There are environmental conditions that limit N-fixation. Cold and heat. High soil N levels. When soil N levels are too high, nodule number and activity decreases. Poor plant growth does not allow the plants to sustain nodules and plant growth.
Nodule activity is sacrificed.
If soil pores are filled with water, not air, there is no N to fix. If there is no air, there is no N to fix. Using inoculants N-fixing bacteria are fragile organisms. Inoculants need to be handled with care. Proper storage is critical.