Silage Density and Dry Matter Loss in Silo Bags

Mike Rankin
Crops and Soils Agent
University of Wisconsin - Extension

        Silo bags have become a popular and effective silage storage method on many farms throughout Wisconsin.  Unlike tower silos, bags don't have the inherent forces of weight and gravity at work to help insure maximum density.  Hence, silage is packed mechanically.  A new study by University of Wisconsin agricultural engineers, Richard Muck and Brian Holmes, is quantifying dry matter densities and losses in silage bags.  Their efforts to date point to some interesting findings.

What was done?

        A total of 25 silage bags were filled on three different research farms (Arlington, Prairie du Sac, and West Madison) using machines manufactured by Ag Bag or Kelly-Ryan.  All loads of forage (haylage and corn silage) going into the bags were weighed and sampled for moisture, quality, and particle size.  Similarly, all silage was weighed and sampled coming out of the bags. Good and spoiled feed was weighed separately.  To date, 15 of the 25 bags have been emptied.

Density analysis

        As dry matter of silage increased, both density (lbs. dry matter/ft³⁾ and porosity also increased.  In other words, the drier the silage, the more dry matter was packed into a given volume but the more susceptible it was to air movement and dry matter losses.  Densities also tended to decrease as particle size increased.  Researchers also noted that densities varied with the person operating the machine.  The average adjusted densities for the various locations and baggers are presented in Table 1.

        Average densities at the three locations ranged from 11.5 to 17.0 lbs. D.M./ft.³.  This is similar or slightly below the range we might find in a set of properly filled bunker silos.  Perhaps the more striking result of the study is the wide range of densities found across the face of the silo bag (Figure 1).  The density of silage around the top outside half of the bag was only about 40 percent of the most dense region on the bottom center.  This has some direct management ramifications.  Any holes that occur in the top half of the bag allow for the free flow of oxygen and high amounts of spoilage throughout the silage in the top part of the bag.  Also, it is apparent that higher feed removal rates will be needed to keep silage on the top perimeter from spoiling.

Figure 1. 

Dry Matter Losses

        Total dry matter losses (gaseous, seepage, and spoilage) ranged from 0 to 38.2 percent.  Average dry matter loss across all bags was 14.2 percent (similar to a well managed bunker).  However, if the worst three bags were eliminated, the average loss dropped to about 10 percent.  A few of the trends noted to date include

• Seepage losses only occurred when dry matter was less than 32 percent.

• Unnoticed bird damage to the top of one of the bags caused a spoilage loss of 22 percent.

• Losses tended to be higher when silage was either too wet (gaseous/seepage losses) or too dry (spoilage).

• There was little or no spoilage in over half of the bags filled.

Key Conclusions to Date:

• Based on management, loss of dry matter from silo bags can vary from extremely low to extremely high.

• To reduce loss and obtain acceptable density, harvest silage crops at 30 to 40 percent dry matter.

• Correct operation of bagger is critical to get a smooth bag of high density.

• Monitor for and patch any holes.

• Feed-out at least 2 ft. of silage per day off the bag face.