Let's see how the things we learn in A-Level Chemistry can be applied to daily life and practical use in the agriculture industry! It's related to biology and geography!
Addition nitrogen to soil
Nitrogen-fixing bacteria
Some bacteria in the soil and in legume (peas, beans) root nodules can covert nitrogen gas to ammonium ions. N2(g)+ 8H+(aq) + 6e- ⇨ 2NH4+(aq)
Lightning, burning hydrocarbon fuels and natural fibres
All produce nitrogen oxide, which are released into the atmosphere and are then deposited into the soil.
Transformations in the soil
Mineralisation
Soil bacteria and other micro-organisms break down organic nitrogen compounds into simpler molecules andions. Any nitrogen not needed bythe organisms is released into the soil as ammonium ions, which are held by clay minerals.
Nitrification
Ammonium ions are oxidised by certain aerobic bacteria in the soil to form nitrate(V) ions occurring at several stages.
Ammonium Ions to Nitrate(III) ions:
The bacteria used is called Nitrosomonas, with an optimum pH of 7-9.
NH4+(aq) + 1½O2(g) ⇨ NO2-(aq) + 2H+(aq) + H2O(l)
Nitrate(III) ions to Nitrate(V) ions:
The bacteria used is called Nitrobacter, which can tolerate dry conditions and a higher acidity than Nitrosomonas. NO2-(aq)+ ½O2(g) ⇨ NO3-(aq)
Losses of nitrogen from the soil
Denitrification
At low oxygen content, anaerobic bacteria reduces nitrate(V) ions. This can be high in flooded soils (low O2 content).
NO3-(aq) ⇨ NO2-(aq) ⇨ NO(g) ⇨ N2O(g) ⇨ N2(g)
Leaching
Mainly lost as nitrate(V) ions, which are not held by clays or humus in temperate soils. Quantities lost depends on the soil structure, amount of rainfall and concentration of nitrate(V) ions.
Loss of ammonia gas
Ammonium ions are converted into ammonia under alkaline conditions, which disperses into the atmosphere. NH4+(aq)+ OH-(aq) ⇨ NH3(g)+ H2O(l)
Uptake by plants
In natural systems, only relatively small quantities of nitrogen are removed. However, crops cultivated to give high yields need much more nitrogen to make plant proteins necessary for growth.
Drafted by Eunice (Chemistry)
References
https://biologydictionary.net/the-path-of-nitrogen-through-its-biogeochemical-cycle/
https://ib.bioninja.com.au/options/option-c-ecology-and-conser/c6-nitrogen-and-phosphorus/nitrogen-cycle.html
https://kids.frontiersin.org/articles/10.3389/frym.2019.00041