Concrete frost: formation and implications
January 31, 2012
This has been another year of uncharacteristic weather in many areas of Wisconsin. Unlike last year that had above average snowfall, this year has been unseasonably warm with lower than average snow. We did finally have a cold snap a few weeks ago that resulted in the rapid development of frost depth in the soils as a result of the lack of snow cover to insulate the ground. Subsequently we had another warm-up last week and many areas in northeastern Wisconsin had over an inch of rain. Water ponded in many areas that are typically well drained and significant runoff was observed in many areas.
Commonly termed “concrete frost,” this soil condition is a result of most of the pore space in the surface of the soil being occupied with frozen water. During warming conditions, especially when additional precipitation in the form of rain is received, the water on the surface begins to infiltrate into the soil and then is frozen when it reaches the frost layer below. In some situations, the upper profile of the soil becomes nearly saturated with water that then freezes during the night when temperatures drop below freezing (Figure 1). 
Concrete frost removes the soil’s ability to infiltrate additional water as the entire surface pore space is already filled with ice. Additionally, it takes higher and/or prolonged temperatures to remove concrete frost conditions as compared to frost in the soil formed during unsaturated conditions.
Data collected by Discovery Farms has shown that during concrete frost conditions, little to no infiltration occurrs in the soil. Nutrients applied to soils during concrete frost conditions have a very high likelihood of loss via surface runoff. Nutrient applications should be avoided during concrete frost conditions. This is not always possible, so nutrient applications that need to be made during concrete frost conditions should utilize internally drained land (closed depressions) or low sloped (flat) land.
In areas of Wisconsin where concrete frost has formed, it is likely that this condition will remain until after the frost comes out of the ground, typically in mid-March. The extended warm conditions that are forecasted for this week may potentially remove the concrete frost in some areas. Fields should be observed for standing surface water during frozen ground conditions for an indication of concrete frost formation and these fields should be avoided for nutrient applications.
Written by Eric Cooley, etcooley@wisc.edu