Soybean Irrigation during Reproductive Growth

Authored by Emma Matcham and Shawn P. Conley

In our past article about early season soybean irrigation, we shared some thoughts on soybean water needs from planting through vegetative growth. To recap, if you’re planting into dry conditions, you might need to apply some water to aid germination. Between soybean emergence and beginning R3 growth stage, yield reductions start when soil water deficits are in excess of 50-75%.

Water deficits quantify how much water is available within the soil profile compared to the maximum amount of water the soil could potentially hold. For instance, soils at 30% deficit contain 70% of their maximum water quantity (more explanation of depletion). Deficits occur because water is evaporating off the soil surface or being released through plants’ transpiration at a rate faster than soil water is being replenished by rainfall and irrigation.

Understanding why transpiration varies can help us understand why soybean plants need frequent rainfall or irrigation during reproductive growth. The biggest drivers of transpiration are environmental factors like temperature, relative humidity, and wind speed. But, plant species, size, and growth stage can also affect transpiration rates.

As soybean plants grow and develop their transpiration increases, and soil water depletion happens faster. Soybean vegetative growth only require 0.7 inches of water per week, but flowering (stages R1 and R2) plants need twice that amount (1.4 inches of water per week). Once bean pods are elongating (R3), soybean water use increases to 1.4-1.75 inches of water per week. A soybean crop uses more water and is more likely to have lower yields due to water deficit during the pod-fill stage than they are earlier in the season.

Water usage continues to increase throughout the season, to around 1.75-2.45 inches per week from R4 through R6. Soybean producers that apply 5-7 days’ worth of water at a time lose less water to canopy evaporation than more frequent applications, but they need to keep future water need increases in mind when planning irrigation.

As you plan future irrigation timings, you may choose to start your sprinklers before soil water deficit surpasses 50%, particularly on hot days when water is actively being depleted. Sprinkler systems take time to move across the entire field, so starting irrigation before the field reaches 50% depletion gives you adequate time to make sure that irrigation is completed before the end of the field incurs yield loss due to low moisture availability.

Looking towards the remainder of the season, soybean plants need less water during R7 than during R6; and roughly 0.3-1.4 inches per week to get from R7 to full maturity. Soybean only spends around 10 days in R7, so between R7 and maturity soybean only needs around an inch of water in total.

Even though soybean needs only a small amount of water in R7, yield losses due to insufficient water during this growth stage can be as high as 0.75 bu/acre/day on sandy soils. By entering the R7 growth stage with the soil in excess of 60% of its water holding capacity, you can reduce yield loss due to late season water stress.

Weather is the main factor that determines if more irrigation will be needed after entering R7. Precipitation in the forecast would negate the need for irrigation, but hot and dry conditions can increase transpiration rates, depleting the soil water before soybean reaches maturity. Typically, in similar environments to what we have in WI, additional irrigation after reaching R7 is not necessary. Using an irrigation planning tool like WISP can account for precipitation and soil variables, or you can follow step by step guides like those published by UMN to estimate if you will need to apply more water after reaching R7.

#Plant20 is going well…but the Bean Team is ready for #Grow20!

Authored by: Lindsay Chamberlain, Spyridon Mourtiznis, John Gaska and Shawn P. Conley

#Plant20 went by in a flash for many – but with a chilly past week across the Midwest, many are wondering how long will it take for early-planted soybean to emerge. To take a stab at this question, we pulled out some data from a 2008-2009 study that looked at impact of seed size and days to emergence on yield and quality of soybean (Mourtzinis et al., 2015). At the Arlington site for this study, emergence notes were done every day, and soil temperature probes were buried before planting. With this data, we can roughly assess the GDUs (Growing Degree Units) accumulated between planting and emergence for these two site-years. Before getting into the results, here is a little bit of housekeeping on how we calculate GDUs…

