By Dr. Harold Willis
Most people grow soybeans in a crop rotation sequence, typically with a non-legume such as corn, small grains, sorghum or cotton. The yield of the non-legume is improved because of the left-over nitrogen from the soybean root nodules. Also, disease, pest and weed problems are reduced in rotations compared to growing one crop continuously. These disadvantages can be overcome if soil is in peak fertility and condition.
Soybeans are also often grown in a double-cropping system, with two crops being grown in the same year. Winter wheat followed by soybeans is the most common; snapbeans or peas followed by soybeans is another. Timing is critical in more northerly areas.
Intercropping, in which two crops are planted in alternating rows or strips, or in which one crop is broadcast into the other, has been tried with mixed success. Sometimes aerial seeding was used. Conditions must be just right. Examples include planting soybeans in standing small grain, small grain into growing soybeans, ryegrass or clover into growing soybeans, alternate strips of corn and soybeans, corn and soybeans in the same rows, and early soybeans into a growing late variety. Interseeding grasses or legume-grass mixtures into soybeans at the leaf-yellow or leaf-drop stage will provide an excellent erosion reducing ground cover over the winter that can be worked into the soil next spring.
Source: How to Grow Super Soybeans