September 2, 2016
You cannot eye-ball harvest moisture to predict when to start corn silage harvest. Iowa State University Extension field agronomist Brian Lang suggests you subsample some corn plants from a field. Then chop them up (wood chippers work great) and subsample from this using a moisture-tester to help target harvest time.
What’s the most accurate way to determine the moisture of these samples? Lang suggests you read this short article from the University of Wisconsin explaining whole plant moisture variability in the field, desired moisture for putting silage in various storage structures, and procedures for moisture determination of corn silage. The article is online at midwestforage.org.
CHOP AT RIGHT TIME: Proper harvest management is critical for producing high-quality corn silage; it starts with harvest timing. Best way to measure corn silage moisture is with a special tester; or you can use a microwave oven.
1) Check moisture of corn silage with tester or microwave
The most accurate means of checking silage moisture is with the Koster Tester kostercroptester.net or a similar product, says Lang. Neither endorsement of companies, individuals or their services mentioned is intended, nor is criticism implied of similar companies, individuals or their services not mentioned.
With that in mind, directions for using a microwave oven are included in the following publication: store.extension.iastate.edu.
Following are recommendations from an article on “Harvesting High-Quality Corn Silage” from University of Minnesota that summarizes many aspects of corn silage harvest. The author is Jeff Coulter, Minnesota Extension corn agronomist.
2) How to harvest, handle and make high-quality corn silage
Proper harvest management is critical for high-quality corn silage, and it starts with harvest timing. This ensures that the harvested crop is at the optimum moisture for packing and fermentation. Silage that is too wet may not ferment properly and can lose nutrients through seepage. If silage is too dry when harvested, it has lower digestibility because of harder kernels and more lignified stover. In addition, dry silage does not pack as well, thus increasing the potential for air pockets and mold.
Optimum silage moisture at harvest ranges from 50% to 60% for upright oxygen-limiting silos, 60% to 65% for upright stave silos, 60% to 70% for bags, and 65% to 70% for bunkers, he says. Due to variability among hybrids and growing conditions, it is necessary to measure silage moisture using a commercial forage moisture tester or microwave oven rather than simply estimating it from the kernel milk line.
3) Corn kernel milk line is indicator of when to collect samples
Instead, kernel milk line should be an indicator of when to collect the first silage samples for moisture testing. A general guide is to begin moisture testing when milk line is 25% of the way down the kernel for horizontal silos, and 40% of the way down the kernel for vertical silos. Then, assume a constant dry-down rate of about 0.6% per day, and measure moisture again prior to harvest.
Length of cut and crop processing are also important for obtaining high-quality corn silage. This is because breakage of cobs and kernels increases surface area; which improves digestibility, reduces cob sorting, and results in higher density silage that packs better. Although crop processors are expensive, the higher-quality silage produced can increase milk production by 300 pounds per cow per year.
The benefit of crop processors is greatest when there are harder kernels resulting from delayed harvest or drought. When using a crop processor, chopper cut length can be increased to reduce horsepower requirements while maintaining optimum particle size. For unprocessed corn, ideal chop length is 0.375 inch theoretical length of cut. For processed corn, the recommended settings are a 0.75 inch theoretical length of cut with 0.08 to 0.12 inch roll clearance.
4) Generally recommended cutting height is 4 to 6 inches
A 4- to 6-inch cutting height is generally recommended for corn silage, as it maximizes silage yield and milk per acre. However, drought-stressed corn can accumulate nitrate in the lower part of the stalk, thus increasing the potential for nitrate poisoning, particularly in older livestock on lower-energy rations. The potential for high nitrate silage can be even worse if drought-stressed silage is harvested within 10 days of rainfall, since rainfall increases crop uptake of soil N. Silage with high nitrate levels can be managed by dilution with other feeds or by increasing the cutting height to 12 inches.
Silage cut at this greater height has been shown to have 8% less silage yield and 2% less milk per acre. This same study found that a cutting height of 18 inches resulted in 15% less silage yield, 12% greater milk per ton, and 4% less milk per acre when compared to a 6 inch cutting height. Increased silage quality with high cutting is due to a higher ratio of grain to stover. However, cornstalks are a good source of fiber and the lower tonnage with high-chop silage typically makes it difficult to justify in the absence of high nitrate levels. When harvest begins, fill silos rapidly to reduce exposure of silage to oxygen and to reduce fungal growth. For bunker silos, pack silage as tightly as possible in progressive wedges in depths of 6 inches or less.
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