Strategic Farming: Let's talk crops! focused on planter settings and soybean planting considerations

By Angie Peltier, UMN Extension crops educator & Brian Luck, Univ. of Wisconsin-Madison Extension machinery ag systems specialist and Seth Naeve, UMN Extension soybean agronomist

On March 29, 2023, Brian Luck and Seth Naeve joined UMN Extension crops educator Dave Nicolai for a conversation about planter setting and soybean planting considerations. This was the final episode in the 2023 Strategic Farming: Let’s talk crops! series of webinars.

To watch this episode: https://www.youtube.com/watch?v=ZQ665VJf82E

Which closing wheels provide the best corn emergence?

For three years over multiple locations (13 site-years), Dr. Brian Luck’s team researched what had initially come to him as a question from a local watershed group in Wisconsin about which closing wheels worked best in heavy residue or when planting into a living cover crop. In plots long enough (80 ft) so that the 140-170 horsepower tractor could reach and maintain a speed of 5 mph under RTK guidance, Luck’s team tested standard John Deere closing wheels and those manufactured by four other companies (note: no endorsement is implied by mention nor disparagement by lack of mention) that were of interest to the watershed group: Dawn Curvetine, Martin Spike and Yetter Paddle.

Dr. Luck’s crew used a tractor-mounted, weighted toolbar with seed boxes feeding four row-units. His tractor and 5000 lb planter (capable of providing about 1000 lb of pressure per row) were modified to run an electric seed plate powered by an add-on generator, provide hydraulic down-force and variable depth control, and provide variable pneumatic closing wheel depth and pressure. All assessments were done in the center of plots so that the tractor reached 5 mph, a speed at which many farmers plant, before the planter was lowered for planting and assessments weren’t made where speeds were increasing or decreasing, but steady.

One thing that the team noticed was that when using steel closing wheels, one needed to be extra careful with down-pressure settings, particularly if the closing wheels have a spring, to avoid throwing seed back out of the furrow. It is recommended that one check and double-check behind the planter that down-pressure settings are correct for soil conditions.

In Wisconsin in spring of 2017, soils warmed quickly and weren’t too wet or too dry, but ideal for planting; this was the first year of three in which closing wheel performance was tested. In individual rows in 2017, the team found that the aftermarket steel closing wheels provided 2% better corn emergence than the standard rubber closing wheel. They also found that none of the four aftermarket closing wheels tested out-performed any other.

Closing-wheel BMPs

• Soil types and conditions will impact closing wheel performance.
• Heavier soils require more aggressive closing wheel settings.
• If aftermarket closing wheels are something that you are interested in pursuing, buy a handful to test, rather than purchasing enough for your planter.
• If you are in the market for aftermarket closing wheels, consider ones that have a gauge on them that limits their working depth.

What about down-force?

In the higher soil moisture years of 2018 and 2019, Luck’s team tested down-pressure in addition to aftermarket closing wheels, testing a high down-force of 300 pounds per square inch (psi) and a low down-force of 150 psi, as measured at the gauge wheel, confirming their 2017 results that no one aftermarket closing wheel out-performed any other aftermarket closing wheel. 

Corn emergence was again approximately 2% higher when using low down-force than high down-force. All told, the standard, rubber closing wheel provided the best corn emergence under low down-force and emergence was not statistically different from aftermarket closing wheels operated at either low or high pressure. Operated under high pressure however, the standard rubber closing wheel resulted in 3% less corn emergence (89.5%) when compared to the same closing wheels operated at low pressure (92.5%). 

The team concluded that with aftermarket closing wheels, down-force pressure made less of an impact on corn emergence in a wet year providing uniform emergence regardless of pressure. When planting with the standard closing wheels under wet soil conditions, however, using high down-force tended to bury the seed deeper, and didn’t provide the small bit of tillage that the steel tine-type aftermarket closing wheels did which may have helped with emergence.

Down-force BMPs

• Using spring-based down-force systems is fine but be sure to make sure that you adjust down-force to make sure that the row unit gauge wheels maintain contact with the soil at speed.
• Having someone watch the planter perpendicular to the direction of travel can help to ensure that the row units maintain contact with the soil.
• Active down-force systems maintain gauge wheel load and maintain a steady load across the field by lifting and alleviating some pressure or providing down-pressure.

