Maturity

Corn silage is a grass plant containing digestible fibre with high-moisture corn attached. Corn silage maturity at harvest has a dramatic impact on the nutritional value of individual hybrids.

Pfister martina
Ontario Dairy Specialist / Corteva Agriscience, Agriculture Division of DowDuPont

Increasing starch content as the plant matures is responsible for most of the improvement in feed quality as harvest approaches.

If we can have enough patience to let the corn silage whole-plant dry matter (DM) go from 30 percent to 33 percent, we could be gaining an average of two points of starch.

If grain corn is worth $5 per bushel, we could be adding $144 per acre of increased starch content in our corn silage by waiting those extra couple of days.

However, it becomes even more critical to properly process corn silage as DM increases. These gains of increased starch content come without reducing fibre digestibility in hybrids with excellent late-season plant health, stalk strength and standability.

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Plant breeders have made important strides in improving late-season health, which is why we don’t see the decrease in fibre digestibility that was common in the past.

Hopefully you marked your calendar when your corn silage was silking, since 35 to 45 days later it will be approaching silage harvest maturity.

corn silage maturityAn interesting fact is that higher relative maturating corn hybrids also take 35 to 45 days after silking to reach harvest maturity; the difference in hybrid maturities derives from the length of time between emergence and silking.

Current recommendations are to target a minimum of three-quarter-kernel milk line and a whole-plant DM closer to 35 to 38 percent.

The traditional recommendation was to harvest when the milk line is between one-half and two-thirds. However, there is considerable variation in the progression of the kernel milk line and the moisture percentage of the whole plant.

University of Wisconsin data over many years show a range in whole-plant moisture at one-half milk line of 28 to 48 percent with an average of 37 percent DM.

Research suggests silage that is not processed achieves maximum net energy yield at 32 to 34 percent DM. Silage processed with a kernel processor achieves a maximum net energy yield of 37 percent DM.

Monitoring silage moistures before and during harvest can help achieve the right balance among yield, starch and DM. If the DM is too high, we increase the risks of poor packing and slower fermentation. If the DM is too low, we increase the risk of seepage and an extended fermentation, resulting in increased nutrient losses.

Sampling fields is the best way to monitor plant maturity and harvest timing. To do so, you should gather 10 plants from multiple field locations and then chop the plants in a chipper or shredder.

To assess the moisture content, cook a 100-gram sample in a Koster moisture tester until no further weight loss occurs. The matter percentage will be 100 grams minus the grams of moisture obtained.

For instance, if 65 grams of moisture are removed, the dry DM content is 35 percent. Keep in mind that on average, the corn will dry down 0.5 to 1 point moisture per day in the field.

Kernel processing/starch digestion

One of the main reasons for feeding corn silage is its high starch content (energy). Much of the starch yield potential is determined earlier in the growing season. At the V6 stage, corn is in the rapid growth stage, which will determine the yield potential for our silage.

Ear girth and numbers of kernels around the ear is determined at this stage as well; any environmental or management stresses can cause significant yield decline at this time.

Once the corn reaches the VT stage (tassel), the ear size and length and the number of kernels per row is determined. Fertility and water requirements are significant in this stage. Research has found that newer corn hybrids take up to 29 percent more nitrogen post-flowering than older hybrids.

Although we are not able to control the effect the environment has on starch production, we can control how much of that starch the cows can utilize through proper kernel processing.

The optimum goal for corn silage kernel processing is a score of 70 percent or higher when tested in a lab. Lab testing is great for post-harvest evaluations but not as efficient while harvesting.

corn cobA quick and simple on-farm technique to check the degree of kernel processing is to collect a 1-litre (two big handfuls) sample of chopped silage.

Spread out the collected sample on a clean surface and manually sift through the entire sample, counting all kernels that are half or larger. Increases in the rate of passage through the rumen of high-producing dairy cows have made the old standard of “a nick is enough” no longer true.

The recommended guideline is not to exceed a total of four half or whole kernels.

If your kernel processing score is less than 70 percent or you are finding more than four whole or half kernels in the 1-litre sample, some adjustments may need to be made to the harvester. Some areas to examine are the chopper knives and roller mill to ensure they are in good working condition.

Nicked knives and worn shear bars should be replaced and the roller mill checked for wear on the teeth. The gap setting between the rollers should be 1 to 2 millimetres to ensure it cracks all the kernels.

If no adjustments are made and the processing is inadequate, the starch in the kernels is less available to be digested by the rumen. In this case, additional grain will need to be added to the ration to meet the cow’s requirement.

Therefore, achieving a 70 percent kernel processing score reduces the need for supplemental grain in the ration and thus results in a ration cost savings.

Chop length

Corn silage in North America is typically chopped at between 9.5 to 19 mm (three-eighth- to three-quarter-inch) theoretical length of chop (TLC). One of the most important factors when it comes to TLC is its uniformity.

Longer chop can create difficulties in packing, keeping a clean bunker face at feedout, reduced effectiveness of the kernel processor (allowing more kernels passing in the manure) and preferential sorting of stover or larger cob pieces in the TMR.

Chopping shorter than 9.5 mm TLC is conducive to better compaction (especially with late-harvested, dry crops), which can increase storage structure capacity and improve the percentage of kernels damaged by the cutter head. However, it requires more power, may slow harvesting and significantly reduces the peNDF of the corn silage.

Ensiling process

Corn silage should be harvested and ensiled as rapidly as possible. Filling delays will result in excessive respiration and increased silage DM losses. Compaction should begin immediately when storing silage in bunker silos.

The piece of equipment used for packing should never sit idle; even when loads are getting dumped, keep packing. Proper moisture aids in silage compaction, which helps transition the silo to an anaerobic environment.

As mentioned earlier, excess moisture can lead to seepage or prolonged fermentations, resulting in higher acid levels and increased protein degradation, whereas limited moisture can make a crop prone to heating during the front end of the fermentation and yeast and mold problems, especially during feedout.

Once filled, the bunker silo should be sealed with an airtight cover to prevent surface spoilage losses from penetration of air and rainfall into the silage mass. Ideally, cover bunkers with an oxygen barrier film along with 4- to 6-mil plastic, or at the minimum 4- to 6-mil plastic, and seal the edges with sand bags.

Place tires edge-to-edge to hold down the plastic. Cutting tires in half will double their use and prevent water from collecting in the center and serving as a breeding ground for rodents and insects.

Another common approach to protecting silage is putting plastic down the inside of the bunker walls.

This creates a “bag within a bunker,” which will significantly reduce side spoilage because water will run off between the plastic and the bunker wall rather than seeping into the silage mass. Research has demonstrated a net return of up to 2 to 1 for properly covering corn silage and up to 4 to 1 for alfalfa silage.

Inoculation has become a routine management step for many silage producers. I would argue that it does not make economic sense to incur the cost of seed genetics, fertilizer, herbicides and planting/harvest costs and then allow fermentation to proceed in an uncontrolled manner.

Different classes of inoculants can improve dry matter recovery, enhance bunk life, ensure more consistent silage, improve palatability and, with certain products, improve nutrient availability.

Corn silage is a key ingredient for many dairy rations. Adhering to the management recommendations for maturity, kernel processing, chop length and ensiling methods will help producers get the most out of this valuable crop.  PD

References omitted due to space but are available upon request. Click here to email an editor.

PHOTO: Staff photo.

Martina Pfister
  • Martina Pfister

  • Dairy Specialist – Western/Central Ontario
  • Dupont Pioneer – Canada
  • Email Martina Pfister