RICE RATOONING - IRRI books - International Rice Research Institute

82 RICE RATOONING2. High cutting height (17-30 cm). High cutting-height ratoon with high yield(about 7.5 t/ha) and 55-60 d ratoon growth duration can fully utilize therice-growing season to get a higher yield from the two crops. Such a ratooncould fit well with single crop medium-duration rice. Single crop mediumdurationhybrid rice ratoon is promising.Intensive water management is needed for a low cutting-height ratoon crop;otherwise, an increase in number of missing hills and a decrease in regeneration ratewould reduce grain yield considerably. In addition, severe weed competition, lowfertilizer efficiency, and widespread occurrence of insect pest incidence contribute togreater loss. Since high cutting-height ratoon did not fully use the available growingseason in the double rice cropping area, low yield was obtained.Experiments on and production of ratoon rice in the conventional doublecroppingareas were discontinued in the late 1970s.On the other hand, in the single-crop, medium-duration rice area, the prospectof good ratoon varieties and hybrids and high yield was still attractive to riceworkers. A new breeding program was started to develop high-yielding varieties orhybrids for main crop and ratoon ratoon yields, which would fit in well in themidseason ratoon cropping system. For example, a ratoon collaborative experimentalnetwork was set up in 1979; more than 2,000 varieties were screened andevaluated for the breeding program.With this approach to line selection, it is possible to get good ratoon varietieswith high yield for main crop and high inherent ratooning ability. On the other hand,evaluating ratooning ability according to tillering after cutting has not led to thesuccessful development of a good ratoon variety (14). High sterility in the main cropmay result in high tillering in the ratoon crop. In such cases, the main crop yield is toolow to get a high yield for both main and ratoon crops.From this research it was learned that• ratooning ability should be evaluated when the main crop is at the ripeningstage and shows high yield traits.• number of germinating buds on stubble and elongating length (3-6 cm orabove) rather than tillering after harvest should be used to identify ability.In the meantime, some physiological and cultural studies on ratooning werecarried out in Guangdong, Hubei, and Yuanan Provinces: (Studies on thedistribution of photosynthetic products and the absorption of nitrogen nutrients inregenerative rice by using isotopes 14 C and 15 N (19), and others.)All such research served as foundation for ratoon rice development in thesucceeding years.The above information involves research and utilization of short-staturedvarieties and hybrid rice ratooning in the 1970s.Trend toward expansion of ratoon cultureA new ratoon variety. 40-1 is an early medium-duration hsien (indica) varietydeveloped by the Food Crop Research Institute, Hubei Academy of AgriculturalSciences. Its growth duration is 132 d for the main crop and 60 d for the ratooncrop (1). When the main crop ripens, the buds at ground level and above elongate orgrow out of the leaf sheaths. The main crop still set well (filled grain = 87%,