Temporal and spatial variability in 3D soil macropore characteristics determined using X-ray computed tomography

Purpose Preferential flow via soil macropores can have a large effect on water quality. Hence, it is important to quantify soil macropore characteristics to better understand preferential flow behavior in soils. Currently, little information exists on the changes in soil macroporosity in response to topographical position within a field and how macropore characteristics change temporally. The objective of this study was to use X-ray computed tomography (CT) and image analysis to quantify temporal and spatial variability in 3D soil macropore structure in a 0.40 ha pasture field. Methods A total of 36 undisturbed soil columns, 150 mm in diameter and 500 mm in length, were collected during May and September of 2019 from a pasture field located in Alabama, USA. The image analysis was performed to quantify spatial and temporal variability in soil macropore characteristics. Results and discussion The macropore characteristics varied significantly between different topographical positions and sampling seasons, especially at the surface layer (0-100 mm) depth. The soil macropores at the downslope position were sparsely distributed in the surface soil layer. This was attributed to a relatively higher degree of grazing-induced compaction due to higher soil moisture as compared to the upslope and midslope locations. In contrast, dense macropore networks were observed at the downslope positions for depths greater than 250 mm. Conclusions The results of this study show that macropore characteristics varied as a function of topography and time. Except macropore diameter, all other macropore characteristics showed an increasing trend from season 1 (spring) to season 2 (fall). The regeneration of macropores was mainly attributed to the wetting and drying cycles that promoted formation of smaller macropores (0.70-1 mm) at the surface soil, thereby reducing the average macropore diameter. Significant differences in the macropore characteristics were observed mostly in the surface layer (0-100 mm).

Automated summary

The study showed that soil macropore characteristics varied with topography and time. Besides macropore diameter, all other macropore characteristics exhibited an increasing trend. Significant differences in macropore characteristics were mainly observed in the surface layer (0-100 mm) and between different seasons.