Abstract
To contribute to the development of a volunteer-rice control technique, we examined the effects of cyanamide in lime nitrogen (LN) on the dormancy and germination ability of rice seeds using the indica-type cultivar ‘Takanari’ and the japonica-type cultivar ‘Moeminori’. In the seeds soaked for 5 days at 15°C in cyanamide solution (CS), which was prepared by adding water to LN, the germination rate at 20 days after seeding was high when the cyanamide concentration was 170–340 mg L-1, and it gradually decreased with increasing cyanamide concentration beyond 340 mg L-1 in both cultivars. When the cyanamide concentration was 3140–3377 mg L-1, the germination rate at 20 days after seeding in the seeds treated with CS for 0.5–3 days was high and that treated for more than 3 days was low. These results showed that LN was capable of disrupting dormancy as well as inhibiting the germination ability of rice seeds depending on the amount and treatment period. These results suggested that LN application to the paddy field after harvesting could be used to suppress the generation of volunteer-rice because it prevented the germination ability or the withered sprouts appeared due to dormancy breaking during winter. The effects of CS treatment differed with the cultivar, and even in the same cultivar, with the seed production year or the degree of seed dormancy. It is therefore necessary to consider these differences in future field experiments for developing volunteer-rice control techniques using LN.
