ILSOYADVISOR POST

Understanding the Critical Factors That Influence Soybean Yield

Over the last several years, multiple factors have been studied that need to be considered to maximize soybean yields. One thing that we know for sure is that there are not any “silver bullets” that alone can help us achieve our goals, but rather a system of multiple yield-influencing factors. Some of the most influential factors that we have noted are planting date, variety selection, seed treatment, foliar fungicide and insecticide, plant nutrition, row spacing, and weed management.

Multiple years of studies have been conducted at the BASF Midwest Research Farm in Seymour, Ill., to better understand the impact that planting date has on soybean production and why it is so important. We know that soybeans are light harvesters and desire bright, sunny, conditions during pod fill. The challenge is that, unlike corn, soybeans are “source” limited and one of the most limiting factors that we have in soybeans is light interception, so developing strategies to help maximize canopy photosynthesis will lead to increased yields. One of the biggest advantages seen from early planting is the increase in light interception by the first day of summer. As you can see from the pictures taken in 2017 and 2018, the mid-April planting increased canopy closure anywhere from 17-43% compared to the mid May planting. Other physiological differences are influenced by early planting that can lead to increased yields. These include an increased number of main stem nodes, which means more pod opportunities, as well as beginning reproductive stages earlier and extending the duration of the reproductive phases. A five-year summary of planting date trials conducted at the Midwest Research Farm shows a strong trend of increasing yield when planting in mid-April vs delaying planting until mid-May. 

Variety selection has also shown to greatly influence yield. Choosing the highest yielding variety with the disease package and adaptability to your soils plays a large role in maximizing soybean yields. We know that variety selection can have as much as a 10 to even 20 bushel/acre impact on yield. While everyone wants to plant the plot winners, unfortunately not all of our fields are the same and it becomes very important to understand each variety’s strengths and weaknesses.  In the chart below, we see the last 10 years of testing from the University of Illinois OVT trials. To illustrate the difference variety selection can make, the highest yielding varieties and the lowest yielding varieties are compared to the test average. On average, there was a difference of 18.7 bushels between the highest performing varieties and the lowest performing varieties.

Not only is selecting the top performing varieties important, but also placing them in the correct environments to excel. Below we see a comparison of three high performing varieties, and their average yields across all environments are very similar. But as you start to look at how they perform in different environments, you start to see there could be as much as a 10 bushel/acre difference if they are placed in an environment that doesn’t match their strengths.    

Foliar applications of fungicide and insecticide at the R3 growth stage have shown to be one of the most consistent practices to maximize yield from field to field and year to year. Fungicide and insecticide applications have proven to be able to protect the plant from not only fungal diseases and insect pests that may be present, but also help mitigate environmental stresses like drought and high temperatures that impact our crops most every year. Trials conducted this year at seven locations across the state had anywhere from a 2-8.5 bushel/acre response to a fungicide and insecticide application. Surprisingly, the biggest yield responses this year didn’t necessarily come from disease protection but rather stress mitigation. The location with the largest yield increase was the location that experienced the most critical dry period. 

Maintaining plant health and delaying senescence also had an impact on seed fill and seed weight. From the trials mentioned above, 152 seed samples were collected, 76 treated with Revytek and Fastac and 76 untreated, and 1000 seeds were weighed per sample. When the samples were averaged and compared, Revytek plus Fastac treated seed weighed 5.6 mg/seed more than the untreated. Assuming an increase of 2 mg/seed equals a 1 bushel/acre increase, the combination of Revytek and Fastac provided a 2.8 bushel/acre increase from seed weight.

Plant nutrition is also a very important component for maximizing yields, but it is hard to put together a blueprint to fit all fields. There are many factors that influence plant nutrition that vary from field to field, such as soil fertility, soil biological populations, and the physical structure of the field. What we do know is maintaining good soil fertility levels and keeping the pH around 6.5-6.8 is a must. Although each field is different, we are seeing an increase in the number of fields that are showing sulfur deficiencies and a response from an application of sulfur. There are also fields that have shown positive responses to biologicals and inoculants in certain situations. Plant nutrition is important, but it is a factor that needs to be evaluated on a field by field basis that addresses the most limiting yield factor.

Weed control is also a very important factor for protecting soybean maximum yield potential. Emerged weeds in our fields compete with our crop for space and sunlight as well as water and nutrients. It is important to develop a comprehensive weed management plan that includes starting clean and utilizing residuals like BASF’s herbicide Zidua® PRO that bring multiple modes of action for controlling challenging weeds. Follow that up in season with an application planned to target small weeds and an additional residual herbicide for successful weed control and maximized yield.

There are many factors that influence soybean yield from year to year, and there is no “silver bullet”. Producing high yield soybeans requires building a system to manage factors that affect yield. Understanding these key factors that influence yield and putting together a strong plan that addresses the challenges that you face on your farm will help you get the most yield that you can year in year out.                         


Greg Ury

Greg is a BASF Seed Agronomist in Illinois. He grew up in Southern Illinois on his family farm where they raised soybeans and corn, as well as cattle and hogs. He received his B.S. degree in Agronomy from Murray State University and his M.S. degree in Agronomy from the University of Illinois and has been a Certified Crop Advisor since 1999. He has worked in various roles in ag industry over the last 24 years working with growers on implementing new practices to improve production in corn and beans.



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