Planting into HEAVY (ex. organic, no-till + cover crop system for weed management) residue BMPs

• Using a no-till coulter increased corn emergence by 2.8% compared with not using a no-till coulter.
• Having enough down-pressure is key to getting good soil contact with row unit, as under heavy residue conditions, the row-unit would otherwise just ride above and not through the residue, wasting seed.

Reminders for planting in 2023

• Double, triple and quadruple check to make sure that you are getting your desired seeding depth and seed spacing.
• Don’t test your planter only in the farmyard, but rather with your planter in the ground and at speed. Only then check seeding depth.
• Remember that in older planters without the central seed hopper, individual seed boxes will lose weight as you plant and so you may need to increase down-pressure as seed weight decreases.
• Heavier soils will require greater down-force to ensure that the row units maintain soil contact but be sure to not have it set too high or risk side-wall compaction and smearing.
• When inspecting for seed spacing, don’t rely on on-cab gauges. Check multiple rows across the planter width.

Soybean planting considerations

Should I plant corn or soybean first? One common topic of debate on social media and in the farm press relates to how early one should consider planting soybeans, and whether it makes sense to do so before planting corn. Rather than thinking about planting date and order from a yield standpoint, consider thinking about it from a risk-avoidance standpoint. This is because soybean yield potential with planting date tends to be flat through the middle of May in Minnesota, and yield potential drops only by ½ to 1% per day that follows. High yields are still possible when soybeans are planted through the end of May. Risks tend to increase in both early and late spring, with the beginning of May being the “sweet spot” between maximizing yield potential and minimizing risk due to a hard frost or other early-season challenges like cold and wet seedbeds.

Oftentimes it is possible to replant soybean and not risk a significant drop in yield potential as one would encounter with corn. The key is waiting to plant until soil conditions are fit and with the 10-day weather forecast in mind. While certain seed lots of varieties with certain physical characteristics can lend themselves to imbibitional chilling injury when planted into cold soils and planting into warmer soils is always preferred, imbibitional chilling injury is a rare occurrence and isn’t worth agonizing over.

Soybean maturity 

One should, however, consider planting fullest-season soybean varieties earliest. While shorter season varieties will not gain yield potential with an earlier planting date, a longer-season variety will, adding another couple of nodes of pods when planted earlier compared to later.

It takes approximately 125 growing degree day units for soybean seedlings to begin to emerge from the soil, and it might be of use for people trying to time soybean planting to plant approximately 125 heat units earlier than the date of the last 32 degree frost.

Changes to the USDA-RMA earliest planting date 

Fig. 1. New earliest planting date map by county for a
federally insured soybean  crop. Source:USDA-Risk
Management Agency.

Recently, a multi-state group of university-based soybean agronomists noticed that the maps that the USDA- Risk Management Agency developed for the earliest planting date that would be allowed for a soybean crop to be insured seemed to have artificial borders not based on real-world risk – one example being the stark 10-day difference in earliest planting date on either side of the Red River of the North in Minnesota and North Dakota.

To develop more realistic earliest planting dates based on recent warmer temperatures, the agronomists took planting date data that they had generated over the years and used them to develop a series of models. The resulting planting dates are now more relevant to states in the upper Midwest (Figure 1).

Fielding audience questions

Drs. Luck and Naeve answered numerous audience questions including: Do you think seed firmers will be beneficial this year? How much seed firming pressure is too much? Are off-set double disk openers available? Any thoughts on drag chains? In terms of down pressure, if you have a system with springs how do you know if changing down pressure is needed? What about row placing cleaners on the toolbar or row unit? In MN we are starting to get more high speed planters on the landscape – what about seed singulation at speed?

Registration open for Strategic Farming: Field Notes program

University of Minnesota Extension’s Strategic Farming: Field Notes program will take place on Wednesday mornings from 8 to 8:30 am beginning May 10. This webinar-based program will feature timely topics and relevant U of M results. Audio will be captured during each week’s program and posted later in the day each Wednesday so that farmers and other professionals involved in crop production can take the program with them on any podcasting app.

Timely and relevant topics will be solicited each week from in-field observations throughout the crop production regions of the state.

Registration is free, but required to participate. During registration one can share with program organizers information about the topics of most interest. One only needs to register once to attend any (or all) of these 30 minute-long sessions throughout the growing season.

Thanks to the Minnesota Soybean Research & Promotion Council and the Minnesota Corn Research & Promotion Council for their generous support of this program!