Abstract
To control volunteer rice derived from dropped seeds of forage rice, we examined the effects of the timing of seed embedding on the overwintering ability at two places. In Fukuyama city, Hiroshima, altitude 2 m, viability index (VI:percentage of seeds germinable after wintering) of cultivar “Kusanohoshi” embedded into soil in mid to late October was lower than that of the seeds embedded in mid-November to early-December and that of those overwintered on the soil surface. Similar results were observed in the deeper dormancy line “Chugoku-shi 189”. However, degree of the decreasing VI due to embedding in “Chugoku-shi 189” was smaller than that in “Kusanohoshi”. There was a negative correlation between VI and the percentage of seeds with a trace of germination after wintering (PT) in Fukuyama. These results suggest that seeds embedded in mid-late October had a low VI due to easy germination during wintering. PT increased with increasing cumulative air and soil temperatures (lower limit temperature, 10°C) up to 100°C and 130°C, respectively, by the end of the year. Thus it is suggested that generation of volunteer rice can be reduced by plowing in autumn when the effective cumulative temperatures are obtainable. In Iinan town, Shimane, altitude 425 m, VI of seeds embedded into soil in mid-October was lower than that of seeds overwintering on the soil surface. However, degree of the decreasing VI of “Kusanohoshi” due to embedding in Iinan was smaller than that in Fukuyama. PT in Iinan was not as high as in Fukuyama. Such regional differences may be caused by precipitation and soil temperature after autumn. Thus, appropriate selection of cultivar and setting of timing of plowing may be necessary.
