Soybean Management Strategies to Facilitate Timely Winter Wheat Establishment in 2016

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Winter wheat acres across WI have declined over the past few years due to high corn and soybean prices and late grain harvests, however current economic realities suggest an opportunity for increased wheat acres moving forward. As farmers get ready to kick off the 2016 growing season here are a few suggestions to help get your 2016/17 winter wheat crop established on time.

    • Plant early. If weather and soil conditions allow for it plant the acreage you intend to go to winter wheat first. This is regardless of which crop you plan to follow (soybean, corn silage or field corn). Remember the optimal planting date window for most of our WI winter wheat acres is the last week of September through the first week in October. In Figure 1 below you will notice that for every 3 days planting is delayed we see 1 day delay in harvest, so delaying planting by one week equates to about 2 days later maturing. However when planting is delaying past June 1stit turns in to more of a 1: 1 relationship. Also remember in WI it normally takes another 5-8 days for the soybean crop to move from R7 to R8 (full maturity).
      Table 1. Calendar date for reaching R5 (beginning seed fill) and R7 (beginning maturity) growth stage by planting date and maturity group for the 2014 & 2015 growing season at Arlington and Hancock, WI.
      Date of Growth Stage Initiation
      R5
      R7
      Planting Date
      Maturity Group
      Arlington
      Hancock
      Arlington
      Hancock
      May 1st
      2.5
      5-Aug.
      3-Aug.
      14-Sept.
      15-Sept.
      2.0
      1-Aug.
      1-Aug.
      8-Sept.
      13-Sept.
      1.5
      29-July
      29-July
      2-Sept.
      9-Sept.
      May 20th
      2.5
      9-Aug.
      10-Aug.
      20-Sept.
      22-Sept.
      2.0
      6-Aug.
      7-Aug.
      14-Sept.
      18-Sept.
      1.5
      3-Aug.
      5-Aug.
      8-Sept.
      16-Sept.
      June 1st
      2.0
      12-Aug.
      12-Aug.
      21-Sept.
      24-Sept.
      1.5
      10-Aug.
      11-Aug.
      16-Sept.
      19-Sept.
      1.0
      8-Aug.
      8-Aug.
      12-Sept.
      13-Sept.
      June 10th
      2.0
      16-Aug.
      18-Aug.
      27-Sept.
      30-Sept.
      1.5
      15-Aug.
      17-Aug.
      24-Sept.
      26-Sept.
      1.0
      13-Aug.
      15-Aug.
      21-Sept.
      22-Sept.
      June 20th
      1.5
      23-Aug.
      21-Aug.
      2-Oct.
      4-Oct.
      1.0
      21-Aug.
      18-Aug.
      28-Sept.
      28-Sept.
      0.5
      19-Aug.
      18-Aug.
      24-Sept.
      24-Sept.
      • Crop rotation matters. Our long-term rotation data suggests winter wheat yields are greatest following soybean, followed by corn silage and lastly corn for grain.  Therefore plan your rotation accordingly to maximize yield and system efficiency.
      • Consider an earlier maturity group soybean. Plant a high yielding, earlier maturity group soybean to help get that soybean crop harvested on time. Though later maturing varieties “on-average” produce the greatest yields, data from our 2015 WI Soybean Variety Test Results show the maturity group range that included a starred variety (starred varieties do not differ from the highest yield variety in that test) was 1.9-2.8, 1.1-2.4, and 1.1-2.0 in our southern, central and north central regions respectively. This suggests that the “relative” maturity group rating is trumped by individual cultivar genetic yield potential. Therefore growers have options to plant an early maturity group soybean that will be harvested on time and not sacrifice yield.
      • Manage for the system not necessarily the crop. If you are serious about maximizing wheat grain and straw yield on your farm one of the biggest contributing factors for both of these in WI is timely wheat planting. Make management decisions to facilitate that. *We all know what inputs can extend maturity that don’t necessarily guarantee greater yields. So instead of listing them and fielding angry emails I am being strategically vague here*  As a producer is it better to sacrifice 0-2 bushels of soybean yield or 10-20 bushels of wheat grain yield and 0.5 tons of straw?  

