Cover crop effects on X-ray computed tomography-derived soil pore characteristics

Authors: KAUR, PREETIKA - Auburn University; LAMBA, JASMEET - Auburn University; Way, Thomas - Tom; SANDHU, VISHAWJOT - Auburn University; Balkcom, Kipling; SANZ-SAEZ, ALVARO - Auburn University; Watts, Dexter

Submitted to: Journal of Soils and Sediments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2023
Publication Date: 7/26/2023
Citation: Kaur, P., Lamba, J., Way, T.R., Sandhu, V., Balkcom, K.S., Sanz-Saez, A., Watts, D.B. 2023. Cover crop effects on X-ray computed tomography-derived soil pore characteristics. Journal of Soils and Sediments. 24:111-125. https://doi.org/10.1007/s11368-023-03596-7.
DOI: https://doi.org/10.1007/s11368-023-03596-7

Interpretive Summary: 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 the effect of cover crops on 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. The main crop, planted the following spring, was strip-tillage cotton. Following cotton harvest, we collected cylindrical soil cores (150 mm diameter and 500 mm deep) from areas of the field where cover crop had grown and areas where no cover crop had grown. X-ray computed tomography scans which are CT scans used in medicine, were used for measuring pores in the soil and for determining the connectivity of soil pores. For the 0-100 mm soil depth, the volume of soil pores was greater for the cover crop soil cores, compared to the no cover crop cores. For 200-400 mm depth, the connectivity of the pores was greater for the cover crop cores, compared to the no cover crop cores. These results are expected to be useful in determining soil characteristics and conducting computer modeling, to retain nutrients in the crop root zone and to minimize quality degradation of groundwater and water in streams, rivers, lakes, and other waterbodies.

Technical Abstract: Cover crops have been used as effective soil management practices that enhance soil health. However, cover crops can generate connected pore networks, which can cause preferential transport of nutrients and other solutes to the groundwater or surface water via subsurface flow pathways. Our objective was to determine the effect of cover crops on 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. The main crop, planted the following spring, was strip-tillage cotton. Following cotton harvest, six replicates of intact undisturbed cylindrical soil cores (150 mm diameter and 500 mm deep) were collected from each treatment class i.e., cover crop (CC) and no cover (NC). The soil cores were subjected to non-invasive X-ray computed tomography (CT) scanning which gave images of 0.35 mm resolution. The images were analyzed to get pore statistics including pore area, pore number, and pore volume. The CC soil cores had comparatively higher values of porosity and pore number density for the top 100 mm of the soil, compared to the NC cores. Pore geometry metrics such as tortuosity did not show significant differences between the CC and NC treatments. Significant correlations were observed between CT-derived pore characteristics and root characteristics, so cover crop roots influenced the X-ray CT-derived pore properties. We found that the X-ray CT-derived soil pore characteristics are greatly influenced by the presence or absence of cover crop. Most of the significant differences occurred in the surface layer (0-100 mm depth). Volume descriptors (porosity and pore number density) and geometry descriptors (circularity and macropore diameter) were significantly greater for the CC than for the NC cores. For the 200-400 mm depth range, connectivity metrics (connection probability and Euler number density) had higher values for CC, than for NC. When correlations were performed, significant relations were found between the X-ray CT-derived macropore properties and scanned root properties determined using a root scanner.