Section 10 – Manure Sampling and Testing

Why test manure?

There are “book” values for the amounts of nutrients in manure. However, actual test results from manure samples can vary greatly from these. That is due to differences in animals, diets, environmental conditions, and methods of handling and storing manure. It is usually well worth the effort to get tests of the manure being utilized for fertilizer.

Sampling procedures

Because manure can be variable, it is important to get an adequate number of sub samples and mix them well to get a composite sample. A clean tiling spade or similar device and a clean five-gallon plastic bucket work well for sampling solid manure.

Solid manure piles
• Take at least 20 sub samples
• Sample various locations and depths in the pile
• Mix thoroughly
• Take a two pound composite sample
• Place the composite sample in a plastic bag
• Expel air from the bag and seal it
Liquid manure storages
• Agitate or mix the manure to suspend solids (This is usually done before emptying the storage.)
• Take about five sub samples of the agitated manure from the storage structure or from the pump or manure wagon.
• Thoroughly mix the subsamples
• Take a composite sample of whatever size the laboratory requires
• Put the sample in a plastic bottle, leaving some room for expansion or gas
• Secure the lid on the bottle and put the bottle in a plastic bag

Important note: All samples should be refrigerated or frozen if they cannot be transported to the lab immediately.

Timing of sampling

Sampling and testing just prior to manure application will let you calculate the application rate necessary to meet the crop requirements. However, if that is not possible, take samples of the material as it is being spread. The test results will still be valuable.
• Manure samples taken from the spreader will more accurately represent the material actually being spread.
• You will know what nutrients amounts have been applied, so you can account for them in future nutrient application planning.
• You will begin to create a useful record of your operation. Although manure composition varies greatly from one AFO to another, it tends to be more consistent from time to time on a given AFO unless the type of livestock or the feed ration is changed.

What information do you want from the manure test?

For certain
• Total nitrogen
• Phosphorus
Maybe
• Inorganic and organic nitrogen (indicates how quickly N is available to plants
• Moisture content
• Potassium
• Total salts (electrical conductivity)

How should the information be reported?

• Nutrient content should be reported on an as-is basis rather than a dry matter basis because that is how you will be land applying it.
• Nutrient concentration should be reported as pounds per ton or pounds per 1000 gallons because that is how you will be calibrating the application machinery.
• Phosphorus content should be reported as P2O5 equivalent rather than as elemental P, because that is how fertilizer recommendations are made.