Variety selection is one of the most important management decisions that influence soybean production. Maturity, seed quality, herbicide and disease resistance, and yield potential are key plant traits when choosing a variety.
Maturity group and yield
Soybean varieties are classified into maturity groups (MGs) based on their relative maturation times. These groups range from MG 000, suited for northern latitudes with shorter summer nights, to MG 9, which is adapted to tropical climates with high temperatures and shorter days. MGs are sometimes expressed using Roman numerals. A general guideline is that a difference of one maturity group equates to roughly a ten-day difference in maturity. Decimal numbers are often added to indicate finer gradations within a maturity group (e.g., MG 2.8 or 3.5), with each decimal representing about one day. Soybean breeders assign these MG numbers, and many commercial varieties include the MG number (and often a decimal) in their names, such as Brand ABC34.
In Illinois, most soybean acres are planted with MGs 2, 3, or 4, depending on the region (north to south). Early MG 2 varieties are typically grown in the northernmost part of the state, while early to mid MG 4 varieties are better suited for the southernmost areas. Using soybeans that fully utilize the growing season can improve yield, provided growing conditions remain favorable. However, very late-maturing varieties may not always produce higher yields than those maturing slightly earlier, even if they complete seed filling before frost. Figure 1 illustrates the yield response to maturity groups from the University of Illinois Variety Testing trials conducted over the past 15 years (2009-2023). In these trials, planting dates ranged from May 5 to May 15. Across all regions, mid-maturity varieties consistently outperformed both early and late varieties. On average, though, varieties within one bushel of the highest yield spanned about 0.5 maturity units on either side of the maximum yield.
Agronomic traits
Herbicide resistance
When selecting a soybean variety, herbicide-tolerance traits are crucial, especially in areas where herbicide-resistant weeds have affected production. There are many herbicide-tolerance trait packages available on the market that can be used individually or in combination to improve weed control. Additionally, consider the variety’s genetic resistance to common diseases on your farm. Most seed companies provide information on how their varieties respond to diseases, though complete resistance may not always be available for certain diseases.
Yield stability
Yield and yield stability are key factors to prioritize when choosing soybean varieties. Since environmental conditions vary from year to year, look for varieties that consistently perform well across multiple locations and seasons in your region. Selecting varieties within 0.5 units of the maturity group (MG) with the highest yield allows crops to mature over a week or two, which helps stagger the harvest without significantly affecting grain yield. It’s also important to consult knowledgeable seed company representatives, as they have the most accurate information on variety performance.
There are hundreds of soybean varieties on the market — nearly all developed by private companies — and choosing the best ones for your field may be challenging. To producers access unbiased soybean yield information, the University of Illinois Variety Testing Program conducts annual crop performance tests, including data on yields, average yields from the past two to three years, and protein and oil content. The results are published shortly after harvest and can be accessed here . While the number of varieties in these trials has decreased over time, producers can supplement this information with performance data from seed companies. Seed companies are highly competitive, which means that less-productive varieties are often not produced and sold.
Giovani Preza Fontes, Extension Agronomist
Reviewed in 2024