BW-03
Cover crops & keyline ponds
Sèvre-Basse,
France
46.6021° N, 0.9843° W
( Site file
Cover crops and keyline ponds on 2,316 ha across 41 farms. After three seasons, soil organic carbon in the top 30 cm rose by 0.47 pt.
The problem
Sèvre-Basse is a flat, open plain where water runs off in winter and goes missing in summer. In 2025, soil probe S-12 spent 71 days below the soil moisture alert. Bare ground between crops was losing both water and carbon.
What we built
From 2022, 41 farms on 2,316 ha moved to winter cover crops and keyline ponds. The ponds follow the contour of each field, slow the run-off and hold it where the soil can take it in. Every change was agreed farm by farm, and each farmer kept their own rotation.
We take soil cores every season on fixed plots, and Northfield Soil Laboratory runs the analysis. After three seasons, soil organic carbon in the top 30 cm went from 2.31 % to 2.78 %, a rise of 0.47 pt. Between 30 and 60 cm, it moved from 1.04 % to 1.12 %.
The probes report moisture at 30 cm every ten minutes. Each farm sees its own plots; the register shows the plain as a whole.
Coordinates
46.6021° N, 0.9843° W
Commissioned
Structure
Winter cover and 14 keyline ponds on 41 farms
Scale
2,316 ha of farmland
Partner
Lône-Vire Water Agency
Homes behind the line
0
Sensors
64
Status
Monitoring
+0.47 pt
soil organic carbon, 0–30 cm
( Readings
What this site measures,
and who checks it.
R-0431
Soil organic carbon, 0–30 cm
+0.47 pt
Northfield Soil Laboratory
Verified
R-0432
Days of soil moisture below wilting point
−15 days
Northfield Soil Laboratory
Reported
