We can’t fully understand the process of carbon movement from one life form to the next in a paddock, until we understand how nitrogen fits in.

When any living thing dies or is consumed, plants included, it becomes the food source for another living thing. All the nutrients and trace elements are important for the next consumer, but nitrogen is a key player. It has to be passed (along with carbon) in adequate quantities down the food chain to ensure ongoing life.

Put simply, nitrogen is always moving just like carbon is always moving. However, carbon can’t move from one life form to the next, driving production and landscape health, if there is not enough nitrogen to go with the carbon.

Carbon compounds provide energy and cellular building blocks, while nitrogen is a crucial component of proteins, necessary for cell growth and function. It is nitrogen that builds tissue. Nitrogen is a component of amino acids which are the building blocks of protein.


How much carbon and nitrogen any life form requires, be it a plant, soil microbe, worm, insect or animal, is referred to as the carbon:nitrogen (C:N) ratio of that life form.

Suppose a plant sample is made up of 40% carbon and 2% nitrogen. Dividing 40 by 2, the result is 20. The C:N ratio of this material is 20 to 1, which means 20 times as much carbon as nitrogen. The ratio is often shortened and just written as 20.

Humans are 18% carbon and 2.5% nitrogen, so we have a C:N ratio of 7.2.

Variations in carbon:nitrogen ratios


Organic matter consisting of deceased life or their waste products also has a C:N ratio, which indicates its value for consumption by soil life.

As a rule of thumb, a C:N ratio of approximately 25 is somewhat of a watershed. The further the organic matter is above this value (i.e. higher amounts of carbon per gram of nitrogen) the slower will be the rate of decomposition. On the other hand, with a C:N ratio lower than 25, the faster the rate at which organic matter decomposes. This is why, say Lucerne (C:N ratio of 12 – 15), doesn’t last long in the soil compared to wheat stubble (C:N ratio of 90 – 160).  


As plants are the start of the food chains, above and below ground, their C:N ratio sets the scene for the efficiency of a grazing paddock i.e. how quickly consumption occurs in the paddock as one life form consumes another. For this reason, it is important to ensure that animals do not eat out the species with the lower C:N ratios.

We can improve the C:N ratio of plants through better management (i.e. higher carbon flows) that improves the fertility of the soil. In general it could be said that any specific plant type in a properly functioning landscape will have a higher nutritional value (including better C:N ratio) than one in a dysfunctional landscape of the same soil type. The protein level of wheat changes when fertiliser is added, which is another example of the principle. 


The C:N ratio is an important concept for producers to understand. The ratio is always being mentioned in scientific literature however it rarely seems to rate a mention in extension to the grazing industry. This is unfortunate as the ratio helps producers better understand how a paddock and everything in it functions.

A broader understanding of how carbon and nitrogen combine in the paddock would lead to better Reef protection. If management is not focused on maximising carbon flows into the paddock, to bind up nitrogen, then there is more chance of nitrogen getting on the loose and promoting algal growth on the Reef. Nitrogen on the loose is also a lead cause of soil acidification and nitrous oxide emissions. Besides the environmental consequences, it is money literally down the drain. 

It is the movement of carbon and nitrogen that is central to the profits of the grazing industry and this will be discussed further next week.