Use caution when applying manure on snowpack

January 31, 2014

For most of the state, the ground is covered in a thick blanket of snow with likelihood of more to come.  With approximately 1 to 1 ½ months before the snowmelt period, it is time to think ahead if you haven’t already done so.  Nearly every winter has a freeze-thaw-freeze period in which concrete frost forms in the ground.  Discovery Farms research has shown that manure applied on snow-covered or ice-crusted ground has a high potential for loss when snow melts.  This has been evident on multiple farms monitored.

In one example of a manure application on a heavy snowpack, 76% of the annual ammonium loss (54% of the annual total nitrogen loss) occurred from two runoff events shortly after an application.  Ammonium is an indicator of raw manure.  Snow readily absorbs ammonia and can result in high concentrations of ammonium/ammonia in runoff (Sawyer & Helmers 2008).

Figure 1 shows a second example. Using runoff events in each basin during the same time period, a relationship between ammonium and runoff volume is fairly constant except for one data point in Basin 1 (indicated by a triangle in figure 1).  Manure was applied in basin 1, but not in basin 2 within a week prior to that runoff event.  There was heavy snow and ice-crusting of the soil in both basins.  The recently applied manure in Basin 1 had elevated ammonium loss in the subsequent runoff.  There was not a similar point in Basin 2 during its concurrent runoff event indicating that the odd data point was not a normal reading for this farm.

Figure 1: Relationship of ammonium yield to runoff volume.  The “event” is a runoff event shortly after a manure application on snow-covered, ice-crusted ground.

Figure 1: Relationship of ammonium yield to runoff volume. The “event” is a runoff event shortly after a manure application on snow-covered, ice-crusted ground.

If manure applications need to be made during conditions of heavy snowpack, concrete frost or ice crusted soils, target internally drained land or low-sloped fields far from water bodies or contributing flow paths.  This will minimize the release of nutrients to freshwater systems and retain the nutrients for the following year’s crops.

Reference: Sawyer J and Helmers M. 2008. “Surface Waters: Ammonium is not Ammonia, part 3”. (www.extension.iastate.edu/cropnews/2008/0521JohnSawyerMattHelmers.htm)

Written by Aaron Wunderlin, Research Specialist  aaron.wunderlin@ces.uwex.edu

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