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Corn must be ensiled at the proper moisture to get fermentation for preservation. It can be difficult to determine when to harvest corn at the right whole plant moisture The optimum plant moisture for ensiling is slightly different for each type of storage structure. Harvesting too wet will result in reduced yield potential, souring and seepage. Harvesting too dry can reduce yield potential, cause mold to develop, and lower digestibility, protein and vitamins A and E.1
For best ensiling results, corn silage should be harvested at the moisture content appropriate for the type of silo being used. Moisture content should be 80% for bunker silos and bags, 63 60% for conventional tower silos, and 40% for limited-oxygen silos.1,2 13;10;To determine optimum silage harvest time, chop a sample at the full dent stage, just as the milk line appears, and estimate the moisture content. Total plant moisture content should be measured rather than estimated. Then estimate the harvest date by using a drydown rate of 0.50 percentage units per day in the month of September.1,2
The kernel milk line growth stage is a common visual tool to estimate kernel moisture content (Figure 1). The milk line represents starch content of the grain. Break a corn ear and take a look at the milk line on the developing kernels. As a general rule, when the milk line is 1/2 to 2/3 down from the kernel crown, total plant moisture content is between 60 to 70%. A more accurate tool to measure corn moisture content is using a microwave oven/drying ovens or a commercial forage moisture tester.
Figure 1. Corn ear at 50% milk line.13;10;
Corn silage is traditionally harvested at a height 6 to 8 inches above ground level. Increasing the cutting height to 18 inches above ground level may improve silage quality because the lowest portion of the corn stalk is typically higher in fiber and lower in digestibility; however, research has shown that increasing the cutting height of corn silage decreases yield potential due to the extra stalk that is left in the field.3
Silage can be affected by plant diseases, mostly caused by fungi. Loss of dry matter because of tissue death, early plant death resulting in poor ear fill and small kernels, and stalk lodging can be caused by fungal disease and result in reduced yield potential and reduced general quality.4 In addition, certain fungal organisms can contaminate grain and stalks with mycotoxins, such as vomitoxin, causing serious quality problems. If fungicides labeled for corn silage are used, growers need to pay close attention to the label for pre-harvest interval information.
1Lauer,J. August 29, 2016. Timing corn silage harvest. Integrated Pest and Crop Management. University of Wisconsin. http://ipcm.wisc.edu.
2Roth, G. and Heinrichs, A. Corn silage production and management. http://extension.psu.edu.
3Nennich, T. and Harrison, J. 2005. Corn silage harvest guidelines and options. Western Dairy News, volume 5, No.9.
4Isleib, J. and Chilvers, M. March 5,2012. Diseases on corn for silage. Michigan State University Extension. http://msue.anr.edu.