Laboratory Setup for Sensing Root-Induced Changes of Soil Hydraulic Properties in Soil Columns

Structural porosity is a dynamic soil property with high spatio-temporal variability affected by many factors. In order to develop a quantitative understanding of root driven changes in soil hydraulic properties adequate measurement setups are required. A modular soil column setup for drainage experiments providing all data for inverse determination of soil hydraulic properties was developed. The aim of this paper is to present the overall setup, and to assess if the influence of an experimental factor (plant roots) can be captured by the system.

The designed setup facilitates simultaneous measurements of soil water content (TDR-sensor), matric potential (tensiometer) and column bottom flux (balance) in 12 soil filled columns. In total 144 soil water sensors ensure a high spatial and temporal resolution (six 10 cm layers per column, time steps ≥ 5 min). An initial drainage experiment with 12 unplanted columns was combined with a second (final) drainage run investigating the variants mustard (Sinapis alba L.), rye (Secale cereale L.) and an unplanted control in four replicates. A specific data acquisition system was developed to operate the devices, and for data synchronization and management. The included semi-automatic trouble-shooting routine sustained long-term experiments. Our analyses showed very low inter-sensor variability for TDR-sensors and tensiometers (0.2 ‑ 0.5% and 1.2 ‑ 4%, respectively). Cumulative outflow data indicated only a minor contribution to variability (6.1%) between columns due to heterogeneity from filling. Therefore, a significant effect of the experimental factor plant root was not overlaid by higher variability due to undesired effects, and could be clearly identified. We concluded that the setup is adequate to identify root induced changes of soil hydraulic properties using designed experiments.