The plants in the ground take in the nitrates from the air and use it to grow they also help with the process of photosynthesis. Most of the nitrate comes from the air but some can come from water. NItrate is a gas but if it goes through sublimation it can also be a liquid
During precipitation the nitrogen that is in the atmosphere gets into the soil. The water can then pile up and becomes ground water.When it sits there it is slowly getting evaporated or running off into streams and oceans. The water can also go through infiltration so then it goes into the ground soil.
when the water runs off it normally goes to the ocean. As in runs through the rivers it will pick up sediments and drop them off in different places this process is called deposition. Once it reaches the ocean it will sit there until it eventually goes through evapotranspiration. then the whole cycle will restart again.