Calculating GDUs

Growing Degree Units (GDU), also called degree-days, or sometimes heat units, are used in crop growth models to estimate growth and development. There are some assumptions behind GDUs, most notably that the growth or process being predicted has a linear relationship with temperature (hotter = faster growth). This relationship only has to be true between the base (minimum) and maximum temperatures, which are typically thought of as 50°F and 86°F, since these are the values used for corn. These assumptions are true for corn growth – between 50°F and 86°F, corn grows and develops, passing through growth stages faster with more heat. This relationship is less studied for soybean (and less consistent due to soybean’s photosensitivity) but we generally use the same minimum and maximum temperatures when discussing GDUs in soybean. One possible change for soybean versus corn GDUs would be lowering the base temperature to 41°F (Setiyono et al., 2010). This increases the accumulated GDUs, especially early in the season (Fig 1). This is simply due to the way GDUs are calculated:

Daily GDU = {(Daily Minimum + Daily Maximum/2) – Base Temperature}   (Campbell and Norman, 1998)

Accumulated GDUs from each day are then added together. If the daily average temp is below the base temperature (which is often true early in the season if using 50°F as a base), the GDU for that day is 0, not negative. It is important to note that the daily average temperature is calculated by taking the average of the recorded daily minimum and maximum, not the overall average temperature. These values are publicly available for many locations across the US (, including the Arlington Ag Research Station.

A final assumption of using GDUs to predict growth is that the growing point of the plant is at air temperature. This is obviously not true before emergence! Strictly speaking, GDUs are designed to be calculated with air temperatures, not soil. Since we have data available for both – we used both!

Accumulated GDUs in 2008/2009

To start out, we calculated GDUs accumulated (with planting date as day 0: May 8th in 2008 and May 6th in 2009) for both years, from soil temperature, air temperature, and with two different base temperatures (41°F and 50°F). A few things can be taken away from this figure: it is obvious that using a lower base temp (blue lines) results in faster accumulation of GDUs – but we already knew this would happen. The reason it might be important for soybean would be the days where the average temperature is between 41°F and 50°F – base 50 counts these as 0 GDU’s. Since base 50°F is more widely used, we decided to present the emergence results with the higher base temperature, but we saw very similar results (just higher numbers) using 41°F.  Clearly, more research needs to be done to determine a more accurate base temperature for soybean.

Outside of base temperature, this graph tells us some other things. First – it was warmer in 2009 (lighter shades of blue and orange). Second – GDUs calculated with soil temperature (solid lines) accumulate faster than with air temperature (dashed lines). Soil and air temperature are certainly linked, but soils tend to stay warmer at night, which drives up daily average temperature and daily GDU. Since pre-emerged soybeans are experiencing soil temperatures, but GDUs should be calculated with air temperature, the results are presented both ways.

Fig 1. Accumulated growing degree units (GDUs) for 2008 (darker colors) and 2009 (lighter colors) at the Arlington Ag Research station, calculated with different base temperatures (blue = 41°F, orange = 50°F), with soil temperatures (solid lines) and air temperatures (dashed lines).

Results – GDUs to emergence was not consistent between years.

We used regression analysis to estimate the GDUs to emergence, which were greater in 2009 than in 2008 (Table 1, Fig 2). Growing degree units (GDUs) to 50% emergence, as calculated by air temperature, was estimated to be 57 in 2008, but 179 in 2009. Values for 90% emergence and GDUs calculated with soil temperatures are displayed in table 1. Similar results were noted across the 6 varieties of soybean included in the study, see table 3 at the end of the post for estimated GDU to emergence for each variety.

The increased number of GDUs accumulated before emergence in 2009 compared to 2008 is driven (mathematically, NOT biologically) by two main factors: heat and days to emergence. It was warmer in 2009, yet the beans actually took longer to emerge (Fig 3). Factors other than temperature, like planting depth, moisture, and other soil conditions likely have an impact on time to emergence. Rainfall in May in 2008 was about 3.1 inches total, and 3.5 inches in May 2009 (precipitation is also available at – so rainfall alone does not explain the delayed 2009 emergence compared to 2008.

Table 1. Estimated GDUs (Base 50°F) and days after planting to 50% or 90% emergence for 2008 and 2009, determined by regression analysis (see fig 2 for regression lines). Planting date in 2008 was May 8th, in 2009 it was May 6th.



% Emergence





Air GDU (°F)





Soil GDU (°F)





Days After Planting






Fig 2. Percent emergence of soybean by growing degree units (GDU, Base 50°F) as calculated by air (left) or soil (right) temperature at the Arlington Ag Research station in 2008 (top) and 2009 (bottom). Points are shaded by variety. The black lines indicate the regression function determined for each set of points. Planting date in 2008 was May 8th, in 2009 it was May 6th.


