Agronomy Degree Practice Exam

Which specific bacteria is known to fix nitrogen for soybeans?

1. Bradyrhizobium japonicum

2. Bradyrhizobium betae

3. Bradyrhizobium canariense

4. Bradyrhizobium tropiciagri

The correct answer is: Bradyrhizobium japonicum

The correct choice is associated with Bradyrhizobium japonicum, which is specifically known for its symbiotic relationship with soybean plants (Glycine max). This bacterium establishes root nodules on soybean roots, where it converts atmospheric nitrogen into a form that the plant can use for growth. This process is essential for enhancing soil fertility and improving crop yields. Bradyrhizobium japonicum is particularly well-suited for this interaction due to its efficient nitrogen-fixing abilities, which are beneficial for soybeans, a leguminous plant that thrives on this symbiosis. The relationship not only allows soybeans to access vital nutrients but also contributes to the overall nitrogen content of the soil, benefiting subsequent crops in rotation. In contrast, the other choices, although they belong to the same genus, do not have the same established association with nitrogen fixation in soybeans. Each of them may play roles in different contexts or with different host plants, but none have the specific, well-documented interaction with soybeans that Bradyrhizobium japonicum has. Understanding the specific interactions between plants and nitrogen-fixing bacteria is crucial for agronomy, especially in sustainable agriculture practices.