The day that you choose to harvest your corn silage can actually have the most significant affect on quality out of all of the management decisions. The moisture content of your silage greatly impacts how well your feed stores, ferments and ultimately determines feed quality. It is very important to harvest your corn silage at the correct moisture content as you have one chance per year to get it right.
Determining the Correct Silage Moisture for Your Farm
The type of storage that you use is the main factor determining the ideal harvest moisture content. Since you have already have your storage in place it is easy to match the ideal moisture content to your storage type. The key principal to proper silage storage is to pack the silage tight enough to remove as much of oxygen as possible out of the silage. This helps reduce aerobic bacterial growth which causes dry matter loss and bunk shrink. We want the silage to begin anaerobic fermentation as quickly as possible. Higher moisture silage will pack tighter, however too much moisture can cause seepage from the silo. The taller the silo, the larger the bunker pit and heavier the packing tractor will allow you to move to the lower end of these moisture ranges as the weight of the silage will help compact and displace air pockets. See the chart below to determine your ideal silage moisture content.
How to Determine Moisture Content of your Standing Corn Silage
Milk Line Estimate
The milk line is a physical line that appears on the bottom side of the kernel during grain fill. It progresses from the top of the kernel at Dent down to the tip of the kernel where it will eventually black layer at maturity. This is a guide line that helps producers estimate whole plant moisture while in the field. There will some variation on accuracy depending on weather and the individual hybrids. Below is a graph from the University of Wisconsin showing the approximate whole plant moisture compared to the milk line. Note that ½ milk line is approximately 65% moisture. This should be only used as a guideline and actual sampling to determine moisture content is much more precise.
This is a great way to get an accurate sample of your whole plant moisture. Take 6-12 representative stalks of corn from your silage field and process them through a wood chipper or silage harvester. Collect the sample and mix thoroughly so that the sample contains a homogenous blend of cob, leaf and stalk. Use a Koster tester, microwave or accredited lab to determine the moisture content of the silage. These are often done prior to harvesting to give an estimate of how long to wait until the corn has reached a desired moisture. An example would be if the sample came back at 68% and the producer wants their silage at 65% to harvest. Approximately 6 days from the sample being taken the corn will reach the desired moisture content (0.5% moisture loss per day on average).
Physical Appearance of the Corn Plants
Generally visual appearance of corn plants can provide some indication of the moisture content. However this is very subjective to each individual and varies from year to year. There are many different factors such as hybrid characteristics, leaf diseases, fertility and environment that can alter the appearance of the corn plants. Modern hybrids also have better Stay Green traits that make them appear ‘wetter’ in the fall then they may actually be. The improved stay green will allow the plant to stay alive longer while starch accumulates in the kernels and the cob moisture content decreases.
Factors Affecting Dry Down in Corn Silage
Silage specific hybrids such as the FeastPlus family of silage specific hybrids from Maizex Seeds are selected and bred for corn silage production. Generally these hybrids will have a slower dry down curve to allow for a wider harvest window in the fall. This is generally due to kernel texture and the husk on the cob, some of these hybrids will have a longer and/ or tighter husk which slows down the grain content dry down.
Dual purpose type hybrids including the EnergyPlus hybrid family from Maizex Seeds are grain corn hybrids that have suitable characteristics for silage production. Because these hybrids are generally selected primarily for grain production, fast dry down is often a key characteristic. For silage this can narrow the ideal harvest window for your silage which can be challenging when targeting the correct harvest date. Producers using Dual Purpose type varieties need to be very diligent to catch the rapid dry down curve of their hybrids at the right point.
Hybrid Maturity for Your Area
The dry down of a corn plant is a physiological process. Today we have hybrids that range from 1950CHU to 3300CHU. It is important to know the maturity of your hybrids and how they will adapt to your area. Matching up maturity with planting date, maturity zone and expected harvest date will all help you target the ideal moisture for harvesting your silage. Generally the recommendation is to grow a silage variety that is 150-200CHU longer than adapted grain corn for the area. If your silage hybrid tends to be close to the adapted grain hybrids for your area, you should expect to harvest early in the season. If you have an ultra-long maturity hybrid you would expect to be towards the end of the harvest season.
Fungicides on Corn Silage
When fungicides have been applied to corn silage fields, this they will tend to keep corn plants healthier and alive longer, essentially delaying their maturity and dry down and as a result harvest date. Side by side comparisons of corn treated with fungicides and without will show that the treated corn will be on average ~3% wetter. During some harvest periods this may add a week delay in harvest to get to the ideal moisture content.
As farmers we are always at the mercy of the weather. The weather we encounter each harvest season will greatly affect how fast your silage dries down. Hot, dry weather can greatly accelerate the dry down to over 1% loss per day. And cool, wet weather can virtually stall dry down. On average we tend to say that corn silage will drop 0.5% moisture per day or 3-4% per week.
Why it is Important to Have the Right Moisture Content
|Silage too wet||Silage too dry|
|-Seepage from bunk or silo (loss of nutrients)||-Not packed enough|
|-Clostridia fermentation||-Heating during fermentation|
|-Higher loss of Dry Matter during fermentation||-Mould and toxin issues|
|-Sour smelling feed||-Shorter silage storage life|
|-Lower yield||-Higher loss of Dry Matter during fermentation|
|-Lower feed intake||-Lower fibre digestibility|
|-Lower starch content||-Lower starch digestibility|
It is critical for you to know your ideal moisture content and even more important for you to harvest at the correct moisture. There are a number of ways to determine the moisture content of your corn silage, with a physical test being most accurate. Patience and attention to detail at harvest time will pay dividends as you feed through the year.