KindHarvest summary: Soil organic carbon is often associated with better water storage, but older estimating equations did not capture management-driven changes well. Researchers used intact soil cores from long-term field experiments to build new equations linking soil carbon, texture, carbonate status and plant-available water.
A broad field dataset
The Soil Health Institute-led study used samples from 124 long-term research sites across North America. The experiments included management treatments such as reduced tillage and cover cropping that had produced measurable differences in soil organic carbon.
The carbon response depended on the soil
For each 10 grams per kilogram—approximately one percentage point—increase in organic carbon, the new equations estimated an average increase of 3.0 millimetres of plant-available water per 100 millimetres of non-calcareous soil. The average response in calcareous soil was 1.2 millimetres. The non-calcareous estimate was about twice the size of earlier commonly used estimates.
What the equations can and cannot do
The work provides a better way to estimate how carbon-building management may change a soil’s water reservoir. It does not promise a fixed drought benefit on every farm: texture, carbonate content, rooting depth, rainfall, structure and crop demand all influence the outcome. The equations are most useful when paired with local soil measurements and realistic changes in carbon over time.
Related KindHarvest coverage
KindHarvest has also summarised the practical implications in Can Soil Organic Carbon Reduce Drought and Flooding?.
Source and credit
This KindHarvest Team research brief revisits 2022 reporting by Brownfield Ag News. The original news page is no longer available, so the source link now points to the open-access paper by Dianna K. Bagnall and colleagues in the Soil Science Society of America Journal. Read the full research paper and abstract.