What effect does a high C:N ratio have on nitrogen availability?

In the context of nutrient management, a high Carbon to Nitrogen (C:N) ratio indicates that there is a greater amount of carbon relative to nitrogen in the organic matter present, such as plant materials or soil amendments. When organic matter with a high C:N ratio is added to the soil, microorganisms that break it down utilize nitrogen from the soil along with the available carbon.

As a result, this increased microbial activity can lead to the immobilization of nitrogen, meaning that nitrogen is temporarily held up or 'locked' within microbial biomass, reducing its availability to plants. Consequently, plants may face nitrogen deficiency until the microbial populations die off and release the nitrogen back into the soil.

This dynamic illustrates the importance of understanding C:N ratios in managing soil fertility and ensuring that sufficient nitrogen is available for plant growth, especially when incorporating organic materials with varying C:N ratios into the soil.