Composted animal manure has been used as a soil amendment for years. When done well, its benefits include plant disease suppression, pathogen destruction, manure volume reduction, and improved soil health. For these reasons and more, composting has been growing in popularity as a way for livestock producers to handle manure.

Intensive management of compost windrows will yield the most effective and efficient results, 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 sampling. Nowadays, most labs want samples of this nature sent in plastic jars rather than a plastic bag. Shelley noted that some locations 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, you need to 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 in the pile. If the pile is fairly consistent throughout, one composite sample should be enough. If you know the pile has a lot of variation in terms of the type of manure or type of bedding used, plan to 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.

Use a permanent marker to label the jar with the date, source of the compost, and which pile you pulled the sample from if there are multiple piles. He said to put the sample in the freezer so it doesn’t undergo a transformation in the vessel, and ship it early in the week so it gets there promptly. Shelley advised wrapping newspaper around the vessel before putting it in the mailing box to help protect and insulate the sample.

Some laboratories may have a test available 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.

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(c) Hoard's Dairyman Intel 2023
September 21, 2023

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