Quantifying the toposequential distribution of environmental resources and its relationship with rice productivity in rainfed lowland in Northeast Thailand

Japanese Summary 93105 (released in 1959) and RD 6 (released in 1977) (Bunduang and Uchin, 1990), which head out around the terminal period of rainy season, are still planted at a half of paddy fields in Northeast Thailand (Miyagawa et al., 1999).Consequently, these effects seem scarcely to improve the productivity of rainfed rice in the area.Not only low soil fertility or drought, but also their interaction makes the problem complicate and difficult to solve.Depending on the magnitude of water stress, soil fertility may differently affect rice production (Fukai et al., 1999a).Spatial and yearly variabilities in soil fertility and water availability are also too large and complicated to analyze rice responses to growth conditions in fields.For dealing with the variability This study could be concluded by supports of so many people.First, I would like to express my deep gratitude to Professor