      As we all know mother nature holds the ultimate trump card on whether we will get our winter wheat crop established in that optimal window. These aforementioned strategies are relatively low risk to the farmer and regardless of what weather patterns we run into are agronomically sound.

      Soybean Planting Date and Maturity Group Considerations for 2016.

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      Authored by Adam Gaspar and Shawn P. Conley

      Early May planting in Wisconsin has been documented to increase yield due to increased light interception (Gaspar and Conley, 2015).  In theory, earlier planting can potentially intercept greater amounts of solar radiation due to a longer growing season and therefore longer maturity group (MG) soybean varieties may be better suited to maximize yield if they can mature before a hard fall frost.  2015 provide many WI growers with a longer than normal growing season due to favorable early spring planting condition and a later than normal fall frost.  Yet, in some instances (weather or logistical problems) planting can be delayed or replanting may be needed. Therefore, investigating the effect of different MG’s at multiple planting dates across the state would be useful.  Thus, DuPont Pioneer and the Wisconsin Soybean Marketing Board have funded a 3-year study to examine proper MG selection at 5 different planting dates across the state to maximize yield.  So let’s look at the 2014 and 2015 preliminary data:

      Trials were conducted at Arlington, Hancock, and Spooner, WI.  The five planting dates at each location were planting roughly on: (1) May 1th, (2) May 20th, (3) June 1st, (4) June 10th, and (5) June 20th.  Planting after June 20th is not recommended in WI.  Two varieties within each realistic MG from a 2.5 all the way down to a 00.5 were tested depending upon the location and planting date and are displayed in Table 1.  
      Table 1. Maturity Group’s tested within each location and planting date.
      Planting Date
      Arlington
      Hancock
      Spooner
      1 (May 7th)
      2.5, 2.0, 1.5
      2.5, 2.0, 1.5
      1.5, 1.0, 0.5
      2 (May 20th)
      2.5, 2.0, 1.5
      2.5, 2.0, 1.5
      1.5, 1.0, 0.5
      3 (June 1st)
      2.0, 1.5, 1.0
      2.0, 1.5, 1.0
      1.0, 0.5, 0.0
      4 (June 10th)
      2.0, 1.5, 1.0
      2.0, 1.5, 1.0
      1.0, 0.5, 0.0
      5 (June 20th)
      1.5, 1.0, 0.5
      1.5, 1.0, 0.5
      0.5, 0.0, 00.5
      I’ll start with the easy and redundant part, get your soybeans in the ground ASAP to maximize yield.  This is very evident again in this trial, where Figure 1. shows the effect of planting date across all MG’s (varieties) tested in 2014 and 2015.  Interestingly the yield decline for delaying planting was similar between years at Hancock and Spooner of approximately 0.46 and 0.23 bu/a/day, respectively.  However, at Arlington the yield decline was not as severe in 2015 compared to 2014, which was likely due to the abnormally late fall in 2015.  Never the less, if the soil is fit, soil temps are near 50 ˚F, and the forecast is favorable….. get the planter rolling!

      Figure 1. Dots represent the mean yield within each planting date for each location.  The average yield loss per day for delaying planting past May 1st is presented in the legend.
      However, the question still remains for many producers, should I use a longer maturating variety in early planting situations (very possible again in 2016) and should I switch to an earlier maturing variety when planting is delayed? 
      Table 2. Effect of Maturity Group on Yield tested within each location and planting date, during 2014 and 2015
      Planting Date
      Arlington
      Hancock
      Spooner
      1 (May 1th)
      2.5
      2.5
      1.0
      2 (May 20th)
      2.5
      2.5
      1.0
      3 (May 30th)
      2.0
      2.0
      0.5
      4 (June 10th)
      2.0
      2.0
      0.5
      5 (June 20th)
      0.5
      0.5
      0.5
      The numerically highest yielding MG for each planting date and location.  MG that are bold and colored red were significantly higher at the  P ≤ 0.05

      Combining the 2014 and 2015 data, 8 out of 15 location x planting date combinations displayed a significant effect of MG on yield (Table 2). 

