Most permitted animal feeding operations are required to sample manure storage facilities at least annually. Frequency of sampling is typically outlined in the permit. For non-permitted facilities, manure testing is a voluntary but essential step in using manure as a fertilizer for crop production. Typically, nutrient management guidelines suggest sampling manure at least once a year.
For liquid manure, taking the sample after agitation and during hauling will provide the most representative sample of the nutrient values.
When manure is handled as a solid, multiple samples can be collected from loads and mixed together, and then a subsample of that material is submitted for testing.
More frequent manure testing is needed when you have reason to believe there has been a significant change in nutrient concentration of the manure. Such changes can be caused by changes in animal diet, bedding type or frequency, other additives mixed with the manure, the amount of water added to the storage, and/or seasonal changes. For example, Missouri research showed that unagitated anaerobic lagoon effluent has higher nitrogen concentrations in spring compared to fall, so sampling these facilities at least twice per year is appropriate.
Always track the manure test history for a manure storage. If you see dramatic swings in nutrient concentration from sample to sample, more frequent sampling is warranted. Also review the sampling technique to ensure a representative sample is collected. For recommendations on sampling manure, review Manure Sampling.
Recommended Reading: Livestock Manure Sampling (University of Minnesota)
Author: John A. Lory, University of Missouri
