Soybean Seeding Rates and Seed Treatments: What Did We Learn?

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1 Soybean Seeding Rates and Seed Treatments: What Did We Learn? Freeport, IL- In 2018, Highland Community College decided to develop their 8-acre research farm in order to provide an outdoor classroom for students to gain hands on experience with experimental design and crop production. With donations from local sponsors and a large commitment of time and hard work from community members Jace Kempel and Keith Hinrichs, this exciting opportunity became a reality. To best take advantage of this opportunity, Highland partnered with University of Illinois Extension to develop meaningful research projects to provide insight to local producers. The goals for 2018? testing the effects that various soybean seeding rates and seed treatments have on both yield and return on investment. Soybean producers are facing exceptionally tight margins, and as such the need for increased efficiency and return on input investment are paramount to a successful operation. Due to improved genetics and production practices, soybean growers are now more aware of the importance of using appropriate seeding rates and seed treatments; this is meant to reduce risk and economically improve yield goals. The 2018 growing season was a challenge for producers to say the least. A cold, wet spring prevented us from getting the crop in the ground as early as we wanted, but as soon as we planted things changed in a hurry. Above average temperatures and rainfall throughout May and June led to rapid plant growth and development and had producers expecting record breaking soybean yields across the state. Before we knew it the crop was mature and ready to be cleared out of the field, but mother nature had something to say about that; cool temperatures and excessive late season rains severely delayed harvest into December. During this time, many other issues popped up including: insect pests, disease, lodging, and pod shattering. One can only imagine what the state-wide yields would have been had we been able to clear the fields on time... This truly was a strange year in Northern Illinois. This research project culminated in a field day, bringing together over 70 local producers, agronomists, and most importantly students; attendees were able to see presentations regarding production issues from University of Illinois Extension staff including Dr. Nathan Kleczewski, Phillip Alberti, and Russ Higgins. This partnership will continue into 2019 and beyond as research projects are underway to assess how nitrogen application timing and cover crop implementation impact yield potential and nitrate loss in Northwest Illinois. We are greatly looking forward to the future of this partnership, and the implications it has on producers, students, and the community. Now, let s talk about the research project The experiment was conducted in 2018 at the Highland Community College test plot in Freeport. There were two separates experiments which were conducted. The first experiment assessed soybean seeding rates (90, ,000 seeds ac -1 ) while the second experiment assessed seed treatments (control, rhizobial inoculant, PPST, and PPST + ilevo); the seeding rate used for the seed treatment study was 155,000 seeds ac -1. Seed treatment PPST contains an insecticide and fungicide component; ilevo is a seed treatment used as protection against Soybean Cyst Nematode (SCN). Separate soybean varieties were used in each experiment. For both experiments, a fungicide/insecticide application and a control were also included to evaluate their impacts on

2 yield on return on investment. 600 foot strips were planted in the first week of May on 30-inch rows with fungicide/insecticide applications applied in mid-july; strips were harvested in Late- October. Importantly, the results of this study are from one site-year only and thus conclusions about these seeding rates or treatments can t be made; however, observations from this study can still provide value to local producers and are worth discussing. Return on investment was primarily used as a learning tool in the classroom, so exact values will not be given here; for more information about varieties, seed treatments, and insecticide/fungicide applications contact Phillip Alberti, Crop Science Educator with University of Illinois Extension in the College of Agricultural, Consumer, and Environmental Sciences at palberti@illinois.edu, or on Twitter (@NorthernILCrops). 82 Soybean Yield in Response to Seeding Rate Soybean Yield (bu ac-1) Seeding Rate (1000 Seeds ac-1) With Insecticide/Fungicide Application Without Insecticide/Fungicide Application Observations - Seeding rate of 90,000 seeds ac -1 resulted in the greatest yields and return on investment; yields were comparable among fungicide/insecticide applications and control. Return on investment was greatest in the control. - Reduced seeding rates (90, ,000 seeds ac -1 ) with an insecticide/fungicide application resulted in comparable yields of ~78 bu ac -1 - As seeding rates increase, the benefit from a fungicide/insecticide application becomes more apparent. Discussion If populations are too high, plants compete with each other and lodge. If the rate is too low, the producer is wasting space and lowering yield potential. Plant stands at ~100,000 plants ac -1 with good seeding establishment and development have been shown to produce optimal yields on highly productive soils;

