Andrey Repin
Composting specialist, consultant.
The C/N ratio is the ratio of Carbon to Nitrogen. This ratio is widely used in agriculture to control soil quality and fertilizer application. It is no less important when producing compost for champignon mushrooms. The C/N ratio forms the basis for developing compost formulas, selecting components, and is a key indicator of compost quality. Quality compost is the key to a high yield on a mushroom farm. The optimal C/N ratio in Phase 1 compost is 18-20, in Phase 2 compost is 15-17, and in Phase 3 compost is 14-16.
To calculate the C/N ratio, we need to know the ash content in the compost (ash is the inorganic part of the compost), the percentage of total nitrogen (determined in the lab), and the percentage of carbon, which we do not measure but calculate. First, we need to find out how much organic matter is in the sample – (100% – Ash). It is assumed that organic matter contains 50% carbon. Thus, Carbon = (100% – Ash) / 2. Finally, the C/N ratio = Carbon / Total Nitrogen.
How can we regulate the C/N ratio? The simplest and most accessible way is by changing the nitrogen level in the compost. The higher the nitrogen in the compost, the lower the C/N ratio will shift, and vice versa. Here, we are primarily limited by the need to remove ammonia from the compost during Phase 2 in the upper part and the required nutrient level and compost activity at the lower level. Influencing the carbon level is more complex and multifactorial. First of all, it’s about the quality of raw materials. Straw – if it gets wet during harvesting or has sand impurities – will start with a high ash content (inorganic part), and the carbon level will be lower. Chicken manure – if it’s from laying hens, calcium supplements like sand or granules are added to their feed to make the eggshells stronger. These additives are excreted almost unchanged in the manure, significantly raising the ash content in the chicken manure. The storage and mixing area for the manure also matters. Ideally, it should be a concrete platform, both at the poultry farm and the composting facility. The more impurities there are, the higher the ash content, and the lower the carbon content.
If we calculate a high nitrogen level in the compost formula, the composting process will be more active, releasing a large amount of ammonia, utilizing a significant amount of carbon, and resulting in a notable increase in ash content by the end of Phase 1. Such compost will appear dark, the moisture will feel higher than what the lab will later show, there will be a strong ammonia smell, the structure will be short, and the straw in the compost will be soft. Such compost may cause issues during Phase 2. Ammonia will be released for a longer time, and the compost will be “greasy.” In Phase 3, the colonization will be slow and uneven. In the finished Phase 3 compost, there will be dark spots of uncolonized compost with an unpleasant ammonia smell.
If, on the contrary, a low nitrogen level is calculated, the compost’s activity will be low both at the compost production stage and at the mushroom farm. In this case, the carbon level will remain higher, and there won’t be enough nitrogen to transform the easily degradable carbohydrates into harder-to-degrade carbohydrates. This will lead to the compost not being selective (selective compost is compost that provides nutrition only for champignons) and will result in the growth of competing molds and other diseases.
Secondly, the production schedule itself is important. During compost production, energy is mostly consumed through carbon. Therefore, during the production process, the carbon level decreases, and the inorganic part – ash – increases. With modern production methods, composting time can be significantly reduced. If the production schedule is shortened, the compost uses less carbon and forms less ash, which ultimately provides more nutrition and energy for mushroom production. Such compost looks lighter, fluffier, the structure is usually longer, the straw is quite tough, and the moisture content is low. However, with this type of compost, there is a risk that not all production stages (especially fermentation) were completed sufficiently, and there is a higher risk of disease, which could affect mushroom quality.
With a longer production schedule, all processes take longer, resulting in more carbon loss, and the ash content becomes high. The compost looks over-composted, dark, with poor, short structure. There may be issues with aerating such compost in both Phase 1 and Phases 2/3. A lack of oxygen due to improper aeration will negatively affect compost quality.
In conclusion, the C/N ratio is a complex reflection of the entire composting process, including the compost formula, production schedule, and raw material quality. It is crucial to maintain balance across all parameters to adhere to the “golden” mean. Striving for low ash, sufficiently high nitrogen, and an optimal schedule is essential.
