Abstract
Weeding measures are an important issue for forage sorghum because it is inferior to corn in early growth and there are not many different kinds of herbicides applicable to sorghum. Since the concern about organic animal products and environmental problem is increasing, cultivation without herbicide application is needed. Therefore, research was conducted on seeding rate for cultural weed control in the broadcasting and dense sowing of forage sorghum. Test samples were "Hazuki" for sorghum and "HSK-1" for sudangrass. Seeding rate was 2kg, 5kg, and 8kg per 10a for sorghum and 4kg per 10a for sudangrass. Hazuki grew shorter in plant length, smaller in culm diameter, and more in the number of tillers in both weeded and non-weeded plots as seeding rate increased. The amount of weed at the harvest time in without herbicide application was large when the number of sorghum tillers was few but decreased with increase in the number of tillers. Dry matter yield gradually increased as the number of tillers increased. The optimum number of tillers (the number of individual plants) was determined to be about 200m^<-2> from the amount of weed and the dry matter yield of sorghum. From the above, forage sorghum cultivation without herbicide application was judged possible by securing the number of tillers at the seeding rate of 8kg 10a^<-1> in broadcasting regardless of sowing time.
