RICE RATOONING - IRRI books - International Rice Research Institute

N fertilizer managementfor maximum ratoon crop yieldsFred T. Turner and W. O. McllrathAgricultural Research Center, Beaumont, Texas, USAABSTRACTMain crop rice in Texas sometimes appears to be N deficient during grain filling, whichmay restrict ratoon crop yields. A 2-yr experiment was designed to determine if Napplied near main crop heading would increase ratoon crop yields. Field plots of twocultivars received common N rates before the reproductive stage plus one of the fivefollowing treatments during the reproductive stage: N applied at panicle differentiation,one-half at panicle differentiation and one-half at heading, at heading, 2 wk after initialheading, or no N applied during main crop reproductive stage. In addition, a main croppostharvest N application of 0, 56, or 112 kg/ha was applied to each of the 5 main cropN treatments. N applied at or near main crop heading rather than at panicledifferentiation tended to increase ratoon crop yields but decreased main crop yields,resulting in little effect on total (main crop + ratoon crop) yields. However, since ratooncrop yields were not affected by main crop yield or main crop N applied before heading,it seems probable that a N application at panicle differentiation plus an application nearheading will increase total yields. Applying N at heading, 2 wk after initial heading, orone-half at panicle differentiation and one-half at heading rather than at panicledifferentiation resulted in quicker tiller regeneration and ratoon crops that matured7-10 d earlier. Postharvest N application to main crop consistently increased ratooncrop yields.An annual frost-free growing season exceeding 250 d in the U.S. Gulf Coast region isfavorable for producing a 120-d main crop of rice and an 80-d ratoon crop. Riceratoon crops require minimal inputs (mainly N fertilizer and water) and may yield upto one-third that of the main crop. Usually, the ratoon crop is more economical thanthe main crop. Increasing ratoon crop yields should increase annual profits from riceproduction (9).Nitrogen fertilizer rate and application frequency are critical managementfactors in ratoon cropping worldwide. In the southern U.S., ratoon crop N isgenerally applied after main crop harvest; yield responses to 60 kg N/ha or morehave been demonstrated (1, 4, 7). Ratoon yield responses to applied N and otherinputs depend upon early main crop harvest, so that the ratoon crop can developbefore days become shorter and cooler in fall (10). Although ratoon tillerdevelopment is determined by genotype and a number of management andenvironmental factors, Chauhan et al (2), Hsieh et al (5), and Ichii (6) showed that N