Despite the cool weather that we had in July, corn and soybean fields are heading towards maturation. The rains that we have had in August along with some much needed heat has helped us get caught up a little bit. One of the next jobs on the farm will be chopping corn silage. Most of our beef and dairy producers put up some corn silage that will be an important part of the beef and dairy ration for the year.
Proper harvest management is critical for high-quality corn silage, and it starts with harvest timing. This ensures that the harvested crop is at the optimum moisture for packing and fermentation. Silage that is too wet may not ferment properly and can lose nutrients through seepage. If silage is too dry when harvested, it has lower digestibility because of harder kernels and more lignified stover. In addition, dry silage does not pack as well, thus increasing the potential for air packets and mold.
Optimum silage moisture at harvest ranges from 50-60 percent for upright oxygen-limiting silos, 60-65 percent for upright stave silos, 60-70 percent for bags and 65-70 percent for bunkers. Due to variability among hybrids and growing conditions, it is necessary to measure silage moisture using a commercial forage tester or microwave oven rather than simply estimating it from the kernel milkline. Instead, kernel milkline should be 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 of about 0.6 percent per day, and measure moisture again prior to harvest.
Length of cut and crop processing are also important for obtaining high-quality corn silage. This is because breakage of cobs and kernels increase surface area; which improves digestibility, reduces cob sorting, and results in higher density silage that packs better. Although crop processors are expensive, the higher quality silage produced can increase milk production by 300 pounds per cow per year. The benefit of crop processors is greatest when there are harder kernels resulting from delayed harvest or drought. When using a crop processor, chop length can be increased to reduce horsepower requirements while maintaining optimum particle size. For unprocessed corn, ideal chop length is 0.375" theoretical length of cut. For processed corn, recommended settings are at 0.75" theoretical length of cut with 0.08 to 0.12" roll clearance.
A 4 to 6" cutting height is generally recommended for corn silage, as it maximizes silage yield and milk per acre. However, drought-stressed corn can accumulate nitrate in the lower part of the stalk, thus increasing the potential for nitrate poisoning, particularly in older livestock on lower-energy rations. The potential for high-nitrate silage can be even worse if drought-stressed silage is harvested within 10 days of rainfall, since rainfall increase crop uptake of soil N. Silage with high nitrate levels can be managed by dilution with other feeds or by increasing the cutting height to 12". Silage cut at this greater height has been shown to have 8 percent less silage yield and 2 percent less milk per acre. This same study found that a cutting height of 18" resulted in 15 percent less silage yield, 12 percent greater milk per ton, and 4 percent less milk per acre when compared with a 6" cutting height. Increased silage quality with high cutting is due to a higher ratio of grain to stover. However, corn stalks are a good source of fiber and the lower tonnage with high-chop silage typically makes it difficult to justify in the absence of high nitrate levels.
When harvest begins, fill silos rapidly to reduce exposure of silage to oxygen and to reduce fungal growth. For bunker silos, pack silage as tightly as possible in progressive wedges in depths of 6" or less.