Contents & Foreword, Characterizing And ... - IRRI books

Table 5. Estimated maximum farm yields (t ha –1 ) for different types of riceland in 11 Asian countries.Country Irrigated Supplemental Rainfed Upland anddry-season irrigated wet-season lowland deepwaterPhilippines 5.94.6 3.5 2.0India 6.8 5.4 4.0 2.0Indonesia 5.94.8 3.6 2.0Thailand 4.4 3.7 2.5 2.0Bangladesh 6.6 4.93.7 2.0Vietnam 5.8 4.1 3.1 2.0Sri Lanka 5.7 5.3 4.0 2.0Myanmar 6.0 4.8 3.6 2.0Pakistan 6.0 – – –Nepal – 4.8 3.6 2.0Malaysia 6.0 4.8 3.6 2.0Source: Chandler (1979).as Bangladesh, Brazil, India, Myanmar, Nigeria, the Philippines, Thailand, and Vietnamwere still below 4 t ha –1 , indicating the limited improvement in rice productivityin other ecologies.In 1997, about 54% of the world’s rice harvested area came from irrigated ecologies,30% from rainfed lowland ecologies, 11% from upland ecologies, and 5% fromother ecologies such as deepwater and tidal wetlands or mangroves. Irrigated rice wasresponsible for about three-quarters of the world’s total rice production, indicatingthe limited contribution of rice production in other ecologies. This further confirmsthe observation on the limited success of activities aimed at improving rice productivityin rainfed environments during the past 30 years.The yield potentials of high-yielding rice varieties (HYVs) in tropical areas,however, have not improved further after the development of IR8 in the late 1960s,although yield efficiency of rice varieties has been improved with the development ofearly maturing HYVs. Increasing efforts have therefore been made to develop newrice varieties with higher yield potentials. Since 1982, the Japanese government hasbeen promoting a project to develop super-high-yielding varieties with the target ofincreasing rice yield by 50% in 15 years based on wide crosses between indica andjaponica varieties. Breeding for the new plant type that could increase the yield potentialof tropical rice by 25% to 50% began at IRRI in 1989. Tropical japonica varietieshave been used as sources for desirable traits in this project. After learning of thesuccessful application of this technology for increasing rice production in China, FAO,IRRI, and several other national institutions have been promoting the developmentand use of hybrid rice (Tran and Nguyen 1998). The West Africa Rice DevelopmentAssociation has made considerable efforts to develop rice varieties for low-inputmanagement areas in West Africa from crosses between Oryza sativa and O.glaberrima. Therefore, new and more vigorous characterization and classification ofCharacterizing environments for sustainable rice production 43