Early season, The Bean Report

The Bean Report – May 10, 2023

May 10, 2023

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Optimizing Early-Season Establishment of Soybeans 

Seeding Date and Residue Management Experiments (2018 – 2021)

Recently completed research conducted at Brandon, Carberry and Indian Head by Dr. Ramona Mohr, AAFC – Brandon, compared early (May 8 – 11) and late seeding dates (May 24-29) in combination with different residue management treatments (tilled, burned and no-till with tall or short stubble heights and straw kept or removed).

At early seeding dates, soil temperatures were cooler (6 to 15 °C) than late seeding dates (14 to 31°C). Residue management less frequently had an effect on soil temperature, with temperature differences among treatments in the range of 1 to 3°C. In terms of soil moisture, effects of seeding date were inconsistent – sometimes earlier seeding was associated with more moisture, while sometimes it was drier. Tillage and stubble burning more commonly resulted in drier soils than no-till treatments. Soil moisture tended to be greatest in no-till treatments with straw kept.

Soybeans emerged 6 to 8 days faster with later seeding dates. At early seeding dates (May 8-11), soybeans took 20 to 28 days on average to emerge. Comparatively, soybeans planted two weeks later took 13 to 20 days to emerge on average. Differences in days to emergence among residue management treatments were small, generally 1 day or less.

The height of the lowest pods were greater than 3″ on average. Early seeding increased lowest pod heights in 2 of 7 site-years (+0.8-1.2″) and decreased pod height in 1 of 7 site-years (-0.6″). At some sites, pod height was higher in the burned stubble. However, pod height response to seeding date and residue management practice was limited and inconsistent. Neither seeding date nor residue management practice appeared to be reliable tools to improving pod heights.

Early seeding dates (May 8-11) resulted in similar or greater soybean yields than late seeding dates (May 24-29). Yields of soybeans direct seeded into standing stubble were the same or greater than yields of soybeans seeded into burned residue or tilled soil. Tall stubble resulted in similar (7 of 9 site-years) or greater (2 of 9 site-years) yields than shorter stubble, with the benefits of taller stubble most common in drier growing conditions (at Indian Head). Removing straw resulted in similar (6 of 9 site-years) or greater yields (3 of 9 site-years) than where straw was chopped and returned to the field.  

Do different seed-related factors influence soybean germination success?

Dr. Mohr and her team further investigated the impact of temperature and seed-related factors on soybean germination through a series of controlled environment studies. Seed-related factors considered included soybean seed size, variety, conditions under which the seed was grown (i.e., if the seed was grown under excess moisture, drought or rainfed conditions) and seed P concentration.

Temperature had the greatest influence on soybean germination, regardless of different seed-related factors. At lower temperatures, there was more variability among seed-factor treatments, suggesting that these factors may be more important when seeding into less than ideal conditions for germination. Germination occurred in under 4 days when temperatures were above 15 °C, in a week when temperatures were 10 – 12.5 °C and complete germination (>90% of seeds germinated) did not occur within 21 days when temperatures were below 7.5 °C.

Soybean Seeding Information

Seeding Date

Soybean seeding date is flexible in Manitoba. Aim to seed in the second to third weeks of May. Soybean yields did not differ among seeding dates from May 1 to May 24, but yields were reduced by 15%, on average, when seeding was delayed until May 31 – June 4 in previous research conducted in Manitoba. In the research described above, seeding dates of May 8 to 11 resulted in greater soybean yields than later dates of May 24 – 30.

Seeding Rate and Target Plant Stand

Target a living plant stand of 140 – 160,000 plants/ac to maximize yield. Take into account expected germination and survivability to calculate seeding rate. In on-farm trials, soybean seed survival has been 81% on average (82% with planters and 80% with air seeders).

MPSG’s On-Farm Network has been evaluating different soybean seeding rates on-farm since 2012. There have been 107 trials comparing soybean seeding rates to date, with another 14 trials planned for 2023. Most of the time (82%), lowering soybean seeding rates by 30,000 seeds/ac from a farmer’s traditional seeding rate has not changed soybean yield. From these trials, seeding above 190,000 seeds/ac has not provided a consistent return on investment. Generally, seeding rates of 150,000 to 180,000 seeds/ac has maintained soybean yield while minimizing seed costs. Dropping below 150,000 seeds/ac is not recommended since it introduces much more risk, especially in terms of weed control.

Row Spacing

Narrow row spacing results in soybean yields that are similar to or greater than wide rows according to research conducted in Manitoba. In small-plot research, where narrow rows of 10″ were compared to wide 30″ rows, narrow rows had a consistent yield advantage (+1.5 to +11.6 bu/ac). Where intermediate 16-24″ rows were compared to narrow 10″ rows, yields were similar between row spacings.

MPSG’s On-Farm Network has conducted 19 row spacing trials on-farm since 2019. Nine trials compared narrow 7.5-10″ rows to intermediate 15-20″ rows and 10 trials compared intermediate 15″ rows to wide 30″ rows. Seeding rates were held constant between row spacings. Soybean seed survival was 7% lower in 30″ rows. Narrow rows improved yield over intermediate rows 44% of the time (on average by 1.8 bu/ac). Intermediate 15″ rows improved yield over 30″ rows 20% of the time.

