Corn Silage: Part 1 Predicting Harvest & Moisture Level

With corn silage, you only get one shot to harvest so it’s important to time it out right. There are several methods you can use to accurately predict the optimal time to harvest silage. In this podcast series, UW-Extension specialists will give you all of the best tips and tricks for this harvest season.


Liz Binversie, Brown County UW-Extension Agriculture Educator


Joe Lauer, PhD, Corn Agronomist, UW-Madison/UW-Extension

Kevin Jarek, Outagamie County UW-Extension Crops, Soils, and Horticulture Agent

Randy Shaver, PhD, Dairy Nutrition Specialist, UW-Madison/UW-Extension


Time: 8:15 minutes


Liz Binversie: Greetings, I’m Liz Binversie, Brown County UW-Extension Agriculture Educator and I will be your moderator for today. On the panel is Joe Lauer, Corn Agronomist for UW-Madison and UW-Extension; Kevin Jarek, Crops, Soils, and Horticulture Agent for UW-Extension in Outagamie County; and Randy Shaver, Dairy Nutrition Specialist for UW-Madison and UW-Extension. In this podcast series, we’re going to talk about corn silage. It’s a major part of the cow’s diet here in Wisconsin, and it’s a crop where you only get one shot to harvest it at the right time. There are several different factors to help producers decide when to harvest. Joe, what should producers consider when deciding when to harvest their corn silage this year?

Joe Lauer: Thank you, Liz. There’s a number of indices and guidelines for predicting corn silage harvest. It’s really a season long kind of decision. One of the first things that 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 intended for corn silage use. As the season progresses, about halfway through the season, it’s a good idea to note the tasseling or silking date. One of the things about corn is that the grain filling period of corn is relatively consistent. If you know the tasseling date, then about 42 to 47 days after silking, those kernels are going to be close to that 50% kernel milk stage of development. Later on as that crop begins to dent and that kernel milk line begins to move, we have a number of kernel milk triggers that help us time that corn silage harvest. Usually when you’re at about 80% kernel milk, it’s a good idea to do a dry down to see where you’re at in terms of moisture. In the field many agents, county programs and coops and industry people will help with this. Once you know that moisture, assume about a ½ percent per day dry down rate to predict when that fields going to be ready. There is an overall accumulator of the information from Wisconsin at a website. If you search on UW corn silage dry down, you can get information about neighboring counties and also other people in your area. Once you’re really close to doing chopping, you can do a final check again to kind of 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 probably need to be ready to cut. One way to adjust that in the field is to just 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 that cutter bar one foot, you can lower that silage moisture about 2 to 4 moisture points with that. The wettest 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. Kevin, what do you see at the county level?

Kevin Jarek: Thank you, Joe. At the county level, the forage councils serve an important role. You mentioned earlier as far as coops and other places that will help farmers determine silage moisture. There’s primarily 2 ways 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 so to say, and let it cook for 20 to 25 minutes, 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 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 forage councils do provide koster testing without charge. What we have found as far as the difference in moisture between the koster testers and the NIR samples is about 2 points. Producers are going to want to add a point or 2 of moisture to the koster tester reading since we simply haven’t been able to cook all of that moisture out in that short period of time. When it comes to predicting the harvest date, a lot of that comes down to the structure itself. I know that when we look at 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. Randy, do you have some thoughts on that?

Randy Shaver:  Well, 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 then 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. 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 from the very wet and the very dry that we need to avoid as much as possible.

Liz Binversie: Thank you to our wonderful panel today. If you’d like to reach any of our specialists, you can do so by email. Tune in next time when we talk about the proper settings for your harvesting and processing equipment to get the most out of your corn silage this season.