Survival of rice during complete submergence: effect of potassium bicarbonate application

The effect of potassium bicarbonate application to floodwater on the surviv al and growth of submergence-tolerant (FR13A) and -intolerant (IR42) rice c ultivars during complete submergence was investigated. Potassium bicarbonat e, applied at different rates to enhance floodwater carbon dioxide concentr ations, increased the floodwater oxygen concentration. The treatment that h ad CuSO4, added alone to reduce algal growth showed the lowest O-2 concentr ation at the time of submergence and after 10 d of submergence. Potassium b icarbonate at higher rates tended to maintain the floodwater pH near neutra lity while copper sulfate affected pH increase during a 10-day period of co mplete submergence. Potassium bicarbonate addition led to 100% survival of tolerant FR13A. Potassium bicarbonate, even at 0.01 mol m(-3) enhanced the survival of intolerant IR42 to 69% and at 0.1, 0.5 and 1.0 mol m(-3), the s urvival was above 85%. Dry weights of submerged plants showed increases in both rice cultivars in floodwater treated with potassium bicarbonate. The d ry weight and leaf chlorophyll concentration of both cultivars increased wi th increasing rates of potassium bicarbonate. Algal chlorophyll concentrati on of floodwater treated with potassium bicarbonate was comparable to that of the control without copper sulfate. The findings suggest a possibility o f environmental manipulation of floodwater by potassium bicarbonate applica tion to enhance the survival and growth of rice cultivars during complete s ubmergence.