Fig 3. Percent emergence of soybean by days after planting at the Arlington Ag Research station in 2008 (top) and 2009 (bottom). Points are shaded by variety. The black lines indicate the regression function determined for each set of points. Planting date in 2008 was May 8th, in 2009 it was May 6th.

What does this mean for 2020?

Although it won’t perfectly predict your early-planted soybean emergence, all this GDU talk might have you interested in how many we have accumulated this year. Table 2 summarizes the GDUs accumulated since April 15th at the Arlington Ag Research Station. If you are interested in totaling these for your area, you just need daily minimum and maximum temperatures. Also, don’t count any accumulated GDUs from the day you planted – that is day 0. For those thinking about other crops – remember that the base temperature is crop specific! The base temperature for winter wheat, for example, is 37°F! (Campbell and Norman, 1998)

Overall, the data presented shows that we need more research to understand factors driving time to soybean emergence. The data indicates that GDUs are not a consistent predictor for soybean emergence, so other factors will likely need to be considered.

Table 2. Daily temperatures and GDUs accumulated at the Arlington Ag Research Station since April 15th.

Date T max (°F) T min (°F) T ave (°F) GDUs (Base 50) GDUs (Base 41)
15-Apr-20 36 18 27 0 0
16-Apr-20 36 20 28 0 0
17-Apr-20 45 27 36 0 0
18-Apr-20 49 29 39 0 0
19-Apr-20 61 33 47 0 6
20-Apr-20 56 32 44 0 3
21-Apr-20 62 27 44.5 0 3.5
22-Apr-20 49 30 39.5 0 0
23-Apr-20 57 36 46.5 0 5.5
24-Apr-20 51 36 43.5 0 2.5
25-Apr-20 53 35 44 0 3
26-Apr-20 57 36 46.5 0 5.5
27-Apr-20 66 40 53 3 12
28-Apr-20 60 40 50 0 9
29-Apr-20 67 42 54.5 4.5 13.5
30-Apr-20 51 42 46.5 0 5.5
1-May-20 66 38 52 2 11
2-May-20 66 47 56.5 6.5 15.5
3-May-20 74 45 59.5 9.5 18.5
4-May-20 73 32 52.5 2.5 11.5
5-May-20 56 36 46 0 5
6-May-20 54 32 43 0 2
7-May-20 66 41 53.5 3.5 12.5
8-May-20 63 30 46.5 0 5.5
9-May-20 47 25 36 0 0
10-May-20 59 36 47.5 0 6.5
11-May-20 44 31 37.5 0 0
12-May-20 54 30 42 0 1
Cumulative (April 15 until May 12) 31.5 158

 Table 3. Estimated GDUs and days after planting to 50% or 90% emergence for 2008 and 2009, for 6 different soybean varieties, estimated by regression analysis.

Soil Temp GDUs to Emergence Air Temp GDU’s to Emergence
2008 Variety 50% 90% 50% 90%
DSR-199RR/STS 133 166 60 78
DSR-2300RR 122 147 53 68
DSR-2600RR 130 156 58 74
KB2409RR 126 154 56 72
KB249RR 131 164 59 77
Trelay 2233 131 155 59 73
2009 DSR-199RR/STS 306 343 177 196
DSR-2300RR 307 341 178 195
DSR-2600RR 306 339 178 195
KB2409RR 307 342 178 195
KB249RR 313 349 181 199
Trelay 2233 313 344 182 197


Literature Cited

Campbell, G.S., and J.M. Norman. 1998. An Introduction to Environmental Biophysics. 2nd ed. Springer.

Mourtzinis, S., J.M. Gaska, P. Pedersen, and S.P. Conley. 2015. Effect of seed mass and emergence delay on soybean yield and quality. Agron. J. 107(1): 181–186.

Setiyono, T.D., K.G. Cassman, J.E. Specht, A. Weiss, A. Dobermann, and H. Yang. 2010. SoySim User Manual. Univ. Nebraska-Lincoln Dep. Agron. Hortic. Inst. Agric. Nat. Resour.Available at


Early Season Soybean Irrigation

Authored by Emma Matcham and Shawn P. Conley

Did you know that roughly 500,000 acres of WI cropland are irrigated? Interestingly, most of WI irrigated land is used for vegetable (potato, sweet corn, etc.) or seed corn production. You might notice that soybean is not highlighted on the preceding list, however soybean is frequently grown in rotation or used as a “set up” crop with potatoes and corn under these irrigation systems.

