Livestock manure is a variable compound, both in the amount of solids and the amount of nutrients.Variation in manure can be caused by animal type, diet, additional byproducts, bedding material, storage and processing.

Lee karen
Managing Editor / Progressive Dairy

These inconsistencies can result in environmental consequences and crop yield loss, Becky Larson reported at a lagoon agitation demonstration in northwest Wisconsin this past summer.

Larson, a biowaste engineer and extension specialist at the University of Wisconsin – Madison, said agitation and sampling frequency are key factors in reducing these inconsistencies.


When manure is stored, stratification becomes an issue. The settling of solids and nutrients changes the composite of manure in each layer. The goal of agitation is to obtain uniformity throughout the stored manure, therefore reducing application inconsistencies.

Agitation has the ability to significantly reduce variation. Larson reported seeing variability at less than 10 percent when the manure was agitated and more than 30 percent without agitation.


Preliminary data from a study she conducted showed increased variation in storage units with higher solids content. She also noted farms that utilized an agitation boat maintained a fairly steady amount of solids while emptying the storage, whereas other farms saw a general increase in solids, indicating their agitation method may not be as effective.

Regardless of how the manure storage was agitated, Larson said there remained a lot of variation with phosphorus.

“Ammonia was pretty consistent with the boat,” she added. “A lot less variation than what we’ve seen in the past.”

Proper agitation can take a number of days, or at least 24 straight hours, before emptying the storage to ensure consistent manure.


Some producers may prefer not to agitate in order to have two different types of manure – a more liquid form with a low solids count on top for irrigation and a thicker layer with high solids on the bottom.

When taking this approach, Larson said, “The important thing to remember is to sample those layers differently. You can’t just take one sample.”

Without agitation, she has found 40 or more samples are needed to account for changes in the material coming out of storage. Just five samples were found to be sufficient for well-agitated manure.

She also recommended new samples be taken if there is an extended time (a couple of weeks or more) between applications from the same storage unit.

Sampling is only useful if producers are using the results to match what is being applied in the fields.

“Further steps down the line are not effective if the values used to determine application are incorrect,” Larson said. Therefore, it is important to sample as needed to provide correct information to the applicator.

When in a hurry to empty manure storage, it can be tough to sample often and make appropriate changes. Therefore, utilizing agitation to create uniform manure can help reduce the amount of samples required and lessen any inconsistencies in application. PD

PHOTO:Photo by Mike Dixon.