Laboratory analysis is the best way to evaluate the nutrient content of manure on a specific farm. When sampling is not or cannot be done, farmers rely on “book values” to develop nutrient management plans, design manure storages, and create best management practices for land application. Book values show a range of nutrient values that can be expected from typical manure storages, but many of these averages are decades old and may not reflect current production practices. Factors such as animal diets, genetics, housing, and manure handling and storage all impact the nutrient content of the manure.

Researchers from the University of Minnesota set out to evaluate the change in manure from when the Midwest Plan Service last published its Manure Characteristics booklet in 2004. They partnered with three laboratories in the Midwest that shared data from the last 10 years. Nutrient averages for beef, dairy, poultry, and swine manure were evaluated.

For the liquid dairy samples, there was a decreasing trend over time for nitrogen and phosphorus and an increasing trend for ammonium-

nitrogen. In liquid beef manure, there was a rising trend for more nitrogen, ammonium-nitrogen, and phosphorus. The liquid poultry manure had an increasing trend for ammonium-

nitrogen and potassium with reducing levels of phosphorus. Without knowing more details about the liquid swine manure samples, including age of the animals and the type of manure storage system, the researchers were unable to determine nutrient changes.

For solid manure from swine, dairy, and beef operations, they found an upward trend for total nitrogen, phosphorous, and potassium. The solid poultry manure had a rising trend for total nitrogen and potassium.

The team recognized that knowing more details about the samples would be beneficial, since animal age, nutrition, housing, and manure storage can impact nutrient levels. The project’s next step is to formulate a manure nutrient database, called Manure DB, to help keep book values up to date.

This article appeared in the November 2022 issue of Journal of Nutrient Management on page 9.

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