RICE RATOONING - IRRI books - International Rice Research Institute

ALTERNATIVE TO DOUBLE CROPPING IN TROPICAL ASIA 9missing hills significantly, from 12% to 37%, and the growth period of the ratooncrop from 73 d to 86 d.In studies with cultivar Intan in Karnataka, cutting the plants at 8, 13, and18 cm did not affect ratoon yield (21).However, interactions between cultivars and cutting height do exist; somecultivars tiller better when cut high above ground, while others produce better tillerswhen cut at lower levels.Because of the genetic variability among cultivars, there is scope to fix thecutting height to realize the optimum yield specific to cultivar and site, rather than todepend on general findings.Time of harvestThe best time to harvest the main crop for raising a good ratoon crop is when itsculms are still green (24). Stalks should be cut before the main crop is fully matured.In Brazil, Oliveira and Neto (18) studied the effect of sowing date on ratooncrop yield. They planted 3 cultivars — De Abrill, IR841-63-5, and IR889-55-6-4-6 at30-d intervals 18 Sep to 18 Feb. The September-seeded crop gave the best ratooncrop yield. Grain yields decreased with each successive seeding date, and no ratooncould be obtained with the November seeding.Seedling age and the effect of number of seedlings per hill of the main crop onratooning ability need thorough investigation.Sowing time, temperature, daylength, and other factors, have a profoundinfluence on main crop duration. Harvest date of the main crop and its effect on riceratooning also vary. Very little work has been done on this aspect.The work done at Mandya and in Ponnampet (Karnataka) has shown thatlow temperature (below 18 °C) will prolong main crop duration. Hence, any delay inplanting the main crop will delay harvest and affect ratoon crop yields as well. Thesefactors need further research.Water managementBahar and De Datta (2) noted that irrigating the fields immediately after harvestmay cause the stubbles to rot, especially where plants are cut close to the ground,resulting in missing hills. Studies suggest that fields should not be flooded until thenew ratoon tillers are 10-15 cm high.However, Mengel and Wilson (12), in their studies on the effect of irrigationand N requirement on the grain yield and milling quality of the ratoon crop ofcultivar Labelle, observed that shallow irrigation given as continuous floodingimmediately after main-crop harvest gave better grain yields and plant charactersthan short-term delayed flooding (Table 5).In-depth studies on water management of ratoon rice are needed because ofcontradictory reports on the subject.Fertilizer managementEvatt and Beachell (7), in their studies on fertilizer requirement for ratoon rice, notedthat ratoon crop yields were high at nitrogen levels of 75% of the main crop.