It can be difficult to time corn silage harvest at the perfect moment, when starch content is high and yield potential is at its peak. It pays to maximize your ability to hit that moment and get the most out of your acres.
Each year and every acre present different challenges. Weather and pest pressure are two variables that can drastically impact corn drydown. As the crop matures, keep walking fields and taking notes of progress so you can make informed harvest plans. In particular, be sure to note the silking date. The corn plant approaches silage harvest maturity around 35 to 45 days, or about 900 growing degree units (GDUs), after silking.
Carefully track conditions to determine the perfect drydown point. Drought-stricken corn silage with small ears, or no ears, dries very slowly, so you can delay harvest in those fields. Well-eared corn silage will dry more quickly because the ear consumes a lot of the plant’s moisture. Those fields should be among the first harvested when they hit the ideal moisture level.
Maturity at harvest has a dramatic impact on the nutritional value. As the plant matures, starch content increases, which accounts for most of the improvement in feed quality. However, high dry matter (DM) content reduces fiber digestibility. Although the fiber digestibility drops at a slower rate than starch increases, growers should manage harvest moisture to balance these two trends (see chart). Superior late-season plant health helps improve starch content and slow the decline of fiber digestibility.
Harvesting before plants reach optimal moisture levels reduces yield per acre and starch deposition, resulting in hidden economic loss. Harvesting corn silage at moisture levels above 70 percent not only reduces yield, but also may result in seepage and undesirable fermentation.
Research suggests that unprocessed silage achieves its maximum net energy yield at 34 percent DM (66 percent moisture). Silage processed with a kernel processor achieves a maximum net energy yield of 37 percent DM (63 percent moisture), if properly processed. Sampling is the best way to monitor plant maturity and harvest timing.
A quick way to determine if a corn silage crop is nearly ready for harvest is to break a cob in half and look at the kernels. A whitish line on the kernels, the milkline, shows where the solid and liquid parts of the kernels are separated. This line progresses from the outer edge of the kernel toward the cob. When the milkline reaches the cob, a black layer will be visible. Silage harvest typically begins when the milkline reaches the halfway point in the kernel.
Milkline progression only provides a rough reference point, however. It’s important to test a representative sample from the field to determine the moisture level more accurately. Process plants in a chipper/shredder and determine DM with one of several methods. You can send a sample to a lab, or check it using a drying oven, a food dehydrator or an old microwave.
DM is affected by storage structures: Each has a different target. A DM of 32 to 38 percent works for most silage bunkers and drive-over piles. You may need 35 to 40 percent DM when using a silage bag. Upright silos vary by structure type. Harvest your corn silage at the correct moisture range for the storage structure you have on hand and adjust to meet your feeding needs.
Timing is critical, but it can be a challenge. Corn plants lose an average of about one percentage point per day when they hit the optimum moisture range. Adjust the start of harvest to maximize the amount of time the crop is in the correct range. Try to plan harvest so a continuous supply of silage cut at the proper moisture level is arriving at the storage structure. This can be difficult because you can’t account for breakdowns, weather and other interruptions. Still, carefully planning which fields to harvest first often pays off in higher-quality silage. With thoughtful planning and good data, you can put the drydown period to work for you.