Manure is valuable, should be treated like fertilizer

Jan Shepel

DE FOREST -   As farmers rush between rain events this spring to empty their manure lagoons, clean out their pens and haul out their stockpiles of manure before they work their fields, they might take a moment to think about the value of that manure.

As farmers spread manure this spring to get ready for cropping season, they should think about the value of that manure as fertilizer and try to spread it like fertilizer. That was the advice from one Iowa State researcher at a recent watershed conference.

According to Dr. Daniel Andersen, PhD, associate professor of Agricultural and Biosystems Engineering at Iowa State University, there is about $24 worth of nutrients in 1,000 gallons of dairy manure.

“It has lots of potential value but it’s got to get to the right field at the right time and in the right amount,” he said. “There might also be a right and wrong way to spread it in such a way that it minimizes losses of nitrogen before and after application.”

In Iowa, there has been a lot of public interest in manure and its nutrients because of several lawsuits pitting the Des Moines city water utility against three agricultural counties in the state that encompass the Raccoon River basin. That river is essential to the city’s water supply.

The Water Works department brought suit against the three counties involved for damages, but lost in the Iowa Supreme Court in January. The utility lost another case in federal district court in mid-March when the court dismissed its claims, suggesting that the Iowa Legislature should be the place to address a water quality problem.

The case was filed in 2015 against county supervisors from the three counties, claiming that the mostly agricultural drainage districts were responsible for high nitrate levels in the Raccoon River. Andersen said the Water Works has invested in the world’s largest nitrate reduction system.

The court ruled that the utility has no standing to sue drainage districts but did not address whether or not agricultural drainage tile lines are a “point source” rather than a non-point source – something the utility had asserted.

Since the lawsuits began several years ago, there has been a concerted effort – supported by millions of federal and private industry dollars – to reduce nitrate runoff through sustainable practices on farms in Iowa.

Andersen has been part of that nutrient reduction strategy, helping do research on best practices for spreading manure. He was a speaker at the recent Yahara Pride Farms watershed conference in De Forest.

“If manure is a fertilizer source we need to treat it like a fertilizer,” he said. “And that means uniformity.”

He and his colleagues have tested various manifolds on manure spreaders, looking for those that would “make manure spreading as precise as an anhydrous bar.” The Iowa State researchers have also looked at better flow meters for manure spreading.

Andersen said that Iowa State research has shown that manure does a better job of holding onto phosphorus than DAP fertilizer. Diammonium phosphate or DAP is the world’s most widely used phosphorus fertilizer.

He compared surface application of manure to injection and told his farmer audience that when manure is spread on the ground 25 percent of the nitrogen is volatilized but with injection only 1 percent is lost to volatilization.

Research has also focused on how far it is economically feasible to haul manure. Iowa hog farmers have been told that for them that limit is one mile, based on the value of their manure. However, Iowa turkey farmers can economically haul their litter 10 to 12 miles, he said.

Andersen can be found on Twitter @drmanure and his blog is at where he provides information about getting the most value from manure as well as protecting the environment.

In Iowa, farmers are generally told that manure shouldn’t be applied in the fall, because there is a mismatch between when the nitrogen is there and when the crops need it.

Analysis of the amount of various nutrients in poultry, cattle and hog manure can show varying ranges of nutrients. An online search located a series of tests that showed Nitrogen (N) in tested manure from cattle (dairy and steer) ranged from 4.7 pounds per ton to almost 28 pounds per ton. Phosphorus (P) was about 5 pounds per ton in cattle manure and potassium (K) average 7.5 pounds per ton in cattle manure tested.

Poultry manure was much higher in all categories: 52 pounds per ton of N, 54 pounds of P and 44 pounds of K while swine manure came in at an average of almost 10 pounds of N per ton, 7 pounds of P and 6.3 pounds of K.

Researchers note that only a portion of the nutrients – especially nitrogen – are available to crops right away. Some may be lost as Andersen noted, or they can get tied up in the soil.

A Wisconsin study done by Bill Jokela, USDA-ARS in Marshfield and John Peters of the University of Wisconsin looked at 10 years of data on dairy manure. These manure analyses provided an opportunity to look for changes in nutrient content of dairy manure over time – changes which might be due to shifts in animal diets or other management practices.

They found significant year-to-year variation and noted some trends over time. While the nitrogen (N) content didn’t vary much, there was a slight decline over the 10 years and potassium (K) content increased over time. But phosphorus (P) they found decreased by 30 percent over the 10-year period in Wisconsin.

Their study was based on 14,000 dairy samples in Wisconsin over 10 years.

The researchers concluded that for nutrient management planning purposes farm-specific samples should be used as there is high variability in the nutrient content of dairy manure.

Andersen earned a B.S. degree in Mechanical Engineering at the University of Wisconsin-Platteville and then earned a Masters and PhD at Iowa State University. As part of his extension appointment, Andersen leads the Iowa Manure Applicator Certification program, which annually certifies about 5,000 manure applicators.