Dr. Ronald L. Boman
USU Extension Dairy Nutritionist

    Fall is in the air and it's time to be making preparations to properly harvest corn for silage. Harvesting and storage conditions have a significant effect on corn silage quality. Maximum grain and silage dry matter (DM) will be harvested when corn is chopped at physiological maturity or kernel black layer stage. Check for black layer development by splitting kernels lengthwise to locate the black layer at the tip of the kernel. Another measure of optimum maturity is the location of the milk line and the degree of indentation of the kernels. The milk line is the point where the liquid and solid portions of the kernel meet. It appears when the kernels have dented in their crown portion. Cut the kernel lengthwise to determine the milk line location. When the milk line has moved down 1/2 to 2/3 of the way from the crown, the corn plant has attained its maximum yield and energy content. It also has an ideal moisture content (65-70%) for tight packing into a silo for optimum fermentation. Harvesting earlier can result in decreased yields and seepage losses. Later harvests result in dropped ears, stalk breakage, and leaf loss which reduces yield. More important is that over mature and drier corn is more difficult to conserve as silage because of entrapped air and lower lactic acid production. Moisture is perhaps the most important factor in ensuring good fermentation and packing during the ensiling process. Corn silage stored in bunker silos should go in at 65-70% moisture.

    The recommended theoretical length of cut for corn silage is 1/4 to 3/8" at physiological maturity. Over 90% of the kernels will be scarified at this chop and passage of kernels into manure will be minimal. The recommended theoretical length of cut for silage harvesters equipped with a processor is currently 3/4" based on recent Wisconsin research.

Filling and Packing the Bunker Silo

    Once we've defined the optimum maturity, moisture content, and length of cut for corn silage, we need to take every precaution possible to achieve a desirable fermentation to preserve the corn silage. The following are three extremely important steps:

1. Rapid filling,
2. Adequate leveling and packing, and
3. Covering with a plastic sheet and weighting it down as soon as filling is complete.

    In order to appreciate the importance of these three steps, we need to understand the different phases of silage fermentation:

     Phase 1 - The living cells of freshly-chopped corn plants continue to respire and use oxygen. In well-packed forages, the amount of oxygen is minimal and is used up rapidly. Carbon dioxide and heat are produced in this phase. Rapid filling and adequate packing reduces heating and allows the second phase to proceed quickly.

    Phase 2 - After the oxygen is depleted the anaerobic bacteria take over and acetic acid is produced from the fermentation of corn plant sugars and carbohydrates. The pH of the ensiling material drops from about 6.5 to 5.

    Phase 3 - As the pH declines, lactic acid producing bacteria take over and convert the abundant corn plant sugars and carbohydrates into lactic acid.

    Phase 4 - Lactic acid production continues until pH 4 is reached. This is normally achieved within 4 to 5 days after filling. Final lactic acid concentrations of well-preserved corn silage will be 4 to 10% on a dry matter basis. If the corn silage is properly covered and remains undisturbed and anaerobic conditions are maintained, the corn silage will stay well preserved and be stable for months and even years. However, if oxygen or air invades the ensiled material from leaky silos (uncovered) or if the lactic acid concentration is diluted by rain or snow, then heating and molding will begin reducing silage quality.

    One last note on covering bunker silos! USDA research conducted at Beltsville, Maryland, shows that every 3 to 4 inches of spoiled crust on top of uncovered bunkers or piles of corn silage represents 10 to 12 inches of original material. Another way to look at it is that 10 lbs. of silage is wasted for every square foot of uncovered silage surface. Intake, digestibility, and nutrient density of uncovered silage is also reduced compared to properly preserved and managed corn silage. ©