Do Soybeans Deplete the Soil?

Plants Use Nitrogen

• Most plants solely use the nitrogen found within the soil for their nourishment. If the nitrogen is not returned to the soil through decomposed organic material or other chemical supplements, the nitrogen will gradually be used up and become depleted.

Legumes

• Soybeans are legumes, which include peas, beans and peanuts. Legume plants take in nitrogen from the air and in a symbiotic relationship with the bacteria Bradyrhizobia japonicum, store it in nodules alongside the roots. This nitrogen then nourishes both the plant and the bacteria during the bean production. A single soybean plant may have several hundred nodules.

Soybeans

• Soybeans are among the better nitrogen fixers and an acre can produce 250 lbs. of nitrogen. In some soils, the newly established soybeans may need extra nitrogen, but generally speaking they do not need any nitrogen fertilizer to grow and thrive.

Stress

• Stress such as hot weather or drought interferes with soybean nitrogen fixing. When the stress goes away the production comes back.

Giving Back

• While the plant does not take nitrogen from the soil, it does not give much back either. Little nitrogen is left over for the soil when the soybeans are harvested. Plowing the leaves, stems and roots back into the soil does not provide much since it is not stored in those areas.