Monitoring field moisture content key in silage harvest

Jamie Patton
Monitoring field moisture content key in silage harvest this fall.

What a fall! Silage harvest is off to a late and slow start and it seems nothing is predictable about current plant moisture contents.

Watching regional Extension silage drydown results in northeast Wisconsin, similar corn hybrids planted on the same day have had more than a 10% spread in moisture percentages. With our compressed harvest window and continued rainy weather, this variability in moisture content makes it even more difficult to sequence which fields to harvest and when to harvest for optimal forage quality and field trafficability.

Monitoring field moisture content is key to ensuring we are harvesting corn silage that will pack and ensile well, while reducing leachate losses. We all know the optimal silage harvest moisture recommendations by heart, but it never hurts to review.

Most universities recommend chopping silage at 1/3 to 2/3 milk line and 62 to 68% moisture. Harvesting drier than recommended silage tends to reduce fiber and starch digestibility.

Dry silage is more difficult to pack, potentially resulting in excessive heating and molding. Wet silage, particularly silage over 70% moisture, can result in leachate losses and butyric acid formation, which often leads to decreased animal consumption and performance.

Optimal final silage harvest moisture contents can further be refined based upon the silage storage structure. Optimum silage moisture percentages for upright oxygen-limiting silos ranges from 50-60%, 62-67% for upright concrete stave silos, 60-70% for bags, and 65-70% for horizontal bunkers.

Because leachate seepage often results from silage ensiling and compaction, upright silos can be more prone to leachate formation with wetter silages than properly managed bags, bunkers, and piles, due to the overlying weight of the forage compacting materials within the storage system.

Harvesting silage at the proper moisture content to avoid leachate formation is key to maintaining forage quality and to protect water quality. As inferred above, leaching can occur when silage moisture contents are above 70%.

Research has shown silage leachates contain, on average, 5% dry matter, and 1,500 to 4,400 mg/L total nitrogen, 300 to 600 mg/L phosphorus, and 3,400 to 5,200 mg/L potassium. To put this in perspective, a typical dairy manure may contain 2,600 mg/L total nitrogen, 1,100 mg/L phosphorus and 2,500 mg/L potassium. From the feeding perspective, leachate production represents a loss of soluble nutrients that would have been immediately available in the rumen, thereby reducing overall forage quality.

In addition to forage quality degradation, leachate loss can also lead to forage shrink. In his article “Shrink is a Deceptive Term”,  Biological Systems Engineering Professor Emeritus, Brian Holmes, quantifies potential leachate and dry matter losses from a 30’x150’x12’ bunker (silage bulk density @ 45 lbs as fed/ft3).

In his scenario, if corn silage was harvested at 73% moisture, at a leachate solids content of 5%, approximately 290,000 lbs of leachate would be produced, containing more than 14,500 lbs of dry matter. This equated to approximately a 12% shrink loss and a 2.2% dry matter loss from leachate.

Depending on a farm’s forage stock, a 2.2% dry matter loss combined with a forage quality loss could be considerable, particularly when combined with additional packing and ensiling losses common in wet silages.

Not to be overlooked, loss of nutrients and dry matter from wet silage are also a concern for water quality. Silage leachate has a high biological oxygen demand, meaning that if the leachate enters a water body, it can lead to oxygen depleted waters and compromised aquatic life. To minimize risk, proper collection and management of leachate, where necessary, is critical.

As silage harvest continues across the state, continued monitoring of crop moisture content is imperative to ensure both feed quality, as well as feed quantity. While not specific to your fields, you can monitor statewide corn silage dry down results at

I also encourage you to visit the Extension Team Forage website for more information on harvesting corn silage in non-optimal years or talk to your agronomist or county Extension Agriculture Educator.

Jamie Patton

Patton is the Senior Outreach Specialist of Nutrient and Pest Management Program

UW Extension