Nitrogen is a gas in the atmosphere that is critical for survival of life, including the survival of plants. However, plants cannot independently acquire Nitrogen from the air without the microbial processes of nitrifying bacteria, archea, and other organisms in the soil.
What happens when nitrogen is applied to the soil?
Nitrogen is one of three of the major macronutrients responsible for plant health. It produces chlorophyll in the leaves, which is why it is often associated with the green growth of plants. Chlorphyll converts sun rays into energy that the plant uses to grow and produce.
Nitrogen deficiency often causes plants to appear yellow, stunted, and in poor overall health.
Building Soils for Better Crops by Fred Magdoff and Harold Van Es
Nitrogen is very volatile, meaning it can convert from mineral form in the soil back to the air easily. No-till, mulching, and cover crops all help reduce its exposure to oxygen and contain it to the soil.
Applying more nitrogen than is necessary for plant health can increase weeds, pest pressure, and can cause a toxic level of nitrates to leach into groundwater. High nitrates have been associated with hypoxic conditions in the Gulf of Mexico, related to agricultural and lawn runoff. Even when using organic amendments, it's important to understand the overall health of the soil to determine whether or not adding any level of nitrogen is necessary. A soil test by your agricultural extension office is a good place to start.