Ever have a frustrating day with a silo unloader and an upright silo? Or have the kids complain about having to cover the silage pile in the hillside trench with wooden walls and dirt floors? Or maybe you were the farm kid who spent Saturday mornings cleaning up silo bag plastic?

Although the challenges of these storage methods are different, the juice leached from the freshly harvested fermenting crop is the same. This juice, also known as leachate, is not only unpleasant on the farm; its high concentration of phosphorus, nitrogen and other components make it dangerous for nearby water resources.

In an effort to understand losses from feed storage areas, University of Wisconsin Discovery Farms spent three years monitoring the liquid leaving these areas on three private farms. “It is really remarkable just how highly concentrated leachate from silage storage can get,” says UW Discovery Farms Senior Research Specialist Aaron Wunderlin.

“Under the right conditions, leachate nutrient concentrations are much greater than any edge-of-field numbers we have seen in our 12 years of water quality monitoring on private farms.”

There are two ways liquid from silage can leave the storage area. First, silage leachate can flow from the silage pile without precipitation. This usually occurs when the silage crop is harvested at a relatively high moisture level.


The second and more common way leachate is transported from bunker systems occurs when precipitation from a rain or snowmelt event comes into contact with feed, picks up nutrients and solids, and is transported away from the feed storage area in runoff.

Although concrete bunker silos solve some of the previously mentioned challenges and offer many benefits, they can be more vulnerable to runoff losses than their upright counterparts. Their large impervious area and feed sources more readily expose them to precipitation.

Water from precipitation can interact with any exposed silage (e.g., spoilage piles and open face) and lead to feed storage runoff. In fact, more than 60 percent of the rainfall and melting snow will result in runoff. Precipitation can then transport the nutrients in leachate to nearby waterways.

But how do the losses from this very small area compare to the rest of managed farmland? Average edge-of- field losses from Wisconsin Discovery Farms are 2 pounds per acre of phosphorus and 8 pounds per acre of nitrogen. Nitrogen and phosphorus values in runoff from a 1-acre feed storage area can be similar to losses from 200 acres of cropland.

Joe Bragger, a dairy farmer in western Wisconsin, has worked hard to control the amount of nitrogen and phosphorus leaving his farm fields. However, Bragger says, “Learning that my feed storage area could be a significant part of my nutrient loss is a great concern.”

“And it is not just the high nutrient concentration that is a concern,” Wunderlin says. “Leachate’s biochemical oxygen demand (BOD) is extremely high, even more so than manure.” A high BOD means that leachate can consume a large amount of oxygen – oxygen needed by fish and other aquatic life. It can remove so much oxygen from the water that there is none left for their survival.

There are three management practices that lead to less leachate produced from feed storage areas and minimal nutrients and other components in the feed storage runoff.

1.Harvesting forages at the appropriate moisture content can do more than decrease spoilage and leachate losses; it can increase feed quality, too. That means more profit for your bottom line with happier, healthier cows.

2.Covering silage and retaining walls well means there is less contact between stored feed and precipitation. Less interaction through the storage time means better feed, even with a longer storage period and less overall runoff from the feeding area.

3.Removing or covering spoil piles means waste feed doesn’t clip you twice. It is already spoiled; don’t let it also become an environmental concern by tainting water that runs off the area.

Farmers with bunker silos can also utilize capture systems to further reduce losses. With previous feed storage systems, capturing the waste liquid was very difficult.

The use of designed concrete feeding areas means water is directed to flow to specific areas, and a capture system can be added in those areas of concentrated flow. This engineering method is meant to capture the hottest waste before it leaves the storage area.

Many farmers already have capture systems installed on their farms, but they question whether these systems perform their job the way they were intended to do.

Results from the UW Discovery Farms leachate project will provide valuable data needed to better characterize runoff coming from feed storage systems. The ultimate goal is to enhance future collection system designs to more effectively collect the high-concentration leachate. PD

For more information on the UW Discovery Farms leachate project, visit UW Discovery Farms on the web or contact Aaron Wunderlin by email.

Both at UW Discovery Farms, Callie Herron is an outreach specialist and Amber Radatz serves as co-director.

PHOTO: Nitrogen and phosphorus values in runoff from a 1-acre feed storage area can be similar to losses from 200 acres of cropland. Photo courtesy of UW Discovery Farms.