Effect of image resolution and soil core diameter on soil pore characteristics quantified using x-ray computed tomography

Authors: KAUR, PREETIKA - Auburn University; LAMBA, JASMEET - Auburn University; Way, Thomas; Balkcom, Kipling; Watts, Dexter

Submitted to: Journal of Soils and Sediments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Strip tillage in agricultural row crops is a system with reduced tillage, compared to conventional tillage in which the complete soil surface is typically tilled. Cover crops typically reduce soil erosion, improve soil fertility and soil quality, and suppress weeds, pests, and diseases. The roots of cover crops often generate connected pore networks in the soil. These networks can be pathways for nutrients and other solutes carried by water, to flow down into the groundwater or to surface water via subsurface flow pathways. Our experiment investigated soil macropore characteristics in the soil profile. The cover crop, a mixture of cereal rye and crimson clover, was planted in the late fall on a loamy sand soil. Cotton was the main crop, planted the following spring. We collected cylindrical soil cores, 150 mm diameter and 76 mm diameter, each 500 mm deep, from conventional tillage and strip tillage portions of the field, in the fall, following cotton harvest and before planting a cover crop, and the spring, after the cover crop had matured. X-ray computed tomography scans which are CT scans used in medicine, were used for determining physical characteristics of the soil pores. We found differences in the detected pore characteristics depending on the soil core diameter and the CT scanning resolution. These results are expected to be useful in conducting computer modeling to retain nutrients in the crop root zone and in minimizing quality degradation of groundwater and water in streams, rivers, lakes, and other waterbodies.

Technical Abstract: Image resolution and size of the soil core can impact X-ray Computed Tomography (CT)-derived soil morphological properties. The soil physical properties (e.g., soil pore size and pore connectivity) can substantially influence contaminant transport through the soil profile. Improved understanding of soil physical properties can help elucidate contaminant transport processes through the soil profile. Cylindrical soil cores, from the soil surface to a depth of 500 mm, with diameters of 76 and 150 mm, were collected from the loamy sand soil in a cotton field. Soil cores were collected from conventional tillage and strip tillage portions of the field, in the fall, following cotton harvest and before planting a cover crop (season 1), and the spring, after the cover crop had matured (season 2). The main goal of this study was to compare the influence of CT scanning resolution and soil core diameter on the detected soil pore properties. Specific objectives were 1) to quantify the effect of scan field of view on detected soil physical properties (0.35 mm vs. 0.1875 mm) 2) to determine the impact of soil core diameter (150 mm vs. 76 mm) on detected soil macropore properties, and 3) to determine the effect of chosen volume of interest for image analysis (140 mm vs. 96 mm diameter region of interest). The results of this study help our understanding of how the soil core size and the resolution at which the cores are scanned can impact detected soil physical properties. The ImageJ digital image processing program was used to analyze all the images attained from CT scanning. Results on change in soil pore properties as a function of soil core diameter and resolution show that a smaller field of view, which gave higher resolution, showed a greater number of isolated pores with greater values of anisotropy. The 76 mm soil core diameter had significantly fewer detected pores compared to 150 mm diameter cores, but the connectivity of pores was greater for the 76 mm diameter cores. Most of the significant differences were found among the cores which were collected from the conventional till treatment from season 2. There will always be a trade-off between a finer resolution and a larger field of view or a smaller sample size. The sampling procedures must be defined according to the research objective.