Abstract
As a fundamental investigation of controlling Alopeculus aequalis, one of the dominant weeds in wheat and barley cultivation on paddy fields, the seasonal variation in the distribution of the seeds in the soil of the field was studied. The results are as follows: 1. Dormancy of the seeds buried after their ripening in spring disappeared almost completely until the middle of or late in September. The longevity of buried seeds was found comparatively ahort; about a year in well-drained fields, and about 2 years in poor-drained fields (Table 3). 2. The density of viable seed populations top in soils decreased from day to day after the field had been drained in autumn, and process of the decrease varied wideiy with the depth of soii layer, and also with tillage practised or not (Table 4). 3. The vertical distribution of viable seed populations in top soils changed remarkably as the time elapsed after drainage of the field. Moreover, the distribution varied with the methods of tillage prior to transplating of rice plants, and with the autumun tillage (Fig. 2). 4. Based on these relations, a schema showing seasonal distribution cycle of the seeds in the soil was illustrated (Fig. 3).
