Freezing Temperatures and Topsoil Compaction
Last weeks polar vortex stuck around long enough to cause a pretty significant freeze on our soil surfaces. With our temperatures swinging from 0 to 60°F, we have certainly had the conditions for freeze/thaw in our soils, which is considered a physical weathering process.
Studies of soils have observed reduced compaction following freeze/thaw conditions, particularly in the upper 4 inches (Jabro et al., 2014). The actual effects of a freeze depend on how compacted your soil is, and even the type of clay. A clay thank can shrink and swell will also reduced compaction with wet/dry cycles, even without the effects of a freeze. Wet/dry cycles probably don’t have such a strong effect on sandy, coarse textured soils.
Compacted soils benefit the most from freeze/thaw, with most enjoying increased water conductivity due to cracks and wedges formed by ice wedges. Typically, the value of this decreases after a soil has been frozen three or more times (Othman et al., 1992). Soils seem to move towards a similar state, as compacted soils become less dense or dispersed particles aggregate (tilled soil), but soil aggregate stability decreasing in less compacted (e.g. no-till) soils (Wang et al., 2012). Frozen soils can also have a detrimental effect on soil carbon, as the breakdown of aggregates releases organic matter(Christensen and Christensen, 1991), but the flush of carbon decreases after four freezes.
So what are the effects on your soil type? It just depends on you have already managed it. Any compaction caused by equipment in our wet springs or fall this past year are probably being ameliorated (on the surface) with our current weather. However, those farmers with no-till fields may actually be losing larger aggregates with freezing temperatures. For no-till soils, this is probably not a largely negative effect, but simply leaves you with the strongest aggregates when spring planting arrives.