Rainfed lowland rice in Thailand had low grain yield and high risk for production because of uncertainable rainfall distribution in a year. Consequently, the knowledge about physiological respnses of rice under rainfed lowland condition should be usable for variety improvement and better cultural practice in rainfed lowland rice in Thailand. It was conducted to three experiments as followed by rainfed lowland condition : 1. To study the capacity of shoot and root growth under water deficit at early seedling stage 2. To study the effects of soil water regimes levels; such as flooding, field capacity (FC), 75%FC, 50%FC, and 25%FC, on growth and development of rice during tillering; and 3. Tostudy physiological responses to grain yield potentialunder different patterns of water treatments in paddy field. Six rice varieties; Khao Dok Mali 105, Niaw Sanpathong, Sue Mae Jan, Nam Sa-gui19, and R258 were grown in these experiments
