Manure sampling for nutrient management
When testing manure, your nutrient management plan is only as good as your ability to obtain a representative sample. And your manure test results are only as good as your sample. There are a number of different types of sample collection processes that must be undertaken for different manure situations, so doing it right is invaluable.
During loading: The recommended sampling for solid manure is to sample while loading the spreader. Sampling the manure pack in a barn directly has been shown to result in very variable results and is not recommended. Take at least five samples during the process of loading several spreader loads and save them in a bucket. When all of the samples are collected, thoroughly mix the samples and take a subsample from this to fill the lab manure test container.
During spreading: Spread a tarp or sheet of plastic in the field and spread manure over this with the manure spreader. Do this in several locations and with several loads of manure. Collect the manure from the tarp or plastic sheet in a bucket. Mix the manure collected from different locations and spreaders, and take a subsample from this to fill the lab manure test container. This procedure is usually only practical for more solid manures.
Daily haul manure: Place a five-gallon bucket under the barn cleaner four or five times while loading the spreader. When all of the samples are collected, thoroughly mix the samples and take a subsample from this to fill the lab manure test container. Repeat this several times throughout the year to determine variability over time.
Stockpiled manure: Take 10 samples from different locations around the pile at least 18 inches below the surface. When all of the samples are collected, thoroughly mix the samples and take a subsample from this to fill the lab manure test container. Large diameter auger bit and portable drill or soil sampler can be used to access manure deep within pile.
In liquid manure storage, agitation is critical to spreading uniform manure and to getting a representative sample. Agitating for two-four hours is the minimum. Depending on the type of storage, longer agitation times may be required.
The agitation for sampling should be similar to the agitation done when the storage is emptied. For this reason, the most practical time to sample is when the storage is being emptied for field application.
If the storage is not adequately agitated, there will likely be stratification which vastly impacts the distribution of nutrients. In one example of stratification, the last 15 loads spread from storage had two to three times more phosphorus than in the first 45 loads spread. If the storage is known to be stratified, separate samples should be taken as the manure consistency changes during emptying.
As manure storage is emptied: Agitate the storage thoroughly before sampling. Use a bucket to collect at least five samples during the process of loading several spreader loads and save them in the bucket.
When all of the samples are collected, thoroughly mix the samples and take a subsample from this to fill the lab manure test container. When filling containers with liquid manure, never fill the container more than 3/4 full. If samples are collected over a several-hour period, the bucket with manure sample should be stored on ice to limit ammonia losses.
From the manure storage: Sampling a storage directly is much more difficult and likely to result in more variable results than sampling as the manure is loaded into the spreader. Agitate the storage thoroughly before sampling.
Use a small bucket or tube to collect at least five samples from different locations in the storage. Be wary of working around liquid manure storage locations as fumes can easily overcome the sample-taker.
During application: This method is good for irrigated manure. Place buckets around the field to catch manure from the spreader or irrigation equipment. Place these to collect manure from more than one spreader load. Combine and mix the manure collected from different locations, and take a subsample from this to fill the lab manure test container. This method may give you “crop available ammonia nitrogen” as any ammonia losses may have already occurred prior to reaching the bucket. What reaches the bucket is likely to soak into the soil and be available to the crop.
For more information on manure sampling strategies for testing nutrient availability, contact your test facilities for their preferred methods of sample collection. More information can be found by contacting your local Extension office. — WLJ