RICE RATOONING - IRRI books - International Rice Research Institute

ALTERNATIVE TO DOUBLE CROPPING IN TROPICAL ASIA 5CROP IMPROVEMENTChoice of varietyThe varietal choice for ratooning in a given area is determined by the geography andthe climate. Early-maturing cultivars are reported to perform well as ratoon crops inthe Texas Gulf and temperate areas; however, studies indicate intermediate- tolate-maturing cultivars are required for raising a good ratoon crop in tropical hillsand valleys.The success of a good ratoon crop depends on the care with which the maincrop is cultivated in the growing season. Agronomic practices and the care withwhich the main crop is protected against insect pests and diseases determine thesuccess of ratooning and crop yields in ratoonable cultivars.The best time to cut the main crop for good ratooning is when the culms arestill green (9) and physiologically viable for ratoon tillering.Low temperature at postmaturity of the main crop will reduce the tilleringability and yield performance of the ratoon significantly.Blast incidence on the main crop could carry over to the ratoon, resulting intotal failure. Such cases have been recorded in experiments with Intan atPonnampet, Karnataka.Hence, there are no set rules with regard to choice of cultivar for ratooning. Agood agronomic cultivar of the area could also be a good ratooner, like Intan inKarnataka.Several cultivars have given ratoon grain yields of more than 2 t/ha (Table 2).Some of the important cultivars discussed in this paper are D52-37 (l), IR28 (2),C3810 (6), Labelle (12), IR8 (20), Intan (21), IET 7191, IET 9667, IET 9668, andIET 9670 (17), IR42, and IR2058-78-1-3-2-3.Ratooning abilityVarieties differ greatly in their ratooning ability. Hence, the genetic inheritance ofratooning ability could be exploited. A high ratoon rating indicates less than 5%missing hills and at least 16 tillers/hill with excellent vigor.In Malagasy, japonica varieties have better ratooning ability than indicas.Japonica/indica crosses such as Mahsuri have shown high ratooning (16) inexperiments at Mandya, Karnataka.Varietal differences also exist with respect to emergence of ratoon tillers fromdifferent nodes of the stubbles. The tillers may emerge from all nodes of the stubblesor from only the lower nodes or from any specific node number. Many findingssuggest that the ratoon crop will yield better if the main crop stubble is cut with 2-3nodes left.Variations in soil, water, light, and temperature greatly influence ratooningability. Their interactions need to be properly studied for manipulating ratooningability agronomically.Tiller development is highly influenced by the carbohydrates that remain inthe stubbles and roots after harvest and by nitrogen in the soil. Plants with thickculms store more carbohydrate than those with thin culms.