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University of Minnesota Extension

Harvest strategies for corn silage

A great time to begin planning for corn silage harvest is when Minnesota corn crop reaches the milk stage (Figures 1 and 2).

Proper harvest management is critical for high-quality silage, and it starts with harvest timing. This ensures the harvested crop is at the optimum moisture for packing and fermentation.

Corn in the milk (R3) stage.
Figure 1: Corn in the milk (R3) stage.
Corn in the milk (R3) stage.
Figure 2: Corn in the milk (R3) stage.

Silage moisture

Silage that’s too wet may not ferment properly and can lose nutrients through seepage.

If silage is too dry when harvested, it will have lower digestibility because of harder kernels and more lignified stover. In addition, dry silage does not pack as well, increasing the potential for air pockets and mold.

Optimum moisture levels

The optimum silage moisture at harvest ranges from:

  • 50 to 60 percent for upright oxygen-limiting silos.

  • 60 to 65 percent for upright stave silos.

  • 60 to 70 percent for bags.

  • 65 to 70 percent for bunkers.

Measuring silage moisture

Due to variability among hybrids and growing conditions, measure silage moisture using a commercial forage moisture tester or microwave oven rather than simply estimating it from the kernel milkline.

Instead, treat kernel milkline as an indicator of when to collect the first silage samples for moisture testing.

A general guideline is to begin moisture testing when the milkline is 25 percent of the way down the kernel for horizontal silos, and 40 percent of the way down the kernel for vertical silos. Then, assume a constant drydown rate of approximately 0.6 percent per day, and measure moisture again prior to harvest, according to a presentation given at the 2003 4 State Forage Conference.

Cutting length and crop processing

Cutting length and crop processing are also important for obtaining high-quality corn silage. Breaking cobs and kernels increases surface area, which improves digestibility, reduces cob sorting and leads to higher density silage that packs better.


Filling silos

When harvest begins, rapidly fill silos to reduce silage exposure to oxygen and reduce fungal growth.

For bunker silos, pack silage as tightly as possible in progressive wedges in depths of 6 inches or less.

Jeff Coulter, Extension agronomist

Reviewed in 2021

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