Planting Date and Row Width Effects on Soybean Production in Southwestern Japan.

Early and narrow-row planting are promising tools that increase soybean [Glycine max (L.) Merr.] growth and yield in southwestern Japan, but optimum planting date and row width have not been established. We conducted the present study in 2012 and 2013 to assess the effect of early (mid-June) and narrow-row (20 and/or 35 cm) planting on agronomic traits of soybean and weed emergence using a new promising short-stem cultivar, Sachiyutaka Al, in comparison with conventional planting date (mid- to late July) and row width (75 cm). The light interception exceeded 90% more than 14 d earlier in narrower-row treatments than in the 75 cm row width. This result might lead to 60 and 98% greater suppression of weed emergence at harvest in the 20 and 35 cm row width (3 and 53 g m^-2 ), respectively, compared with the 75 cm row width (153 g m^-2 ). Early planting increased shoot dry weight by 200 g m^-2, leading to a 2-yr average significant yield increase of approximately 9% in early planting compared to normal planting (266 vs. 244 g m^-2 ). Averaged across the experimental year and planting date, Sachiyutaka Al planted at the 20 cm row width had the lowest lodging score of 1.6 (most lodging resistance) among the row widths tested. These results suggest that planting Sachiyutaka Al in mid-June at a 20 cm row width leads to a higher seed yield than conventional planting date and row width, with minimal or less weed emergence and lodging of the plant. [ABSTRACT FROM AUTHOR]