Packing Silage – Get It Right

Brian J. Holmes
Extension Agricultural Engineer
Biological Systems Engineering Department
University of Wisconsin-Madison
4-25-06

Proper filling of bunkers and piles of forage pays big dividends.  Dry matter losses occurring during filling, storage and feedout will be higher in silage packed at low density (< 14 lbs DM/Ft³).  Higher density also allows more feed to be placed into a silo, thus reducing the cost of additional storage capacity.  One dairy producer was not satisfied with the 14-15 lbs DM/ft³ in his silage pile, while others using the "same" filling procedures were achieving significantly higher density.  The producer increased the weight of one packing tractor, added a third packing tractor, and reduced the thickness of forage prior to packing.  The dairyman estimates the capacity of the same volume pile increased by about 50%.  This represents an estimated density of 21.5 lbs DM/ft³.  Dauphin County, PA Extension Agent Paul Craig measured density in fourteen bunker silos before and after producers were advised about how they might improve density in their silos.  Before instruction, two of the fourteen producers were achieving an average dry matter density of 14 lbs DM/ft³ or greater.  Following instruction, six of the fourteen producers achieved an average DM density at or above 14 lbs DM/ft³.  Employees of Vita Plus have been measuring density on the face of bunker/pile silos and have found the average density for hay silage is 13.7-16 lbs DM/ft³ and 11-12 lbs DM/ft³ for corn silage.  The appreciably lower DM density in corn silage could be related to the higher harvest rate for corn versus hay while not making the appropriate changes in forage packing procedures.

Silage density in a bunker/pile silo is influenced by:  packing tractor weight, layer thickness, forage delivery rate, forage moisture content, depth of forage in storage, and forage particle length.  Brian Holmes (UW Madison) and Rich Muck (US Dairy Forage Research Center) provide spreadsheet tools on the Harvest and Storage page of the Team Forage web site, <http://www.uwex.edu/ces/crops/uwforage/storage.htm>.  These tools help producers consider what changes they might make to improve the density in their bunker/pile storages.  The "Storage Density Calculator" spreadsheet can be used to estimate the density currently being achieved in the storage.  The producer uses a TMR wagon scale to measure the weight of feed removed from the storage over a period of time.  After measuring the volume removed, the spreadsheet is used to determine average wet density.  If dry matter is measured, DM density is also calculated.  Spreadsheets for predicting estimated density before packing bunker silos and pile silos are also downloadable from the web site.  Input variables include dimensions of the storage cross-section, harvest rate, packing tractor weight, number of packing tractors, layer thickness, and dry matter content.  If the measured or estimated density is insufficient, the producer can change those variables which are under his/her control to determine if those changes will result in adequate predicted density.  The most influential factors within the "Bunker Silo Density Calculator" and the "Silage Pile Density Calculator" spreadsheets are packing tractor weight and layer thickness.  Packing tractor weight can be increased by adding weight to existing tractors, adding more packing tractors, and/or adding heavier packing tractors.  Layer thickness can be reduced by pushing less forage onto the filling face before packing or by increasing the area of the filling face before packing.  Most producers do not know the depth of the filling layer before packing.  Another spreadsheet, "Floor Length to Achieve Bunker/Pile Silo Filling Layer Thickness Calculator," is available to help achieve a desired layer thickness.  Input variables include:  desired layer thickness, height and width of bunker/pile, and dimensions of forage transport truck/wagon.

Producers should be aware they may not be achieving adequate density in their bunker/pile silos, especially if they have increased harvest rate by using high capacity forage harvesters.  They should check achieved density to see if they are getting the packing job done correctly.  If higher density is needed, consider using the spreadsheet tools to determine what changes might be made to make improvements.