Yields are increasing about one-third of a bushel per acre per year due to genetic improvement.
Example of Wisconsin Soybean Variety Trial Results
Most soybean varieties have genetic yield potentials well over 100 bu/A.
The best measure of variety performance is a multi-location average and consistently high performance.
GxE interactions
- When a set of varieties is tested for yield over a range of environments, their rank order commonly changes, which indicates that some varieties are better adapted to a specific environment than others.
- Sometimes it is best to select varieties with characteristics that will help them perform well in the cultural system and environment to be used rather than on yield alone.
- For example, if excessive growth and lodging are problems, then select varieties that are medium to short in height with good standability. If the field has a history of Phytophthora, then select resistant or highly tolerant varieties to address that problem.

Maturity

Maturity groups (000-X)
Photoperiod
Types
- Determinant: at flowering, plant height growth stops.
- Indeterminant: at flowering, plant height growth continues (typically found in WI)
- Determinant semi-dwarfs: plants shorter in stature than determinant varieties
- Semi-determinant: plants that continue to grow slightly after flowering begins

With the exception of yield, which reflects the total response of a variety to a set of growing conditions, maturity is the most important criterion in selecting a variety. If a variety is too early or too late at a location, it will be limited in potential performance.

Soybean varieties are classified into 13 maturity groups, from Group 000 grown in Canada to Group X grown in the tropics.

Generally, each 10-day delay of planting in May delays maturity 3 to 5 days in the fall.

The earliest and latest varieties within a group may differ by as much as two weeks in maturity.

Maturity information should be used to select varieties that mature at different times to allow for timely harvest in the fall. Group II through 00 varieties are best adapted to Wisconsin conditions. The lines across the map are approximate limits of adaptation and are not meant to represent rigidly defined areas where a variety is or is not adapted. Cultivars from Group II to 00 when planted in mid-May in Wisconsin, will reach maturity by early September to early October, depending on the weather, location, and planting date.

The average date of maturity of most currently available soybean varieties is evaluated in the variety tests in Wisconsin.

Maturity is noted as when 95% of the pods have turned brown. This is not harvest maturity, but is the time when seeds are physiologically mature and additional dry matter will not be accumulated. Harvest maturity will be reached 10 to 20 days later, depending upon the weather.

Photoperiod

Soybeans are photoperiod (number of hours of light) sensitive.

When varieties are moved south of the area where they are typically grown:

they mature faster than normal,
resulting in seed fill occurring during the hot, dry period of July and August.

When varieties are grown north of where they are adapted:

maturity is delayed,
resulting in seed fill during the cool, short days of fall.
Frost before the crop reaches maturity is a possibility.

The latest variety used should be one that reaches physiological maturity just prior to the date when there is a 20 percent chance of a killing frost in the fall.

Yield performance will often tell us when a variety is too late or too early, since yields of these varieties-will be lower than those of adapted varieties.

The onset of flowering in soybeans is photoperiod controlled. Soybeans are classified as "short-day plants," which means the plants will develop vegetatively until a critical daylength is reached that "triggers" the flowering response. In Wisconsin, flowering usually begins in early July as the daylength decreases after the maximum daylength on June 21. This period is the time of the most flowering activity for adapted soybean varieties in Wisconsin.

Flowering

Indeterminant Types

Nearly all of the soybean varieties in maturity groups II and 00 are indeterminant types, with flowering activity
Flowering is spread over a 3 to 5 week period once the critical daylength has occurred.
In indeterminant types, flowering begins at the lower nodes and progresses upward on the plant.
The long flowering period allows these types to adjust to the effects of short-term stress or unfavorable environmental conditions.

Determinant Types

Determinant types of soybeans have a much shorter flowering period (2 to 4 weeks)
They cease main-stem growth once flowering has been "triggered," although vegetative branching may continue.
Flowering in determinant soybeans is generally simultaneous at all nodes.
Determinant varieties have about half the plant height and number of nodes compared to indeterminant types.
Determinant varieties may require higher seeding rates or narrow-row planting to provide more plant-to-plant competition and to produce greater height from the ground to the lowest pod.

