“ Let not even a drop of waterobtained from rain, flow to the

sea without benefiting mankind “

Parakramabahu the Great( 1153 – 1186 ) AD

Water requirement and

management in paddy

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 

  

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

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

Physical characteristics of Rice plant

• Plant height ∞ Depth of water in paddy

• Lodging susceptibility ∞ plant height• due to decreasing Culm strength

• Tiller number = 1 Water depth

Effects of flooding

• Show better growth

• Produce high grain yield

•Water affect on-1.Physical characters2.Nutrient and physical characters of soil3.Weed growth

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

•

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

Effect of temperature of water

High temperature

• Rice yield

• Si uptake

• Tiller number

• % of unfilled grain

Low temperature

• Tillers

• Panicle size

• Delay panicle initiation

• sterility

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

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

Seedling stage

Vegetative stage

Reproductive stage

For raise seedling

• Nursery preparation 150-200mm

• Irrigation 250-400mm

For 30 - 40 days

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

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

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

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

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

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

Field irrigation

• Need large amount after transplanting

• 800 – 1200mm for 90 – 120 days

• Daily consumption – 6 – 10mm

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 determination1.Hydrological approach2.Micrometeorological approach Pan Evp. = 0.7546+0.0096 *Rs ET(mm/day) = 0.9 + 0.0115 * Rs

Plant response to soil moisture

• Soil moisture

>70 -80 % 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

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

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

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

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

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

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

Con.

• In 2025, water shortages will be more prevalent among poorer countries

• Growing conflicts with agricultural water user

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

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

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 getlegally recognized decisions on cultivation

• Participatory Irrigation Management introduced

New Approaches

• The System of Rice Intensification (SRI Method) Cut 50% from Total water requirement

• Nava Kekulama

• Aerobic rice cultivation

THANK YOU