Irrigation Water Management in Paddy

Paddy crop is strongly influenced by water supply. Water should be kept standing in the field throughout the growth period. In water scarcity areas, saturated soil in a chemical reduced stage is desirable. The characteristics of flooded soil which are conducive to high yields are: (i) greater availability of nutrients such as phosphorus, iron and manganese, (ii) suppression of weed competition, (iii) elimination of moisture stress as a limiting factor, (iv) micro-climate favourable to crop production.

• Excess / limited / no water leads to reduction in yield.
• Rice a semi – aquatic plant requires near submergence
• Submergence helps in - suppressing weed growth  and more availability of certain nutrients
• Daily consumptive use of rice is 6 – 10mm
• Total water requirement of rice is 1200 – 1400 mm
• 2000 - 3000 litres of water required to produced 1kg of rice

• Highly saline and brakish water not good for irrigation
• Application of FYM or incorporation of green manures reduce adverse effects of excess salts
• Application of FYM or compost or green manures increases water holding capacity of light textured soils and thus saving of water
• Thorough puddling creates impermeable layer which reduces deep percolation losses
• Perfect leveling maintains uniform depth of water throughout field
• Maintenance of water depths in field as recommended for high water use efficiency and yield
  

 

Table 1. Water requirement of rice crop at different growth stages

Stages of growth Avg. water requirement (mm) % of total water requirement (approx.) Nursery 50-60 5 Main field preparation 200-250 20 Planting to Panicle initiation (PI) 400-550 40 P.I to flowering 400-450 30 flowering to maturity 100-150 5 Total 1200-1460 100.0

Table 2. Depth of water to be maintained during different crop growth stages of rice

Stage of crop	Depth of water (cm)
At transplanting	Shallow (2 – 3cm)
After transplanting  (5 to 20 days)	(4– 5cm)
During tillering  (22 to 42 days)	Shallow(2 –3cm)
Mid – season drainage                                      (24 – 48 hours),  20 – 25 DAT (heavy soils) 20 – 25 DAT (very heavy), 40 – 45 DAT soils	---
Reproductive stage ,Panicle emergence, Booting ,Heading & Flowering	(4 –5cm)
Ripening stage  (21 days after full flowering) Milk stage, Dough stage & Maturity	Drain the field gradually to Saturation  Withdraw water 12 days before Harvesting

Drain the field to saturated stage before top dressing with N and reflood next day to reduce N – loss.

      Critical Stages of Water requirement

Critical stage refers to a stage when water scarcity or deficit of water causes comparatively greater reduction in yields which cannot be made by favourable water supply at earlier or later stages. Hence, water deficit during these stages should be avoided. Following are the important critical crop growth stages for water stress.

  a) Tillering         

 b) Panicle initiation          

c) Boot leaf stage

 d) Heading/ panicle emergence      

 f) Flowering/anthesis (Reproductive phase)

 During these stages, soil moisture level should be maintained at saturation level

• Moisture stress at active tillering phase -   30% yield reduction
• Moisture stress at reproductive phase    -   50 - 60% yield reduction

Table 3. Water requirement and losses of water in rice fields

Particular	Clay Loam	Silty Clay	Loam	Sandy Loam
Water requirement	1583	1602	1995	2261
Irrigation	1125	1200	1500	1775
Runoff	207	191	193	161
Percolation	893 (56%)	870 (54%)	1187(60%)	1515 (67%)
Evapotranspiration	690 (44%)	732 (46%)	808 (40%)	745 (33%)

• Summer ploughing minimises water requirement for land preparation
• Seepage and percolation reduced to considerable extent by puddling and perfect leveling
• Application of FYM or compost or green manures reduce evaporation, percolation and seepage

