Determining the Optimum Seeding Window for Soybeans in Manitoba
Kristen P. MacMillan, University of Manitoba
Scott Chalmers, WADO Melita
The objective of this study is to determine the optimum seeding window for soybeans across Manitoba growing regions. Traditional recommendations are to plant soybeans when soil temperature has warmed to at least 10°C, which is typically May 15-25 in Manitoba (Manitoba Agriculture and Resource Development). However, farmers have started to seed soybeans earlier and recent work by Dr. Yvonne Lawley and Cassandra Tkachuk (2017) supports this trend. They evaluated seeding dates across a range of soil temperatures from 6 to 14°C in 2014 and 2015; the earliest seeding dates maximized yield regardless of soil temperature and it was concluded that calendar date is a superior indicator. To update seeding date recommendations across a wider range of environments and using defined calendar dates, this study was initiated at Arborg, Carman, Dauphin and Melita in 2017 and 2019 was the last year of testing.
The preliminary combined analysis from 2017 to 2018 indicates that soybean yield was affected
by the main effects of environment (E) and seeding date (SD), and their interaction (E x SD).
Overall, soybean yields were below average to average in these dry growing environments, ranging from 21-40 bu/ac, with the exception of Dauphin18 which yielded 64 bu/ac. Looking at individual environments (data not shown), yield maximization occurred in the first seeding window for 3 out 7 environments, out yielding the second and third dates by 2-12%.
In the other 4 out of 7 environments, yield maximization occurred in the second seeding window
(early) by 1-14% compared to the first and third dates. In 2 out of those 4 environments
(Carman17 and Melita17), soybeans in the first seeding date were beginning to emerge and were exposed to spring frost which is an important consideration for very early seeding. Yield
differences among the first three seeding windows were statistically similar in 5 out of 7 environments and reduced yield with late seeding was consistent across all environments
contributing to a meaningful overall effect of seeding date (Figure 1). Overall, soybean yield was
statistically similar when seeded between April 28 and May 24, seeding beyond which reduced
soybean yield by 20% on average. At Arborg18, soybean yield was statistically higher at the
second seeding date compared to the first and last date. Due to this occurrence and associated
frost risk observed at two other environments, farmers may want to consider waiting until the 2nd
week of May to seed soybeans in Manitoba. Other measurements being collected include
emergence, crop phenology, maturity and seed quality. This data continues to be analyzed to help refine overall seeding date recommendations.
Traditional recommendations are to plant soybeans when soil temperature has warmed to at least
10°C, which is typically May 15-25 in Manitoba (Manitoba Agriculture & Resource Development). However, farmers are starting to plant soybeans earlier and recent work by Tkachuk (2017) supports this trend. Tkachuk investigated soybean seeding dates across a range of soil temperatures from 6 to 14°C at Carman, Morden and Melita in 2014 and 2015. At three site-years, soybean yield was optimized with the earliest planting date.