Challenges in monitoring the undisturbed top soil pore scale structure of an agricultural field

Numerous reviews and meta-analyses have examined the vast body of literature evaluating the impact of the different agricultural soil preparation or of the various steps of cultural itinerary on plant growth, water regulation, carbon storage, etc… in short, on soil functions and services, which inherently depends on the soil processes occurring at the pore scale.

For example, the largest pores in the soil (macropores) significantly contribute in regulating the soil water cycle, as they improve infiltration capacity and drainage rates. There is however limited knowledge about the interactions between initial and boundary conditions with the topology and geometry of macropore networks in natural soils, and their influence on water flow. More long-term monitoring data, and dynamic experimentations, are needed to evaluate and model the impact of agricultural management practices on the soil resilience to maintain its functions.

One method to quantify the arrangement and the size distribution of the soil macropore network is X-ray computed tomography (X-ray CT), which is now routinely used world-wide. Images acquisition, pre- and post-processing, and pore structure quantification protocols are increasingly refined and tending towards standardization, thereby contributing to shared and comparable knowledge.

We initiated a research project aiming at monitoring the soil macropore network in agricultural soil and evaluate its response to different management practices (tillage recovery and multispecies cover cropping) using X-ray CT. We are developing a sampling device to extract soil samples (100 cm³) for analysis with X-ray µCT at time zero, after which the samples will be reinserted and embedded into the field for a six-months period before being extracted again. This process will be repeated at least four times.

We hypothesize that tillage, occurring above the sample, where it creates a connected isotropic soil pore structure with a low spatial extent, will modify the living and biochemical equilibrium of the soil and therefore modify the macropore network inside the sampling cylinder, located below the plough pan. On the opposite, we estimate that resistant macropore would remain when no tillage is applied, with an increased resistance under a covered soil. We also hypothesize that persistent macropore network is preferentially used by the main plant roots, as the macropores network created by roots is also the primary contributors of the network connectivity.

The experimental set up will be installed in the field in February 2026 for a short-term trial involving monthly sample extractions in order to assess the feasibility and accuracy of the method. The study per se will be conducted afterwards.  We will present the encountered challenges with this initial trial as well as the first quantifications of temporal changes of the soil macropore network with time.

Sarah Smet, as a post-doctoral research fellow, acknowledges the support of the National Fund for Scientific Research (Brussels, Belgium).