Burbrink, Jeff

Corn silage is a high-yielding, high-energy, low-protein forage commonly used to feed dairy heifers, lactating dairy cows and beef. The fermentation process that is created in silos and bunkers helps to lock in nutrients and make the feed more palatable.

The length of the cut is important. Too fine, and milk fat tests in cows drop, while too coarse leads to too much oxygen in the silo, leading to waste due to poor fermentation. A practical rule of thumb is that most silage particles should be about ½ inch long, with 15-20 percent of the particles being about 1 inch in length. If the silage is dry (i.e. below 60 percent moisture), the chop length should be reduced to ¼ inch to promote better packing.

Rapid filling and tight packing are essential to reduce the amount of air in the pack. Packing is generally recommended after each load in a bunker silo. When the silo is full, it is typically crowned in the center to shed moisture and covered and sealed with polyethylene. To maintain a tight seal, old tires are often cut in half and strewn about on the plastic. Others have used about 4 inches of sawdust over the top of the plastic wrap.

The moisture at which the corn is chopped is also important. Too wet, above 70 percent, results in fermentation by undesirable acid forming bacteria, large losses in volume of desirable nutrients that leak out through seepage, and poor animal consumption of the feed. Too dry, and fermentation may be slowed significantly, resulting in large losses of quality feed.

Forage to be stored in horizontal silos should be near 70 percent moisture in order to facilitate tight packing and air exclusion. Most upright silos should be filled with 60 to 66 percent moisture forage to avoid seepage; however, this will vary somewhat depending on the height and diameter of the silo, since packing is achieved due to the height of the column of forage. Nevertheless, factors such as degree of packing, type of silo, and presence of additives can influence how wet a silage may be stored.

It would be great if there were a way to glance at corn and know the exact moisture content. However, there is a great deal of variation among hybrids and field conditions that make that a bit of a guessing game.

Under normal conditions, plants that are ready for harvest will exhibit some browning of the lower leaves while the upper 3/4 of the plant will be green. Husks will be dried to a tan color, ears will have fully dented and glazed kernels, and whole plant moisture will be in the range of 60 to 68 percent.

In addition to the general physical appearance, there are two specific characteristics that have been used to estimate plant maturity and grain moisture concentration. These characteristics, black layer formation and milk line position, are also related to whole plant moisture concentration.

A corn plant continues to increase in dry weight until it is physiologically mature. At maturity, black layer formation occurs when several layers of cells at the tip of the kernel die. When these cells die, dry matter accumulation ceases. The black layer can be used as an indication to begin harvesting because the onset of black layer and desirable moisture content for ensiling tend to coincide.

Although black layer formation can be a useful indicator of crop maturity, it is sometimes difficult to decide when the layer is truly “black.” Variability in the intensity of the black layer can be confusing to the inexperienced observer. Also, there seems to be some variation in the intensity of the black layer among hybrids.

The milk line is a visual indicator of kernel maturity. If an ear of corn is broken, the tip portion of the ear will show the endosperm face of the kernels. It is here that the milk line can be observed. As the plant develops and the kernels mature to the full dent stage, a distinct line can be seen progressing from the kernel crown to the base. The milk line separates the solid from the liquid portion of the kernel.

When the milk line is half way between the crown and the tip, kernel moisture is about 40 percent. At the half milk stage, over 90 percent of the “normal” yield of grain can be expected. When the milk line has reached the kernel base and becomes indistinct, the kernel base can be probed with a knifepoint to see if milk remains. Kernels containing no milk are physiologically mature and should contain a fully developed black layer.

Black layer development and milk line position may aid in estimating whole plant moisture percentage, but plants with a fully formed black layer or with little or no milk remaining in the kernel are too dry for optimum silage harvest.

Jeff Burbrink is an extension educator with Purdue Extension Elkhart County. He can be reached at 574-533-0554 or jburbrink@purdue.edu.

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