RICE IN SRI LANKA-Water Management
Water requirement for rice crop growth
After crop establishment water requirement for rice crop for its growth and development functions vary with the growth stage.
Water requirement is low
If the water stress is not severe the effects during this stage could be recovered
Water stress during vegetative stage reduces plant height, tiller number and leaf area
Effects during this stage varies with the severity of stress and duration of the crop. Long duration varieties cause less yield damage (as they have adequate time to recover) than short duration varieties .
Leaf expansion during vegetative stage is very sensitive to water stress. Cell enlargement requires turgor and gradient in water potential is required for water to move into cells. Therefore, water stress may result decreased leaf area, affecting light interception capacity. Rice leaves may also wilt during mid-day due to high transpiration rate.
Rice plants transpire at its potential rate even if soil is at field capacity, which explains the importance of maintaining the saturated water regime to increase grain yield.
If the weed pressure is high, standing water could be maintained until the closure of the canopy and then be managed at saturated levels.
Most susceptible stage to water stress .
Water stress at or before panicle initiation (PI) is one of the factors that might reduce panicle number, while potential spikelet number is affected after PI..
Water stress at heading reduces rate of exertion of the panicles. Within reproductive stage anthesis and ripening is highly affected by water stress.
Water stress (and resulting increase of canopy temperature above 28OC) during anthesis increases unfilled spikelets. Spikelet sterility decreases with decreased leaf water potential during meiotic stage of pollen development.
Stress during grain filling decrease translocation of assimilates to the grain which decreases grain weight and increase empty grains.