A Snapshot of Soil Fertility Levels in the Region Heading into Spring

The following maps and graphics illustrate average soil nutrition and fertility levels from soil samples analyzed by Agvise Laboratories last fall.  With laboratories in Northwood, N.D. and Benson, Minn., Agvise (www.agvise.com) provides soil testing and plant analysis for crop consultants, fertilizer retailers and producers.

The amount of residual soil nitrogen was expected to be quite high following dry conditions in 2006.  This is illustrated in regional trends for soil nitrate levels when comparing 2006 wheat and corn values to 2005 values. In the figures, AGVISE Laboratories summarized the average fall soil nitrate levels following wheat and corn production (lb/ac 0-24” samples) in the Dakotas, Minnesota and Manitoba.  The bold values indicate the areas where the average soil nitrate test was much higher in 2006 compared to 2005.

The comparative results are striking.  For example, areas of South Dakota that had average soil N levels of 52, 54, and 58 lb/ac following corn in 2005 had 100, 102, and 107 lb/ac of residual soil N, respectively, following corn in 2006. This is a tremendous amount of residual soil N, and there will be many cases in drought-affected areas where the amount of N needed for the subsequent crop will be much less than a normal application.

Following a drought, soil P and K levels don’t change much compared to what they were the previous year. Dave Franzen, North Dakota State University Extension Soil Specialist, points out that this is usually the case in most years, due to the small amount of these nutrients removed in a single year by even a bumper crop, but especially so in a small, drought-affected yield.

John Lee, soil scientist with Agvise in Northwood, cautions that these numbers are just big picture snapshots to help gauge soil fertility trends.  “As averages, you can expect half of fields to be more, and half of the fields less,” he says.  While it is interesting to look at the big picture to see the overall trends, the only way to know for sure what nutrients your fields need (or don’t need) is through soil sampling analysis.