September 28, 2012

Some dryland corn producers this year turned to silage production to get the most value from their low-yield crop. Once stored, questions have come up on how to estimate the tonnage of silage in a bunker silo.

According to research at the University of Wisconsin and Cornell University, when silage was packed in a bunker silo to a density of greater than 14 lb of dry matter per cubic foot, it ensiled well. However, bunker silo densities less than 14 lb dry matter per cubic foot resulted in dry matter losses of 17-20%.

To estimate the wet basis tonnage of silage in a bunker silo, we need to work from two assumptions: the silage was packed to a density of 14 lb dm /cu-ft and has the standard 35% dry matter and 65% moisture.

Example Calculation

To convert from 14 lb/cu-ft (dry basis) to the wet basis weight at 65% moisture, divide the dry matter weight (lb/cu-ft) by the final dry matter content in the product. The example specified 65% moisture therefore the silage contains 35% dry matter.

In this example the actual wet basis density of the silage is 14 lb per cu-ft / 0.35 = 40 lb /cu-ft

The pounds of silage in the silo is calculated by multiplying:

Length (ft) x width (ft) x depth (ft) x density (lb/cu-ft) at the final moisture content.

For example the silo is 50 feet long by 30 feet wide and the silage averages 12 feet deep.

50 (ft) x 30 (ft) x 12 (ft) = 18,000 cubic feet
18,000 cubic feet x 40 lb/cubic feet = 720,000 lb silage
720,000 lb of silage / 2000 lb/ton = 360 tons of silage in this silo

Tom Dorn
UNL Extension Educator