Monitoring of water balance in soils dominated by arable farming – development of a measurement concept for the Erosion and Runoff Laboratory (EARL)

Soil erosion damages many fertile regions world-wide. At the same time, scientists expect more frequent and intense erosive precipitation events and droughts with proceeding climate change.

The Erosion and Runoff Laboratory (EARL) of the Bavarian State Research Center for Agriculture (LfL) is an extraordinary experimental site under construction in Lower Bavaria (Germany) to study the physical, social, and economic factors driving the change in landscape water balance, as well as the increase in surface runoff and erosion under agricultural use. During the twenty-year study period, future-proof cropland systems (i.e., a combination of crop rotation and soil management regimes) will be investigated in terms of their effect on water retention, erosion protection, as well as contaminant and nutrient leaching in the hills.

Volumetric water content and matric potential are measured at three depths in 36 plots, each measuring 330 m² (55 m long and 6 m wide), and the data are validated using a central cosmic ray neutron scattering sensor. Surface and interflow runoff are monitored continuously for each precipitation event. Runoff samples collected automatically by samplers will be analyzed in the laboratory regarding the transported materials and substances. Root growth scans and regular drone flights provide data on phenological growth and soil conditions, while soil water sampling and an extensive meteorological station including distrometers and precipitation-impulse gauges ensure the boundary conditions.

We believe that this design enables comprehensive process-based modeling and a validated balance of energy, water, and material flows on the hillside scale for each individual plot. As the EARL is designed as a collaborative research facility, the created dataset will enable the scientific community to understand critical processes within agricultural soils’ vadose zone better.

Comparatively high financial resources for long-term monitoring projects in the vadose zone are very rarely available. However, the precise measurement of water fluxes in the vadose zone is difficult, the availability of non-destructive measuring instruments is limited, and the results are often compromised by individual unconsidered aspects. Consequently, the risk of an erroneous measurement design and the associated bad investment due to the naturally limited perspective of a small research group is high. Therefore, we want to present our measurement concept for the vadose zone in detail and discuss it with experts before the final installation of the measuring equipment in summer 2025.