Nitrogen (The Glamour Ingredient) – versus Carbon (50 Shades of Brown)
Of the many elements required for microbial decomposition, carbon and nitrogen are the most important. Carbon provides both an energy source and the basic building block making up about 50 percent of the mass of microbial cells. Nitrogen is a crucial component of the proteins, nucleic acids, amino acids, enzymes and co-enzymes necessary for cell growth and function.
The roles of nitrogen and carbon in composting are all-important and both are vital to the process. Composting, i.e. the decomposition of plant and animal matter, is the basis of the Nitrogen Cycle and the Carbon Cycle, two of the Cycles of Life that allow us to exist on this planet. These are essential compost ingredients in any bin.
A carbon dioxide molecule
A nitrogen molecule
When considering nitrogen and its vital role in the production of ‘black gold’, I always smile. To me, this is the glamour ingredient and the materials that contain it are interestingly fresh. They are green, or some other bright colour and pleasantly juicy – or at least moist. They are things that we eat regularly, leaves, fruit, and vegetables – familiar and a part of our daily lives. They may be a bit mouldy, but hey! – they are still showing signs of life and that is good. On the flip side, in bulk they can be toxic – lurid green (the traditional colour of poison) densely matted (think grass clippings or silage) foul smelling and anaerobic – ruinous to our compost, but still lush. All of this is in contrast to carbon-rich ingredients. Dry twigs, wood shavings, cardboard, paper, dead leaves and plants that have dried to a crisp. How boring – nothing glamorous here! Browns, browns, and more browns and dry on the palate.
They are two of the essential compost ingredients, however. Nitrogen, in the form of ‘green’ materials, is needed by the microbes working on your waste to build cell structure and to enable reproduction. Carbon is used for supplying energy, getting all those bad boys on the hop. Indeed, it is the processing of carbon, in the form of your ‘brown’ materials that raises the temperature of your pile.
To emphasise, both elements, are essential and without them the operation is a non-starter. Without an adequate supply of nitrogen, microbes will be inhibited in their development and will perform at a less than optimum level, leaving the pile cold and slow to be processed. Decomposition could take years. (Consider a pile of firewood or dry sticks.)
Without carbon, your pile may well suffer from an excess of nitrogen, which will overwhelm the micro-organisms available to process it. The excess will be converted to ammonia with its attendant smell. If the pile becomes anaerobic, a stinking rotten mess with a ‘rotten egg’ whiff will be the result. Balance is clearly all-important and it is by controlling this balance between the two essential elements that we can manipulate compost production. The accepted carbon-to-nitrogen (C/N) ratio is quoted as 30:1, that is, 30 parts of C to 1 part of N.
So – to recap, micro-organisms need ‘greens’ for building strength to work and reproduce and they need ‘browns’ as a source of energy, to give them zing and zest, and to sustain them at peak condition. Without a proper supply of these essential compost ingredients, in the more or less correct ratio, activity will grind to a halt and death or dormancy will be the result. Plodding carbon damps down the excesses of glamorous nitrogen and keeps everything under control. Isn’t composting marvellous?
-
- Compost microbes
-
- Actinobacteria, a plant re-cycler
-
- compost microbes
Incidentally, if you do end up with a heap that is reeking because of too much ‘greens’, you can overcome the problem by adding a good load of ‘brown’ ingredients such as wood chips, dry leaves, shredded paper or cardboard.
Resource: Cornell Composting Science and Management, Cornell Waste Management Institute 1996 : http://compost.css.cornell.edu/chemistry.html
