Grassland conversion to croplands impacted soil pore parameters measured via X-ray computed tomography

Abstract

Soil porosity estimated conventionally cannot provide the spatial distribution and geometrical properties of pore networks. This on-farm study assessed the impacts of grassland–cropland conversion on soil pore characteristics. This study aimed to quantify the microscale changes in pores near the soil surface (0–10 cm) under grasslands converted to croplands managed with a rotation of corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] (CS); an integrated crop–livestock system (ICLS) of corn–soybean–oats (Avena sativa L.)–cover crops (CCs), with livestock grazing on corn and soybean residue after harvest and on CCs; and the native grassland (NG). Intact soil cores (diameter: 76.2 mm; length: 76.2 mm) were collected in three replications from CS, ICLS, and NG areas located adjacent to each other. Soil cores were scanned via X-ray computed tomography (CT) (pixel resolution: 0.226 by 0.226 mm; slice thickness: 0.5 mm). Soils under CS converted from NG significantly decreased CT-measured macroporosity eightfold. However, it increased sevenfold when CS was converted to ICLS. Higher connected porosity, connection probability, and macroporosity under ICLS and NG enhanced the saturated hydraulic conductivity (Ksat) compared with CS. The soil organic carbon (SOC) stock was increased by 13% at 0- to 10-cm depth, when soils under CS were converted to improved management (ICLS). Significant correlations of CT-measured pore parameters were found with Ksat. We conclude that CS converted from grasslands degraded SOC, pores, and other hydro-physical properties, which can be enhanced by integrating CCs and grazing on CCs and crop residues.