How to Test Manure Nutrient Content (and Why It’s Worth Doing)

Most growers wouldn’t build a fertility program around a bag of commercial fertilizer without knowing its analysis. Manure often gets treated differently, applied by habit or history rather than by what’s specifically in each load. Given that manure is so widely accepted as a fertilizer application, it’s surprising there’s not a better understanding of how variable it can be. 

The only way to know what a given load is actually delivering is to test it.

Why Manure’s Nutrient Content Varies So Much

Unlike a bagged fertilizer with a guaranteed analysis, manure’s nutrient content shifts based on a long list of variables, like: 

• Animal species
• What it was fed
• Bedding used
• How the manure was stored
• How long it sat before testing or application. 

Ruminant manure (cattle, dairy) and non-ruminant manure (hogs, poultry) don’t behave the same way, and even two loads from the same operation can differ if storage time or conditions vary.

That variability is exactly why a single “typical” nutrient value for manure isn’t reliable enough to build a real fertility plan around. Testing replaces an estimate with an actual number.

When to Test Your Manure

Testing makes the most sense at a few key points. 

Test before building a nutrient management plan for the season, so applications can be matched to actual crop needs rather than a rough average. Test before and after any treatment or amendment, if the goal is to understand how much a management practice is actually changing nutrient availability. And periodically test over time for any operation storing manure long-term, since nutrient content shifts the longer manure sits in a pit, lagoon, or compost pile.

If manure is being treated to accelerate breakdown, whether through composting, inoculation, or another method, testing before and after treatment is the only way to know how much that treatment is actually doing.

How to Take a Representative Sample

A manure test is only as good as the sample behind it, and manure is not uniform, which makes sampling technique matter more than it might seem.

For liquid manure, agitate the storage system thoroughly before sampling. Liquid manure separates over time, with nutrients unevenly distributed between the surface, the middle, and settled solids at the bottom. A sample taken without agitation will skew toward whatever layer it happened to catch, usually understating the nutrient value that’s actually going to reach the field once the whole system gets mixed and pumped.

For solid or composted manure, take multiple sub-samples from different points in the pile, rather than one sample from a single spot, and combine them into a composite sample. Avoid sampling only from the outer crust or surface layer, which tends to be less representative of the pile as a whole, the core of an actively composting pile is usually further along in breakdown than the edges, and a sample from just one location won’t reflect that difference.

For any manure type, work with a qualified agricultural laboratory that specifically handles manure analysis, and follow their sample handling and shipping instructions closely. Nutrient content can change after a sample is taken, especially nitrogen, which can shift form after collection, so timely handling matters as much as the collection method itself.

What a Manure Test Actually Measures

A standard manure nutrient analysis typically reports nitrogen, phosphorus, and potassium content, along with organic matter and moisture content. Many labs also report secondary nutrients and micronutrients, along with pH, which can matter depending on the crop and soil the manure is going to. Moisture content matters beyond the nutrient numbers themselves, since it affects how manure handles, spreads, and how its nutrient values are usually reported (as-is versus dry matter basis).

Understanding which basis a report uses is worth double-checking with the testing lab, since comparing an as-is result to a dry matter result can make manure look more or less nutrient-dense than it actually is.

Using the Results

Once gathered, test results should inform application rates, matched against what a specific crop actually needs rather than a standard rate applied across every field. They’re also the baseline for understanding whether a management practice, composting, inoculation, or storage changes, is genuinely improving nutrient availability, since without a before number, there’s no way to measure an after number against it.

It’s also worth tracking results over time rather than conducting one-offs. An operation that tests the same pit, pile, or system every season starts building its own baseline, which makes it much easier to spot whether a change in management (a new bedding source, a different storage duration, a treatment program) is actually moving the numbers, rather than relying on a single snapshot to make that call.

This is also, practically speaking, the same kind of data collection built into structured manure programs like PhycoTerra®’s Manure Value Initiative, where nutrient sampling before and after treatment isn’t just a recommendation, it’s a program requirement, because that before-and-after comparison is what actually proves whether a treatment is working.

Manure testing isn’t complicated, but it does take intention. The nutrient value sitting in a pit, a pile, or a spreader is either an estimate or a known number, and only one of those is useful for building a real fertility plan. Testing consistently can directly tie to improved nutrient availability, and higher overall ROI on manure applications.