Soil converts nitrogen into a form plants can use. Nitrates in soil and water are converted to nitrogen by bacteria, fixed by lightning and released into the air where plants absorb it to use in photosynthesis.
Plant and animal waste are the primary sources of nitrates in the soil. Nitrifying bacteria convert ammonia to nitrates. Then, the denitrifying bacteria take over, converting the nitrates to nitrogen. From there, combustion and lightning fix the nitrogen in the atmosphere, making it readily available for plants to use for photosynthesis.
Although nitrogen is abundant and necessary for life, too much can be detrimental . When too much nitrogen runs off into ponds and rivers, it causes large algae blooms that block sunlight from reaching the water, harming aquatic life.