Impact of freeze–thaw cycles on soil structure and soil hydraulic properties

Abstract. The ploughing of soils in autumn drastically loosens the soil structure and, at same time, reduces its stability against external stresses. A fragmentation these artificially produced clods during wintertime is often observed areas with air temperatures fluctuating around freezing point. From pore perspective, it still unclear (i) under which conditions frost action has a measurable effect on structure, (ii) what impact hydraulic properties is, and (iii) how many freeze–thaw cycles (FTCs) are necessary to induce changes. aim this study was analyse cumulative effects multiple FTC for two different textures initial structures. silt clay substantial amount swelling minerals silty loam fewer swell/shrink dynamics were either kept intact undisturbed cores taken from topsoil grassland or repacked ploughed field nearby. FTCs simulated controlled changes ≥ 48 µm regularly recorded using X-ray µCT. After 19 FTCs, measured, resolution structural characteristics enhanced towards narrow macropores subsamples scanned 10 µm. dependent texture, number FTCs. Frost induced consolidation clods, resulting systematic reduction sizes macropore connectivity. In contrast, systems only slightly affected. Independent macro-aggregates larger than 0.8 1.2 mm increased connectivity pores smaller 0.5 mm. unsaturated conductivity all treatments by factor 3 matrix potential range −100 −350 hPa, while water retention affected soil. Already 2 5 enforced well-connected system treatments, but steadily improved further implications milder winters caused global warming twofold. soils, beneficial seedbed will be less intense. have reached dynamic equilibrium that experienced making, there increase supply through increasing continued might also efficient future.