Carbon Paper Interpretive Summary

Interpretive Summary of the Technical Paper:

“An evaluation of carbon indicators of soil health in long-term agricultural experiments”

Organic carbon is the basis of the soil food web. When soil microbes feed on carbon as a source of energy, it affects nutrient cycling, water cycling, and greenhouse gas emissions. These biological processes provide nutrients for plants and create aggregates in the soil that help increase water infiltration and reduce erosion. A wide variety of measurements have been suggested to assess important aspects of carbon cycling in soils, yet selecting the right indicator has been difficult because:

  • There are many measurements to choose from, and it is hard to compare different measurement methods;
  • The measurements can be highly variable across landscapes and time; and
  • Local climate and soil characteristics affect the measurements.

To address these issues, the Soil Health Institute collaborated with approximately 100 partners to assess soil health measurements for a range of management practices at 124 research sites across North America. We compared seven measurements (soil organic carbon, loss on ignition, 24- and 96-hour potentially mineralizable carbon, water extractable organic carbon, permanganate oxidizable carbon, and beta-glucosidase enzyme activity) to understand which ones best characterize soil health. These measurements quantify the amount of different types of carbon or the potential for microbes to cycle that carbon. We assessed:

  • The relationship of each measurement to a suite of soil inherent properties and climate variables;
  • The response of each measurement to management practice;
  • The effect of soil type and climate on response to management; and
  • The relationship among indicators in their response to management practices.

Across North America, all C measurements responded to reducing tillage, cover cropping, utilizing organic sources of nutrients, and retaining crop residue, but did not respond to changing a cropping system’s diversity. We examined the effect of tillage in more detail because many research sites had tillage experiments. We found that reducing tillage generally resulted in higher levels of all C measurements regardless of soil texture, and this response was generally greater in wetter climates. We concluded that, while many of these C measurements provide insight into soil health, soil organic carbon and 24-hour potentially mineralizable carbon are recommended based on their ease of interpretation, availability, and relative low cost.

Learn more about this study by reading the peer-reviewed manuscript here: