Rice

Water Management

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 seedlings. 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 transplanting	Shallow (2 - 3cm)	Shallow transplanting is possible Helps in good tillering
After transplanting (24 - 48 hours)	Deep (5 - 7cm)	Better establishment of seedlings Quick development of new roots Reduction in transpiration
Duringtillering (60 - 65 days)	Shallow (2 - 3cm)	Excess water reduces 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
Reproductive stage Panicle emergence Booting Heading Flowering	Deep (5 - 7cm)	Moisture stress Impaired panicle growth Increased sterility Excess water delay in heading stem weakens a 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.

Critical stages of water requirement

1. 1. Active tillering phase -- 30% yield reduction
2. 2. Reproductive phase (Panicle Initiation)(Flowering) -- 50-60% reduction

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.

Losses of water in rice fields

• Evaporation (E) 180 - 300mm unavoidable
• Transpiration (T) 200 - 500mm unavoidable
• Seepage and percolation 200 - 500mm reduced to some extent by thorough puddling and perfect levelling

• Average Evapotranspiration (ET) is 7mm/day (kharif) and 10mm/day (rabi)

• Application of phosphatic fertilizers increases the transpiration.
• Application of FYM or compost or green manures reduces evaporation, percolation 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.

Water quality and critical values

Major considerations of water quality are, Salinity Water infiltration rates Specific ion toxicity

Types of problems and critical values

* 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
• Abnormal pH, damages 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 causes 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 Salinity
• Ece = Soil Salinity a measure on a saturation extract
• SAR = Na/(Square root (Ca + Mg/2)); Na, Ca and Mg in me/l

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