Intensive management of compost windrows will yield the most effective and efficient results in terms of pathogen destruction, plant disease suppression, manure volume reduction, and improved soil health, but even casual composters can benefit from the microbial breakdown of organic matter that occurs within a compost pile. To best utilize the end material, it is helpful to submit a sample for laboratory testing.

During a Composting Field Day hosted by the University of Wisconsin Division of Extension, Kevin Shelley showed attendees how to collect a composted manure sample. Shelley, an outreach educator for the Nutrient and Pest Management Program at the University of Wisconsin-Madison, said the first step is to select a laboratory that does this type of testing. He noted that some labs have an option for you to order a sampling kit that would contain the jar, the submission form, and, in some cases, a mailing label.

Next, collect a composite sample. “You want something that represents the pile the best you can,” Shelley stated.

To do this, Shelley recommended using a clean shovel to pull compost from at least half a dozen places. If the pile is fairly consistent throughout, one composite sample should be enough. If the pile has a lot of variation in terms of the type of manure or bedding, pull subsamples from each area and then make a composite sample from each segment of the pile.

Thoroughly mix the subsamples in a clean bucket or tub, then grab the composite sample. Shelley reminded attendees that the sample is only about one handful from the whole pile, and a lab will only test a few ounces from that sample, so it is important to mix it well.

Label the jar with the date and source of the compost. He said to put the sample in the freezer and to ship it early in the week so it gets there promptly.

Some laboratories may have a test specifically for composted manure. If they don’t, or if you are using the compost on your own fields and not selling it to others, then a less comprehensive analysis is probably sufficient. Shelley said dry matter content, the macronutrients of nitrogen, phosphorus, and potassium, and the carbon-to-nitrogen ratio would be useful data to receive.

This article appeared in the November 2023 issue of Journal of Nutrient Management on page 21. Not a subscriber? Click to get the print magazine.