Manure testing and utilization

AgSource Labs in Bonduel, Wis. is already starting to receive manure samples

It’s important for those livestock producers to remember that the nutrients in manure are valuable and should be handled appropriately and responsibly to make the most of them. While there are generally accepted “book values” for various kinds of manure – based on the kind of livestock it’s generated from and how it has been stored – it’s a much better practice to test that manure and know exactly what nutrients are in it.

Jim Friedericks, who is the Director of Outreach and Education for AgSource Laboratories, notes that how animals are raised, fed and handled will affect their manure. Sows in a farrowing house will produce manure that is different from hogs in finishing houses. Dairy cows in freestall barns will have different manure than heifers in a loafing shed. “The best practice is to take a sample of the manure and have it tested by a certified laboratory,” he said. “How manure is stored will also have an impact and should be accounted for when pulling samples for testing.”

“Taking a sample lets you find out what’s in it, but the samples have to be taken in such a way that they truly represent what’s in the manure,” he said. If the manure is stacked, he recommends taking samples three feet into the stack rather than taking dry material on the outside of the pile. Taking five to 10 samples from various locations and then mixing them together in a bucket is the best way to assure there is a good, representative sample.

Lagoons or manure pits are a bit trickier since that manure will stratify the longer it is stored. Manure in pits is generally very stable but it’s somewhat tougher to get a representative sample. The best samples would be taken once manure is agitated. Some farmers or custom manure haulers take samples as they pull manure out of the pit. Pulling one gallon for every million gallons incorporated will give the farmer a good idea of how well manure agitation is working and offers a great average manure nutrient rate to work with. Previous year’s samples are then used as a guide for manure application rates.

Once manure samples are collected, they should be cooled or preferably frozen right away. If samples are frozen they are completely stable. AgSource Laboratories in Bonduel, Wis. is already starting to receive manure samples from farmers in anticipation of crop harvest and manure spreading. If sending in samples, please use plastic containers supplied by the laboratory for manure samples which can be loaded and safely shipped to the lab.

 

What farmers and manure applicators should be most concerned with when reviewing their results are total nitrogen (N), total phosphorus (P), total potassium (K) and sulfur (S). Generally, the nitrogen number is the one that determines spreading rates, unless regular soil testing shows high levels of phosphorus – which then becomes the most important criteria and limiting factor for manure spreading. Additionally, a manure report will typically include percentage solids or dry matter.

For most Midwestern farmers, the nitrogen information will be the most important criteria when it comes to deciding how to use it on the land. Nutrient management plans are generally designed to provide enough manure-based nitrogen for the crop that will grow in that soil in the coming year. Due to phosphorus restrictions and the crops being grown, manure may not be able to be spread on a field every year.

How the manure is applied is critical to the availability of nitrogen for the following crop. For example, if liquid manure is injected, 98 to 100 percent of the nitrogen is considered to be available to the crop in the first year. If the manure is surface-applied and incorporated within one hour, 80 percent is considered to be available to the crop in that first year.

The least desirable option, which is land spreading without incorporating, means that only 60 percent of the nitrogen will be available for the crop in the first year because ammonia in the manure will volatilize and be lost from the soil. It should be noted that nutrient management plans are also conservation plans. In some cases where incorporation is not an option, to meet tolerable soil loss levels, other best management practices should be implemented.

 

The lab report will show how much of each nutrient the farmer can expect to carryover for the second year’s crop and the third year’s crop based on the manure analysis and the type of manure.

Manure reports will also inform the farmer about how much of each nutrient is there in various measurements – pounds per thousand gallons or pounds per ton of manure.

While spreading manure closer to the time when the crop will need it would be ideal – which is to say in the spring – that’s often not possible, given the workload on a farm and time constraints in the spring. As a result, fall spreading and emptying of manure pits is a time-honored tradition. Testing of manure, coupled with regular soil testing, will make that tradition more productive and allow the manure’s nutrients to best be used.

Jan Shepel is a dairy farmer and freelance writer in southern Wisconsin.