Obtaining a representative sample is important in evaluating the nutrient content of manure. The sample should be representative of the manure that is actually being applied to the land. Ideally, the manure should be sampled and analyzed before it is spread so the data can be used to adjust spreading rates, but this may not be possible in all cases.
Generally, a solid manure storage structure should be sampled at a minimum of 10 locations to obtain a representative sample. The subsamples should be mixed to form a composite sample of about 1 quart in volume. A freezer bag is an ideal container in which to store and ship a solid manure sample.
Liquid manure storage structures may or may not be agitated for emptying. If the facility is agitated, sampling should be done during agitation. For liquid samples, a 1 pint volume is generally sufficient for the laboratory to perform a nutrient analysis. Tightly sealed plastic bottles are adequate for collecting and shipping liquid manure samples.
The container selected should be rinsed out and reasonably clean. If you are sampling a liquid (such as a lagoon), a final rinse with the effluent being sampled is good practice. The container selected should be suitable for mailing, as most manure samples are carried through the regular postal system. Increased postal security, especially if your sample is liquid manure, dictates that you take the package inside and tell them the contents of the package before shipping.
Experience and research with manure samples have shown that preservation measures such as acid stabilization or cooling/freezing do not significantly increase the accuracy of the analysis compared to sample storage at ambient temperatures for periods up to seven days. Hence, for routine manure fertilizer nutrient analyses, the difficulty associated with procuring and handling acid and refrigerating or freezing samples is not justifiable on the basis of increased accuracy. Effort should be made to minimize the elapsed time between sample collection and its arrival at the laboratory. Also, samples should not be allowed to "lie around" in conditions of extreme heat, such as the trunk of a car or the cab of a truck in the summer. Gases generated by bacteria in the sample can burst the sample container under these conditions. Sample bottles should have lids tightly closed and secured with tape. They should be mailed in a cardboard box large enough to allow packing material to be placed around the bottle. This will minimize the effects of rough handling in the postal system. Samples should be collected so that they can be mailed to the laboratory without being in the postal system over a weekend.
A typical manure nutrient analysis would include the following tests.
• Total Kjeldahl nitrogen
• Ammonia nitrogen
• Total phosphorus
• Potassium
• Moisture content (or dry matter)
You should coordinate with the testing laboratory to specify which tests you need and to schedule sample arrival at the lab.
Many states maintain a list of laboratories providing a manure nutrient analysis service. Contact your local land-grant university Extension Service, NRCS, or a qualified professional for assistance in obtaining a manure nutrient analysis. Information on manure sampling and analysis is usually available electronically through university or NRCS resources in your state. Examples of such information are as follows.
