Soil Hydraulic Properties for Measuring Soil Health

Healthy soils develop structural units that allow water to infiltrate into the soil, slowing surface runoff of water from rainfall, reducing erosion and loss of nutrients, and storing water for plants’ needs. Farmers, scientists, and other soil health stakeholders need indicators to measure and interpret how well a soil performs these water-related functions.  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;
  • Local climate and soil characteristics affect the measurements; and
  • Soil health management systems take time to establish, so measurements taken in soils with newly established management will be different from those taken after the management has been in place for several years.

To address these issues, Soil Health Institute Scientists and their partners conducted a study to evaluate over 30 soil health measurements at 124 long-term agricultural research sites across the U.S., Canada, and Mexico. We compared physical soil health measurements to determine which ones are most useful for characterizing the water cycle in soils. We assessed:

  • The relationship of each measurement to a suite of soil inherent properties and climate variables;
  • The response of each measurement to soil health management practices;
  • The effect that soil type and climate had on the soil health response to management practices; and
  • The relationships among soil health responses to management.

We concluded that “field capacity” measured on intact soil cores was the best measure of soil physical health as it pertains to the water cycle. Field capacity is the amount of water remaining in a soil after it has been saturated and allowed to freely drain for usually 1-2 days. Because a soil’s structure influences field capacity, it is most accurately measured in the laboratory using intact soil cores that preserve the soil’s structure. We found that field capacity responded to management, represented a direct measure of soil physical health, is easily interpretable, and its response to management was not significantly influenced by inherent and climatic variables. Other suitable physical measurements were bulk density and aggregate stability, which responded to management and may be more practical because bulk density and aggregate stability are easier to measure compared to intact field capacity. Learn more about this study by reading the peer-reviewed manuscript here: