Soil Moisture - too much of a good thing?

Anyone growing up in Saskatchewan is well acquainted with soil moisture even if they don't realize it.  Everyone can remember a summer when farmers would say things like, "we need at least two inches of rain in the next week for the crops to be decent this year."  People like to talk about moisture a lot in Saskatchewan, or more accurately, the lack of moisture.  Saskatchewan is a mid-continental, semi-arid province which means that we rely on precipitation to replenish the majority of soil moisture.  It isn't just rainfall that is important either, snowfall accounts for approximately one third of the annual precipitation.  As well, there is a geographical distribution of precipitation in Saskatchewan with higher annual precipitation in the north declining to the south.  However, it seems more often than not, that precipitation is  widely variable and can strongly affect how crops will perform from one year to the next.

2009 and 2010 are recent examples of how dramatically moisture can change in two consecutive years.  In 2009, conditions were cool and dry.  Most of the stress experienced by crops was due to lack of moisture and lack of heat.  Soil moisture completely changed in 2010 when the rain wouldn't stop all summer.  It was difficult to seed crops in the spring because it was so wet and many fields remained flooded for much of the summer.

Map of Saskatchewan showing cumulative rainfall throughout growing season in 2009.  Map is from the Government of Saskatchewan 2009 Crop Report.  A full version of the report can be found at http://www.agriculture.gov.sk.ca/crprpt091222

Map of Saskatchewan showing cumulative rainfall throughout 2010 growing season.  Map is from the Government of Saskatchewan 2010 Crop Report.  A full version of the report and maps can be found at http://www.agriculture.gov.sk.ca/crprpt101104

Just at first glance, it is obvious that the two years were very different in regards to rainfall.  The different rainfall regimes influenced soil moisture and crop production dramatically.  Many of the crops grown in Saskatchewan are more drought-tolerant than moisture tolerant, so the large surplus of moisture did not benefit crops particularly well in 2010.  According to the Saskatchewan Crop Reports, in 2009 crops were average to above-average in quality and yield.  However, in 2010 the yields were average to above-average, but the quality was below-average.  There were several reasons for this including seeding late, crop loss due to flooding, plant stress from too much moisture, and plant disease.  All of these issues were related in part to excess soil moisture.

The soil moisture surplus in 2010 also carried through to 2011.  In the fall of 2010, much of the soil was fully saturated or had a higher moisture content than usual for that time of year.  This meant that when the ground froze, much of the pore space was filled with water.  In the spring of 2011, areas all over Saskatchewan experienced flooding because the winter snowpack started to melt and there was very limited infiltration into the soil.  My field site was not spared from the flooding.  All of my study plots were submerged for most of the spring in 2011.

Water as far as the eye can see.  Me (Morgan) at my field site near Scott, SK in April 2011.

Do you have any stories about the excess moisture we experienced in 2010? Or the flooding in 2011? Please feel free to share your stories in the comments section.

The role of soil moisture will also be discussed in more detail later in the soil formation and organic matter posts; however, it is clear that soil moisture is vital to crop production, but sometimes you can have to much of a good thing.

Information and maps from the Government of Saskatchewan Crop Reports was obtained from

http://www.agriculture.gov.sk.ca/Crop-Report.  For more detailed information, check out the Crop Reports from various years.