Harvest Timing Critical to Corn Silage

Carole H. Knight – Bulloch County ANR Agent

Corn silage is a high-quality forage crop that is used on many dairy farms and on some beef cattle farms in Georgia. Its popularity is due to the high yield of a very digestible, high-energy crop, and the ease of adapting it to mechanized harvesting and feeding. The object of silage making is to preserve the harvested crop by anaerobic (without oxygen) fermentation. This process uses bacteria to convert soluble carbohydrates into acetic and lactic acid, which “pickles” the crop.  To produce high-quality corn silage, it is important to do a good job in harvesting and preserving the crop.

Corn silage that has been produced properly should have a green/yellowish color and a light, pleasant, slightly vinegar odor. If it is dark brown, or has another odor such as fruity, burnt or a rancid smell, improper fermentation or excessive heating may have occurred. Understanding the fermentation process may help explain some of the problems that can arise in silage production.

The fermentation process

When a corn plant is chopped and put into some sort of storage facility, the cells of the corn plant are still alive. The respiration of these plant cells and the microorganisms in the silage produce carbon dioxide and heat. This is called aerobic respiration, because oxygen is used. As the carbon dioxide level increases and the oxygen level decreases, this respiration will decrease and stop, and anaerobic (without oxygen) fermentation begins. In this process, desirable bacteria use the soluble carbohydrates in the cells to produce primarily lactic acid.  Lactic acid causes a drop in the pH. Fermentation will occur until enough lactic acid is produced to drop the pH to approximately 4.2, at which point all bacterial action stops. This usually occurs within three weeks after the silo, trench or bunker is filled. If low levels of lactic acid have been formed, then butyric acid, a foul-smelling acid, is produced and the silage spoils.

Harvest at the correct stage

Proper timing of harvest is one of the most critical factors that will influence the quality of the corn silage produced. The stage of maturity of the corn will influence the quality of the corn silage because of the amount of nutrients in the plants as well as the amount of moisture present. As a corn plant matures, the plant begins to dry down, and the moisture content in the plant drops. If the moisture content is too high when the silage is cut, there can be seepage. This seepage contains high concentrations of soluble nutrients, which are lost. The seepage can cause considerable damage to upright silos. Another problem with chopping silage with too much moisture is that a larger amount of lactic acid is needed to reduce the pH. This results in a longer period of time before the silage becomes fermented, producing a lower quality silage. In the opposite situation, if the plant does not contain enough moisture, then it will not pack well in the silo, more oxygen will be present and it will take longer to get through the aerobic phase into the anaerobic phase of fermentation. Nutrients will be used for respiration during the aerobic phase, the temperature of the silage will increase and possibly burn. This also results in a lower quality silage. The proper moisture content of corn chopped for silage is   Squeeze the chopped forage tightly into a ball for 20 to 30 seconds, and then release quickly.  Forage chopped into 3/8 to 1/2-inch pieces should be used. The condition of the ball and the approximate moisture levels are found in the following table.

between 60 and 70 percent. In bunker and trench silos, where packing is a problem, the upper side of this range is recommended. If the silage is going into an upright silo, packing is generally not a problem, so the lower end of this range will work satisfactorily. The kernel milk line can be used to help estimate moisture. The milk line proceeds from the top to the bottom of the kernel as the plant matures. Generally, when the milk line is 1/2 to 2/3 down the kernel, the moisture will be in the 60 to 70 percent range. The approximate moisture level of chopped silage can be determined by means of a “grab test”.

Condition of the forage ball                                                Approximate moisture content

Ball holds its shape and there is considerable free juice         over 75 percent

Ball holds its shape but there is very little free juice              70 to 75 percent

Ball falls apart slowly and there is no free juice                     60 to 70 percent

Ball falls apart rapidly                                                            below 60 percent

            Successful corn silage production starts with corn variety selection and a good crop, but harvesting at the correct time can help insure that it is a quality feedstuff.