• Evaporation losses can be minimized by 50% when the soil is kept at saturation under  levelled field conditions
• Addition of clay or tank silt (to light textured soils only) @ 150m³/ha reduce the percolation loss by 20 –25%
• Higher the transpiration higher the yield (a normal crop of 4.5t/ha with an irrigation period of 100 days consumes 6mm/day by transpiration. When figure declines to 1.4mm/day the yield decreases to 1t/ha when it increases 10.5mm the crop yield will increase to 7.5t/ha )
• Maintain thin film of water at the time of planting (2cm)
• Life irrigation should be given on 3^rd day  and up to 7 days, 2cm water level should be maintained  Gradually raise water level to a depth of 5 cm up to maturity
• Moisture stress during rooting and tillering stage cause poor root growth leading to poor crop establishment and low yield.
• Spray Cycogel @ 1000ppm (1ml of commercial product in one litre of water) under water deficit situations to mitigate ill effects moisture stress.
• Split application of potassium 50% at basal and 25% each at tillering and panicle initiation stage along with Azospirillum (seed inoculation, seedling dipping or soil application) alleviates harmful effects of the soil moisture stress

 

Water quality and critical values

Major considerations of water quality: 

1. Salinity    2. Water infiltration rates    3. Specific ion toxicity

Table 4. Types of problems and critical values to be considered for irrigation

Potential problem	Units	No problem	Slight to moderate problem	Severe problem
pH	No units	6.5-8.5	<6.5: > 8.5	<6.5: > 8.5
Salinity ECw	Ds/m=m mol/cm	<2.0	2.0-2.6	>2.6
Salinity ECe	Ds/m	<3.0	3.0-3.8	>3.8
TDS*	Mg/l	<450	450-2000	>2000
Specific ion toxicity	No units	<3	3-9	>9
Chloride	me/l	<4	4-10	>10
Boron **	me/l	<0.7	0.7-3.0	>3
Bicarbonate	me/l	<4	>4	>>4

*TDS = Total dissolved salts
** B toxicity is encountered on highly sodic soils or under use of brackish water.

• For each 1ppm element in the water, the input is 1000mm equivalent to 10kg/ha
• If pH is out of range (6.5 - 8.4) but with low salinity (<0.2 Ds/m) then there is likely no problem as the water has very low buffering. However, additional checks should be pursued for possible nutrient imbalance
• High bicarbonate levels in irrigation water can cause Zn deficiency
• High sodium water cause deflocculation of soil particles leading to increase stickiness and compactness and decrease permeability
• Specific conductivity of ideal water : (K x 106) < 7500
• Boron < 1ppm
• S.A.R. Index < 10
• Ecw = Irrigation water salinity
• Ece = Soil salinity a measure on a saturation extract

        SAR = Na/ (Square root (Ca + Mg/2)); Na,    Ca and Mg in me

Measures of efficient water management in rice

One ploughing by mould-board plough and puddling twice by disc harrow gave the best result in terms of crop establishment, water use efficiency and yield.

Studies conducted for evolving design criteria for different methods of irrigation for efficient use of water indicated that maximum water-use efficiency for rice can be obtained with check basins with size in between 250-300 m² area.

Recycling run-off water in flood-irrigated rice can irrigate 10% additional area

 In command areas where field to field irrigation is common cost effective recycling structures may be constructed for reusing drainage water.

A mixture of fly ash and clay with 50% cement was found to be a suitable lining material for field channels.

Pre-cast structures for water management work under different land situations will improve water-use efficiency by about 50%.

Perpendicular orientation of field channel to main supply found superior to parallel orientation. The interval between outlets should be 425-450 meters rotation areas for parallel orientation and 650-700 m for perpendicular orientation.

 

Recommendations of CRRI-Cuttuck

Irrigation schedules of alternate wetting and drying or saturation till tillering followed by maintenance of 5 to 8 cm water thereafter could save 50% of water as compared to continuous submergence without affecting the yield.

ET at initial stages of crop growth was close to open pan evaporation, but at flowering, it was about 1.5 times than open pan evaporation, when open pan evaporation was 5.5 to 5.6 cm/day.

Providing drainage in lowland rice at early tillering stage is essential.

During dry season, application of water could be delayed till complete disappearance of ponded water.

 

Recommendations of UAS, Dharwad and Bangalore

Maintain water to an extent of 2.5cm height in the field during first 10 days of transplanting and afterwards increase the height up to 5cm through out the crop growth.

