Soybean Reseeding

Determine the Initial Plant Stand

Before you make any replanting decisions, the first step is to assess the existing plant stand (live plants/ac). Use the hula hoop method for narrow rows (<15″) and the row length method for wide rows (>15″). The Bean App Plant Stand Assessor (also available in the App Store and Google Play store) helps you easily assess plant stand using either method, accounting for various hula hoop diameters (28.25″ diameter has a multiplication factor of 10,000 for plants/ac). If plant stand loss is from extreme weather, wait 3-5 days to assess the field.

Plants will not survive when:

They are cut off below the cotyledons.
They are heavily bruised and folded over.

Plants will survive when:

They are missing only one cotyledon.
They are missing both cotyledons but the growing point is still intact.
They are cut off above the unifoliate leaves.
They are lightly bruised on the stem.

Adapted from University of Wisconsin-Madison Extension

Replanting Threshold

According to soybean plant population research in Manitoba, the replanting threshold is considered to be approximately 80,000 plants/ac. Before taking action on replanting soybeans, consider the existing crop’s planting date, its current development stage and crop insurance deadlines. If it’s already June, yield potential has been lost and it may not be economical to replant or top up your current plant stand. If soybean development is advanced, you may end up with a stagey crop, although the summer solstice triggers flowering on even young soybean plants. The development stage of the current crop may also influence the amount of damage inflicted if you are topping up your plant stand. Also consult with your crop insurance agent to go over any insurance implications.

Soybean yield response to plant population from early to mid planting dates/May 4-26 and late to very late (June 2-23) planting dates at Carman, MB and Carrington, ND (2014-2015).¹

Soybean yield response to plant population (as a percent of the highest yielding treatment within each site-year) based on 13 site-years of data in Manitoba (2011-2013).²

Replanting Options

If a soybean plant stand is below 80,000 live plant/ac, you are faced with the decision to fill in the existing plant stand or terminate the crop and replant. In some cases, it may be acceptable to leave the crop as-is if you are hovering around 80,000 plants/ac.

According to research conducted by University of Wisconsin-Madison, termination by tillage followed by replanting was only economical if the plant stand was as low as 37,000 plants/ac.³ For low plant stands greater than 37,000 plants/ac, top up the existing stand to 140,000 plants/ac if it is still May and to 100,000 plants/ac if it’s June.

References

¹ Tkachuk, C. 2017. Evaluation of soybean planting dates and plant densities in the northern growing regions of the Northern Great Plains. M.Sc. Thesis. University of Manitoba.
²Mohr, R. 2018. Agronomic management of soybeans in Manitoba: row spacing and seeding rate. Manitoba Pulse & Soybean Growers Pulse Beat Science Edition. 2:11.
³ Gaspar, Conley and Gaska. 2014. Think twice before replanting soybeans. University of Wisconsin-Madison Extension.