Developing more efficient and effective weed control strategies in soybean is a major concern of growers in the Setouchi region. Field experiments were conducted at a location in Hiroshima Prefecture that has gray lowland paddy soil. The objectives of this project were (1) to determine whether application of post-emergence herbicides is necessary based on the residual period for a selective pre-emergence soil-applied herbicide and (2) to compare the effects of a conventional treatment with a new weed control treatment in narrow-row soybeans. The conventional treatment consisted of applying a dimethenamid/linuron mixture as a pre-emergence herbicide followed by mixed application of bentazon and quizalofop-ethyl at the third trifoliate leaf stage of soybean seedling development. The new treatment consisted of applying a dimethenamid/linuron mixture as a pre-emergence herbicide followed by a post-emergence directed application of glufosinate at the fifth or seventh trifoliate leaf stage. The predominant weeds infesting the experimental fields were Digitaria ciliaris and Amaranthus viridis. Field evaluation of weed emergence showed that the soil-applied herbicide was effective for about 3 weeks in the mono-cropped soybean field where the soil organic matter and cation exchange capacity values were lower; however, the soil-applied herbicide lost effectiveness at 12 days in the double-cropped wheat-soybean field where the soil organic matter and cation exchange capacity values were higher. In the mono-cropped field, no post-emergence herbicides were necessary for weed control in narrow-row spaced soybeans, although in the double-cropped field, post-emergence herbicides were required for season-long weed control. In the double-cropped field, the new treatment using two herbicides, especially when glufosinate was applied at fifth trifoliate leaf stage, was equal to or greater than the conventional treatment using three herbicides.