Freeze-thaw effects on pore space and hydraulic properties of agricultural soils – a summary of studies and implications for the temperate-boreal zones in a changing climate

Freeze-thaw (FT) cycles have shown to affect the evolution of the pore space of agricultural soils, thereby affecting their hydraulic properties. In the temperate-boreal zones, FT patterns are projected to shift from relatively long and uniform freezing periods to more frequent fluctuations around 0°C as a result of climate change. To better anticipate potential consequences for water storage and flows in agricultural soils, a thorough evaluation of the importance of FT cycles in this context is required.

Here we summarize the findings of studies investigating the effects of FT cycles on various pore-space characteristics (e.g. macroporosity, pore connectivity, percolating pore space) and hydraulic properties (e.g. infiltration capacity, hydraulic conductivity, water retention) of agricultural soils. This includes the results of a laboratory experiment where we simulated different FT scenarios representative for current and future winter conditions in the temperate-boreal zones.

Our findings suggest that a shift in FT patterns with climate change indeed has the potential to alter, at least temporarily, water retention properties and (near-)saturated hydraulic conductivities of agricultural soils. We highlight that this is despite most changes in pore-space characteristics seem to occur in pores with a diameter smaller than 50 µm. The persisting increase in pore connectivity of specific soils with an increasing number of FT cycles appears to be decisive in this respect. However, to assess fully the magnitude of changes in soil water functions at the field scale may require modelling. We finally stress that the sensitivity of hydraulic properties to FT patterns questions the transferability of results of some previous studies to the natural environment, applying unrealistic temperatures and rates of freezing and thawing.