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Soybean planting date has been shown to have a large impact on a crop’s yield potential. Typically, early-season soybean planting has shown improved yields compared to when planting is delayed.
However, it is largely unknown how other management practices should be adjusted based on planting date in Michigan. Michigan State University Extension has conducted both on-farm and small-plot research from 2018 to 2021 to better understand not only how soybean planting date affects yield, but also how other management decisions might change based on planting date.
Planting date
On-farm trials were conducted to compare early-season soybean planting dates with normal soybean planting dates in 2019, 2020 and 2021. Growers were asked to plant soybean three weeks apart in a randomized strip trial design with four replications and collect yield data from each strip.
Early-season planting resulted in significantly higher yields at five out of nine locations in 2019 (average yield increase of 2.6 bushels per acre, some fields had in-season pesticide application along with early planting), at five out of 12 fields in 2020 (average yield increase of 1.2 bushels per acre), and at seven out of 13 fields in 2021 (average yield increase of 3.4 bushels per acre). One field in 2021 reported significant yield loss from ultra-early planting (April 8), indicating potential risks associated with such plantings.
Figure 1. Yield difference (early through typical planting, separated by around three weeks) across various Michigan locations during the 2019-21 growing seasons. *Denotes locations with significant yield differences. +Denotes 2019 locations with fungicide/ insecticide spray at R3 (beginning pod) in early planting. Branch-2, 2021 utilized an ultra-early planting date (April 8).Small plot research trials were conducted between 2018 and 2021 using 3 to 4 planting dates ranging from late April to late June. Results from these studies show that optimal soybean planting is during or before mid-May.
Delayed planting after mid-May resulted in a yield penalty, which increased as planting was delayed. On average, soybean yield was reduced by 0.33% per day between the mid-May and early-June planting dates. Furthermore, planting after early June resulted in an average yield reduction of 1.2% per day.