Don’t harvest this year’s drought-stressed silage corn too dry – or too wet, says Jeff Coulter, University of Minnesota Extension agronomist. Dry silage will have harder kernels and more lignified stalks, which will lower digestibility and not pack well.

“In comparison, silage that is too wet when harvested may not ferment properly and can lose nutrients through seepage,” he says. Optimum silage moisture at harvest should range from 50% to 60% for upright oxygen-limiting silos, 60% to 65% for upright stave silos, 60% to 70% for bags and 65% to 70% for bunkers.

Measure corn silage moisture using a commercial moisture tester or microwave oven, he says. That’s better than estimating it from the kernel starch line, because moisture content varies so much within and among fields.

“The kernel starch line can serve as an indicator of when to collect the first silage samples for moisture testing,” he suggests. “A general guideline is to begin moisture testing when the kernel starch line is 25% of the way down for horizontal silos and 40% of the way down for vertical silos. Then, assume a drydown rate of 0.6% per day and measure moisture again before harvest.”


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Proper crop processing and the correct length of cut are also important. “Breakage of cobs and kernels increases surface area, which improves digestibility, reduces cob sorting and results in higher-density silage that packs better,” Coulter says.

Silage corn cut at a 6” height can maximize silage yield and milk per acre. “However, drought-stressed corn can accumulate nitrate in the lower part of the stalk. This increases the potential for nitrate poisoning, particularly in older livestock on lower-energy rations. The potential for high-nitrate silage is enhanced when drought-stressed silage is harvested within a few days of significant rainfall, since rainfall stimulates crop uptake of soil nitrogen.”

Corn silage with high nitrate levels should be ensiled before it’s fed, Coulter says. That will reduce nitrates by one third to one half. Increasing cutting height to at least 12” or feeding the crop with other feed sources can also dilute the nitrates. Test any silage with suspected high nitrate levels before feeding, even after ensiling, he warns.

Visit the University of Minnesota Extension website for more information.

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