3 however, researchers feel safer when plant populations are in-between 100, ,000 seeds ac -1 as shown here. Although these populations seem too low to reach optimal yields, there is a safety factor built in due to their ability to flex. Soybeans have the ability to adjust growth and development in response to seeding rates and environmental conditions. Variation in plant development is often expressed in the amount of branches and pods the soybean plant develops. For instance, lower plant populations often compensate for reduced stands by increasing lateral branching and subsequent pod formation; conversely, higher plant populations may produce taller, thinner plants with reduced pod formation. These responses are important to consider as it is pods per acre, and ultimately seeds per acre that determines yields and not plants per acre. If we consider this study in terms of the 2018 growing season, we can make some important observations. Growing conditions in 2018 appeared to favor reduced seeding rates (90, ,000 seeds ac -1 ) with an insecticide/fungicide application. Above average temperatures, moisture and good soil fertility provided an environment which allowed the soybean crop to develop vigorously. Due to the suitable growing conditions, the soybeans in the reduced seeding rate treatments were able to flex to maximize yields. These alterations in plant development can have beneficial, or detrimental, impacts on yield, harvestability, and pest management. For example, soybeans planted at lower seeding rates are often shorter with pods closer to the soil line which can make harvest more difficult; higher seeding rates can produce taller plants with reduced branching and pod formation, reducing yields. It is for these reasons that choosing the appropriate seeding rates is so important to maximize profitability and productivity. Plant population also impacts pest and disease management. Greater plant populations create higher levels of competition between plants and produce a thicker canopy, trapping moisture and providing a suitable environment for insect and disease pressures to impact plant development. In fields in which white mold is prevalent, for example, dropping seeding rates can be the first line of defense when combatting the fungal pathogen. In 2018 harvest was delayed so yield was likely lost due to prolonged exposure to pests, disease, and the elements (which can result in lodging and pod shatter); this is particularly true in the higher seeding rates in which diseases and pest pressure was greater allowing the reduced seeding rates to have greater performance. Additionally, higher seeding rates illustrated the need for insecticide/fungicide applications to optimize yield, particularly when late season weather is not conducive for dry-down and harvest. Since greater plant populations don t necessarily mean greater yields so this will continue to be a crucial management decision as seed prices continue to rise. With traited seed costs as high as they are, input costs can drop substantially by cutting seeding rates down, even marginally. For example, at $60/unit, producers could save ~$10/acre just by dropping seeding rates from 175,000 to 150, 000. Take a look here and see how much you could save by adjusting seeding rates! Finding the right rate for you may take some on-farm trials, but the research is there to support these claims.

4 78 Soybean Yield in Response to Seed Treatment Yield (bu ac-1) With Fungicide/Insecticde Application" Without Fungicide/Insecticde Application " 62 Control Rhizobial Innoculant Seed Treatment PPST-Full PPST- Full + ilevo Observations - Seed treatments resulted in increased yields when compared to the control. - Insecticide/Fungicide applications resulted in greater yields (all treatments) and return on investment (for all treatments except the control). - ilevo resulted in a ~2 bu ac -1 yield increase over full seed treatment (PPST) alone. - Full seed treatment (PPST) + ilevo with fungicide/insecticide treatment resulted in greatest yields and return on investment. Discussion Seed treatment efficacy varies due to seed quality and environmental conditions. In many cases use of a seed treatment with high quality seed has shown little effect on seedling emergence and vigor; however, use of seed treatments on low quality seed can increase field emergence significantly. Environmental conditions during germination can also influence the efficacy of seed treatments; in situations where conditions at planting are conducive, seed treatments may not be effective. Alternatively, if conditions at planting favor disease, seed treatments may be an effective option. Cost and active ingredients for seed treatments are important, so decision making using pest and disease history and active ingredients can go a long way. Cold, wet conditions at planting provided an environment suitable for many seedling diseases which were present in the field with varying severity. Conditions like this can result in areas with poor stands early on in the season due to damping off (pythium, phytophthora, rhizoctonia). Suitable growing conditions during vegetative and (mostly) throughout flowering provided optimism for exceptional yields, however the impacts of the cool, wet spring became evident later on in the growing season when some soybeans began to die pre-maturely due to SDS and brown stem rot.

5 The results from 2018 show that soybean yields and return on investment responded positively to seed treatment. While the full seed treatment (PPST only) provided a substantial yield benefit over the control, the full seed treatment (PPST) + ilevo provided the greatest yields and return on investment when used in conjunction with a fungicide/insecticide application. These results also show that soybean yields and return on investment responded positively to insecticide/fungicide applications; this can likely be explained due to the excessive late season rains which delayed harvest enabling prolonged exposure to insect pests, disease, and other abiotic stresses. Overall, these results suggest that a seed treatment package and/or fungicide application can be beneficial when cool, wet conditions are present at planting or when late-season conditions are not conducive for harvest.