Rainfed lowland rice: physical environment and cultivar requirements

The physical environment of the rainfed lowland ecosystem is often characte rised and grouped according to the surface hydrology of rice paddies and ri ce cultivars have been developed for each subecosystem. Rainfall is an impo rtant determinant of the yield of rainfed lowland rice, but other factors s uch as topography and soil fertility also affect grain yield and choice of cultivars, The growing environment and also rice yield vary greatly within small areas as well as across seasons. This causes great difficulty in dete rmining the target population of environments fur a rice breeding program. This paper reviews past work on characterising the variability in the physi cal environment, and rice production in the rainfed lowland ecosystem. It e xamines possible connections between this variability and slow progress in developing new cultivars that are widely adapted to the rainfed lowland ric e ecosystem. (C) 1999 Elsevier Science B.V. All rights reserved.