What Your Soil Isn’t Telling You: The Power of Pairing Respiration with Organic Nitrogen

Soil Respiration: A Measure of Microbial Activity

Soil respiration refers to the process by which microorganisms in the soil decompose organic matter, releasing carbon dioxide (CO₂) into the atmosphere. This microbial activity is a critical component of the soil’s life cycle. The rate of soil respiration is often used as a proxy for microbial activity and overall soil biological activity. A higher rate of respiration generally indicates a higher level of biological activity and healthier soil.

Organic Nitrogen: The Hidden Key to Soil Fertility

Organic nitrogen refers to nitrogen that is part of organic compounds in the soil, typically found in plant and animal residues, microorganisms, and decaying organic matter. Unlike inorganic nitrogen, which exists in simple forms like ammonium (NH₄⁺) or nitrate (NO₃⁻) and is directly used by plants, organic nitrogen is more complex and tends to be bound up in proteins, amino acids, and other organic molecules. Soil microorganisms play a critical role in transforming organic nitrogen into forms that plants can absorb, such as ammonium (NH₄⁺) and nitrate (NO₃⁻) through processes like mineralization and nitrification. Measuring organic nitrogen helps us understand nutrient availability in the soil, soil fertility, and nutrient cycling processes.

Healthy soils typically have a well-balanced nitrogen cycle, where organic nitrogen is broken down and converted into plant-available forms by a robust and diverse microbial communities

The Complementary Relationship

Soil respiration and organic nitrogen are intimately connected, and together they provide a more complete picture of nutrient availability.

For soil to be truly healthy, it requires two things:

1. A strong microbial community—a diverse and active population of soil organisms that can break down organic matter and support nutrient cycling.
2. A reliable food source—enough organic matter (including organic nitrogen) for these microbes to feed on and thrive.

Measuring soil respiration can tell you that the microbes are active at a certain moment, but it doesn’t provide the full picture of soil health. Respiration rates can fluctuate based on immediate conditions (like temperature or moisture) and might not always reflect the long-term health of the microbial community. For example, respiration might be high because microbes are briefly in a favorable environment, but if the soil lacks organic nitrogen (a key food source), the microbial community might not be sustainable in the long run.

By also testing for organic nitrogen in the soil, you’re getting more information about whether there is a steady, long-term food supply for the microbes. This gives you a more complete understanding of the sustainability of the microbial community. If there’s enough organic nitrogen, the microbes will have a steady food source to support their activity and growth. Without it, the microbial community might struggle over time, even if respiration rates appear healthy for short periods.