Corn Silage Harvest Preparations

 By Michael Cox for American Dairymen Magazine

 Several factors influence the quality and quantity of corn silage harvest on our dairies. While weather and growing conditions can have huge effects on corn crops, we still have many variables under our direct control that will influence the type of corn silage we will feed out to cows in the future.

 Harvest timing
Timing of harvest is the most important consideration when aiming to achieve good yields and high digestibility silage. Several factors will dictate harvest timing, such as crop dry matter, variety type, whether the crop is a hybrid or not, spacing between the crop rows and the weather conditions. Dry matter level will dictate when harvest should begin and will be influence by all of the above factors. University of Kentucky research suggests that bunker silage should be harvested between 30-35% dry matter, with standing silos being able to accommodate higher dry matters of 35-40%. Dry matter levels have a direct influence on how the silage will ferment and the amount of shrink during storage. If silage is too wet, nutrients will be lost through seepage during storage. Harvesting high dry matter silage increases the risk of air pockets in the silo and also reduces digestibility, as the kernels will be drier, physically harder and more difficult to breakdown in the cow’s digestive tract. Harvesting outside of the target dry matter parameters will result in poorer fermentation and greater shrink than desired. As dry matter in standing crops generally increases by .5% daily, it is crucial to have frequent samples and assessments of the crop prior to harvest. Milkline position is a simple way of estimating dry matter levels. As the crop matures, the milkline will move slowly down the kernel towards the center. The optimum stage of harvest is when the milkline is 3/4s of the way down the kernel.  Although judging the milkline position and black layer development are simple ways to estimate dry matter and harvest timing, it is advisable to check whole plant dry matters from various fields before harvest. If testing moisture levels using a microwave, having finely chopped samples will give most accurate results. Finely chopped samples allow for a more representative subsample to be tested.

Processing and stem height
Most dairies have now recognized the benefits of kernel processing on the greater availability of starch when digested by the cow. If on-line processors are not available on the harvester, chop length should be reduced to ½ inch to compensate for the lack of processing, compared to ¾ inch chop length for processed silage. Roller clearance of .12 inches in on-line processors should be sufficient for good kernel processing, but kernel breakage must be monitored, and rollers adjusted up or down as necessary. A quick and easy way to check if enough kernels are being broken is to count the number of whole kernels from a given sample. Producers should target having at least 55-65% of kernels broken.
If high nitrate levels in the crop is a cause for concern pre-harvesting, raising the cutting height can lower nitrate levels in the forage, as the lower part of the plant stem contains the largest amount of nitrates. Nitrate levels can be increased in crops that receive rain after a drought period, during cloudy, overcast weather, in more mature plants and in very thick, high population crops. Raising the cutting height can reduce nitrate levels and increase quality and digestibility of the silage, but it will also obviously reduce the overall yield of the crop. In well fermented silage, nitrate levels will reduce by 50% from harvest levels, so ensuring good fermentation can be a more desirable option than raising cutting heights in some cases. Higher cutting heights will also influence dry matter levels. Raising cutting height by 12 inches will typically raise dry matter in the silage by 2%. The intended animal group that will eat the silage can also influence stem height levels. If the silage is for dry cows and heifers, lower quality and greater yields may be more desirable, and therefore cutting heights can be lowered. If silage is intended for peak lactation cows it may be cost effective to produce higher quality silage by leaving higher stalk residues in the field.    

Final results
After all the time, effort and cost that is involved in raising and harvesting a corn crop, it is crucial to take a forage sample for analysis and get the cold hard facts of what is actually in the bunker. Pre-harvest estimates of dry matter and kernel processing during harvest are typically less accurate than laboratory analysis. When taking forage samples to test for quality and dry matter, the size of the sample can affect the accuracy of the results. Research from Cornell University suggests that sample weights from 400g to 600g per sample are best for consistency and accuracy. Lighter sample weights show more variation between samples than heavier weights, which will have pooled forage for a more accurate representation from the silo.