      At Arlington and Hancock, using the longest MG resulted in the highest yield within dates 1-4 and was significant 7 of 8 times. Within planting date 5 the shortest MG (0.5) yielded the highest numerically, but this was not significant and the MG 1.5 varieties did not mature before the fall frost in 2014.  Therefore, planting a portion of your acres to slightly longer MG than normal within May can provide the opportunity for greater yields with no additional dollars spent.  In addition, when planting is delayed into June, switching to a variety much more than 0.5 MG earlier than a full season variety (2.5 MG) may limit yield potential.  However, if planting is delayed until mid to late June or more likely replanting is needed, a variety that is at least a full MG earlier should be considered to avoid fall frost damage.
      At Spooner, MG selection was not as critical and only planting date 5 saw a significant effect of MG on yield where the 0.5 MG out yielded the 0.0 and ultra-early 00.5 MG varieties.  Therefore, northern WI growers can maximize yield and avoid fall frost damage using varieties within a narrow MG range (1.0  – 0.5). However, growers may consider trying a slightly longer maturing soybean on a portion of their acres when early planting is possible, because of the “potential”, but not guarantee, for higher yields with no additional dollars spent.
      In conclusion, variety selection heavily based upon the MG is not a silver bullet to increasing yields, however it does provide the “potential” for higher yields with no additional dollars spent. Therefore, growers should give consideration to MG when selecting varieties, but past local and regional performance, disease package, scn-resistance, and etc. should take precedence.
      References:
      Gaspar, A.P. and S.P. Conley. 2015. Responses of canopy reflectance, light interception, and soybean seed yield to replanting suboptimal stands. Crop Sci. 55:377-385.

      Wisconsin Soybean Marketing Board Continues Free Nematode Testing Program for 2016

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      Four out of every five animals on earth today is a nematode so it is not surprising that agricultural fields are home to many nematode species. Fortunately, most nematodes are beneficial to crop growth and soil health because their activities help decompose crop residues and cycle nitrogen and other nutrients. Pest nematodes do not threaten yield if their numbers remain low. The key to avoiding population explosions of nematode pests is to be proactive – know what the situation is and take appropriate measures when nematode numbers indicate a problem is brewing. 
      The WSMB sponsors free nematode testing to help producers stay ahead of the most important nematode pest of soybean, the soybean cyst nematode (SCN) (Figure 1). 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.

      Figure 1. WI Counties Confirmed to Have SCN as of 2013.

      In 2016, the WSMB is again offering the expanded 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.

      Free soil sample test kits are available now and can be requested at (freescntest@mailplus.wisc.edu).
       

      For more information on SCN testing and management practices to help reduce the losses from this pest, please contact: Shawn Conley: spconley@wisc.edu; 608-262-7975 or visit www.coolbean.info. 
      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.

      Factors to Consider While Assessing Your 2016 Winter Wheat Crop Stand and Spring Nitrogen Timing

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      As the snow begins to melt and we finally put the 2015/16 winter behind us, many growers and consultants alike are beginning to venture out to their winter wheat fields to assess winter injury and nitrogen timings. Though it is a bit premature to make any rash decisions regarding crop destruction here are a few considerations for assessing your spring 2016 winter wheat stands.

      1. As you look across your wheat landscape vibrant green patches will be interspersed with drab brown areas. The brown areas do not necessarily indicate those plants are dead.
        2016 Arlington Winter Wheat Variety Trial – Roadside Assessment
        2016 In Field Stand Assessment
        2016 Planting Depth and Tiller Assessment
        Growers and consultants can either reassess in a week or pull plants from the field and place in warm environments. Milk houses and kitchens work perfect. Root regrowth will appear from the crown and will appear as vibrant white roots as shown below.
        Spring Root Regrowth in Winter Wheat

        If plants do not recover our critical threshold for turning over a field is 12 to 15 live plants per square foot. Below this threshold is an automatic replant.

