Question: How to naturally add nitrogen to my soil?
Option 0: Beans and peas are climbers, and they add nitrogen to the soil.  When they die back, their foliage fertilizes the soil, strengthening the next plants. Swiss chard and kale add nitrogen also.
Option 1: Beans and peas are climbers, and they need a lot of nitrogen which depletes the soil. Add swiss chard and kale to replenish the missing nitrogen along with some potash if accessible.
Answer: 0