Here’s how to measure corn plant moisture

The most important guideline for corn silage harvest is to harvest when the whole plant moisture is correct for the storage system used.

County Extension Educator

Wide variations in field conditions has been a theme in crop discussions this year. Keep an eye on things.

With good weather, corn development can change pretty fast. Each of the steps from milk stage to late milk to soft dough to early dent to full dent to half milk line takes just four to five days.

This year, maybe more than some, it might not be enough to watch the neighbors. Don’t bank too much on what you see from the road. Take a look at individual fields. Walk in the field. Pull some husks back. Maybe take a look from the top of a silo (carefully) to see how much field variation there might be that could affect harvest decisions.

The most important guideline for corn silage harvest is to harvest when the whole plant moisture is correct for the storage system used. For bunkers and piles, that’s generally 65 – 70 percent moisture, for bags 60 – 70, for upright concrete stave silos 60 – 65 and for oxygen limiting silos 50 – 60 percent. Your past experience and personal preferences are important to consider.

Plant development stages offer some clues about what whole plant moisture might be like, and when a chopped sample moisture test could be useful. At early dent there may be kernels along the entire ear that are beginning to dent and the whole plant moisture might be somewhere around 73 percent.

At full dent, about five days later, all kernels are well dented, kernels can be easily cut with your finger nail, and the whole plant moisture might be around 71 percent. When we get to where the corn is fully dented, whole plant moisture might drop one-half of a percent per day, depending on weather and soil conditions.

At 3/4 milk line, the whole plant moisture might be between 65 – 70 percent. I’m describing 3/4 milk line here as when the milkline is 3/4 of the distance up from the tip of the kernel. Break the cob about 1/3 of the way from the tip and look at the cross section of the tip portion.

At half milk line the whole plant moisture might be around 65 percent.

At 1/4 milk line the whole plant moisture might be around 63 percent.

When the milk line disappears, the whole plant moisture might be around 60 percent. The grain moisture might be around 32 percent. The black layer might be starting to show up on the tip of the kernel. This is also close to where we’d start to think about snaplage and earlage and high moisture corn would not be too far off, either.

Don’t let the color of the crop fool you. Sometimes the leaves and stalks can be very green yet and the crop is still maturing and the whole plant moisture really can be right for chopping silage. Plants might be turning yellow and browning because it’s running out of nitrogen, short of potassium, or drying up in a drought year. In these situations, the corn might be wetter than you think.

There are several ways to check whole plant moisture. Some feed labs and farm stores will grind whole stalk samples that you bring in to test for moisture. Some farms do some day-to-day green chopping and take samples to a lab, or test on the farm. In this case we encourage people to only chop what they can feed each day to keep the feed fresh. That’s not as convenient, but better for livestock.

We have directions for using a microwave oven to dry chopped samples. A wet sample is weighed, then dried, then weighed again. The difference is the moisture lost and you do the math to calculate the percent. A Koster Tester is a unit about the size of a 30-cup coffee percolator that is used to dry a crop sample. Again the difference in wet and dry weight is used to calculate moisture percent.

You can estimate moisture by squeezing a chopped sample in your hand for 90 seconds. If you can squeeze juice out of the sample, it’s probably still 75 to 80 percent moisture. If the ball slowly expands when you open your hand, with little dampness on your hand, the sample might be 60 – 70 percent moisture.

One of the keys to any of these is your confidence that the sample is representative of the field. If you’d like more information about any of these, you’re welcome to give us a call. Stearns (320) 255-6169, Benton (320) 968-5077 or Morrison (320) 632-0161.

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