      2. Hot off the press (word press that is)…the N timing decision just got easier.  New research from Dr. Carrie Laboski’s program indicates that the optimal time to apply nitrogen to wheat in WI is green-up regardless of tiller count. For more detailed information check out her new blog article here entitled: Time your spring nitrogen applications to maximize winter wheat yield.
      3. Lastly remember that wheat grain in itself is only part of the revenue you capture with winter wheat. The price of winter wheat straw remains strong so please consider that revenue stream before any replant decisions are made.

      Winners of the 2015 WSA WI Soybean Contest are Announced

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      The 1st place winner in Division 4, Bahr Farms Inc. of Belmont, grew Asgrow AG2535 and harvested 89.23 bu/a.  In second place, Riley Bros. Farms of Darlington grew Asgrow AG2433 and harvested 88.85 bu/a.  In Division 3, David and Karen Wilkens of Random Lake won 1st place with NK S20-T6 Brand at 77.15 bu/a, and in 2nd place, Echo-Y Inc. of Loganville harvested 75.93 bu/a with NK S20-T6 Brand.  In Division 2, Oeh My Farm of Abbotsford achieved 79.72 bu/a from Asgrow AG1431 for first place.  In 2nd place, J-Mar Hillside Acres of Luxemburg harvested 74.17 bu/a from Steyer 1140L soybeans.  In Division 1 at 75.67 bu/a was David Lundgren from Amery who planted Croplan R2C1494.  2ndplace winner in Division 1 was Jerry Koser from Almena.  He harvested 60.27 bu/a from DuPont Pioneer 91M10. 

      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 608-262-7975 or spconley@wisc.edu

      Finalists for the 2015 WI Soybean Yield Contest are Announced

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      The 2015 growing season proved to be a unique challenge for many WI soybean growers.  Given these widespread challenges however, we again experienced great interest in the 2015 WSA/WSMB Soybean Yield Contest.  The top two entries in each division (in no particular order) were:

      Division 4: 
      • Jon Riley, Darlington (planted Asgrow AG2433)
      • Dale and Kevin Bahr, Belmont (planted Asgrow AG2535)
      Division 3:
      • David Wilkens, Random Lake (planted NK S20-T6 Brand)
      • Derek Yanke, Loganville (planted NK S20-T6 Brand)  
      Division 2:
      • Jim Salentine, Luxemburg (planted Steyer 1140L) 
      • Craig Oehmichen, Abbotsford (planted Asgrow AG1431) 
      Division 1: 
      • David Lundgren, Amery (planted Cropland R2C1494) 
      • Jerry Koser, Almena (planted DuPont Pioneer 91M10)
      The final ranking and awards will be presented at the 2016 Corn Soy Expo to be held at the Kalahari Convention Center, Wisconsin Dells on Thursday February 4th 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 608-262-7975 or spconley@wisc.edu

      Start Managing for Fusarium Head Blight Now Before You Plant the 2015/16 Crop

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      By Shawn P. Conley and Damon Smith

      The 2014 and 2015 WI winter wheat crops both endured significant Fusarium head blight (FHB or scab) incidence as well as mycotoxin (vomitoxin) dockage and outright rejections. Here are a few considerations for managing FHB before the 2015/16 crop even goes into the ground.

