Manure: What’s It Worth?




Calculating the value—either in terms of nutrients or dollars—of manure isn’t easy. But understanding the variables and tuning into innovative tools can help.

Photo courtesy of Steve Werblow


Manure: What’s It Worth?


by Steve Werblow

Most farmers and agronomists agree that manure has enjoyed a change in status in recent years, from a waste material to a valuable resource. But the challenge remains in figuring out just how valuable that resource is.

One example from Purdue University agronomist Brad Joern shows that there could be big money in a manure pit. Assuming commercial nitrogen is worth 35 cents per pound, 2.2 million gallons of liquid hog manure on an Indiana farm could yield about $27,000 in nitrogen, and an equal value of phosphorus and potassium. That’s nearly $60,000 worth of fertilizer.

But Joern is quick to point out that there are a lot of variables in calculating the value of manure. Some are chemical, some are biological, and some are regulatory. All require careful consideration.

What’s valuable about it?
One of the challenges of setting a value on manure is considering whether all of its contents are actually delivering a benefit. Manure is only valuable if it causes a crop response, notes Jon Rauch, Extension program director for The Ohio State University’s Environmental Management program.

Part of predicting crop response is recognizing which nutrient(s) are boosting yields. Commercial fertilizer can be tailored to match crop needs, in proportion, for each nutrient in a single application. Manure, on the other hand, tends to be relatively high in P and K and low in N. As a result, applying enough manure to supply the nitrogen needs of certain crops can cause an over-application of P and K. Conversely, setting manure rates by P and K levels leaves the crop hungry for more N than the manure can provide.

“P and K saturation [in the soil] reduces the value of the manure from a farmer’s perspective because it’s then worth just the value of the nitrogen,” notes Rauch. “In that case, they may be better off moving that manure over to someone who can utilize all the nutrients.”

High nitrogen prices and stiff limitations on phosphorus loading in some areas add economic and legal parameters to an already-tough balancing act.
Location, location, location
Even just focusing on nitrogen value is tricky. Joern is careful to note the difference between nitrogen and potentially available nitrogen. Though P and K are generally assumed to be 100 percent available relative to commercial fertilizers, not every pound of nitrogen is available to the crop when the manure is applied. So a separate value in the nutrient analysis of manure—potentially available nitrogen, or PAN—includes just the highly available ammonium N, plus the amount of nitrogen that can be expected to mineralize during the growing season in which it’s applied. To make matters even more complicated, estimates for PAN vary dramatically by application method and timing, as well as by which state’s calculation you’re using.

For instance, Joern cites an example of a hog operation with a total N value of 40 pounds per 1,000 gallons and an ammonium N value of 27 pounds per 1,000 gallons. If the manure was surface applied and not incorporated, the official Iowa estimate would assume that there is more than twice as much N available in the first year than regulators in Minnesota would calculate; Wisconsin’s official estimate falls right in the middle. For injected manure, the differences among states are reduced, but the values still vary by about one-third.
Software tool
To help planners navigate the variables in developing a nutrient management plan (NMP) that complies with state and local regulations, Joern spearheaded the creation of an innovative computer software program, Manure Management Planner, or MMP.

The planner enters information about the operator’s fields, crops, storage, animals and application equipment. MMP helps the planner allocate manure—when, where and how much—on a monthly basis for the length of the plan, which could be set for 1 to 10 years. This allocation process helps determine if the current operation has sufficient crop acreage, seasonal land availability, manure storage capacity and application equipment to manage the farm’s manure in an environmentally responsible manner, Joern says.

MMP can be used to generate complete NMPs that meet NRCS and US EPA plan requirements, Joern adds. The NMP contains sections on mortality disposal, nutrient analysis, applicator calibration, recordkeeping—everything right down to emergency contact information for the farm. Farmstead and field maps generated by GIS tools can be inserted into the NMP template created by MMP, too.

MMP currently supports 34 states by incorporating each state’s extension fertilizer recommendations and calculations for manure nutrient availability, as well as 15 state phosphorus indices (PIs).

“Our software will be able to automatically calculate soil erosion with RUSLE 2 this fall,” adds Joern. “Erosion is part of most states’ PIs. By linking MMP’s rate calculator to RUSLE 2 and state PIs, planners will be able to determine what the optimum rate of manure is for any field very quickly. We also hope to be able to automatically insert NRCS conservation plans into the NMP this fall.”

