Proper harvest timing is critical for ensuring corn silage is at the optimum moisture for packing and fermentation.
If silage is too dry when harvested, it has lower digestibility because of harder kernels and more lignified stalks. Dry silage also does not pack well, increasing the potential for air pockets and mold.
In comparison, silage that is too wet when harvested may not ferment properly and can lose nutrients through seepage. 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, and 65 to 70 percent for bunkers.
Due to variability among and within fields, it's better to measure corn silage moisture using a commercial moisture tester or microwave oven rather than estimating it from the kernel starch line. The kernel starch line can serve as an indicator of when to collect the first silage samples for moisture testing. A general guideline is to begin moisture testing when the kernel starch line is 25 percent of the way down for horizontal silos and 40 percent of the way down for vertical silos. Then, assume a drydown rate of 0.6 percent per day and measure moisture again before harvest.
Length of cut and crop processing also are important considerations for high-quality corn silage. Breakage of cobs and kernels increases surface area, which improves digestibility, reduces cob sorting and results in higher-density silage that packs better. The benefit to crop processors is greatest when there are hard kernels resulting from delayed harvest or drought.
A 6-inch cutting height often maximizes corn 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 feeding; doing so can reduce nitrate levels by one third to one half. It can also be managed by diluting with other feed sources or by increasing the cutting height to at least 12 inches. Even after ensiling, silage with suspected high nitrate levels should be tested before feeding.
For more resources on corn production from University of Minnesota Extension, visit http://www1.extension.umn.edu/agriculture/corn/.