      1.      Crop rotation matters. Data from our long-term rotation studies indicate that wheat following soybean provides the greatest yields. The next best options are wheat following corn silage (6.5% less) then corn for grain (21% less). Wheat following alfalfa or another leguminous crop are also good options, though the N credits following alfalfa may best be served going to corn. Furthermore, background fungal pressure (residue on and in soil) from the FHB fungus will be greater following corn then soybean or another legume, however know that spores that infect your wheat crop can arrive from  outside the field. Please click to see more information on the Top 8 Recommendations for Winter Wheat Establishment in2015.  
      2.      Variety selection matters. Data from our 2015 WI Winter Wheat Performance Test shows variable yield and disease performance among the varieties listed. Select those varieties that have both good to excellent FHB resistance and high yield. When evaluating FHB resistance, low numbers for both FHB incidence and severity can be helpful, but the major focus should be placed on FHB incidence (measure of the number of FHB-symptomatic plants in a stand).
      3.      Application timing matters. One of the biggest challenges year in and year out is improper fungicide application timing. Our data suggests that on susceptible (Hopewell) or moderately susceptible varieties (Kaskaskia) equal efficacy of the fungicide Prosaro at a rate of 6.5 fl oz/acre can be achieved when applied between Feekes 10.5.1 (anthesis) and 5 days after anthesis. Given the variability of head emergence and anthesis across a landscape it may prove best to wait a few days until the whole field is flowering than to apply too soon.  If the extruded anthers have turned from yellow to white across the whole field then you are likely too late. Remember it roughly takes a wheat head 7 days to completely self-pollinate.
      Fusarium head blight incidence ratings for four soft red winter wheat varieties treated with Prosaro SC fungicide at 6.5 fl oz/a at anthesis (Feekes 10.5.1), five days after anthesis, or not treated in Wisconsin in 2015.
      Hopewell (Susceptible)
      Kaskaskia (Moderately Susceptible)
      Pro 200
      (Moderately Resistant)
      Sunburst (Moderately Resistant)
      Prosaro SC @ 6.5 fl oz/a (Feekes 10.5.1)
      9.5b
      2b
      0.5
      4
      Prosaro SC @ 6.5 fl oz/a (5 days after Feekes 10.5.1)
      7.5b
      5.25b
      2.75
      2.75
      Non-treated control
      31.25a
      17.5a
      3
      1.5
      Pr>F
      0.01
      0.01
      ns
      ns
      LSD
      6.44
      6.44
      ns
      ns
      4.      Choose the right fungicide class. Make sure you use the appropriate fungicide product and class to manage FHB. The label for products containing strobilurin active ingredients (FRAC group 11) ends prior to flowering. Late application can actually lead to increased mycotoxin levels. Triazole containing products (FRAC group 3) are recommended for FHB control. For a list of products and efficacy ratings, visit the Field Crops Fungicide Information Page. 
      5.      Harvest timing and flash drying. The word on the street is that in 2016 elevators will push growers to harvest early (18% moisture or higher) and subsequently dry grain to mitigate mycotoxin levels. While drying grain to 13% or less moisture is a good storage practice, know this process may kill the pathogen but any mycotoxin levels already in the grain will not dissipate. Vomitoxin is a very stable molecule and IS NOT degraded by heat, freezing, or drying.     

      The Nebulous of Non-Nodulating Soybean in 2015 and Again in 2016 and Again in 2017

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      I have received a deluge (pun intended) of questions regarding the overall lack of soybean nodulation and general pale green coloration of the crop. As a doctor….well Ph.D….I prescribe less rain, sunshine, and call me in two weeks if the problem still exits… Outside of this obvious issue here are the four most common questions I have received and my responses for your consideration.

      1. Why is nodulation such a problem this year? Abiotic stress such as low pH (≤ 6.0), saturated or droughty soils and cool soil temperatures can negatively impact nodulation (Valentine et al. 2011). Duzan et al. (2004) reported that root hair deformations (a physiological precursor to rhizobia infection and nodulation) was 64 and 82% of the control when rhizosphere (root zone) temperatures were 59 and 63 degree F when compared to 77 degrees F. This suggests that the cool soil temperatures we have been experiencing have likely limited the infection sites available for nodulation to occur. This effect has likely been exacerbated in no-till or compacted conditions. In short less nodulation sites on the roots means increased likelihood for less nodules.  
      2.  I double inoculated my soybeans on virgin ground and my nodule count is really low? First, please refer to #1 above regarding abiotic stress on soybean nodulation. Secondly remember to read and follow the application, compatibility, and planting timing of inoculants. In reading through various inoculant labels today, I saw everything from ‘not tested’ to ‘not compatible to plant within hours to weeks to months of application’. Lastly remember there is a poor correlation between nodule number and N2 fixation, so don’t get overly concerned about nodule count; it is nodule efficiency that matters and you can’t measure that by counting. In short, read the labels and make sure everything is compatible and your application and planting window is adequate prior to purchasing the product.
      3. How long will soybeans continue to put on new nodules? Dr. Purcell indicated that they can measure very active N2 fixation almost until the end of seedfill (personal communication). Given the normal life span of an active nodule is 4-5 weeks, this would suggest that soybean will continue to put on new nodules (if the environment is conducive and rhizobia are present) until R6 soybean (late pod fill).   
      4. Should I apply nitrogen to these poorly nodulating soybeans, and if so, how much? My general answer is no and none. First of all, the application of nitrogen to soybean beyond a “starter” rate (≤~30 pounds) will lead to a rapid and dramatic inhibition of N fixation (Sinclair, 2004). Though it does not appear that the applied nitrogen is directly damaging to the N fixation machinery (nodules), it will reduce or stop fixation. If the soil NO3 levels drop, then N fixation can resume in about a week (Sinclair, 2004). Over-application of N will shut down whatever rhizobia is actively working. Furthermore, our 2014 and 2015 data shows that a soybean plant takes up 3.75 pounds of N in above-ground tissue per bushel of grain. So a 80 bu/a crop removed 302 pounds of N/a. This does not account for below-ground uptake or nitrogen loss and efficiency from the applied nitrogen. In short, that is tough math to get a positive ROI on. 

