Impact of Row Spacing, Planting Date and Seeding Rate in Dryland Soybean (Glycine max) Production.

Each spring soybean producers are faced with a difficult decision in selecting an optimal planting date, in conjunction with an optimal row spacing and seeding rate. The common planting window for soybean in Mississippi begins in late-March and continues through mid-June, and in some situations into early-July.  Therefore, with such a wide window for soybean planting, it is important to determine the optimum row spacing and seeding rate combination for maximizing soybean yield within a given planting date.  The objective of this research is to evaluate the effects of row spacing, planting date and seeding rate on non-irrigated soybean growth, development and yield.

This experiment was conducted during 2016 at three locations near Starkville, Brooksville, and Stoneville, MS. A total of 45 treatments were arranged in a split-split plot design with the main plot factor being row spacing, the sub-plot factor being planting date and the sub-sub-plot factor being seeding rate.  Soybean was planted into 3 row spacings consisting of ultra-narrow (38 cm), narrow (76 cm) and wide (96.5 – 101.5 cm) rows during mid-April, -May and –June. Seeding rates of 197,600, 247,000, 296,400, 345,800 and 396,200 seeds per hectare (seeds/ha) were included for each row spacing within the targeted planting dates.  Data collection consisted of final node count, final plant height and yield. 

Soybean yield was greater in ultra-narrow row spacings when compared to narrow row spacings at all locations.  Soybean yield following planting dates in mid-April and –May were greater than yield following the mid-June planting date at all locations.  In addition, greater yield was observed for soybean seeding rates greater than or equal to 247,000 seeds/ha. All plot factors were independently significant and these data suggest using ultra-narrow row spacings, at a seeding rate of 247,000 seeds/ha planted earlier in the planting window to maximize yield potential.