Joern says Purdue’s MMP team will be working later this fall with the NRCS to train NRCS staff and technical service providers (TSPs), the current target audience for the program. “Right now, it’s a tool to help the TSP be more efficient with developing plans,” he says. “If you’re a farmer that uses a computer, we want to move MMP into that realm so eventually any computer-savvy farmer will be able to develop a plan on their own.”
Focus the thinking
For producers and planners who prefer a textbook approach, Rauch points to Midwest Plan Service Publication 18 (MWPS-18), Section 1, which is titled Manure Characteristics. The document features tables, manure production charts, and nutrient book values for N, P and K, making it an outstanding starting point for considering the value of manure on a particular operation. A list of MWPS’s manure publications is available online.

The Ohio Livestock Manure Management Guide 604 also contains book values for nutrients in manure, Rausch notes. With that information, producers or their advisors can compare the cost of applying manure with purchasing and applying commercial fertilizer.
The best of times
Even with properly calculated nutrient values, the monetary value of manure varies by when the manure is applied, or when its value is established. Nitrogen availability is affected by soil temperature and weather. And perhaps more important, the timing is critical—as winter approaches, manure pits should be drawn down so producers aren’t forced into making winter applications.

“Planning ahead is important,” notes Rausch. “The farmer needs to be thinking about applying manure at any opportunity in a way that can use these materials most efficiently. But they’re often aiming for a pretty narrow window. If you’re looking to move all these nutrients in the spring or fall and the weather turns bad, you’re chasing your tail all season long to get caught up.”

Rausch points out that rotating crops and application regimes can help extend the manure application season. “Sidedressing corn, topdressing hay, and topdressing wheat provide another window,” he says. Ohio State researchers have shown that injecting low rates of swine manure—3,000 to 3,200 gallons per acre—has been an effective topdress program for wheat. And the university demonstrated that 6,000 gallons of dairy manure on alfalfa performed as well as a conventional potash program. Researchers across the Corn Belt are also working with pre-sidedress N testing and on-the-go plant sensing to fine-tune fertilizer recommendations.

As results like those are collected, producers and advisors can formulate apples-to-apples comparisons between manure and commercial fertilizers—and learn to build the value of manure by making sure they can utilize it when their storage systems and crops benefit most.

Still, the value of manure fluctuates more than that of commercial fertilizer because of the challenges and variables that surround its use—from the cost to haul a comparatively low-octane fertilizer to the energy of soil microbes to the rules preventing its application where P rates are already high. At Purdue, Joern reminds producers and their advisors not to see manure management plans—even the best-designed ones—in absolute terms.

“In a plan, you don’t know the weather, you don’t know everything that’s going to happen to influence that availability,” he notes. That quickly translates to influencing the value of manure.

Proper Application: Big Shortcoming

Determining crop need and manure nutrient content represent a pair of big challenges to producers. But a Michigan State University paper demonstrated that even if all the numbers are right, just 25 percent of the manure applications measured fell within 20 percent of the reported rate of manure.

The misapplications were equally split between too high and too low, report Dann Bolinger and Natalie Rector. Of course, inadequate rates can result in suboptimal crop response, and overapplication is both wasteful and environmentally risky. The Michigan team strongly suggests calibrating manure application equipment, and shares tips at

Iowa’s calculation of the available nitrogen in the manure from these hogs would estimate twice as much available N than Minnesota’s calculation would (assuming it’s surface-applied and not incorporated). Such disparities in rules and formulae make it tough to pinpoint the value of manure.

Photo courtesy of USDA NRCS

Watch Soil Conditions

A manure management plan is, at best, a plan rather than a recipe. Jon Rausch, extension program director for The Ohio State University’s Environmental Management program, cautions against sticking to a planned manure application if weather or soil conditions don’t warrant safe placement of the nutrients.

“The day of application, look at soil moisture conditions in the upper eight inches of the soil profile,” he suggests. “If the soil can only take 5,000 gallons and you’re trying to apply 10,000, then 5,000 gallons has to go somewhere—and it won’t be pretty.”

About the Writer: Steve Werblow is a freelance agriculture writer based in Ashland, Ore.