Hitting the Sweet Spot: When to Harvest Corn Silage

When to harvest corn silage is one of the most critical decisions a producer makes all year because he’s stuck with this corn silage for the next 12 months. The primary determinate of timing is plant dry matter, which correlates to maturity. As corn plants mature they get drier, which means the nutritional value goes down and the fermentation quality is affected.

“On the one hand, we can have very wet corn – less than 30% dry matter – that is immature, meaning the fiber quality is good, but yields are low and there’s just not enough kernel development or starch in the plant,” said Bill Weiss, professor at The Ohio State University. “Because it’s wet, you can get an overly aggressive fermentation; the pH can be a little too low and the high acetic acid might reduce feed intake. Seepage is also possible, creating not only a nutrient loss but also fluid flowing out of the silo, [which is] a significant environmental issue if it gets into waterways.”

On the dry end, 35% dry matter is about the limit in bunkers, and it’s possible to go up to 38% for bags and upright silos. This is a more mature corn plant, so fiber digestibility is going down. Starch is at a maximum, which is a positive. However, the kernel is also maturing so it’s getting harder with more protein laid down, so starch digestibility is going down.

To hit the sweet spot, producers should harvest corn silage between 30% and 35% dry matter.

“It’s a pretty wide range and probably represents typically a week to a week and a half,” Weiss said. “If you have to make a mistake, it’s generally better to be a little too wet than a little too dry.”

The corn milk line has typically been used to test dry matter, but it’s not a reliable indicator of moisture, he said. It’s best to go out in the field, chop three or four stalks and measure dry matter using the microwave oven method.

Shrink Has Shrunk

With the current technology we have available and improvements in silage making, Weiss said shrink in bunkers can be pretty low.

“Silage shrink in the bunker used to be 10% to 20% that was either disappearing through fermentation losses or it spoiled,” he said. “Now we’re only seeing about 5% or less, which is very good.”

There are two key places shrink still occurs:

Poor fermentation
Moldy feed during feed-out
The keys to fermentation are the amount of sugar present in the plants, the type and amount of bacteria in the silage, and how quickly it becomes anaerobic.

“Usually sugars for corn silage are not an issue; there’s plenty of data showing that a well-researched silage bacterial inoculant is a good thing; even without one there’s usually adequate bacteria, but the inoculant just helps things along,” he said. “The big factor is achieving anaerobic conditions – a lack of oxygen. The way to do that is to squeeze as much air out as possible while packing so you can prevent oxygen from coming back in before sealing the silo. Then normal fermentation will use up the rest of the oxygen.”

Producers have improved their efforts of sealing silos and bunkers and piles. He recommends the following best practices:

Run plastic several feet down the bunker walls and flop the plastic over the top, which helps reduce wall spoilage.
Oxygen barrier films are available that greatly reduce surface spoilage, prevent heating and reduce shrink.
Cover plastic with plenty of tires to ensure a solid seal.
The last major source of shrink is face spoilage. When you open the silage, it should be well-fermented with enough acetic acid (but not too much), which kills mold and yeast.

“If you’re going to have to chop silage a little dry, there’s an inoculant called L. buchneri, and it’s a specific strain that produces acetic acid and it really reduces heating,” Weiss noted. “There’s a lot of research on it and it increases acetic acid, which causes a loss of energy, but it greatly reduces mold growth. On drier silage, this is a recommended practice. On wetter silage, it is usually not necessary.”

Silage Safety Tips

There’s a lot of activity going on when you’re filling bunkers and silos. Here are just a few safety reminders:

Before you begin packing, have a team meeting to make sure everyone knows what they’re supposed to be doing, and review a complete list of safety tips.
No one should be walking around during packing, but if you must, be sure to wear high-visibility clothing so everyone can see you.
Watch driving too close to the edge of the bunker. Forage is typically not packed as densely on the wall. If you’re right next to the wall, the wheels could sink and the tractor could flip over.
Once a face is developed, cave-ins are possible. There’s no reason a person should ever be close to the face of a bunker silo – maintain a proper distance even in a vehicle or tractor.

Headline photo courtesy of Bill Weiss
Bill Weiss, The Ohio State University

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Hitting the Sweet Spot: When to Harvest Corn Silage

JOB TITLE: PRE-SELL DAIRY HYGIENE SUPPLIES SALES SPECIALIST