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

A difficult decision for soybean producers is the selection of an optimal seeding rate, in conjunction with an optimal row spacing and planting date. Current seeding rate recommendations in Mississippi range from 296,400 to 345,800 seeds per hectare (seeds/ha). Previous research indicates that row spacings less than 76.2 cm may result in greater yield when compared to wider rows. The common planting window for Mississippi soybean growers is mid-April to mid-June, with the potential to plant earlier if weather and field conditions permit. 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.

Experiments were conducted during the 2016 and 2017 growing seasons at two locations near Starkville, MS and near Brooksville, MS. Greater soybean yields were observed when planting occurred in mid-April versus mid-May and mid-June. Additionally, greater soybean yields were observed when planting occurred in mid-May rather than in mid-June. No soybean yield differences were observed when comparing seeding rates of 396,200 and 345,800 seeds/ha. Furthermore, no differences in yield of soybean were observed between seeding rates of 296,400 and 345,800 seeds/ha. However, soybean yield was greater for the seeding rate of 396,200 when compared to seeding rates of 296,400 seeds/ha or lower. When evaluating the interaction of row spacing and planting date, all row spacings planted in mid-April resulted in greater yields when compared to narrow and ultra-narrow row spacing planted mid-June. These data suggest that in order to maximize yield, soybean should be seeded at a rate of 345,800 seeds/ha, or plant in mid-April while using an ultra-narrow row spacing.