We thought that subterranean clover (Trifolium subterraneum) has the greatest potential of any annual clovers as a cool season cover crop. So we attempted to investigate the relationship between the persistence of sub clover seedling emergence after seed maturing and seed survival in the soil on the supposition that seeds are buried by tillage. The seeds of sub clover both of Mt. Baker and trikkla which set at the soil surface germinated little during the summer, as these seeds immediately after seed maturing germinated little at high temperature. These seeds sprouted simultaneously in the early autumn, as the decrease of the hard seed ratio of sub clover seeds was effected by fluctuating temperature at soil surface. On the other hands, almost sub clover survived seeds buried at 5-10cm showed hard seeds, so these seeds germinated little in early autumn and will survived for several years in the soil. Therefore we thought that the fields tilled by rotary after sub clover seed maturing, these seeds at soil surface will distribute within the depth of rotary share, over half of the seeds at the soil surface will emerge in early autumn and will reestablish the good stands. Other seeds which were distributed to lower depths by rotary tillage will remain in the soil to make a seed bank. The hard seeds in the deep soil layer will survive for several years, and if these seeds are redistributed to the soil surface by rotary tillage, they may soften rapidly and emerge. These seedlings will be useful to success for good stand. So rotary tillage will make an adequate soil seed bank of sub clover.
Since volunteer wheat normally sprouts from shed seeds, volunteer wheat control in farming should begin with ecological studies of these seeds. The objectives of this study were to clarify: 1) the forms of seeds shed during combine harvesting, and 2) the effects of these forms of seeds on wheat seed dormancy and longevity in the soil.Wheat seeds shed during combine harvesting consist of both loose seeds and unthreshed ears (or ear seeds). The head feeding combine lost 98 seeds/m2 and 121.7 seeds/m2 of loose seeds and ear seeds, respectively, while, the conventional combine lost 18.2 seeds/ml and 42.4 seeds/m2 (Fig. 2). This shows that many of seeds from the unthreshed ears fall in the field during combine harvesting. The results of field experiments showed that the longevity of the seeds of wheat cultivars with a resistance to pre-harvest sprouting was greater than that of cultivars which showed a susceptibility to sprouting.The results also showed that the longevity of unthreshed ear seeds was longer than that of loose seeds in the soil (Table 2, Figs. 4 and 5). Shed seeds of unthreshed ears during wheat harvesting are numerous, thus making the volunteer problem worse in subsequent bar-ley cultivation.
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