The N Cycle

Did you know that the reason why carbon was built on soils was due to the synthetic nitrogen? That’s what scientists have assumed for decades.

The nitrogen cycle is the set of biogeochemical processes by which nitrogen undergoes chemical reactions, changes form, and moves through difference reservoirs on earth, including living organisms.

This would guarantee as a major environmental benefit of synthetic N use. At a time of climate chaos and ever-growing global greenhouse gas emissions, anything that helps vast swaths of farmland sponge up carbon would be a stabilizing force. Moreover, carbon-rich soils store nutrients and have the potential to remain fertile over time— a boon for future generations.

The case for synthetic N as a climate stabilizer goes like this. Nitrogen (N) is an essential component of DNA, RNA, and proteins the building blocks of life. All organisms require nitrogen to live and grow. Although the majority of the air we breathe is N₂, most of the nitrogen in the atmosphere is unavailable for use by organisms. This is because the strong triple bond between the N atoms in N₂ molecules makes it relatively inert. In fact, in order for plants and animals to be able to use nitrogen, N₂gas must first be converted to more a chemically available form such as ammonium (NH₄⁺), nitrate (NO₃^-), or organic nitrogen (e.g. urea - (NH₂)₂CO). The inert nature of N₂ means that biologically available nitrogen is often in short supply in natural ecosystems, limiting plant growth and biomass accumulation (source: John Arthur Harrison, Ph.D.).

Synthetic nitrogen makes plants grow bigger and faster. As plants grow, they pull carbon dioxide from the air. Thus producing crops and the rest – the residue, stays in the field and becomes soil.

These studies lead to sound so alarming. Synthetic nitrogen use, they argue, creates a kind of treadmill effect. As organic matter dissipates, soil’s ability to store organic nitrogen declines. A large amount of nitrogen then leeches away, fouling ground water in the form of nitrates, and entering the atmosphere as nitrous oxide (N2O), a greenhouse gas with some 300 times the heat-trapping power of carbon dioxide. In turn, with its ability to store organic nitrogen compromised, only one thing can help heavily fertilized farmland keep cranking out monster yields: more additions of synthetic N.

Researchers also argue that the loss of organic matter has other ill effects. Injured soil becomes prone to compaction, which makes it easy to runoff and erosion and limits the growth of stabilizing plant roots. Worse yet, soil have harder time holding water, making it rely more on irrigation. As water becomes scarcer, this consequence of widespread synthetic N use will become more and more challenging.

Nitrogen is an incredibly versatile element, existing in both inorganic and organic forms as well as many different oxidation states. The movement of nitrogen between the atmosphere, biosphere and geosphere in different forms is described by the nitrogen cycle. 

It is therefore important to balance both the advantages and disadvantages of it, the human alteration of the N cycle and its effects on the environment.

  

Currently, there are too many researches that scientists are exploring in understanding the effects of nitrogen enrichment in the air, groundwater and surface water.

Scientists are also exploring alternative agricultural practices that will sustain high productivity while decreasing the negative impacts caused by fertilizer use. These studies not only help us quantify how humans have altered the natural world, but increase our understanding of the processes involved in the nitrogen cycle as a whole (source: Of Microbes and Men article).