Evaluation of Weed Control Interaction with Row Spacing on Yeild of Soybeans.

Weed control is a concerning factor in soybean production [Glycine max (L.) Merr.] in Arkansas.  With the increasing number of herbicide resistant weeds, a review of agronomic best management practices to reduce weed competition is essential.  The objective of this study was to determine the interaction of weed pressure with a variety of agronomic practices including seeding rate, row spacing, and plant architecture. In 2013, the studies were located at the Newport Research Station in Newport, Arkansas.  Two studies evaluated the treatment combination on maturity group (MG) IV and V soybean varieties.  The studies were blocked according to row spacing and seeding rate and randomized for weed control and plant architecture. Treatment combination consisted of three seeding rates ranged from 271,700 to 469,300 seeds ha^1-, three row-spacings of 38 cm, 76 cm, and 92 cm, and a variety for each maturity group designated as either having an erect or bushy plant architecture. For the purpose of this discussion we will focus on row spacing and yield as compared to weed pressure.   For both the MG IV and V studies, the 38 cm row-spacing statistically had higher grain yields than the wider spacings.  When the row-spacing was evaluated, the 38 cm row-spacing statistically had higher grain yields as compared to the wider row-spacings.  All weed free treatments consistently had greater grain yields than the weedy treatments.  Weed management was less timely due to the increased canopy closure of the narrower rows.  Weed ratings and size was lower, also, by comparison to the wider rows.  Because of the increase in herbicide-resistant weeds, more emphasis on agronomic practices to decrease weed competition will be required.