1. “ Let not even a drop of water obtained from rain, flow to the sea without benefiting mankind “ Parakramabahu the Great ( 1153 – 1186 ) AD

2. Water requirement and management in paddy

3. Rice plant Rice semi aquatic plant Best habitat – Hydromorphic soil
Water use efficiency – 20-30%
Submergence 
covering completely with water
Not a requirement for maximum yield

4. Water and rice plant Water essential for plant growth Absorb by roots
Use only <5% of absorbed water
Adequate water supply most important factor in rice
Asia suffer by both too much and too little water
Irregular pattern of R.F. and landscape

5. Why need water Vital constituent of cell protoplast
Reagent in chemical reaction
Solvent and mode of translocation for metabolites ,minerals within plant
Essential for cell enlargement through increasing turgor pressure

6. Physical characteristics of Rice plant
Plant height ∞ Depth of water in paddy
Lodging susceptibility ∞ plant height
due to decreasing Culm strength
Tiller number =
Water depth

7. Effects of flooding Show better growth Produce high grain yield
Water affect on-
Physical characters
Nutrient and physical characters of soil
Weed growth

9. Soil toxicity Flooding cause Chemical reduction of Fe (Bronzing) , Mn
Organic acids produced
Acetic , Butyric , CO2 , CH4 , H2S
It retard
Root development
Nutrient absorption
Root rot

10. Nutrient status and water
Increase availability
K, P, Ca ,Si, Fe
With internal drainage
Decrease CO2 concentration and
Fe like reducing substances
But loss water and nutrient

11. Effect of temperature of water
Low temperature
High temperature
Rice yield
Si uptake
Tiller number
% of unfilled grain
Tillers
Panicle size
Delay panicle initiation
sterility

12. Water requirement in paddy
Rice cultivated
as a rain fed
as a supplementary irrigated
as a fully irrigated crop
The system of rice cultivation depends
available rainfall
rainfall distribution

13. Cont… Water requirement for a successful rice crop varies
The method of land preparation
Method of crop establishment
Duration of the rice crop
The soil
Environmental conditions
Management

14. Seedling stage
Vegetative stage
Reproductive stage

15. Nursery preparation 150-200mm Irrigation 250-400mm For 30 - 40 days
For raise seedling
Nursery preparation mm
Irrigation mm
For days

16. Water requirement for Land Preparation
For lowland
W.R. depend on
amount required soil soaking
losses during operations
Maintaining standing water in the field
The requirement vary 30 mm- 125 mm
Dry zone- 150 mm on LHG
-300 mm on RBE

17. Cont… After first ploughing field is inundated with water
It facilitates decomposition
During standing water lost through
Evaporation
seepage and percolation
Bunt leakages and runoff

18. Cont… Water should be supplied to meet
Saturation point
Evaporation requirements
Water requirement increases with the increase in duration of land preparation
Conventional land preparation
2weeks

19. Water requirement during crop growth
ET rice crop = ƒ (leaf area, water availability ,environmental conditions)
ET _ leaf area
ET low - early stages of crop growth

20. Vegetative stage Immediately after transplanting need sufficient water
To facilitate early rooting
After shallow water depth encourage
Tiller production
Firm root anchorage
Excessive water result
weaker plant

21. Reproductive stage Achieve maximum towards heading
Frequency of irrigation should increase towards flowering to meet the increasing demand for water
After yellowish stage no standing water
Drain water 10 days before harvest

22. Field irrigation Need large amount after transplanting
800 – 1200mm for 90 – 120 days
Daily consumption – 6 – 10mm

23. Total water requirement for low land rice
Increases with the age of rice crop
Water requirement Sum of daily ET +
per season Sum of daily S & P
ET determination
Hydrological approach
Micrometeorological approach
Pan Evp. = *Rs
ET(mm/day) = * Rs

24. Plant response to soil moisture
> % saturation
50% WHC
35% WHC
30% WHC
20% WHC
<20% WHC
Plant response
100% yield
33 -50% Yield
Transplanted seedling die
Plants wilt
Plant leaves roll
Plant leaves die

25. Moisture stress Peak water demand b/w
Maximum tillering - Grain filling stage
Moisture stress throughout growth period
Decrease grain yield by 20-25%
Water stress -vegetative stage
reduces plant height
tiller number
leaf area

26. Con… Most susceptible –reproductive stage
At or before PI reduces panicle number
After PI reduces the potential spikelet number
At heading reduces rate of exertion of the panicle
Anthesis and ripening stages most sensitive stage

27. Con. Water stress during anthesis unfilled spiklets Spikelet sterility
leaf water potential during meiotic stage of pollen development
Stress during grain filling translocation of a assimilates
grain weight and empty grains

29. Irrigation systems in Sri Lanka
Water for rice culture in Sri Lanka received
Rainfall (> 50% of rice growing area)
irrigation
Rain fed crop- areas where rain fall distribution the satisfactory to meet the crop water requirement
Crop depends on direct rainfall to the field

30. Supplementary irrigation
Supplementary irrigation - areas where rainfall is not assured to supply water requirement of the crop
Two main categories based on command area
(1) Minor irrigation system
command area is less than 80 ha
Both tank and anicut
(2) Major irrigation system
command areas greater than 80 ha
include both tanks (reservoir) and anicut systems

31. Water management Oceans -97% of surface water
Glaciers and polar ice caps 2.4%
Other surface water rivers, lakes and ponds 0.6%.
Irrigation takes up to 90% of water withdrawn in some developing countries

33. Con.
In 2025, water shortages will be more prevalent among poorer countries
Growing conflicts with agricultural water user

34. Equitable Distribution of Water in past
Village irrigation systems in North Central Province 3 irrigation tracts
Ihala Bage (upper part)
Meda Bage (middle part)
Pahala Bage (Lower part)
Each farmer with a plot in each of these
water short seasons -cultivated the upper tract
Water abundant -cultivated crops in all three tracts

36. Management practices Water usage for land preparation reduces by
- Awareness programs
- Scheduling the cultivation to start with the 1st rain of the season
During rehabilitation process, canal lining introduced to reduce conveyance losses

37. Con.
Introduced 28 improved short term paddy varieties during last two decades by dep't. of Agriculture
Re-activate the “Kanna meeting" (cultivation meeting) to get
legally recognized decisions on cultivation
Participatory Irrigation Management introduced

38. New Approaches The System of Rice Intensification (SRI Method)
Cut 50% from Total water requirement
Nava Kekulama
Aerobic rice cultivation

39. THANK YOU