Ideal corn silage is made when the whole corn plant is between 30 to 38 percent dry matter (62 to 70 percent water). At that moisture level, corn silage ferments well and preserves the most nutrients for the best animal performance.
People use several tricks to guess the moisture level of corn when deciding if it is time to start chopping. One trick is to observe the milk line, the place on the kernel where the sugary “milk” is being converted to starch. Another rule of thumb is to chop the corn soon after the kernels are well dented, but before the leaves and stalks become brown and dry.
As it turns out, neither of these methods is a very accurate way to create the best of corn silage. A Wisconsin study showed that 82 percent of the hybrids tested exhibited a poor relationship between kernel milk-line stage and whole-plant percent dry matter. Research in Ohio backs that up. Geographic location, planting date, hybrid selection and weather conditions can vary the relationship between kernel milk-line position and whole plant dry matter content.
The only reliable method of determining the best time to harvest corn silage is to sample and directly measure the percent dry matter of whole plants. There are numerous references on measuring dry matter content of silage at home using a scales and a microwave oven. Just be aware that these home testing methods have been shown to vary plus or minus 2 percent from laboratory measurements.
If you have to error, it is usually best to error on the side of too wet rather than too dry. Some farmers harvest silage early because they believe they are losing feed value when they see undigested kernels in the manure. This is not true. The digestibility of corn at the dent stage is just as high as corn at the milk stage.
Corn silage that is cut late and has brown, dead leaves and shucks can make fair to good silage. Field losses are greater when silage is harvested late in the season, and additional water may need to be added to enhance the fermentation process. As a rule of thumb, add four gallons of water per ton of silage for each 1 percent desired rise in moisture content.
Add water while the silo is being filled, not after. Water added after the silo is filled tends to seep down the silo walls rather than be absorbed by the chopped corn. This can lead to leaching of silage nutrients and poor fermentation.
Jeff Burbrink is an Extension educator in agriculture and natural resources. Write to him at 17746 E. C.R. 34, Goshen, IN 46528; call 533-0554; or fax 533-0254.