A forage probe is the most reliable and easiest method to estimate corn silage pile density, according to Idaho research comparing it to a density calculator spreadsheet and a silage feed-out spreadsheet.

The three methods were analyzed on southern Idaho dairies, many of which hire out their harvesting.

The University of Wisconsin Silage Density Calculator spreadsheet has the “potential” to be accurate, says Steve Hines, University of Idaho Extension educator based in Twin Falls.

But it requires time and trouble to get several measurements accurate. Those include the silage’s dry matter content as it’s coming in to a pile, the packing layer thickness and the packing tractor weight.

“The few producers who we visited with who own their own harvesters had their own packing tractors, and gave us pretty good data. But when you have to rely on the custom operator, then the data that you get may or may not be quite as reliable,” Hines says.

The feed-out spreadsheet, called the Storage Density Capacity Calculator and also from the University of Wisconsin, was the least accurate method evaluated. It required pile volume before feeding, the daily feed-out weight for a few weeks and then the pile size remaining. The researchers, however, found there were too many variables to the data being gathered.

They found it difficult to accurately measure silage piles, Hines says. “Piles kind of wave in and out and top heights are high and low depending on how they were piled in and packed and were settling.”

Employees also didn’t weigh every load taken off the pile. “They weighed one once in a while so they knew about what a load weighed. And they estimated based on that. So that adds a fair amount of error immediately.”

Hines says the feed-out method would work very well in concrete bunkers, which could be accurately measured.

“The other factor that is difficult to account for is when they remove the plastic layer from the pile, there’s always a little bit of waste. So they kick that down and scoop it out of the way; it’s hard to account for that material when it’s just in a pile pushed off to the side.”

Yet the probe method has its own problems, Hines says.

“A major drawback of the probe method, while it is the quickest and we feel most accurate, is that it is definitely the most dangerous as well. Some universities tell producers not to use the probe method” for that reason.

Many silage piles are built too high to be considered safe to be near. A number of people have stood near or been taking probe samples from silage piles that have collapsed, killing or seriously injuring them. (See “Surviving A Silage Avalanche.”)

“I think we’re going to have to come up with a probe sort of like a soil density probe that the tractor operator can push into the pile, get some sort of rough estimation and determine whether or not he needs to pack some more. We can come up with complex tools for them to sample a pile, but it’s got to be something that these guys can do fast or they’re not going to do it.”

Hines, after compiling the density information, was pleased with the densities coming from area dairies.

“Our densities were averaging about 14.5 lbs/sq ft and 15 is considered minimum ideal, so we’re almost there. And, given the size of tractors, the speed that the material comes in and the size of the piles that they build in this country, I was surprised they were getting that good of packing.

“But I would like to see these numbers push up to 17-18 lbs/sq ft on a dry matter basis,” he says.