Given the Covid-19 crisis we are seeing more irrigated vegetable production going to other crops such as soybean. Here are some things to keep in mind for your early-season soybean irrigation planning.

If you have soybean planted under irrigation this year, the good news is that you can use the same irrigation planning tools you use for other crops to grow a great soybean crop. The Wisconsin Irrigation Schedule Planner is designed for a wide range of crops including soybean, potato, sweet corn, field corn, alfalfa, and more! Find out more about WISP and evapotranspiration data here:

If you’ve already planted but your soybeans aren’t up yet: Phew… you just missed the cold weather! However, keep an eye out for crusting, especially if you got hit with heavy rains last week. On sandy soils with thin crusts, soybeans can usually break the crust on their own. But, if your crust is thicker or you’re on finer soils, you can use a shallow rotary hoeing or even apply some water to help get the beans up.

If you’ve planted and your beans are up: cold temperatures around the state were largely either not prolonged enough or cold enough to damage most emerged soybeans, but microenvironments exist and it never hurts to check. This video shows you what to check for regarding early season damage symptoms, including freeze.

If you discovered that you have frost damage but don’t know if you should replant, remember a stand of ~100k plants/acre at harvest is enough to maximize yield in most situations. Furthermore, our data shows that soybean stands as low as 50k plants/acre typically don’t require a replant. Here’s an article to help you make that choice: Soybean Replant Decisions: Just the Facts Jack.

If you’re ready to plant: and the weather looks dry in your area over the next few weeks. In order to get soybean out of the ground, seeds need to imbibe water and start germinating. Be prepared to provide 0.2-0.5 inches of water to moisten soils to a depth of around 6 inches, which is the length of soybean roots at growth stage VE.

Moving into the early season, here’s some additional information to keep in mind. Most crops begin to experience moisture stress at around 50% soil water deficit, but soybean can handle drier conditions during vegetative growth and flowering without seeing yield decreases. Lyndon Kelley at MSU, suggests that you can reach a 75% soil water deficit before R3 (pod formation) and still not experience yield loss.

In Nebraska, and irrigated finer soils, Jim Specht recommends withholding water until soybeans reach the R3 growth stage.

In Wisconsin we’re primarily irrigating on coarse sandy loams that simply cannot hold substantial water reserves, so withholding irrigation entirely until R3 isn’t typically advisable. Instead, consider setting your deficit threshold somewhere between 50 and 75% without impacting your final seed yield.

Beyond reducing the energy and water demands of your soybeans, there might be some side benefits to reducing early-season irrigation. A soybean crop that is exposed to extreme early season irrigation tends to invest less energy in their root systems and instead grow tall and leafy, making them more susceptible to lodging and diseases like white mold.

Stay tuned as we will continue this conversation about irrigating soybean when we approach R3 (pod formation) soybean.

Mirror, Mirror on the Wall, Will My Wheat and Soybean Crop Freeze and Fall?

Weather forecasts have farmers “sweating” the upcoming cold weather. Here are a few thoughts and resources based on the forecast temperatures my weather app is suggesting for WI farmers as of Tuesday May 5th at 5 am. FYI: my title is courtesy of Disney+ (not an advertisement just a fact) and Princess Movie Marathons during Covid-19 lock-down.

First lets start with the wheat crop which in WI ranges from the tillering (F4) to jointing (F6) growth stages. Cold temperature would need to reach 24 degrees F or less for 2 plus hours before injury occurred. I just don’t see that happening in any major wheat growing region in WI this week so in short don’t fret the wheat crop.

Table 1. Wheat Resistance to Freeze Injury (From: Spring Freeze Injury to Kansas Wheat)

Now let’s talk about soybean. I am cautiously optimistic that if the forecast temperatures hold, most of the soybean crop will in fact be #COOLBEANS, but will survive. My optimism lies in the Nowledge I received in an email from Dr. Jim Specht from UNL a few years ago (modified slightly by me for context). For the most-part, farmers in WI fall within the context of this email.

