Maturity, yield potential, plant type, lodging resistance, seed size, as well as disease and pest resistance each play a major role in how soybean varieties perform. Read on to learn more about these factors and how they affect yield.

Maturity
Photoperiod. Soybean maturity is regulated by both photoperiod (day length) and temperature. Soybeans are classified as short-day plants because short days initiate flowering. Actually, the duration of darkness is the controlling factor—experiments show even a one-minute interruption of darkness can retard floral development. Day length increases in the summer as latitude increases—the farther north you are, the higher your latitude.

 

Northern varieties, in contrast to Southern varieties, initiate flowering with longer days. A variety planted south of its adaptation zone exhibits accelerated flowering, limited growth and reduced yield. Planting a variety north of its adaptation zone will result in delayed flowering with a potential for frost damage.

Temperature. The rate at which soybeans develop and mature also is affected by temperature. Warm temperatures accelerate flowering and maturity, whereas cool temperatures delay these two stages. Therefore, a delay in planting shortens the life cycle of a soybean variety, since it is exposed to both warmer temperatures and shorter days. Because soybeans respond in this manner, it is much more difficult to classify them on the basis of maturity days or growing degree days, as is the case in corn.

Unlike corn, adapted soybean varieties can be planted later without switching to an earlier maturity group. Even in northern growing areas, adapted soybean varieties can usually be planted through mid-June without significant risk of crop failure due to frost, because the total maturation period is shortened.

YIELD POTENTIAL
Some say that most soybean varieties available today have the potential of yielding more than 100 bushels per acre. However, this yield potential is rarely reached because of yield-limiting factors such as moisture stress, pests and low fertility. Many of these factors are out of a grower’s direct control or require input investments well beyond the value of the realized gains in yield.

Spreading risk. Given these production limitations, a grower’s best alternative is spreading risk by planting several locally adapted varieties that vary in maturity, agronomic characteristics and genetic backgrounds, and are purchased from a trusted seed supplier. A grower should manage a “variety portfolio” in much the same way as an investor manages a stock portfolio. The goals of both are to minimize risk and maximize yield.

Variety selection. New varieties and new technologies are being introduced so rapidly that past variety selection methods may not work in today’s world. For example, while a grower may want to see a favorable three-year yield average before selecting a variety, that might not be the best approach. By waiting, the grower may continue to plant an older variety that has been surpassed by releases too new to have accumulated three-year track records.

Expert advice. The credibility, experience, skills, knowledge and trustworthiness of your local seed representative are what you must ultimately rely on to make the best seed choices. Knowledge of multiple crop inputs, products, agronomic practices and your specific needs is critical. With technology becoming much more complicated and the business of farming much more sophisticated, the stakes are too high not to seek expert advice. When selecting varieties to maximize yield, trust the knowledgeable advice you receive from your CROPLAN GENETICS® seed local agronomist.

Growth habit. Soybeans are classified into three types of growth habit—determinate, semideterminate and indeterminate. Stem elongation and flowering time determine the growth habit type.

• Determinate varieties do not get appreciably taller after flowering begins, and flowering lasts for a shorter period of time.
• Semideterminate types have intermediate growth with only a modest increase in height occurring after the onset of flowering.
• Indeterminate varieties have stems that continue to elongate after the initiation of flowering. This type may double or even triple in height after flowering. Most CROPLAN GENETICS® varieties are indeterminate.

Plant Type
Soybean varieties are classified as upright, bushy or intermediate, depending upon the degree of branching.

• Upright varieties have fewer branches and form a more upright plant with a narrow leaf canopy. These varieties perform better when planted in narrow rows, drilled or broadcast seeded.
• Bush-type varieties perform better in wide rows because the plant branches and expands, making use of the available row space. These varieties provide better row coverage and make more efficient use of sunlight.
• Intermediate types fall between upright and bushy types.

Each CROPLAN GENETICS® soybean variety is classified into one of the three groups, but most are intermediate types, providing growers with the most flexible seeding options.

Lodging Resistance
Lodging increases field harvest losses since pods lying on the ground are difficult to harvest. Lodging at or before podfill can reduce yields by as much as 20 to 30 percent. Overplanting, especially with drilled soybeans, can cause plants to lodge because plants grow taller and spindlier as they compete for light. A plant that is too tall and spindly to support itself may lodge. Tall, bush-type varieties tend to be the most susceptible to lodging, especially when seeded in narrow rows or drilled.

CROPLAN GENETICS® varieties are rated on a one-to-nine scale for lodging, with one being best and nine being worst. We also rate a variety’s ability to adapt to wide and narrow rows. Differences in standability have been observed, but most CROPLAN GENETICS® varieties are rated in the one-to-three range (three is very good).

Seed Size
No consistent relationship has been found between soybean seed size and yield. Although genetics play a role, the environment in which the seed is grown probably has the most effect on seed size in any given year. We publish average seed size ranges for varieties in our product tech sheets. After harvest, we make actual seed size information available to our sellers.