Historically, corn silage harvest occurs around 50 percent milkline, but recent research has shown this historical thinking may not work for all situations. Harvesting too early or at a higher than preferred moisture can cause potential spoilage and loss of overall tonnage; on the flipside, moisture levels that are too low can cause yield loss, mold development, poor digestibility and nutrient loss. So, it’s important to carefully time your corn silage harvest for optimum success.
Storage Options Impact Harvest Timing
The type of silage storage facility utilized impacts your harvested moisture goals. The University of Wisconsin suggests 65-70 percent harvested moisture for horizontal bunkers, 60-70 percent for bagged storage, 60-65 percent for upright concrete stave, and 50-60 percent for oxygen-limiting silos. As you may expect, the milkline could be different for each of these storage methods - which is why we don’t want to rely primarily on milkline to determine timely harvest.
Multiple Factors Play a Role
For a traditional silage hybrid, a Brown Mid Rib (BMR) hybrid or a grain hybrid used for both grain and silage, milkline may vary relative to overall plant moisture. Ear size relative to leaf/ stalk matter can impact overall plant moisture, as can soil type or topography within a field. For example, hilltops will potentially have very different plant moisture content than low lying areas. Overall plant health and weather stress - such as drought, excessive heat, humidity or rainfall with cool temperatures - can impact overall plant moisture as well.
Sample Timing and Methods
To figure out when to sample, work backwards, looking at planting date and hybrid maturity. Discuss with your seed supplier the best post-pollination window in which to sample. Many seed companies test silage hybrids during research stages to better understand the proper harvest window. As a general rule, it typically takes around 40-50 days post-flowering to initiate moisture sampling. The number of days varies greatly depending on your location, so check with your local corn silage expert, nutritionist or seed supplier for greater detail. The milkline can help you figure out when to sample, but this should not be the only factor in deciding when to start harvest. Take representative samples across the entire field. Remember this includes the entire plant and not just checking the milkline.
If you have access to a NIR spectroscopy to measure dry samples from a Koster oven, microwave or convection oven, take advantage of this technology. Sample three to five plants in a representative row, put the plants in plastic bag (keeping the sample cool to prevent spoilage), chop the sample as quickly as possible and measure with an NIR. The dry matter percentages can help you estimate your prime window to harvest. If you don’t have access to these tools, be sure to work with your local extension office or your seed supplier to better understand your harvest window.
Lastly, you may have a field where plant stressors vary - causing some parts in the field to be stunted while other areas look normal. This variation will greatly impact overall plant moisture and digestibility, so harvest areas that are similar to limit these variables.
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Sources:
https://ipcm.wisc.edu/blog/2016/08/timing-corn-silage-harvest/
https://www.dairyherd.com/article/time-plan-corn-silage-harvest
https://www.gov.mb.ca/agriculture/crops/production/grain-corn/print,when-to-harvest-corn-silage.html