Rice

Water Management

Introduction Principles Stagewise Requirements Quality And Critical Stages


Introduction

  • Excess/limited/no water leads to reduction in yield.
  • Every crop plant tries to survive under extreme drought conditions but never survives for atlest 1-2 days under excess moisture situations.
  • Rice a semi - aquatic plant requires near submergence
  • Subemergence help is suppressing weed growth
  • more availability of certain nutrients
  • Daily consumptive use of rice is 6-10 mm.
  • Total water requirement of rice is 1240 mm
  • 5000 litres of water required to produced 1 kg of rice
  • Rice accounted for 33% of gross irrigated area
  • Rice consuming 66% of total available irrigation water.

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Principles of water management

  • 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 increase water holding capacity of light textured soils and thus saving of water.
  • Field management for higher water use efficiency.
    • Through puddling imper- meable layer reduce deep percolation losses Perfect levelling maintains uniform depth of water throughout field.
  • Maintenance of water depths in field as recommended for high water use efficiency and yield.

Losses of water in rice fields

  • Evaporation (E)180 –300mm unavoi- dable Transpiration (T)200 – 500mm unavoidable Seepage and percolation 200 – 500mm reduced to some extent by thorough puddling and perfect levelling.
  • Average evopotran- piration (ET) is 7mm/day (kharif) and 10mm/day (rabi).
  • Application of phosphatic ferti- lizers increases the transpiration.
  • Application of FYM or compost or green manures reduce evaoration, perco- lation and seepage
  • Evaporation losses can be minimized by 50% when the soil is kept at saturation.
  • Needless to say such a shallow water application practice requires perfectly levelled land
  • Addition of clay or tank silt (to light textured soils only) @ 150m3/ha reduced percolation loss by 20 –25%
  • Addition of bentonite @ 7000kg/ha
  • 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. The figure declines to 1.4mm/day when the yield decreases to 1t/ha and increases 10.5mm with a crop yield of 7.5t/ha
  • Seepage varies according to topography, depth of ground water table and farming practice
  • Seepage facilitates removal of toxic salts and supply of oxygen to roots
  • Disadvantages with seepage are 1. wastage of water 2. nutrient leaching

Utilization of water under different growth stages

Stage of growth
Avg. water requirement (mm)
% of total water requirement
Nursery
40
3.2
Main field preparation
200
16.1
Planting to P.I
458
37.0
P.I to flowering
417
33.7
Flowering to maturity
125
10.0
Total
1240
100.0
  • P.I = Panicle Initiation

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Water requirement stage wise

Water management in nurseries

  • Puddle the nursery bed thoroughly
  • Level the land perfectly
  • Formulate channels to irrigate or drain the field
  • Drain water completely and broadcast seed uniformly
  • Allow water for 12 hours and again drain (if we broadcast dry seed allow water in the nursery for 24 hours)
  • Allow nursery beds drying upto four days
  • Give irrigation and maintain 2cm of water till pulling of seedling.
  • Avoid excess irrigation poor growth of seeldings Avoid stress deep root growth pulling of seedlings is difficult

Stage of crop
Depth of water (cm)
Advantages in maintaining the recommended depth of water
At trans planting
Shallow (2 – 3cm)
Shallow transplanting is possible Helps in good tillering
After trans planting (24 – 48 hours)
Deep (5 – 7cm)
Better establishment of seedlings Quick development of new roots Reduction in transpiration
During tillering (60 –65 days)
Shallow (2 –3cm)
Excess water reduce tillering
Mid – season drainage (24 – 48 hours) 20 – 25 DAT (heavy soils) 20 – 25 DAT very heavy 40 – 45 DAT soils
Stimulate rooting Check unproductive shoots Non – accumulation of toxic substances* Drains excess N Sterility % reduced Supply of oxygen to elongate internodes Prevent excess mineralisation Prevent lodging Avoids Zn deficiency
Re productive stage Panicle emergence Booting Heading Flowering
Deep (5 –7cm)
Moisture stress –
impair panicle growth
increased sterility
Excess water –
delay in heading
stem weakens à lodging
Ripening stage (21 days after full flowering) Milk stage Dough stage
Drain the field gradually
Early with drawal
increase of immature grains
broken grains
Late with drawal - lodging

*Toxic substances

  • Poor root development, root rot, poor tillering, anaerobic respiration, low nutrient uptake

Note

  • Drain the field to a very thin film of water a day before top dressing with N reflood after 48 hours to reduce N – loss.

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Water quality and critical values

  • Major considerations of water quality Sanity
    Water infiltration rates

Specific ion toxicity Types of problems and critical values

Season
Varieties
Time
Transplanting season
Transplanting season
Ph No units 6.5-8.5 <6.5: > 8.5 <6.5: > 8.5
Salanity ECw Ds/m=m mol/cm <2.0 2.0-2.6 >2.6
Salanity ECe Ds/m <3.0 3.0-3.8 >3.8
TDS* Mg/l <450 450-2000 >2000
Infiltration Mm/day      
Specific ion toxicity No units <3 3-9 >9
Chloride me/l <4 4-10 >10
Boran me/l <0.7 0.7-3.0 >3
Bicarbonate me/l <4 >4 >>4

*TDS = Total dissolved salts

  • 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 (<0.2Ds/m) then there is likely no problem as the water has very low buffering. However, additional checks should be pursued for possible nutrient imbalance. However, additional checks should be pursued for possible nutrient imbalance
  • Abnormal pH damage the equipment as the water is corrosive
  • High bicarbonate levels in irrigation water can cause Zn deficiency
  • Large masses of silt must be avoided for heavy soils
  • High sodium water cause deflocculation of soil particles leads to increase stickyness and compactness and decrease permeability
  • Specific conductivity of ideal water : (K x 106) < 7500

Boron < 1ppm


S.A.R. Index < 10

  • Ecw = Irrigation water salanity
  • Ece = Soil salanity a measure on a saturation extract
  • SAR = Na/(Square root (Ca + Mg/2)); Na, Ca and Mg in me/l

Critical stages of water requirement

  • Active tillering phase - 30% yield reduction
  • Reproductive phase(panicle initiation) (flowering)- 50-60% yield reduction.

  • Critical stage refers to a stage when water scarcity or deficit of water causes comparatively greated reduction in yield which cannot be made by favourable water supply at earlier or later stages.
  • Hence water deficit during these stages should be avoided.

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Karnataka

Rice

Rice Management