First of all 34F will not impact above-ground tissue.  Second, tissue freezing does not even take place at 32F because cell cytoplasm has solutes in it – like a modest anti-freeze, which depresses freezing point of the tissue a degree or two less than 32F – thus air temps surrounding the tissue have to get to below 31 or 30F before tissue freezing can occur.  Third, the soil surface is typically warmer than the air temperature (particularly when the soil is wet) and does not give up heat acquired during a sunny day as fast as the air does after sunset.  In actuality, the interface between soil surface temp and the air temp near that soil surface will be closer to the soil temp than to the air temp which most peopled measure on thermometers viewable at their height (not at ground level).  Biophysically, control of the soil temp over the air temp this is called the “boundary layer effect”).  So don’t trust air temperatures read on thermometers unless you know what the air temperature near the soil surface was (put a thermometer on the soil surface where the cotyledons are and check it just before dawn (when the soil surface temp reaches its nadir for a 24-hour temperature cycle).  Fourth, the cotyledons are a huge mass of tissue that are about 95% water.  That big amount of water-filled tissue is hard to freeze unless the exposure to temps of 30F at the soil-air interface is many, many hours.  Cotyledons will freeze faster (in fewer hours) but only if the soil surface temps get well below 30F (say 25F).  The only concern I would have is when cotyledons are no longer closed and protecting the young stem tip.  However, if that is in fact frozen off, the nodes to which the cotyledons are attached will regenerate TWO main stem tips.  Not an ideal way to start the growing season, but better than having to replant (0.5 bu/ac loss per each day that soybeans are NOT in the ground on May 1). Text courtesy of Dr. Jim Specht (UNL)!

For additional information please view my YouTube video that discusses common early season emergence issues (including frost injury) and just in case the forecast was way off and we get hammered with colder than expected temperatures here is our replant article entitled:

Soybean Replant Decisions: Just the Facts Jack!

FYI: Just so you know we practice what we preach (i.e. early soybean planting) the UW BeanTeam has 7 locations in the ground ourselves!

Soybean Replant Decisions: Just the Facts Jack!

The start of the #plant20 growing season has been more favorable to many Midwestern farmers. Over the last month and more specifically the last 10 days Twitter and my email has been filled with images of early planted soybean going into the ground and we are just starting to see the first images of soybean beginning to crack and emerge. As farmers, agronomists and technical service providers begin to assess the 2020 soybean stands here are a few items to contemplate before re-plant recommendations are made.

  1. Get an accurate stand assessment. We are often drawn to the worst areas of fields and over-blow how bad the overall stand really is. You can go old school and use the tape or hula-hoop method or try a digital approach such as Bean Cam the WSMB funded soybean replant app!
    1. Link to the app store for iPhone and iPad
    2. Link to the app store for Android

      Bean Cam app calculations/results.

  2. An effective stand is obviously important to maximize soybean seed yield. However the downside yield risk for a sub-par stand is minimal until stands fall below 50,000 plants per acre. The synergy of early planting coupled with breeders adding 3x yield to soybean branches at low populations have effectively reduced the yield penalty for thins stands by 1/2 (Suhre et al. 2014) . Therefore we recommend the following.
    • Early planted soybean yield is maximized with stands that range from 100,000 (high yield environment) to 135,000+ (low yield environment) plants per acre.
    • When soybean stands are less than 50,000k plants per acre, inter-plant new seed with a similar maturity into the existing stand. DO NOT TEAR UP THE STAND AND START OVER.
    • When stands fall between optimal and 50,000k plants per acre Think Twice Before Replanting Soybeans! Our data shows a nominal ~2 bu yield increase in this situation. Even if you have a “free replant” guarantee the numbers don’t make economic sense. As a grower you are better off investing $$$ in an effective in-season residual herbicide to control weeds such as Palmer and waterhemp.


Gaspar, A. and S.P. Conley. 2015. Responses of canopy reflectance, light interception and soybean seed yield to replanting sub-optimum stands. Crop Sci.55: 377-385. doi: 10.2135/cropsci2014.03.0200

Suhre, J.J., Weidenbenner, N., ‡Rowntree, S., Wilson, E., S., Naeve, S. Casteel, S.P. Conley, Diers, B., Esker, P., Specht, J., and Davis, V. 2014. Soybean Yield Partitioning Changes Revealed by Genetic Gain and Seeding Rate Interactions. Agron. J. 106:1631–1642.