      Literature cited:


      Gaspar, A., C. Laboski, S. Naeve, and S.P. Conley. 2017. Dry Matter and Nitrogen Uptake, Partitioning, and Removal across a Wide Range of Soybean Seed Yield Levels. Crop Sci. doi: 10.2135/cropsci2016.05.0322 

      Dr. Larry Purcell (personal communication 7/16/15)

      H. M. Duzan, X. Zhou, A. Souleimanov and D. L. Smith*. 2004.Perception of Bradyrhizobium japonicum Nod factor by soybean [Glycine max (L.) Merr.] root hairs under abiotic stress conditions. Journal of Experimental Botany, Vol. 55, No. 408, pp. 2641–2646, December 2004 doi:10.1093/jxb/erh26

      Sinclair, 2004. Improved Carbon and Nitrogen Assimilation. “In: Soybeans: Improvement, Production, and Uses.” Third Edition. Agronomy No.16. Edited by H.R. Boerma and J.E. Specht. 

      Valentine, A., V. Benidito, and Y Kang. 2011. Legume Nitrogen Fixation and Soil Abiotic Stress: From Physiological to Genomics and Beyond. Annual Plant Reviews. 42:207-248.

      Last Night’s Cold Temperatures Had No Impact on Emerged Soybean or Your Wheat Crop

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      Coauthored by Dr. Shawn P. Conley (15%) and Dr. Jim Specht (85%)
      Last nights cold temperature has led to an influx of questions regarding the potential impact on either the wheat crop or emerged soybean seedlings. In short there is nothing to worry about in either crop. In the case of wheat, which is still in the jointing growth stage, cold temperature would need to reach 24 degrees F or less for 2 plus hours before injury occurred (Please see Recent Cold Temperatures will have Little Impact on WI Winter Wheat Crop for more details). 
      In the case of soybean I was fortunate enough to be copied on this email from Dr. James Specht (please see below) which saved me a few hours of library time today so thank you Jim.
      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 tonight where the cotyledons are and check it just before dawn (when the soil surface temp reaches its nadir for a 24-hour temperature cycle) and send out an e-mail blog to your producer colleagues early the next day.   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).

      Soybean Planting Date by Maturity Group Considerations for 2015

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      Article coauthored by Dr. Shawn P. Conley and Adam Gaspar
      Early May planting in Wisconsin has been documented to increase soybean seed yield due to increased light interception (Gaspar and Conley, 2015).  In theory, earlier planting can potentially intercept greater amounts of solar radiation due to a longer growing season and therefore longer maturity group (MG) soybean varieties may be better suited to maximize yield if they can mature before a hard fall frost.  Unlike 2013 and 2014, 2015 may provide growers with an opportunity to plant their soybean crop earlier than ever before. Yet, in some instances (weather or logistical problems) planting will be delayed or replanting may be needed. Therefore, investigating the effect of different MG’s at multiple planting dates across the state would provide WI growers with BMP’s for soybean establishment regardless of planting timing.
      To answer this question field trials were initiated at Arlington, Hancock, and Spooner, WI in spring of 2014.  The five planting dates at each location were planting roughly on: (1) May 7th, (2) May 20th, (3) June 1st, (4) June 10th, and (5) June 20th.  Planting after June 20th is not recommended in WI.  Two varieties within each MG from a 2.5 all the way down to a 00.5 were tested depending upon the location and planting date and are displayed in Table 1.