Irrigate the filed 2-3 days after complete infiltration of the stagnant water and maintain the water level to an extent of 5cm during panicle initiation to panicle emergence stage.

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.

Drain out the impounded water from the fields 10 days earlier to harvesting.

Rice genotype having crop duration of 120 days requires 100-120 cm of water for normal yields.

Recommendations of TNAU, Coimbatore

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%.

Once ploughing by mould-board plough and puddling twice by disc harrow gave the best result in terms of crop establishment, water use efficiency and yied.

Maintain 2.5cm of 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 sunnhemp and 15 days for more

fibrous green manure plants like Kolinchi (Tephrosia purpurea).

At transplanting, a shallow depth of 2cm 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 5cm submergence has to be continued throughout the crop period.

In loamy soils irrigation is to be given one and three days after disappearance of ponded water during summer and winter respectively.

In clay soils irrigation is to be given just before/immediately after disappearance of ponded water during summer or 1-2 days after disappearance of ponded water during winter.

Moisture stress due to inadequate water at rooting and tillering stage causes poor root growth

leading to reduction in tillering, poor stand and lower yield.

During booting and maturity stages continuous inundation of 5cm and above leads to

advancement in root decay and leaf senescence, delay in heading and reduction in the

number of filled grains per panicle and poor harvest index.

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 before  harvest

Table 5. Scheduling of irrigation to rice

Short duration variety			Medium duration variety				Long duration variety
Days	No. of irrigation	Water level (cm)	Days	No. of irrigation	Water level (cm)	Days		No. of irrigation	Water level (cm)
1-25	5-7	2-3	1-30	5-7	2-3	1-35		6-8	2-3
25	-	Thin film of water	30	-	Thin film of water	35		-	Thin film of water
28	-	Life irrigation	33	-	Life irrigation	38		-	Life irrigation
29-50	6	2-5	34-65	6-8	2-5	39-90 or 95		12-15	2-5
51-70	5-6	2-5	66-95	8-10	2-5	96-125		7-9	2-5
71-105	5-6	2-5	96-125	6-8	2-5	126-150		5-6	2-5

Note: Stop irrigation 10 days before harvest Number of irrigation may be decided depending upon the receipt of rain and available moisture content.

Irrigation schedule for rice under limited water resources
          For summer rice under limited resources of water, phasic stress irrigation can be practised to the advantage of saving substantial quantity of irrigation water without any significant reduction in yield. About 20-30% more area can be irrigated with the same water resources by adopting any of the following phasic stress irrigation schedules as given in the following table. Depending   up on the schedule, water saving ranges from 24-36% of the requirement for 5 cm continuous submergence throughout the crop growth. Grain yield reduction in the above practice is only 0.1% to 1.6%.

Table 6. Phasic stress irrigation schedules for rice

Schedule	Stages
	Rooting to max. tillering	Max. tillering to heading	Heading to maturity
Category I	Continuous submergence	Saturation point*	Saturation point*
Category II	Saturation point*	Continuous submergence	Continuous submergence
Category III	Continuous submergence	Continuous submergence	Hair cracking of surface*
Category IV	Hair cracking of surface*	Continuous submergence	Hair cracking of surface*

*Irrigation at 5 cm to be given at these stages.
Precautions for irrigation

Withhold water for few days till the seedlings have established.

Field to field irrigation should be avoided. 

Drain-off water for about 2 days prior to the application of fertilizers.

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 conditions provide open drains about 60cm in depth and 45cm width across the field. Care should be taken not to allow development of cracks.

In canal command area, conjunctive use of surface and ground water may be resorted to for

      judicious use of water.

Where irrigation facilities are not available, store all the rain water in paddy fields by making 25 to 30 cm raised bunds.

Maintain about 8-10 cm of water level in the fields at puddling time and subsequently depth of ponded water may be maintained throughout the growing period

Drain-off water completely for 5 to 7 days following tillering and flowering stages. This helps to remove the toxic substances like sulphides and regulates oxygen supply to roots