Thoughts on Transitioning a Cover Crop into a Cash Grain Crop

My grandfather (whom I nicknamed Fudd), left school after the 8th grade due to farm obligations and may not have had the largest vocabulary nor could write in any legible form (we always teased him that he was a M.D.), but he could rattle off math and markets like no ones business. Today farmers are running their own calculations and right now, corn and soybean margins are TIGHT to say the least.  A common question I have received over the last few days is how we can transition our cover crop acres into cash grain acres. Here a few thoughts to ponder:

  1. Is it legal?
    1. Determine if you have enrolled in any programs or cost-share that prohibit the sale of said crop.
    2. Check to see if there are any plant back restrictions due to previous herbicide or other pesticide use that limit the sale of said grain crop or livestock use of straw for feeding or bedding.
    3. Verify if the seed source has limits for sale due to PVP or genetic licenses.
  2. What cover crop specie(s) did you plant?
    1. Is this a cover crop mixture or a single species?
    2. A cover crop mixture will be difficult to manage for grain yield and straw yield and quality. We can only recommend considering transitioning your cover crop to a grain crop if it is a monoculture cover crop.
    3. Is it rye or wheat?
    4. Do I have a market for rye if I keep it for grain? See #1 above again.
    5. Do I have a market for the rye straw?
  3. What is your cost of production and required yield potential to actually make money? The common numbers I have floated are 90 bushels/acre of grain and 2 ton/acre of straw for wheat. For rye, the yield goals would be similar if not greater based on rye grain and straw price/value. Here are a few agronomic decisions that impact this threshold. These are suggestions generally for wheat. Rye we expect would be similar.
    1. Planting date matters: In WI, we start to lose yield after the last week in September at ~1 bu/acre/day.
      1. Here are a few scenarios to ponder:
        • Scenario #1. Drilled cover crop on October 15th and seeding rate was increased accordingly. There is a good chance we will hit our yield mark. If the cover crop was drilled, but not planted in a standard narrow row spacing (7.5”), grain and straw yields may be lower and weed control may be more challenging.
        • Scenario #2. Broadcast and lightly worked-in cover crop in mid-November. Poor chance we will hit our grain yield mark.
        • Scenario #3. Flew on cover crop into established corn or soybean before leaf drop. If you have less than 12 plants per square foot…tear it up…. poor chance you will hit your grain yield mark.
        • Scenario #4. Planted in August on prevent plant acres or following another small grain (oat or winter wheat). We don’t normally recommend a small grain followed by small grain but typically you can get by in year #2.
          1. Things to consider here: If you are selling for grain to an elevator watch out mixing grains. There is a good chance volunteers will come through and dockage can occur.
          2. Planting too early will put your crop at risk for Barley Yellow Dwarf Virus (BYDV). If the crop looks even and does not have irregular patterns across the field or in pockets you are likely good to go.
      2. For more information on establishment questions: Top 8 Recommendations for Winter Wheat Establishment in 2019
    2. Nitrogen timing matters. Get out there as soon as the ground is fit.
    3. Weed management matters. The value of this crop will be in both grain yield and straw yield and quality. Do not let the weeds get out of control. This is especially true if this was on prevent plant acres. Pay attention to herbicide labels for both crop growth stage and weed height restrictions. We don’t have many options for weed control in WI small grains. Here are a few tools to help in these decisions:
    4. Disease management matters for both grain and straw yield. Disease management is always a huge consideration in small grain production systems. This would even be more evident if this is a second year of small grain on small grain. We recommend scouting and watching the bottom line closely. The Feekes 5 timing that is often tied with a herbicide application is frankly a waste of money in WI unless significant early-season disease pressure is noted. We recommend scouting and estimating disease pressure at Feekes 9 (flag leaf) or Feekes 10.51 (anthesis or flowering). We have also measured an increase in straw yield (~0.5 tons of dry matter) with the Feekes 10.51 timing for fusarium head blight (FHB) or scab. Here are a few tools to help in these decisions:

By the way my grandfather nicknamed me Finkle, after Mr. Weatherman Earl Finkle. His reasoning for this was that I was correct almost as often as he was…. LOL!!

