Why paddock carbon needs ongoing replacement
Did you know that after carbon enters the paddock, it is consumption that allows it to move and, in the process, change from one form to another? During each consumption event, some of the carbon will leave the paddock and return to the atmosphere, hence the need for ongoing replacement. Carbon usually leaves as carbon dioxide (CO2), however some leaves in the form of methane (CH4).
Paddocks become bare quicker if the focus is not on 'maximising' flows from any rain that falls.
Carbon consumption usually involves living things, however fire also consumes carbon compounds such as those in grass. In the case of fire, a lot of carbon leaves in a hurry. While fire is sometimes necessary as part of managing paddocks, it must be remembered that the carbon in burnt grass is not given the opportunity to drive production and soil health by moving through the above and below ground food chain.
When pasture management is discussed with producers, carbon is usually just associated with the soil. However, it is important to think of ground cover in terms of being carbon. When a paddock goes from having a good cover of grass, to bare, this is a reflection that all the carbon that was in the grass (45% by volume) has gone somewhere else. Some of the carbon that was in the grass would now be in the bodies of livestock, some in soil life including microbes, some in organic matter and the rest back up in the atmosphere.
With the mind set of carbon always moving, comes the awareness that carbon levels in the paddock will run down if you do not allow replacement carbon to keep coming in.
One example of how carbon keeps leaving the paddock
The above diagram representing the decomposition of plant residues highlights that it is critical to keep introducing new carbon into a paddock because carbon keeps leaving the system. The arrows on the CO2 sections represent the loss of introduced carbon via consumption i.e. oxidisation. The oxidisation process involves one life form consuming another and releasing CO2 in the process. As discussed, consumption by living things is not the only way carbon moves. Fire also consumes carbon by oxidising it. As we all know, remove the oxygen and the fire goes out.
The diagram highlights that the outcome of photosynthesis is being reversed with every consumption event. You can see that some of the original carbon that arrived as short term carbon is now heading towards longer term carbon as it becomes less and less digestible. This is represented by the horizontal red bar becoming shorter.
The above diagram of what happens in the soil is a similar process to what happens in the rumin (first stomach) of sheep and cattle, where the gut microbes consume the grass that livestock have eaten. The sheep and cattle then consume the gut microbes as their food source and breathe out CO2 in the process. In the rumin, hydrogen is produced as part of the digestive process and microbes, known as methanogens, convert it to methane (CH4), which sheep and cattle burp out of their mouth. What the microbes do not consume becomes manure that then flows through the soil life.
As a general comment, 75-80% of carbon that enters the soil will be gone within twelve months. The actual amount consumed is determined by soil moisture and soil temperature as these two parameters determine how active soil microbes are.
Everything discussed here highlights that if your management is not focused on maximising the introduction of new carbon when the opportunities present after rain, then you run the risk of running short of this commodity, especially above ground.