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• Structure liming modified macropore networks, but not mesopore networks. • Structure lime tended to reduce macroporosity, macropore diameters and connectivity. • Structure liming tended to reduce readily dispersible soil. • Liming effects on pore networks differed substantially between sites. • Although quantitatively different, effects generally pointed in the same direction. Structure liming aims to improve soil structure (i.e., the spatial arrangement of particles and pores) and its stability against external and internal forces. Effects of lime application on soil structure have received considerable interest, but only a few studies have investigated effects on macro- and mesopore networks. We used X-ray computed tomography to image macropore networks (ø ≥ 0.3 mm) in soil columns and mesopores (ø ≥ 0.01 mm) in soil aggregates from three field sites with (silty) clay soils after the application of structure lime (3.1 t ha−1 or 5 t ha−1 of CaO equivalent). Segmented X-ray images were used to quantify soil porosity and pore size distributions as well as to analyse pore architecture and connectivity metrics. In addition, we investigated the amount of readily dispersible soil particles. Our results demonstrate that structure liming affected both, macropore networks and amounts of readily dispersible soil to different degrees, depending on the field site. Significant changes in macropore networks and amounts of readily dispersible soil after lime application were found for one of the three field sites, while only some indications for similar changes were observed at the other two sites. Overall, structure liming tended to decrease soil macroporosity and shift pore size distribution from larger (ε >1.0 mm) and medium sized macropores (ε 0.3–1.0 mm) towards smaller macropores (ε 0.1–0.3 mm). Furthermore, liming tended to decrease the critical and average pore diameters, while increasing the surface fractal dimension and specific surface area of macropore network. Structure liming also reduced the amounts of readily dispersible soil particles. We did not find any changes in mesopore network properties within soil aggregates or biopore networks in columns and aggregates. The effects of lime on macropore networks remain elusive, but may be caused by the formation of hydrate phases and carbonates which occupy pore space. [ABSTRACT FROM AUTHOR]

Soil structure influences water infiltration, aeration and root growth and, thereby, also the conditions for sustainable crop production. Our objective was to quantify the effects of different soil management methods, with a focus on liming, on the topsoil structure of clay soils in Sweden. We sampled 32 intact soil columns (18 cm high, 12.7 cm diameter) from an experimental field with four treatments: conventional tillage (CT), conventional tillage followed by liming (CTL), reduced tillage (RT) and unfertilized fallow (UF). The samples were taken in autumn after harvest, seven years after CaO was applied to the CTL plots. We also sampled in total 72 smaller columns (6 cm high, 6 cm diameter) from the same experiment and from two additional liming experiments where a mixture of Ca(OH)2 and CaCO3 had been applied three years prior to sampling. All columns were analysed using X-ray tomography. One soil aggregate (diameter approximately 5 mm) were isolated from each small column and analysed with the same method. Despite a relatively large number of replicates per treatment for the large columns, there were no significant differences between any of the investigated macropore network properties related to tilled treatments. It is possible that the effects of liming on soil structure was limited to a few years, which means that any effect would have diminished by the time of sampling. The UF treatment, in contrast, exhibited more vertically oriented macropores, which were also better connected compared to the other treatments. This confirms previous findings that tillage may disrupt the vertical continuity of macropore clusters. Liming had generally reduced total imaged porosity for pores >100 μm) for the smaller columns resulting in less connected pore networks. Liming had no significant effects on the pore networks (pores>11 μm) of the aggregates. [ABSTRACT FROM AUTHOR]