Alleviation of the Calcium Nitrate-Induced Suppression of Seedling Emergence by Seed Coating with Oxygen Supplier and Soil Puddling before Seeding in Direct-Seeding Rice in Submerged Paddy Field

The effect of seed coating with oxygen supplier on the suppression of rice-seedling emergence by calcium nitrate applied to control apple snail, was examined in pots and petri dishes. The seed coating with oxygen supplier tended to promote elongation of the seedling in the soil supplied with calcium nitrate. Addition of oxygen supplier to calcium nitrate solution reduced the concentration of calcium cyanamide showing that the oxygen supplier decomposed calcium nitrate. The effect of soil puddling before seeding on the seedling emergence in the soil supplied with calcium nitrate was investigated in pots. The soil puddling before seeding promoted seedling emergence in the soil supplied with calcium nitrate, reducing the concentration of calcium cyanamide in the flood. In the field experiment, the seedling emergence from the seeds coated with oxygen supplier was inhibited by applying 8g nitrogen/m2 of calcium nitrate, but not by 4g nitrogen/m2 of calcium nitrate. Thus, we recommend puddling before seeding and coating the seed with oxygen supplier when apple snail is controlled by calcium nitrate in submerged direct seeding of rice. The suitable dosage of calcium nitrate for the effective control of apple snail without chemical injury was estimated to be 4g/m2 as nitrogen.