Synergic Effect of Flooding and Nitrogen Application on Alleviation of Soil Sickness Caused by Aerobic Rice Monocropping

The "aerobic rice" system is the cultivation of high yielding rice cultivars under non-flooded conditions in non-puddled (aerobic) soil with supplemental irrigation. The major constraint in wide adoption of aerobic rice technology is soil sickness caused by continuous monocropping due to still unknown factors. The possible role of flooding and nitrogen application in alleviating the soil sickness caused by continuous monocropping of aerobic rice was examined by pot experiments. Plants were grown aerobically or anaerobically on the soil collected from a field grown with aerobic rice for 12 consecutive seasons. The results showed that flooding alleviated soil sickness, but not as much as soil oven-heating treatment (120 degrees C for 12 hr). Application of ammonium sulfate improved plant growth up to the level of oven-heating treatment, while ammonium sulfate application and flooding exceeded the soil oven-heating treatment significantly. The synergy of flooding with ammonium sulfate application was greater than that with urea. These results suggest that soil sickness caused by continuous aerobic monocropping can be alleviated by flooding and ammonium sulfate application.