Environmental characterization of floodwater in Eastern India: Relevance to submergence tolerance of lowland rice

Floodwater was characterized through field surveys over three years in rain fed lowland and deepwater rice areas of Eastern India. Measurements focused on dissolved O-2 and CO2, pH and irradiance during flash floods in rice fi elds. Over locations and time, dissolved O-2 concentrations ranged from zer o to 0.28 mol m(-3) (0-1.1 times air-saturated water at 30 degrees C) while dissolved CO2 ranged from 0.28 to 1.96 mol m(-3) (31-217 times air-saturat ed water). Floodwater pH varied from 6.6 to 9.7. Irradiance decreased with depth in the water profile to an extent depending on turbidity. Turbidity v aried greatly over locations and time. The significance of these measuremen ts in assessing rice submergence tolerance is discussed.