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.

Seedling stage

Water requirement is low

If the water stress is not severe the effects during this stage could be recovered

Vegetative stage

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.

Reproductive stage

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 28^OC) 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.