Two modifications are the determinate semi-dwarf and semi-determinate varieties.

Determinate semi-dwarfs
- true determinate varieties
- half the height of normal varieties.
Semi-determinate varieties
- 6 to 10 inches shorter than indeterminant varieties
- add only a small amount of vegetative growth after flowering and podding begin.

Flowering periods of both types are slightly shorter than in commonly grown varieties. Determinate semi-dwarfs and semi-determinates are more lodging-resistant than taller types and may yield more in high productivity environments (50 + bu/A).

Management and Flowering

Because soybean flowering is controlled by photoperiod, planting date affects the size of the plant attained before flowering begins. Soybeans planted later have less time to develop vegetatively and thus will be shorter in size. Planting dates of May 10 to 20 provide long enough times of development for adequate vegetative growth with the indeterminant soybeans and provide good yield potential. Planting after June 1 generally results in lower yields due to reduction in the vegetative size of the plants. Pod formation and seed-filling periods are critical for the highest yield of soybeans. The photosynthetic rates of soybeans are highest at flowering and pod filling. Stress at these critical times, caused by drought, excess heat, mineral deficiency, etc., can cause the greatest yield reduction.

Several high yield potential varieties in maturity groups II and 00 are available for Wisconsin producers. Irrigation tends to delay maturity, and the early varieties have responded better to irrigation. In dryland production, the yield differences between early and late soybeans may not be as much, although full-season varieties will generally outperform early varieties in the long run.

Because of the potential for frost and late harvest, circumstances will seldom dictate choosing a variety that will mature too late. However, the following situations may suggest the selection of shorter-season varieties:

If planting winter wheat is frequently delayed by harvest of full-season soybeans, you may wish to use early maturing varieties for greater timeliness;
If planting is delayed until mid to late July, shorter-season varieties may be required;
If excessive lodging is a problem with full-season varieties, short-season varieties, which normally lodge less, may be used as a second choice to combat standability problems on highly fertile and moist soils.

Standability

Lodging scores are reported in performance test results. These ratings give an indication of standability in various environments and locations. Lodging reduces yield and makes harvest more difficult, so good lodging resistance is important. Lodging of soybeans at the beginning of seed fill, when beans start to increase in size, is most detrimental to yield. Taller varieties are generally more susceptible to lodging. Determinant varieties are virtually resistant to lodging.

Variety dependent

Both the genetic makeup of a variety and the environment in which it is grown can be responsible for standability problems.
Moist, fertile soils normally stimulate vegetative growth in soybeans and lead to tall lodging-prone plants.
Certain varieties are inherently more susceptible to lodging than others.
Use yield trials in which some lodging is present among most varieties, as opposed to trials in which there is no lodging.

Seeding rate

You can also use several management practices to reduce lodging.
Reducing the seeding rate is a first step.
Choosing slightly shorter-season varieties is sometimes helpful. Planting earlier or later than normal is often beneficial. In high-yielding environments (good moisture and fertility) where lodging is a problem even after all of these management practices have been initiated, using determinate semi-dwarf varieties may be indicated. These varieties lodge very little in most situations. However, they require intensive management.

Branching versus thin-line types

Soybean varieties have different growth habits which can be exploited.
The range is from highly branching types to thin-line types which produce a single, main stem.
The type of production system to be used (narrow-row vs. wide-row, irrigation vs. dryland) may make selection of a variety with a specific plant type beneficial. Row width and plant population may alter the growth habit of soybeans enough to somewhat change the degree of branching. For best yields in wide rows, select full-season varieties with a bushy growth habit.
Branching may be beneficial if lodging is a problem or if hail is a risk.

Plant height

Height frequently doubles after the first flowers appear.
Taller varieties are generally more susceptible to lodging.
Shorter varieties tend to out yield taller varieties when irrigation is used.

Pest resistance

Phytophthora root rot
Brown stem rot
White mold
Soybean cyst nematode
Soybean aphid
Bean Pod Mottle virus

Losses due to disease in soybeans can be a serious problem in Wisconsin. Researchers are developing varieties resistant to diseases, nematodes and nutrient problems, but few insect-resistant varieties have been developed. Resistance or tolerance has been bred into soybeans for phytophthora root rot, soybean cyst nematode, root knot nematode and some leaf diseases. Use of resistant or tolerant varieties is the best method of disease control. Changes in production practices, such as crop rotation, may also aid in disease control.

