Corn Silage: Predicting Harvest and Moisture Level for Better Quality

( University of Wisconsin )

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In the first of a three-part video series, the University of Wisconsin Extension team talks about the best time to harvest corn for silage. As our moderator reminds us, you only get one shot to harvest it at the right time.

Liz Binversie, Brown County University of Wisconsin Extension agriculture educator, moderates a panel discussion with the following individuals:

  • Joe Lauer, corn agronomist for University of Wisconsin-Madison and University of Wisconsin Extension
  • Kevin Jarek, crop soils and horticulture agent for University of Wisconsin Extension in Outagamie County
  • Randy Shaver, dairy nutrition specialist for University of Wisconsin-Madison and University of Wisconsin Extension

What should producers consider when deciding when to harvest their corn silage this year?

Joel Lauer: There’s a number of indices and guidelines for predicting a corn silage harvest. It’s really a season-long decision. One of the first things farmers should do when they plant their fields is to note the hybrid maturity of the hybrid and also the planting date of the field that’s going to be intended for corn silage use. About halfway through the season, it’s a good idea to note the tasseling or silking date.

One of the things about corn is the grain-filling period of corn is relatively consistent. If you know the tasseling date, then about 42 to 47 days after silking, all those kernels are going to be close to the 50% kernel milk stage of development. Later on, as that crop begins to dent and the kernel milk line begins to move, we have a number of kernel milk triggers that help us time corn silage harvest. Usually when you’re at about 80% kernel milk, it’s a good idea to do a drydown to see where you’re at in terms of moisture. In the field, many agents, county programs and co-ops will help with this.

Once you know the moisture, assume about a half percent per day drydown rate to predict when that field is going to be ready. There is an overall kind of accumulator of the information from Wisconsin at a website. If you search UW corn silage drydown, you can get information about neighboring counties. Once you’re really close to doing chopping, you can do a final check again to determine where you’re at.

Many people use custom choppers to harvest their corn silage, and when that custom guy shows up at your front door you need to be ready to cut. One way to adjust that in the field is to adjust your cutting height, especially if you’ve got adequate forage needs, and generally this year we’ve got some pretty good forage supplies out there. By raising the cutter bar 1", you can lower the silage moisture about two to four moisture points.

The wettest part of the plant is the lower stalk. The driest part of the plant is the grain. Again, you can adjust that moisture a little bit.

What do you see at the county level?

Kevin Jarek: At the county level, the forage councils serve an important role. You mentioned [them] earlier as far as co-ops and other places that will help farmers determine silage moisture. There’s primarily two ways that we do that out here across the state. The first being using a Koster tester. A Koster tester is simply a heating element where we subsample from the silage, put it on that hot plate and let it cook for 20 to 25 minutes. We get that moisture reading, and that’s going to give us a quick estimate. The same day the farmer brings the sample in they can leave with an idea of where the moisture is at in their field.

The other method would be to do NIR testing at one of the approved labs in the state of Wisconsin. Certainly, from an accuracy standpoint, NIR testing is going to be more accurate because they do dry the samples down in an oven. However, unless you have a sponsor to cover the cost, there is that, whereas most forge councils do provide Koster testing without charge.

What we have found as far as the difference in the moisture between the Koster testers and the NIR samples is about two points. Producers are going to want to add a point or two of moisture to the Koster tester reading since we simply haven’t been able to cook all that moisture out in the short period of time.

When it comes to predicting the harvest date, a lot of that comes down to the structure itself. When we look across the state, we have upright silos, we have bunker silos and bags. Each of those has a specific moisture content that is ideal for them. While we can get a reading from the field itself, you need to look at the individual structure you’re storing in in order to determine when it is time to actually go out and begin harvest.

When should you harvest, from a nutrition standpoint?

Randy Shaver: From the nutrition perspective, we get mainly concerned about harvesting corn silage too wet or too dry. From the too wet, it’s largely because we’re harvesting so early that we haven’t maximized or optimized the starch content of that silage. We’ve also lost some yield, so we typically would like to be at least 33% whole-plant dry matter. When we see silage that’s below 32% whole-plant dry matter, we’ll often see lower starch concentration than we’d like to see. We may see more seepage coming out of silos than desired.

On the upper end, as we get above 38% whole-plant dry matter, we have a risk of harvesting so late that the kernels become very hard and less digestible by the cow. So 38% is kind of an upper limit. As we get above 38% whole-plant dry matter, we really need to make sure that we’re chopping fine enough to have good packing and also ensure that the processing of the kernels is adequate so that we have good starch digestibility.

It does give us a very wide harvest window, from about 33% whole-plant dry matter up to 38% whole-plant dry matter, to really harvest and preserve high-quality corn silage. It’s just on the very wet and the very dry that we need to avoid as much as possible.


By: Liz Binversie, Brown County UW-Extension Agriculture Educator; Joe Lauer, Corn Agronomist for UW-Madison and UW-Extension; Kevin Jarek, Crop Soils and Horticulture Agent for UW-Extension in Outagamie County; and Randy Shaver, Dairy Nutrition Specialist for UW-Madison and UW-Extension

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