 45cm
width across the field.
• Care should be taken not to allow development of cracks.
• In double cropped wetland of command area, raise groundnut / pulse in the
place of Kuruvai rice if water is a constraint

9. Critical Stages of Irrigation
 The stage at which the water stress causes severe yield reduction is also known as
critical stage of water requirement. It is also known as moisture sensitive period.
Critical stages of water requirement in rice are Active tillering
 Panicle initiation
 Booting
 Heading and
 Flowering.
 During theses stages, the irrigation interval should not exceed the stipulated
time so as to cause the depletion of moisture below the saturation level.

10. Water Management Methods
 Continuous Submergence
 Continuous land submergence for rice is, usually, practiced due to the associated major advantages of increase in
availability of nutrients and less weed management problems.
 Shallow submergence of water up to 5 cm depth throughout the crop period is optimum for high yield
 Intermittent Submergence
Continuous land submergence requires huge quantity of water for rice production, so to
minimize the irrigation requirement, the approach of intermittent submergence has been
practiced. Under high humidity and low evaporative demand, the practice of intermittent
submergence i.e submergence during the critical stages of crop and maintenance of saturation or
drying up to hair cracking stage during the rest of the crop stages.
 Intermittent period varied from one to nine days depending on rainfall pattern, depth of
water table and soil texture.
 This practice saves about 30% water

11. Percolation losses in rice fields
 Percolation losses are a function of the local soil and topographic conditions. Therefore, at any time
the amount of rainfall or irrigation water entering the soil becomes greater than its water holding
capacity, losses by downward movement of free water (vertical percolation) will occur. Percolation
is often defined as the movement of water through saturated soils due to gravity, hydrostatic
pressure or both. Thus where the soil is heavy and the water table is close to the soil surface,
percolation losses are low, about 1 – 2 mm/day. On the other hand, where the soil is light and the
water table is deep, percolation losses may be high, about 8 – 15 mm/day, or more. About 50 to 60%
of applied water to rice is lost by deep percolation. The percolation losses can be reduced by
adopting following agronomic practices:
 1. Growing rice on clayey soils
 2. Scrupulous land levelling
 3. Thorough puddling
 4. Shallow depth of submergence
 5. Sub-soil compaction
 6. Application of clay, silt, bentonite etc Research has shown that a percolation rate of 5mm/day
was favourable for supply of dissolved oxygen, the removal of harmful substances and the
maintenance of root activity.

12. Submergence versus saturation
 In most areas rice fields are submerged continuously throughout the crop-growing period, though
not always essential. Studies have indicated that soil saturation is sufficient for kharif rice, while
submergence not exceeding 5 cm seems to be essential and adequate for rabi rice.
Advantages of continuous submergence
♦ Less weed problem
♦ Fixation of nitrogen by Blue green algae
♦ Increased availability of nutrients such as P, Fe, Mn, Zn and silicon
♦ Regulation of soil temperature
♦ Reduction in labour cost
Disadvantages of continuous submergence
♦ Deep percolation losses of irrigation water
♦ Surface runoff losses of irrigation water
♦ Leaching of nutrients particularly nitrogen

13. Average water requirements
 Total water requirement includes water needed to raise seedlings,
preparation of land and to grow rice crop from transplanting to harvest, the
amount is determined by many factors including soil type, topography,
proximity to drains, depth of water table, area of contiguous rice fields,
maintenance of bunds, fertility of both top and sub soil, field duration of the
crop, land preparation method, and most of all the evaporative demand of
the atmosphere during growing season. The daily evapotranspiration of rice
varies from 4 – 5 mm /day during wet season and 7 – 8 mm/day during the dry
season. The total water requirement was estimated to be 1240 mm under
Andhra Pradesh agro-climatic conditions.