Soybean Planting Dates and Plant Populations at the Northern Frontier.

Soybean planting dates and plant populations at the northern frontier

Tkachuk, C.¹ Lawley, Y.¹ Ostlie, M.²

¹Department of Plant Science, University of Manitoba, Winnipeg, Manitoba, Canada

²Carrington Research Extension Center, North Dakota State University, Carrington, North Dakota, USA

Soybean producers in northern soybean growing regions of Manitoba and North Dakota can maximize seed yield and economic return in a short growing season by optimizing planting date and plant population. Despite recent increases in soybean acres, current information on soybean response to delayed planting and stand loss from environmental effects is limited. The objective of this study was to determine optimal plant population and replanting threshold for soybean in Manitoba and North Dakota, and to quantify negative effects from delayed planting and stand loss. Six plant populations ranging from 197,600 to 568,100 plants ha^-1 were seeded on ideal and late dates (May 26, June 9) in 2014, and early to late dates (May 4, May 22, June 10) in 2015 at Carman, Manitoba. Five plant populations ranging from 197,600 to 494,000 plants ha^-1 were seeded on ideal to late dates (May 23, June 5, June 23) in 2014, and early to late dates (May 5, May 19, June 2, June 16) in 2015 at Carrington, North Dakota. Yields in 2014 were significantly higher for earlier planting dates, and increased with increasing plant population. Maximum yields were observed from 345,800 to 494,000 plants ha^-1 at Carrington, and from 494,000 to 568,100 plants ha^-1 at Carman. At Carrington in 2014, yield at the lowest plant population on the first planting date was similar to yield at the highest plant population on the second planting date. A significant yield drop occurred between 271,700 and 197,600 plants ha^-1 for the earliest planting date. At Carman in 2014, soybean yield at 271,700 plants ha^-1 for the first planting date was similar to yield at 419,900 plants ha^-1 for the second planting date. Thus, after the first growing season of this two-year study, reseeding early planted low plant stands would not be recommended.