RICE RATOONING - IRRI books - International Rice Research Institute

76 RICE RATOONINGTAMIL NADUBalasubramanian et a1 (5) studied at Coimbatore the growth attributes and yield ofmain and ratoon crops of four varieties, 27, CO 32, IR8, and JS. They reported that1) varieties differed significantly in ratooning and ratoon grain production abilities;2) ratoon crop duration, growth, and yield were lower than those of the main crop;3) productive tillers were of the same order in both main crop and ratoon crop; and4) N fertilization increased ratoon grain and straw yields. Ramaswami and Haws(15) ratooned IR8 in 4 successive crops and realized in the ratoon crop 46% of themain crop yield in 47% of the main crop duration. Palchamy and Kolandiswamy(13), studying varieties Vaigai and Bhavani, reported that the principal traitdetermining ratoon grain yield was number of filled grains/panicle.UTTAR PRADESHFourteen cultivars, including Patna and IR36, in trials at Kumarganj, producedratoon crop yields ranging from 1.3 to 2.1 t/ha, or 33-67% of the main crop yield;ratoon crop duration was 40-54 d (31-43% of main crop duration). The mostpromising variety was C3810 — it gave the highest ratoon main crop yields. Thisvariety should be further evaluated under the new system (4).WEST BENGALIn field studies on ratooning of five cultures in Kalyani from main crops of twoseasons (wet season: July-October; dry season: January-May) managed without anycare after the main crop harvest, except for supplemental irrigation to keep the fieldmoist, ratoon yields ranged from 0.2 to 1.0 t/ha in 60-70 d. Ratooned variety Ratnawith 15 kg N/ha yielded 1.2 t/ha (8). In another study at Chinsurah (6), ratoonedand freshly sown SR26B, FR13A, Tilakkachari, and Achra 108/1 were compared.Ratooned Tilakkachari and Achra 108/1 yielded more (5.0 and 4.8 t/ha,respectively) than the main crops (3.8 and 3.9 t/ha). In general, the mean yield ofratooned rice varieties equaled that of main crops, indicating the suitability of theratoon cropping system in lowland areas where flood or sudden water stagnationhampers the freshly planted crop during the wet season.CONCLUSIONRatoon crop yields up to 7.7 t/ha and up to 350% of the main crop yield (in anextreme case) suggest high potential for ratoon cropping. Continuous ratooncropping of Intan and maintenance of KMS-1, KMS-4, and KMS-5 male-sterilelines through vegetative propagation for more than 30 yr in Karnataka indicatestrong sources of genetic resistance to virus and MLOs in rice. Thus, fears of possiblevirus and MLO epidemics under ratoon cropping appear unfounded. Ratooncropping has been more frequent and relatively better established in low-