Some diseases are seed-borne. Selection of seed for planting that is free of these diseases is important in reducing loss of production due to these diseases.

Phytophthora root rot, a soilborne disease that affects soybean growth in poorly drained, heavy soils, is another fungus disease. Several different races of the fungus Phytophthora megasperma var. sojae cause this disease. Seedlings "damp off" when this fungus infects the plant, while older plants turn yellow, their leaves wilt, and their roots rot until the plant dies. Use of resistant or tolerant soybean varieties is the best prevention of this disease. Many high-yielding varieties with resistance or good field tolerance to the races of phytophthora found in Wisconsin are available from public and private sources.

Economic insect damage of soybeans in Wisconsin is not extensive. Foliage feeding insects can be present and may cause no yield reduction, depending on time and extent of feeding. Soybeans can tolerate fairly high levels of defoliation (10-35%) during the vegetative development stages without reduction in yield. After blooming, loss of up to 20% foliage will not be detrimental.

Nematodes, particularly soybean cyst nematodes, are an increasing problem in much of Wisconsin. This problem is often first noticed when patches of short, yellow plants appear in the field. However, the pest can be present at levels that reduce yields without causing easily visible symptoms. Roots can be examined for the presence of the cyst nematode. It is preferable to collect soil samples and send them to a diagnostic clinic for analysis. Both number and race of cyst nematodes present can be determined. If conditions are such that a resistant variety is needed, many are available from public and private sources.

County extension centers and reputable seed dealers generally have listings of disease-resistant varieties. First, determine, with their help, what the disease problem is. Then find varieties adaptable to your situation with resistance or tolerance to this disease. It is generally a good practice not to use disease-resistant varieties unless a disease problem is actually present.

Special considerations

crop use
seed cost
seed size
vigor and emergence
shattering resistance

Food uses

For some uses, yellow hila large-seeded varieties are appropriate; for others, small-seeded varieties are preferred. Production for these markets requires that only certain varieties be grown.

Seed cost

Seed cost may influence choice of variety. If costs of two varieties differ, make sure there is enough potential yield difference to justify the extra expense. In most cases, a bushel or two of increased yield will cover any increase in seed cost. It is important, however, for you to shop around to find the best price on the highest quality seed of a given variety.

Seed size

Seed size also merits consideration. Small-seeded varieties do not require as many pounds of seed per acre, so they are worth more per bushel. Because of variance in seed size among varieties, seeding rates should be calculated on viable seed planted per ground area rather than on weight of seed.

The selection of medium or small seed when using a grain drill will improve metering and stand uniformity.

Seed size is not directly correlated with yield potential as several smaller-seeded varieties have high yield records and vice versa.

Seed size is markedly influenced by the environment during the seed enlargement period of growth. Seed size reduction caused by moisture or other stress at the seed-enlargement period can reduce yield substantially.

Larger-seeded varieties could encounter more difficulty in emergence than smaller seeded varieties, particularly in cool soil conditions. However, over the range in seed sizes among varieties grown in Wisconsin (from 12 to 20 g/100 seeds), this effect is not marked. Environment plays a large role in affecting seedling emergence. Heavy rainfall immediately after planting can cause compaction and crusting on some soil types, making emergence difficult. The use of a rotary hoe will help break the crust and enable even the largest-seeded varieties to emerge.

The emergence score of soybeans represents the ability of the seed to emerge under unfavorable conditions in a laboratory test. This test indicates that more than seed size is involved in emergence ability of soybeans. If soybeans are to be grown on soil with a crusting problem, or if planting depth must be deep (sandy soils), the emergence score may be a necessary criteria for variety selection.

Shattering

The development of varieties that do not shatter has improved harvest characteristics of soybeans. Environmental conditions at time of maturity influence shattering. Early maturing varieties tend to be more prone to shattering than later-maturing varieties. Shattering is markedly different from year to year.