Cultivar Selection and Adaptation

Ted Helms

Later maturing cultivars tend to yield more than early maturing cultivars when evaluated at the same location. For this reason, it is only relevant to compare yield of cultivars that are of similar maturity. Although later maturity increases yield potential, late maturity also increases the risk of fall freeze damage. Later maturing cultivars are more risky to grow than earlier maturing cultivars because an early fall frost may kill a late maturing cultivar before the beans have filled the pods and this will greatly reduce yield.

Maturity is the first consideration when choosing a cultivar suited to your geographical region. Cultivars of Maturity Groups 00, 0 and I are suitable to the Red River Valley. Maturity Group 00 is very early and primarily grown in the Northern Valley. Maturity Group 0 is adapted to Traill, Cass, Richland, Barnes, Sargent, and Richland counties. Maturity Group I is primarily suitable for southern Richland county. These maturity groups are further subdivided. For example, a 0.1 maturity is an early Maturity Group 0 cultivar and a 0.9 is a late Maturity Group 0 cultivar.

The best way to select a high yielding cultivar is to use data averaged across several locations and years. Because the weather conditions are unknown in advance, averaging across several past years of data will identify a cultivar that yields well averaged across different weather conditions. For example, in one year there may be a dry August and in another year there is adequate moisture during seed filling in August. Selecting a cultivar that has performed well in both dry and moist conditions is the best way to identify a cultivar that does well regardless of weather fluctuations.

Some cultivars have phytophthora root rot resistance genes. Each gene for resistance confers resistance to different races of phytophthora. A gene may confer resistance to race 3, but not race 4. Select a cultivar that has resistance to the common races in your area. Race 3 is most common in the Red River Valley and race 4 and 9 are also present. Phytophthora root rot tends to be more of a problem in the southern part of the Valley and more of a problem on heavy soils that are poorly drained.

There are genetic differences among cultivars for tolerance to whitemold. Cultivars that are less susceptible to whitemold should be grown on fields where whitemold has a past history of causing problems. Data on whitemold tolerance is available in the North Dakota Extension Bulletin A-843.

Iron chlorosis is a major problem and is caused by the fact that iron is less available as pH and salt content increases. Iron chlorosis symptoms are present in the three to seven trifoliate leaf stage. Plants tend to recover and start to turn green again during the flowering and pod filling stages. However, the iron chlorosis during the early vegetative stages can severly reduce yield. Some cultivars are more tolerant to iron chlorosis than other cultivars. For high pH soils, select an iron chlorosis tolerant cultivar of suitable maturity that is high yielding. Data on genetic differences for iron chlorosis tolerance is available in the North Dakota Extension Bulletin A-843.

Excessive soil moisture during flowering and pod filling stages on heavy clay soils will greatly reduce yield by causing stunted plants. There are genetic differences among cultivars for their ability to recover from water saturated soil conditions. Research is currently underway to evaluate genetic differences for tolerance to this problem. Often those farmers that grow soybeans on heavy clay soil have identified those cultivars that have recovered well from this problem and may be able to advise their neighbors on which cultivars appear the most tolerant.

Soybean cultivars should be chosen for suitable maturity for your area, high yield compared to other cultivars of similar maturity, disease resistance, iron chlorosis, and tolerance to water-logged soil conditions. No one cultivar is the best choice for all conditions. Choose a cultivar that is tolerant of the major yield-limiting problem for your field. Different cultivars may be chosen for each field based on the problems present in that field.

Most soybeans are sold to the elevator and later crushed to extract the vegetable oil and protein. Some soybean cultivars have been developed for human consumption and have special food processing characteristics. Tofu is a white curd that is primarily consumed in Asian countries. Special cultivars have been developed that are high in protein and make smooth textured tofu. These high-protein, tofu types are lower yielding than the oilseed cultivars that are sold to the elevator. Natto is another human food product made from soybean. Natto is a fermented product made from whole soybeans that are cooked. Natto cultivars are very small seeded and tend to yield even less than the specialty cultivars developed for the tofu market. Growers should consult a university bulletin on soybean cultivar performance to determine how much less these specialty cultivars yield compared to oilseed cultivars. Based on the lower yield, a higher price per bushel can be determined to economically justify growing these specialty cultivars. A contract should be arranged prior to growing these special types, so that a market will be available to sell these products.

Transgenic soybeans are the result of incorporating a foreign gene into the chromosome of the soybean plant. An example of a transgenic soybean is resistance to a non-selective herbicide. These transgenic soybeans are sometimes called Genetically Modified Organisms (GMO's).