The WSMB Free Soybean Cyst Nematode Testing Program is Back in 2020!

Ann MacGuidwin, Damon Smith and Shawn P. Conley

The WI Soybean Marketing Board (WSMB) sponsors free nematode testing to help producers stay ahead of the most important nematode pest of soybean, the soybean cyst nematode (SCN). Eggs of SCN persist in the soil between soybean crops so a sample can be submitted any time that is convenient. The soil test report indicates the number of eggs in the sample and is useful for selecting the right variety for the next soybean crop. Retests of fields planted with SCN-resistant varieties over multiple years shows how the nematode population is responding to variety resistance and provides an early warning should the nematode population adapt to host genetics.

In the spring of 2012, the WSMB expanded the nematode testing program to include other pest nematodes in addition to SCN. These nematodes are less damaging to soybean than SCN but can cause enough yield loss to warrant treatment. As is the case for SCN, there are no rescue treatments for nematodes so the primary purpose of this year’s soil test is to plan for next year’s crop. Soil samples collected in corn for nematode analysis have predictive value for explaining yield if they are collected before the corn V6 growth stage. Sampling early in the season will provide information about the risk potential for the current corn crop AND the next soybean crop.

The assays used to recover nematode pests other than SCN in soil require that the nematodes are alive. So, it is important to keep the samples moist and at least room temperature cool. Collecting a sample that includes multiple cores ensures that there will be plenty of root pieces to assay. It is not necessary to include live plants in the sample. The soil test report will indicate which pest nematodes are present and at what quantities and their damage potential to soybean and corn based on the numbers recovered.

For more information on SCN testing and management practices or to request a free soil sample test kits please contact: Jillene Fisch at ( or at 608-262-1390.

Click to view more information on our WI SCN testing program or visit The SCN Coalition.

Remember the first step in fixing a nematode problem is to know if you have one! The WSMB sponsored nematode testing program provides you that opportunity. So Wisconsin farmers….”What’s you number?”

Just the Facts Jack: Soybean Planting Date, Seeding Rate and Seed Treatment Recommendations

When I am asked a direct question from a farmer or a crop consultant my response is always as follows…Do you want the short answer or the long answer as I can say the same thing in 5 minutes or 5 hours. Their response to me is almost always the same…”Just the Facts Jack”. In this blog I will attempt to answer three very agronomically important and challenging questions in a very succinct manner.  However as we all know brevity can be a gift or a curse depending upon the context of the question. With that being said here we go!

Question #1. When should I start planting soybean? My general response is to start planting your soybean crop ~7 to 10 days before you start putting your corn in the ground with the caveat that the soil is fit and you are following your crop insurance replant dates (However…IMHO, Jim Specht acronym,: I do believe that RMA needs to revisit these dates for Northern soybean growers). We have measured soybean yield loss due to delayed planting date as early as ~April 25th however the rapid yield decline (up to 0.5+ bpa per day) occurs at ~May 10th. As you would expect the magnitude of this planting date yield response is soil and climate dependent and yield losses in some areas (TED’s) where as high as 2.8 bpa per week for delayed planting (Figures 1 and 2). For a deeper dig please review the below supplemental documents.


Figure 1. Map of the North Central US region showing nine technology extrapolation domains (TEDs) used in this analysis.

Figure 2. Producer soybean yield plotted against planting date in 9 technology extrapolation domains (TED) in the NC USA region.

Question #2. What is the optimal soybean seeding rate? The quest for the optimal agronomic soybean seeding rate for yield vs. the optimal economic seeding rate has been an ongoing debate. Fortunately a large group of academics and industry (thank you Corteva) were able to combine data sets and address this question (Figure 3). Our results suggest that for “on-time” soybean planting dates the optimal agronomic soybean seeding rate to achieve 99% yield potential ranged from 237,000 to 128,000 seeds per acre (assuming 90% germ) across environments; whereas the optimal economic soybean seeding rate ranged from 157,000 to 103,000 seeds per acre. Thankfully this roughly confirms my original recommendation that you buy a bag an acre (140K) and place ~20% more seed on the low yielding acres and ~20% less on the high yielding acres. If planting is delayed however we do recommend that you increase your seeding rate accordingly (Adjust Your Seeding Rate (Higher) But Not Your Maturity Group For Late May Planted Soybean ). For a deeper dig please review the below supplemental document.

