Planning the Corn Silage Harvest: Time to Think About Cutting Height

By: Jeff Keunen, M.Sc., Ruminant Production & Robot Improvement Specialist

& Gennadii Bondarenko Ph.D., Ruminant Nutritionist

Corn silage cutting height has always been a topic of discussion among dairy producers, especially in years of above average yields or significant carryover from the previous year. Many dairy producers in Ontario consider 12 inches as the optimal cutting height.

Cutting height may significantly impact silage quality, simply because lower portions of the corn stalk are more fibrous and less digestible than the middle or upper portions. Harvesting the same number of kernels but less stalk increases the percentage of starch in the silage as cutting height rises. However, while higher cutting height improves silage quality, it also reduces yield. Research from Penn State University indicates that raising the cutting height from 7 to 19 inches can reduce total NDF by 7%, increase NDF digestibility by about 5%, and increase starch by about 6%, though dry matter yield drops by about 7% (from 8.1 T/acre DM to 7.5 T/acre DM).

Several factors should be considered when deciding on higher cutting height of the corn silage:
01. Abundant inventories and expectation of high yields: Higher yields allow for the option of harvesting less tonnage, but higher quality silage, which should be stored in optimal conditions to minimize losses, rather than harvesting more tonnage of lower quality silage.
02. Weather Conditions: Wet weather during the growing season can lead to corn plants accumulating more lignin and reducing fiber digestibility. Cutting at a higher height leaves more indigestible fiber in the field, which can improve fiber digestibility of the corn silage.
03. Low quality haylages: Unfavourable weather during haylage cuts can result in lower quality haylage. For farms that may not have had great success with their haylage harvest, improving corn silage quality by increasing the cut height offers the opportunity to compensate for the lack of digestible fiber in poorer quality haylages.
04. High Forage Diets: Some producers aim to minimize or eliminate cob meal or added corn in dairy rations, opting for a higher forage ration. With a higher cutting height for corn silage, there are positive benefits with higher starch and adequate digestible fiber coming from the corn plant. In some cases, if enough corn silage is fed, supplemental grain corn may not be required.

In 2023, the growing season was very favorable for high yields of corn silage and at the end of September 2023 we were able to complete some practical trials on a couple of Ontario farms and test various cutting heights.
At the first farm we compared 12 inches vs 21 inches cutting height. Small experimental plots were harvested in the TMR mixer wagon, that helped us to estimate the yield (Figure 1). Representative samples were taken from each plot and sent to the lab for analysis (Table 1).

Figure 1: Harvesting high cut corn silage plot during the trial.

Adding 9” of cutting height resulted in DM yield reduction at 0.9T/acre (about 0.1T DM yield loss per every 1” of cutting height above 12”). At the same time, we observed slight increase of DM%, improvement in starch and reduction of total NDF and undigestible NDF content in 21” corn silage vs 12” corn silage.

Figure 2: 27″ cutting height corn with unusually high location of cobs at the plants.

Having more starch and less undigestible NDF will result in much higher potential intake of the 21” corn silage, that will help to make a higher forage diet with less supplemental corn in it.
Modelling 35 L (4.0% fat) milk rations demonstrated potential savings at $0.50/ cow/day on the ration with 21” corn silage vs 12” corn silage (Table 2.). We were able to raise forages in the ration from 61% to 68%, mainly due to significant increase of corn silage intake (by 15%).

Table 2: Cost comparison of feeding a diet using 12″ vs 21″ cutting height corn silage on a 35L -4.0% butterfat ration. *

*Price assumptions:: Corn silage $65/T, haylage $80/T, ground corn $250/T, protein blend $563/t, premix $1176/T.

On another farm, where corn plants averaged over 10 feet with high cobs (about 5 feet from the ground), the farmer harvested at an unusually high 27-inch cut height to maximize starch content and fiber digestibility, allowing them to eliminate supplemental corn from the ration.
We did a control plot at 12” cutting height and compared estimated yield and quality parameters with 27” cutting height corn silage (Table 3).

As was expected, we lost about 15% of the DM yield at 27” cutting height, but we need to understand that was a loss of the most undigestible part of the corn plant. This helped us to get a corn silage with much higher starch content and significantly lower level of undigestible fiber (28% reduction, from 11.4% to 8.2%).
Modelling a 40 L (4.0% fat) milk rations demonstrated potential savings of $1.36/ cow/day on the ration with 27” corn silage vs 12” corn silage (Table 4).

*Price assumptions: Corn silage $65/T, haylage $80/T, ground corn $250/T, protein blend $563/t, premix $1176/T.

As we can see, making a high cut corn silage with lower level of undigestible NDF will result in much higher forage DM intake (39% increase of 27” cut corn silage DM intake as compared to 12” cut corn silage), that brings so much starch in the ration, that we may significantly reduce or totally eliminate any supplemental corn/cob meal and feed the cows higher forage diets. This will help to reduce potential sorting of the diet, maintain a more stable rumen environment and help maintain butterfat levels in milk.

Soil Health and Environmental Benefits
In addition to gains in cow productivity and reduction of feed costs, we may also think about some benefits to soil health environment. Leaving more stover in the field will allow producers to bring back not only carbon into the soil’s nutrient bank, but also some amount of nitrogen, phosphorus, potassium, calcium, magnesium and sulphur. Over the long-term perspective, it will affect soil organic matter. The impact on other soil properties can be important and immediate. These include soil cover (protection from raindrop impact and erosion control), soil microbial processing that produces materials that help “glue” soil particles together (improving soil aggregation and stability, bulk density, and root growth), total soil N, and nutrient cycling [3].

We may also try to think in terms of carbon cycling and carbon sequestration. Considering that mature corn stalks and leaves contain approximately 45% of carbon [4], leaving in the field about 1 T of DM/acre of additional corn stalk by increasing corn silage cutting height, will return to the soil about 450 kg/ acre of carbon or 45 T of carbon on a 100-acre corn eld. At the start of this or future corn silage harvest seasons, it is worthwhile to take an overall assessment of forage inventories and quality. If there is a need to improve forage quality levels, or you have an abundance of forage stored away, considering chopping your corn silage at a higher height than you normally do, could provide you with some of the ration and cost saving benefits mentioned above. As always, speak with your Grand Valley Fortifiers representative about the various options available and what works best for your operation.

References:
Corn Silage Chopping Height | Cornell Field Crops News.
Considerations in Managing Cutting Height of Corn Silage (psu.edu).
Carbon and nitrogen cycling with corn biomass harvest | Integrated Crop Management (iastate.edu).
Nutrient removal when harvesting corn stover | Integrated Crop Management (iastate.edu).

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