Welcome back to the blog for the next installment of our summer series on the elements! This week we will tackle an important element that is crucial to the growth of virtually all plants and animals on Earth--Nitrogen (N).
Plants and animals alike depend on Nitrogen to promote growth. Plants use Nitrogen in chlorophyll molecules, which are a primary component in photosynthesis. All amino acids contain Nitrogen, and animals need amino acids to synthesize proteins and convert energy for growth and function.
Our atmosphere is approximately 78% Nitrogen, which sounds like there is an abundance of N available for plant and animal productivity, but atmospheric Nitrogen (N2) is unusable by plants and animals, because the N atoms are bound together in a triple bond. For uptake by plants and animals, N2 has to go through a series of conversions.
Nitrogen Fixation - N2 is converted to NH3 (ammonia) by lightning strikes and soil-dwelling, symbiotic bacteria living on leguminous plants.
Assimilation - nitrate (NO3-) and ammonium (NH4+) uptake from plant root hairs in soil
Ammonification - plant and animal waste (detritus) is converted from organic matter into ammonium
Nitrification - conversion of ammonia to nitrites (NO2-) which is then oxidized to nitrates by soil living bacteria
Denitrification - reduction process of nitrates back into atmospheric gas (N2) by bacteria in anaerobic conditions. This last portion of the process is important, because it keeps the cycle in balance.
Agriculture is heavily dependent on the productivity of soil for plant growth. Starting in the first decade of the 20th Century, scientists started synthesizing ammonia by combining atmospheric N2 with Hydrogen gas (H2)--usually derived from methane (CH4). For more on this process, see Haber-Bosch.
While this process creates a readily accessible form of Nitrogen fertilizer for farmers, it can potentially impact the environment in a harmful way. Excess fertilization with Nitrogen and Phosphorus can wash out of farm fields and end in up in water systems.
An overabundance of these fertilizers can lead to a rapid genesis of potentially harmful algal blooms in waterways. Phytoplankton varieties of algae are plant species and react similarly to fertilizers as terrestrial plants would. This rapid growth can cause an over-use of dissolved oxygen in the water creating a hypoxic aquatic ecosystem, forcing out other organisms.
The take home message when it comes to synthetic Nitrogen fertilization is: balance.
Getting to Know the Nitrogen Cycle
One great way to experience the Nitrogen Cycle for yourself is to start a compost heap. The key to a successful compost operation is balancing the relationship of elemental components, or stoichiometry. Creating a Nitrogen-rich compost heap will allow you to safely fertilize a garden while participating in the Nitrogen Cycle.
For more on composting, be sure to check out Let it Rot!, a capstone volume on composting, and other eBooks at your library.