Where Does Nitrogen Go During Composting?

A compost pile can contain nitrogen without having much immediately available to plants. Much of the nitrogen in fresh plant material is part of organic compounds. As decomposers use that material, nitrogen moves among different parts of the living system.

Microorganisms need nitrogen to build proteins and grow. As they consume organic material, they may take up available nitrogen and incorporate it into their cells. This temporary storage in microbial biomass is called immobilization. The nitrogen has not disappeared; it is being held in living organisms.

As microbial cells die, are consumed, and break down, some of their organic nitrogen is converted into mineral forms, including ammonium. This release is called mineralization. Some nitrogen may then be taken up by other organisms, remain in the material, change form, or leave the pile. The amount available at any moment depends on the materials and conditions.

These are shifts among nitrogen pools, not a fixed sequence that every pile follows. A carbon-rich material can support microbial growth while also affecting how much nitrogen is available to those microbes. If usable nitrogen is limited, microbial growth and decomposition may slow.

When you look at a compost material, ask both what it contains and where its nitrogen might be held as decomposition proceeds. What material in your compost might be holding nitrogen in organic form or in living decomposers?

When microorganisms take up available nitrogen and incorporate it into their cells, what is happening?

Nitrogen is temporarily immobilized in microbial biomass.

Nitrogen is destroyed during decomposition.

All of the nitrogen immediately becomes available to plants.

The material has finished decomposing.

2 votes

3 comments

Where Does Nitrogen Go During Composting?