RICE RATOONING - IRRI books - International Rice Research Institute

36 RICE RATOONINGEarly flooding encouraged more rapid, uniform regrowth than delayedflooding and produced significantly better ratoon height and yield (25).Draining the main crop at harvest is suggested to promote ratooning andprevent death of hills due to flooding. However, under rainfed conditions wherewater needs to be retained, the main crop should be cut at 15 cm or higher tominimize the number of missing hills in the ratoon crop and to reduce weed growth.TemperatureOnly a few reports discuss the effect of temperature on ratooning ability. Plantsexposed to low temperature (20/20 °C) at the booting stage of the main crop formed2-3 times more basal ratoon tillers than those exposed to high (35/27 °C) andnormal (29/21 °C) temperatures. Low temperature prolonged ratoon crop growthduration (37).Light intensity near harvestShading the main crop from flowering to 7 d after harvest (28 d) caused significantlylower ratoon yields than shading at the late milk stage to 7 d after harvest (24 d) orshading at harvest to 7 d after harvest. Unshaded plants yielded 7% more thanshaded plants (33). Applying extra N at early and late milk stages and at 15 d beforeharvest in combination with different shading periods did not significantly affectratoon grain yield.Irrespective of growth stage, shading produced a higher percentage of missinghills. Shading plus N topdressing produced 22% fewer missing hills than shadingwithout N topdressing (33).Tiller regeneration ability was not affected by main crop shading. The numberof ratoon tillers produced decreased as shading increased (13). In general, no shadingand 49% shading had similar effects on grain yield, spikelets per panicle, filledspikelets per panicle, 1,000-grain weight, and percentage of sterile spikelets.However, 66% shading reduced ratoon grain yield, which was attributed to fewerspikelets per panicle, fewer filled spikelets per panicle, and increased spikelet sterility(13). Panicles per hill was not significantly affected by shading. More ratoon paniclestended to develop with less main crop shading.Percentage of ratoon tillers, ratoon height, and ratoon weight were highest infull sunlight, followed by 50 and 75% shading 2 wk before cutting. Stem base weightof stubble decreased as shading intensity increased, indicating that percentage ofratoon tillers, ratoon weight, and height may be correlated with stem base traits (20).Growth regulatorsPlant growth regulators did not significantly affect ratoon grain yield or other yieldcomponents, except panicles per hill (16, 33). Promotion of ratoon tillering wasdependent on growth regulator concentration and time of application.Leaf senescence and carbohydrate-nitrogen contentRapid main crop leaf senescence is assumed to be a major cause of low ratoon riceyields. It is believed that if main crop senescence could be delayed, ratoon yieldpotential might be considerably increased.