Height considerations for corn silage cutting

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Corn silage harvest is at the doorstep for many dairy farms across the Midwest. The growing season has been nearly ideal for some while others have dealt with drought and, more recently, hail damage. These growing differences, and other management considerations, make it difficult to have one common recommendation for corn silage cutting height. There is a trade-off between reduced yields and higher quality as more stalk residue is left in the field.
Raising the cutting height when harvesting corn silage is sometimes recommended to improve the quality of corn silage. By leaving the lower portion of the stalk in the field, fiber digestibility will intuitively improve as lignification is greater in the lower portion of the stalk. The percentage of starch content of the feed also increases, but this is simply due to less fiber being harvested.
While these quality differences are real and logical, recent research from Virginia Tech challenges conventional thinking that the differences are extremely significant. They analyzed tissue samples at the first internode above the nodal roots (lower height), the third internode above the nodal roots (upper height) and the first internode above the insertion of the ear of the corn plants. These results showed the neutral detergent fiber concentration ranged only from 48.8% to 50.1%, showing that tissue composition is not exceptionally different at different heights. Their results also showed that NDF digestibility improved by 4.3 percentage units with higher cutting height, which is different but not extreme.
As you think about the quality differences, keep in mind what your total diet composition entails and ask what the additional fiber in low-cut silage is worth. For example, if you have plenty of haylage, but its quality is lower than ideal, the benefits of higher-cut corn silage might be worth considering.
Raising the cutting bar height will certainly result in lower yields. Dr. Greg Roth from Penn State University summarized results of 11 peer-reviewed articles that compare yield and nutritional value of regular-cut corn silage averaging 7 inches to high-cut corn silage averaging 19 inches. Corn silage yields averaged 7.4% lower with this higher cutting range. This yield reduction equates to about 0.5 tons of dry matter per acre or approximately 1.4 tons per acre on a wet basis (35% DM).
If high-chop corn silage is being considered, more acres of silage will need to be planted to realize the same tonnage as a low-cut silage. This can present some challenges agronomically.
The bottom couple feet of a corn plant contain not only higher levels of lignin but also higher moisture levels. In addition, the ear represents a larger proportion of the tonnage in higher cuttings, and the grain is drier than stover at harvest time. The PSU summary showed an average of 6% higher DM content with higher-cut corn silage.
In addition to moisture, the lower stalk also contains the highest concentration of plant nitrates. High-cutting corn silage can help reduce nitrate levels if this is a concern. The dilemma is that the corn that is at highest risk for nitrates is often the drought-stressed, shortest corn where every inch of plant is critical to maximizing yields.
High-chopped corn silage is not for every farm. The term “high-cut” also implies that we need to get to a finite 20-24 inches of cutting height. Moderately increasing cutting height will move the needle on forage quality. Work with your nutritionist to decide what cutting height works for your dairy.
Barry Visser is a nutritionist for Vita Plus.

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