RICE RATOONING - IRRI books - International Rice Research Institute

MORPHOLOGY AND PHYSIOLOGY OF RATOON RICE 35tiller number/unit area. But high main plant density increased the number ofmissing hills in the ratoon crop (2).Fertilizer management. Applying N increased ratoon grain yields (2, 6, 10, 12,29, 33, 36, 38). N should be applied immediately after harvest to promote earlyratooning (12, 21). Applying N fertilizer to the main crop 14 d before harvestincreased ratoon sprouting 10%, but decreased main crop grain yield (17).Fertilizer applied to the ratoon crop should be placed close to the stubble rowsfor rapid nutrient uptake and growth (29, 31). Cultivars differ in response to Napplied to the ratoon crop (3, 36).Applying N fertilizer on ratoon crops has been reported to delay maturity (5);in other reports, it did not (33, 38). Fertilizer application may (17) or may not (2)increase ratoon tillering.Applying high amounts of N fertilizer to the main crop reduced ratooningviability by encouraging excessive growth with weaker plants (18).Split application of 90 kg N/ ha as a basal dose and at panicle initiation, earlymilk stage, late milk stage, and 7-15 d before main crop harvest did not significantlyaffect tillers per m 2 or ratoon crop grain yield (33). No significant interactionbetween fertilizer application time and cutting height was observed.Ratoon crop plant height, panicle length, filled and unfilled spikelets, and1,000-grain weight were not affected by main crop N application method (40).Deep-placed N produced significantly higher yield in the ratoon crop than didbroadcast N. Higher grain yield was associated with more vigorous ratoon plants,more panicles per plant, and more filled spikelets per panicle. Increasing N alsoincreased plant vigor. But at the same N level, plant vigor was less with broadcastapplication than with deep placement (33). Application method did not significantlyaffect the number of missing hills in the ratoon crop (37).Applying P and K to the ratoon crop did not significantly affect ratoon grainyields (6). Applying P to the main crop produced a highly significant increase inratoon yield (10, 12, 24).To promote early, abundant ratooning, which increases grain yield, it isimportant to apply fertilizer immediately after main crop harvest. Although a ratooncrop will grow with only water added, grain yield is significantly higher if fertilizer isapplied.Water management. Water management before and after main crop harvestaffected ratooning ability (2, 14, 23, 32, 44). To promote ratooning, the field shouldbe moist but not flooded for 2 wk at the end of the main crop. Draining the fieldseveral days after main crop harvest encouraged ratooning (9, 22, 29). Draining themain crop increased ratoon panicles per m 2 and decreased the percentage of missinghills and sterile florets (44).When stubble was cut low, delaying irrigation was better than rewatering 1 dafter cutting (2, 15, 31, 32).If plots were drained during main crop harvesting and irrigated 12 d afterharvest, ground-level and 15-cm cutting produced comparable grain yields (2).Many hills died when the crop was cut at ground level and water remained 5 cm deepor the field was immediately irrigated (2, 19). The number of missing hills increasedas the time between harvest and rewatering shortened.