Row spacing influences more than yield. Seeding soybeans on narrow row spacings improves their competitive ability against weeds.

Seeding Depth

Seed soybeans at 0.75″ to 1.75″ deep. Adjust within this range depending on available soil moisture, soil type and equipment.

Inoculation Strategies

Choosing a soybean inoculation strategy will depend on the history of soybeans in a field. Double inoculation (two forms or placements) is recommended for first-time soybean fields, and is typically the combination of liquid on-seed inoculant with granular in-furrow. Once soybean history has been established in a field (two previous well nodulated soybean crops), a single inoculation strategy is sufficient to maintain competitive N-fixing Bradyrhizobia strains. Most often, this is liquid on-seed alone. To facilitate effective nodulation, seed soybeans on fields testing low (<50 lbs N/ac) in residual N.

MPSG’s On-Farm Network has had two types of inoculation trials, comparing 1) double vs. single inoculant strategies (2014-2022) and 2) single vs. no inoculant (2016-2022). On fields with two previous soybean crops, and the last soybean crop within the last four years, double and single inoculant have resulted in the same nodulation and yield. On fields with three previous soybean crops, there has been no difference in nodulation nor soybean yield when comparing single inoculant to none at all. However, liquid on-seed inoculant is fairly cheap to apply compared to a rescue N fertilizer application in-season in the event of a nodulation failure.

Fertility (P, K, Starter N)

Soybeans remove relatively large amounts of phosphorus (P) in harvested seed (~0.85 lbs P2O5 /bu). Field trials at 10 locations across Manitoba (2013-2015) evaluated soybean yield response and seedling toxicity of P fertilizer rates (0, 20, 40 and 80 lbs P2O5 /ac) applied in side band, seed row or broadcast. Soil test P levels ranged 0-10 ppm Olsen P.

Seed-placed P reduced plant stands at 6 of 28 site-years when applied at rates of 80 lbs/ac. Phosphorus fertilizer only increased yield at one of 28 site-years, where 40 and 80 lbs/ac increased yield by 15%, regardless of placement. Despite the low likelihood of seeing a yield response to P fertilizer in soybeans, balancing P levels across the rotation is encouraged. To maintain P levels, apply P during the soybean year and the best placement would be side banding to minimize fertilizer toxicity risk, facilitate higher rates and place fertilizer below the soil surface.

Soybeans also remove relatively large amounts of potassium (K) (1.1-1.4 lbs K2O / bu). There were no yield responses to K fertilizer treatments in field trials conducted across Manitoba (2017-2018) on low K soils (49-117 ppm ammonium acetate soil test K). Potassium rate and placement was evaluated on soils ranging in soil test K levels.

Yield response to K fertilizer may be unlikely in Manitoba, but it is encouraged to maintain K fertility throughout the rotation to support yields of other crops. Use expected K removal rates and yields to estimate the amount of K fertility needed to support other crops in the rotation.

Soybean yield response to starter N fertilizer rates of 0, 15, 30, 45, 60 and 75 lbs N/ac (broadcast and incorporated urea) were evaluated at Carman (2015-2017). There were no differences in soybean biomass, yield, protein or oil.

Seed Treatments

If seeding into saturated soils, or into fields with a history of root rots, consider a fungicide seed treatment to help soybeans establish in the face of seedling and root rots. Additionally, seeding into warm, well-drained soils at 0.75-1.75 inch depths will allow plants to emerge quickly. A strong, healthy plant is better equipped to defend itself against disease.

Insecticide-containing seed treatments will provide protection from wireworms and seedcorn maggots. If your risk of theses insects is low, consider a fungicide-only treatment, or bare seed.


First, consider if you need to roll your soybeans. Do you have rocks, soil clods or corn root balls to manage? If not, rolling may not be necessary in that field.

Soybeans can be rolled immediately after seeding up to two days after seeding, or post-emergence targeting the V1 (first trifoliate) stage on a warm day (+25°C) when plants are flexible.

Early-Season Weed Control

Soybeans need to remain free of weeds until V2 to V4, on average to avoid yield loss. This window of weed control may be extended to R1 when weed pressure is great.

Seeding soybeans on narrow rows, at 160,000 – 180,000 plants/ac results in a competitive crop that can better combat weed pressure. When considering volunteer canola specifically, increasing soybean seeding rates and managing residual soil N were the best tools to minimize yield loss.

For information on pea and faba bean seeding, check out The Pea Report – April 26, 2023  →

Alternatives to Lambda-Cyhalothrin for 2023

Due to the PMRA’s re-evaluation decision of lambda-cyhalothrin, effective April 29, 2023, crops treated with lambda-cyhalothrin (Matador, Silencer, Labamba, Zivata, Voliam Xpress) cannot be fed as livestock feed – including any seed screenings, straw or meal.

For soybeans and pulses, these products are commonly used to manage grasshoppers, soybean aphids, pea aphids and cutworms, among other pests.