Impact of land use and tillage practice on soil macropore characteristics inferred from X-ray computed tomography

Quantification of soil macropores is important to enhance our understanding of preferential flow behavior in soils. However, knowledge of 3D soil architecture for different land uses in a continental climate region is limited. X-ray computed tomography is a novel technique that can provide valuable information about the 3D features of the soil, such as connectivity, length density, and tortuosity, that largely control water flow through the macropores. In this study, X-ray computed tomography and image analysis were employed to quantify the soil macropore characteristics from four combinations of different land uses and soil tillage practices - native grassland (Nat), alfalfa (Alf), conventional till-corn (CT), and no-till corn (NT) systems. A total of 15 undisturbed soil columns, 150 mm in diameter and 500 mm in length, were collected from different fields. The macropore characteristics were distinctively different for different land use and tillage treatments, especially near the surface depth (top 100 mm). The soil macropores under CT were highly connected and concentrated mostly in the surface soil layer. In contrast, macropores under NT were larger and had well-developed pore networks. The Alf field had relatively larger and more vertically oriented macropores as compared to the Nat field. Relatively larger macroporosity and a higher number of macropores were observed in the surface of soils collected from Nat field. Macropore characteristics were mostly similar between Alf and NT treatments. The results of this study facilitate quantitative evaluation of 3D soil macropore features with significant implications for non-equilibrium flow prediction and contaminant transport modeling in soils.