What does the C:N ratio refer to?

The carbon to nitrogen (C:N) ratio is a crucial concept in understanding soil fertility and nutrient availability. It refers to the proportion of carbon to nitrogen present in organic matter, such as plant residues or compost. A balanced C:N ratio greatly influences the processes of nutrient mineralization and decomposition, as microorganisms require both carbon and nitrogen to thrive. When organic materials are added to the soil, microorganisms decompose these materials by consuming carbon for energy and nitrogen for growth.

If the C:N ratio is too high (more carbon than nitrogen), the decomposition process can become nitrogen-deficient, leading to immobilization where soil nitrogen is drawn down to fulfill microbial needs, thus temporarily reducing nitrogen availability for plants. Conversely, a low C:N ratio means that there is more nitrogen relative to carbon, which can lead to rapid decomposition and quicker nutrient release, benefiting plant growth. Understanding the C:N ratio helps in making informed decisions about soil amendments and organic matter management to maintain healthy soil and optimize crop productivity.