      Table 1. Maturity Group’s tested within each location and planting date.
      Planting Date
      Arlington
      Hancock
      Spooner
      1 (May 7th)
      2.5, 2.0, 1.5
      2.5, 2.0, 1.5
      1.5, 1.0, 0.5
      2 (May 20th)
      2.5, 2.0, 1.5
      2.5, 2.0, 1.5
      1.5, 1.0, 0.5
      3 (June 1st)
      2.0, 1.5, 1.0
      2.0, 1.5, 1.0
      1.0, 0.5, 0.0
      4 (June 10th)
      2.0, 1.5, 1.0
      2.0, 1.5, 1.0
      1.0, 0.5, 0.0
      5 (June 20th)
      1.5, 1.0, 0.5
      1.5, 1.0, 0.5
      0.5, 0.0, 00.5

      Let’s start with the easy and redundant part, get your soybeans in the ground ASAP to maximize yield.  This is evident again in this trial, where Figure 1 shows the effect of planting date across all MG’s (varieties) tested in 2014.  If the soil is fit, soil temps are near 50 ˚F, and the forecast is favorable….. get the planter rolling!
      Figure 1. Dots represent the mean yield within each planting date for each location.  The average yield loss per day for delaying planting past May 7th is presented in the legend.
      However, the question still remains for many producers, should I use a longer maturity variety in early planting situations (very possible in 2015) and should I switch to an earlier maturing variety when planting is delayed?  

      Table 2. Effect of Maturity Group on Yield tested within each location and planting date.
      Planting Date
      Arlington
      Hancock
      Spooner
      1 (May 7th)
      NS
      NS
      NS
      2 (May 20th)
      NS
      NS
      NS
      3 (May 30th)
      NS
      **
      NS
      4 (June 10th)
      NS
      NS
      NS
      5 (June 20th)
      **
      NS
      NS
      ** MG had a significant effect on yield at the  P ≤ 0.05 level

      Based upon the 2014 data, only 2 out of 15 location x planting date combinations displayed a significant effect of MG on yield (Table 2).  So the moral of the story is that within a realistic MG range for your region and planting date, variety selection should be based heavily upon the varieties past local and regional performance, disease package, and etc.  Variety selection heavily based upon the MG is not a silver bullet to frequently increasing yields.
      However, there are always caveats…… Growers may consider trying a slightly longer maturing soybean on a portion of their acres because there is a “potential”, but not guarantee, for higher yields with no additional dollars spent.  Within planting date 1, there was no significant MG effect, but MG 2.5 did yield the highest numerically in Arlington and Hancock with no fall frost damage, while the same is true for MG 1.5 in Spooner.  The longest MG tested within each planting date in our study numerically yielded the highest through June 10th(planting date 4). 
      On the back end of the planting season, the inverse was seen.  Within planting date 5 at Arlington and Hancock, MG 1.5 did not mature before the first fall frost and was the lowest yielding.  Therefore, growers may consider switching to an earlier maturing variety as planting is delayed into June.  If switching to an earlier maturing variety, don’t use a variety less than 0.5 MG earlier than a full season variety (2.5 in southern WI) in early June.  However, if planting is delayed into mid to late June then a variety that is greater than or equal to a full MG earlier should be considered.
      Acknowledgements: The authors would like to thank the Wisconsin Soybean Marketing Board and DuPont Pioneer for supporting this research.
      References:
      Gaspar, A.P. and S.P. Conley. 2015. Responses of canopy reflectance, light interception, and soybean seed yield to replanting suboptimal stands. Crop Sci. 55:377-385.