 Location of 211 trial site-years that are included in the database and their respective environmental cluster classifications.

Figure 3. Location of 211 trial site-years that are included in the database and their respective environmental cluster classifications.

Table 1. Agronomic and Economic Optimal Soybean Seeding Rates by Environmental Cluster.

Cluster 1

Cluster 2

Cluster 3

Yield level (bu a-1)

Agronomic/(Economic) Optimal Seeding Rate1,2

< 58




58 – 71




> 72




1Agronomic optimal seeding rate (x1000 seeds) based on 99% maximum yield level.

2Economic analysis based on $62 a unit (140k) for seed and $9 a bushel pricing; soybean price and seed cost fluctuations will change the EOSR.

Question #3. When do I use a soybean seed treatment? I purposely placed this questions last as I know it will draw significant ire; however the data are what they are. Soybean seed treatments should only be used in some early planted soybean situations and/or if you have a history of or have scouted for an insect (i.e. Bean leaf beetle) or a pathogen (i.e. SDS) that exceeds economic thresholds. For a deeper dig please review the below supplemental document.

Th-th-th-that’s all folks!

Winners of the 2019 WI Soybean Yield Contest are Announced

The 1st place winner in Division 4, RnK DeVoe Farms of Monroe, grew Pioneer P28A42X and harvested 91.08 bu/a.  In second place, Venable Farms Inc. of Janesville grew Jung 1213R2X and harvested 87.48 bu/a.  In Division 3, Jim Salentine of Luxemburg harvested 92.44 bu/a with Stine 19BA23 and in 2nd place, Tim Gaffron of Twin Lakes harvested 89.13 bu/a with Pioneer P24A80X.  In Division 2, Wegner Farms of Sparta achieved 75.63 bu/a from Pioneer P23A15X for first place.  In 2nd place, David Lundgren of Amery harvested 64.13 bu/a from Asgrow AG11X8 soybeans.  No entries were submitted for Division 1.

RnK DeVoe Farms of Monroe was the winner of the Soybean Quality contest with 2,967 pounds of protein (34.9%) plus oil (19.4%) per acre from Pioneer P28A42X.

The contest is sponsored by the WI Soybean Program and organized to encourage the development of new and innovative management practices and to show the importance of using sound cultural practices in WI soybean production.

For more information please contact Shawn Conley, WI State Soybean Specialist at 608-800-7056 or

Finalists for the 2019 WI Soybean Yield Contest are Announced

The 2019 season had below average growing conditions for many growers.  We experienced lower entry numbers in the 2019 WSA/WSMB Soybean Yield Contest, likely due to delayed planting and harvest from wet weather causing maturity, time and logistic struggles.  The top two entries in each division (in no particular order) were:

Division 4:

  • Rick DeVoe, Monroe (planted Pioneer P28A42X)
  • Nick Venable, Janesville (planted Jung 1213R2X)

Division 3:

  • Tim Gaffron, Twin Lakes (planted Pioneer P24A80X)
  • Jim Salentine, Luxemburg (planted Stine 19BA23)

Division 2:

  • David Lundgren, Amery (planted Asgrow AG11X8)
  • Mike and Dean Wegner, Sparta (planted Pioneer P23A15X)

Division 1: 

*No entries were submitted for Division 1

The Soybean Quality Contest was optional for any Soybean Yield Contest entrant.  There are no geographical divisions for the Quality Contest.  One cash award will be presented statewide to the highest protein plus oil yield per acre (measured in lbs. per acre). The finalists for the Soybean Quality Contest are:

  • Rick DeVoe, Monroe (planted Pioneer P28A42X)
  • Jim Salentine, Luxemburg (planted Stine 19BA23)

The final ranking and awards will be presented at the Corn Soy Expo to be held at the Kalahari Convention Center, Wisconsin Dells on Thursday February 6th during the WSA/WSMB annual meeting.

The contest is sponsored by the WI Soybean Program and organized to encourage the development of new and innovative management practices and to show the importance of using sound cultural practices in WI soybean production.

For more information please contact Shawn Conley, WI State Soybean Specialist at 608-800-7056 or