How does a soil becomes rich in nitrates when leguminous plants are grown in it?

Leguminous plants, such as peas and beans, have a symbiotic relationship with nitrogen-fixing bacteria (e.g., Rhizobium) in their root nodules. These bacteria convert atmospheric nitrogen into ammonia, which is then transformed into nitrates through soil processes. When leguminous plants die or shed their leaves, the decomposing organic matter further enriches the soil with nitrogen compounds, leading to an increase in nitrate levels. Consequently, growing leguminous plants enhances soil fertility and nutrient availability for subsequent crops.