Effect of different tillage systems on aggregate structure and inner distribution of organic carbon

Tillage is a common agricultural practice affecting soil structure and biogeochemistry. Pore network geometries are crucial to oxygen concentration, gas diffusivity, water location and water movement. Soil aggregates, 4–6mm in diameter and collected from silty loam in Belgium and sandy loam in China, were scanned using a micro-computed tomography scanner. Images with a pixel size of 6.9μm were then processed with ImageJ software for pore network analysis. The treatments were no tillage (C-NT) and conventional tillage (C-CT) in China, and shallow tillage (G-ST) and conventional tillage (G-CT) in Belgium. The results showed that aggregates in conservational tillage (G-ST and C-NT) had numerous connected pores compared with conventional tillage (G-CT and C-CT). The Euler number (Ev) was significantly lower and visible total porosity and surface area (SA) were significantly higher in conservational tillage (G-ST and C-NT) than in conventional tillage (G-CT and C-CT) in both studied locations.The predominant size of pores was significantly higher in conservational tillage (G-ST and C-NT) than in conventional tillage (G-CT and C-CT) (>150μm vs 90–120μm). Pore location within the aggregates also showed differences, with porosity being evenly distributed in the aggregates under conventional tillage (G-CT and C-CT). Under conservational tillage (G-ST and C-NT), the aggregates were heterogeneous, showing higher porosity at the center of the aggregates. There was a higher soil organic carbon (SOC) content in the external layer than in the internal layer in conservational tillage in Belgium (G-ST). In no tillage in China (C-NT), the SOC in the external and internal layers, however, showed similar results.Overall, conventional tillage (G-CT and C-CT) reduced the proportion of the largest pores within soil aggregates, whereas there was no significant relationship between pore morphologies and SOC content. Further investigation is required to measure the active and slow carbon pool distribution in the different layers and under different tillage practices.