Everyone in Minnesota has recognized that the climate of March has changed in recent decades.

It is obvious from many perspectives — including a mean monthly temperature that is now 5 to 7 degrees F warmer than what it used be decades ago, less snow cover except for far northern counties, and relatively more rainfall events than snowfall events.

These measured climate changes have profoundly affected soil behavior as well. This is a significant benefit to the Minnesota farmer.

Throughout the 20th century, soils froze to deeper levels winter by winter, with maximum frost depths on average ranging commonly from 40 to 60 inches — and in extreme years, going to 70 to 80 inches. Further, the maximum depth of frost would typically be measured during the first week of March.

After that, the absence of snow cover, longer day length and higher sun angles would begin to thaw the soil much more rapidly, so that by the end of the month there was little frost left in the ground. Melted snow water as well as subsequent April precipitation could then infiltrate the soil and help recharge the root zone before the planting season began in May.

Over the past two decades, 1998-2017, this historical pattern has been all but absent except during the cold springs of 2002, 2013 and 2014. In most years, soil frost has reached maximum depth in early February, and complete thaw has occurred by the first week of March.

Earlier thaw means deeper moisture recharge
In this context, much of the precipitation that comes in March fell on thawed soils that benefited from the resulting recharge of moisture to deeper layers of the soil. This is a sharp contrast to most of the 20th century, when much of the precipitation in March fell upon still-frozen soils and was lost to runoff.

Having thawed soils for a longer period of time ahead of the planting season from late April to early May allows for the opportunity of more moisture recharge.

This change in soil behavior during March proved to be an asset specifically in the growing seasons of 2007 and 2012. The previous autumn seasons in 2006 and 2011 were especially dry, and therefore soil moisture storage across most of the state was below normal coming into the springs of 2007 and 2012. However, a warm March, absence of soil frost and abundance of precipitation during March and April of those years alleviated the stored soil moisture deficiencies across most of the state just prior to the planting season.

As a result, farm crops were better able to endure the warmer-than-normal summers of 2007 and 2012, and the midseason drought of 2012.

Because the climate of autumn 2017 left some soil moisture deficits in portions of western Minnesota, a warm, moist March 2018 may benefit soil recharge in those areas just ahead of the growing season, as was the case in 2007 and 2012. We shall see.

Seeley is an Extension climatologist with the University of Minnesota.