Home/Nexen, Nitrogen Loss/Understanding the Nitrogen Cycle

Understanding the Nitrogen Cycle

To better understand why plants need nitrogen to grow, it’s important to know what the element does and why the nitrogen cycle is a necessary part of all living matter.

Understanding the Nitrogen Cycle

Nitrogen is a key element, making up the majority of the air we breathe. More than three quarters of our atmosphere is made up of nitrogen, making it the largest source of the element. All organisms need it to live and it’s one of the most essential nutrients involved in plant growth.

“Plants depend on the three primary nutrients: nitrogen, phosphorus and potassium,” explains Ross York, Managing Director KFAUS. “Arguably nitrogen could be called the most important macro nutrient because it impacts so many different metabolic processes in the plant.”

An essential component of plant structure, nitrogen is required to build plant tissue and is integral for reproductive success of the plant. Nitrogen is also the central element of the amine groups which are the key functional groups of amino acids. These are the building blocks of proteins and enzymes, which regulate all plant metabolism. Nitrogen is necessary to determine plant genetics and key to its growth and development, stimulating root growth so that it can take up the nutrients it needs to grow.

“Nitrogen is a critical component of energy transfer and really an essential component of the chlorophyll molecule which enables plants to capture sunlight energy and create green tissue,” says York. “The plant simply cannot optimize yield without nitrogen.”


The nitrogen cycle is a series of continual processes by which nitrogen is chemically and biologically transformed in the environment through various organic and inorganic forms. Nitrogen is in its most stable form when in the atmosphere, but to be easily used by plants, it has to be converted into plant-available ammonium and nitrate.

In its organic form, plants can’t immediately reach out and grab nitrogen. If they did, we wouldn’t really need to use fertiliser. The biological process that takes microbes in the soil to break this down and to release it is what we call mineralisation. It turns the organic form of nitrogen into a mineral form that the plants can then take up.

It takes several different processes to achieve that biological reaction, including nitrogen fixation, nitrification, mineralisation and denitrification.

  • Biological nitrogen fixation is the first step in the nitrogen cycle, occurring when atmospheric nitrogen is ‘fixed’ or converted into ammonium by certain crops, such as legumes.
  • Industrial nitrogen fixation, is the method used by manufacturers, converting atmospheric nitrogen into nitrogen oxides or ammonium ions used by plants and other organisms.
  • Mineralisation encompasses several different processes but is commonly referred to the liberation of ammonium from organic matter by microbes that degrade organic carbon sources.
  • Conversely, nitrogen immobilisation occurs when nitrogen is “tied up” by the microbial pool, rendering the nitrogen unavailable to the crop.
  • Nitrification occurs when bacteria in the soil then converts the ammonium into nitrate.
  • Nitrogen assimilation is the process whereas plants can uptake nitrogen in the ammonium and nitrate form. Almost 80 percent of nitrogen taken up by a plant is in the nitrate form.


Even with some naturally occurring nitrogen in the soil, growers need to add nitrogen fertiliser.

“Adding the right amount of nitrogen fertiliser to the crop is a delicate balancing act and is not as easy as people think” said York. “Growers need to avoid a deficiency while also making sure that they’re not putting on a great excess of N”.

One of the key uncertainties of managing nitrogen is loss. There are three forms of nitrogen loss:

  • Volatilisation is above-ground loss of nitrogen. This happens when the soil’s urease enzymes break the urea molecules into ammonia gas.
  • Denitrification nitrogen loss occurs below ground when nitrate nitrogen is converted back to gaseous forms. It is found most often in soils that are poorly drained or are waterlogged.
  • Leaching is when nitrogen is lost below ground as downward movement of water carries negatively charged nitrate below the plant’s root zone.


Nitrogen fertilisers come in different forms for growers to use on their crops. According to York, one of the most common nitrogen fertilisers applied in Australia is urea. An economical and effective source of nitrogen, urea is a white crystalline solid containing 46 percent nitrogen.

Urea is a compound that has to be hydrolysed, which is the process of being broken down by a biochemical transformation with water. It is converted in the soil by the urease enzyme in order to release the ammonia that makes it plant available.


Growers can protect their fertiliser investment with nitrogen stabilisers and also by following the 4R Nutrient Stewardship.

“Following the 4R nitrogen management framework will help growers optimize their yield potential and profitability, while also protecting environmental resources,” says York. “Selecting the right source of fertiliser, applying it at the right rate, at the right time and with the right placement, a grower is implementing the best practices to sustainably manage nitrogen.”

When it comes to protecting N against above-ground loss caused by volatilisation growers should consider using NEXEN. This nitrogen stabiliser is urea powered by AGROTAIN which has been tested in hundreds of studies across the globe, including Australia. It is one of the few urease stabilisers recognised worldwide as being effective in reducing nitrogen loss and improving fertiliser efficiency.

You can find out more about NEXEN here or by contacting your local representative.

Related Posts