Impact of long-term cover crop treatments on soil hydro-physical and X-ray computed tomography derived soil pore characteristics

Cover crops are one of the most effective field management practices for improving soil organic matter, soil structure, infiltration, hydraulic conductivity, and water retention capacity. Changes in soil structure caused by cover crops can influence soil macropore characteristics, which can impact water and nutrient cycling processes in agricultural systems. The objective of this study was to evaluate the long-term impact of cover crop (CC) vs. no cover (NC) on soil hydro-physical properties and X-ray Computed Tomography (CT)-derived pore characteristics in the field under a cotton crop. The experimental site has more than 125 years of continuous cotton rotation with CC and NC plots. Undisturbed soil samples collected from each treatment, down to a depth of 400 mm, were analyzed for X-ray CT-scanned pore characteristics . Soil hydro-physical properties studied include soil bulk density (ρ b ), soil organic carbon (SOC), wet aggregate stability (WAS), soil water retention characteristics, and saturated hydraulic conductivity. Results revealed that CC had higher soil pore volume characteristics (macroporosity, macropore number density, and surface area density) in the top 100 mm soil layer than the NC treatment, and other depth layers. Cover crop treatment also improved pore geometry features (circularity, tortuosity, and degree of anisotropy) across the overall soil profile. Pore connectivity features (pore interconnectivity and connection probability) showed significant variation along depth, with the top layers (0–200 mm) having better pore connectivity than the bottom layers (200–400 mm). Root architecture in the cores was assessed from X-ray CT data using ImageJ , and the standard root scanning method using a WinRHIZO root scanner. The CC treatment had higher root volume and surface area than the NC treatment, illustrating CC's contribution to increased soil porosity by higher root activity. In the top 400 mm of soil profile, the CC treatment decreased ρ b by 9.55%, and increased SOC by 102% (from 0.43% under NC to 0.87% under CC) and WAS by 62%. Plant available water in the top 50 mm layer increased from 3.38% to 11.27% under CC, corresponding to a 233% increase relative to the lower baseline value under NC treatment. The study illustrates that CC has the potential to improve macropore characteristics and hydro-physical properties. Hence, quantitative and 3D visualization of soil pore structures and their relationships with root characteristics and hydro-physical properties can provide meaningful insights about macropore networks among different soil management practices.