As corn silage harvest gets closer, most of the talk turns to moisture, kernel processing and chop length. But South Dakota State University Extension forage field specialist Sara Bauder says another practice deserves just as much attention: how tightly the crop is packed.
“Packing corn silage is one of those things that’s often overlooked,” Bauder says. “Typically, we can harvest faster than we can pack, so it’s important to focus on how well we pack piles, bunkers and any storage system where equipment is driving over the feed. Poor packing can lead to significant feed losses.”
She notes that every load coming into the bunker or drive-over pile is an opportunity to protect feed value. The tighter silage is packed, the less oxygen remains in the pile. This helps fermentation begin sooner and reduces dry matter loss. When packing falls short, trapped air can lead to heating, mold and spoilage.
Moisture Comes First
Whole-plant moisture plays a big role in how well silage packs. When the crop is harvested at the right moisture, it settles tighter, ferments better and is less likely to lose feed in storage.
“Typically corn silage should be around 60-70% moisture at harvest (depending on the storage method), and that’s basically approximately three-quarter milk line,” Bauder explains.
For years, many producers have used milk line as a quick way to judge harvest timing. It can still give a general idea of crop maturity, but Bauder says today’s hybrids make it less dependable for estimating whole-plant moisture.
“A lot of people use milk line as an indicator, which is kind of old-school,” she says. “It’s a good method to tell you the rate of dry down, but it’s not always that reliable for whole-plant moisture anymore, simply because we have so many different hybrids out there.”
Research has shown just how wide those differences can be. Bauder points to studies where some hybrids at 50% milk line tested close to 50% whole-plant moisture, while others harvested at the exact same milk line measured more than 70% moisture.
That’s why taking time to test moisture can pay off.
“The hard part with silage is you either have to cut plants down manually and chop it up to get the moisture, or you have to go cut part of a load and go take a sample,” she says. “If you don’t have a feed store near you that’ll test it for you, you can use the microwave method, and it just takes time. People don’t like to do it, but it really does help to know what your moisture is.”
Skipping this step can cause trouble before the pile is even made.
When corn silage is harvested too dry, it’s much harder to push the oxygen out during packing.
“If your silage is too dry, it’s going to be almost bouncy,” Bauder explains. “It’s just not going to want to pack very well.”
The leftover oxygen slows fermentation and gives heating and spoilage more room to develop.
Silage that is harvested too wet brings a different set of problems.
“If it’s too wet, it will pack, but we can rupture cells and end up with a effluent loss, where all of our nutrients are draining out of the pile,” she says. “And then, of course, you can have mold issues too.”
Keep Layers Thin
Once harvest starts, each load hitting the pile influences the final density. One of the easiest ways to improve density is by keeping each layer thin.
“Research has proven that the packing layers should be no more than six inches deep,” Bauder says. “If you put on a foot at a time, for example, you’re just not able to get it packed as well as you should because you’ve got too much thickness there.”
Packing tractors cannot squeeze thick layers well. Bauder notes that the top may feel firm, while oxygen is still trapped underneath. Spreading loads into thin, even layers lets tractor weight reach more of the crop instead of only pressing the surface.
This takes patience, especially on busy harvest days when trucks keep coming.
“If we get in too much of a hurry and keep piling feed on top before we’ve packed the previous layer, we’re never really able to catch up,” Bauder says.
Sticking with six-inch layers through the whole harvest also makes the pile more even and easier to manage later during feedout.
Using the “Rule of 800"
Even with thin layers, good density still depends on having enough tractor weight moving across the pile.
Bauder recommends a simple guideline called the “rule of 800.”
“Basically, to calculate the pounds you need for proper packing density, there’s an equation where you take the tons of silage delivered to the pile per hour and multiply it by 800. That tells you how many pounds you need for packing,” Bauder explains.
For example, if crews are bringing in 100 tons of silage per hour, the pile should have about 80,000 pounds of tractor weight packing it. This number surprises a lot of producers once they do the math.
“A lot of times we don’t have enough weight actually driving across the pile to get the packing done properly,” Bauder says. “You know, 80,000 pounds of tractors can be quite a bit.”
This doesn’t always mean adding more equipment. In some cases, it means removing duals to increase pounds per square inch or slowing harvest to give packing equipment enough time to keep up. Other farms may need to dedicate more time and labor to packing rather than pushing feed.
Can You Pack Too Much?
As more producers try to improve density, some ask whether too much packing can cause trouble. Bauder says that usually is not something to worry about.
“People ask about overpacking. It’s actually pretty hard to do, according to a lot of the research studies,” Bauder says. “The only time that overpacking is seen regularly is with the top layer.”
Many operators finish the last load and keep driving over the surface, hoping the extra passes will add density.
“People will put the top layer on, and then they’ll drive and drive and drive,” Bauder says. “But it really doesn’t do any good to pack it any more than you would pack any other layer because it’s only going down so far.”
Rather than making the pile denser below the surface, too much traffic on the finished top can damage the forage.
“That’s why we do six-inch layers,” she says. “It actually just ends up rupturing the plant cells or the cell walls of what’s on top, and you’re just ruining the top layer anyway when you keep driving over it.”
After the final layer has been packed enough, the next job is getting the pile covered.
Keep Safety in the Plan
The same practices that help improve packing density can also lead to bigger, taller piles. As bunkers get bigger, Bauder says safety needs to stay part of the harvest plan.
“Sometimes tractors can roll off the pile,” Bauder says. “It’s important to pay attention to packing practices and how equipment is being used.”
Clear traffic patterns, good communication between operators and high-visibility clothing can help lower the risk of collisions or rollovers during harvest.
When Harvest Outruns Packing
Keeping layers thin and the pile packed well gets harder when custom crews are bringing in silage faster than the farm can handle it. Bauder encourages producers to talk through expectations before harvest starts, not once trucks are already lined up.
“I would definitely let my concerns be known,” Bauder says. “You’re hiring them to put up feed, and you want this feed to last, so you’re asking them to deliver at the rate that you can keep up with.”
If slowing harvest is not an option, producers can still make adjustments.
“We can look at putting more packing tractors, or bigger equipment on the pile in the safest way, of course,” Bauder says. “And we can also look at potentially working with that crew. Maybe having more push tractors and more packing tractors are some factors we could consider.”
Good communication between the harvest crew and the dairy can help everyone make changes before small problems turn into expensive ones.
It Starts on the Pile
For dairies putting time and money into good corn silage, protecting that investment starts on the pile. Packing density may not get as much attention as hybrid selection, kernel processing or inoculants, but Bauder says it has a big effect on how well feed keeps through the year.
Successful packing starts with a few important steps:
- Harvest at the right moisture
- Build the pile in six-inch layers
- Match tractor weight to the delivery rate
- Cover the pile as soon as packing is complete
None of those jobs are fancy, but together they help decide how much of the crop makes it to the feed bunk.
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