Southwest Minnesota farmer Randy Spronk has a simple way to measure the growing interest in using manure as crop fertilizer.
"I get requests weekly for animal manure," says Spronk.
Spronk says he has to tell the callers he plans to use all the manure his hogs generate. Still he understands his neighbors interest. Spronk punches some numbers into his calculator. He and his brother farm about 1800 acres. Most are fertilized with hog manure. He calculates using manure cuts his fertilizer bill by more than half. That amounts to tens of thousands of dollars a year in savings over commercial fertilizer.
"It's very integral, I think, to my long-term sustainability," says Spronk. "What is more sustainable than using a by-product of animal production, which is animal manure, utilizing that to fertilizer the next year's crop, that's going to go back into that animal for feed."
Spronk says manure is so valuable he's literally built his farm around it.
Most livestock buildings are constructed as close as possible to roads so animals and supplies can easily be hauled in and out.
Spronk built one hog barn in the middle of a field, more than a quarter mile from the nearest road. As he drives up to the building in his truck, Spronk says he put the barn there so he can quickly haul manure to the surrounding cropland.
At the barn, Spronk demonstrates how he applies manure to the land. He climbs into a tractor and starts off across the field. The tractor pulls a tank of hog manure. Nozzles spray the liquid onto the ground, then steel discs work the manure into the soil. Computers control the rate of application. The tractor uses satellite guidance to steer on exactly the right course. Spronk says the hi-tech touches pay for themselves.
"We're trying to take a resource that has value and stretch it," says Spronk. We don't want to miss five feet and then have some corn in their next year that doesn't have any fertilizer. We're going to invest in the technology to have it uniformly applied, accurately applied, so that there's not going to be a skip because I didn't get fertilizer somewhere."
That accuracy becomes more important when yield is considered. Spronk says university studies and his own experience show that corn does better on manure fertilized soil than on ground using commercial fertilizer.
“I get requests weekly for animal manure.”Randy Spronk
No one is exactly sure why that is, but Spronk has a theory.
He says the main nutrients in manure are nitrogen, phosphorus and potassium. He says in addition there are other trace nutrients not contained in commercial fertilizers. He says they give manure its extra punch.
"I use a yield monitor in my combine and we can see it to the row when we hit animal manure," says Spronk. "Not just a bushel or two, but it's 10 to 20 bushel an acre advantage to the animal manure."
Nutrients are the major benefit and biggest problem on the roughly 15 percent of Minnesota cropland treated with manure. The same nitrogen and phosphorus that boost corn yields also present a hazard to water supplies. One study says about 10 percent of the excess phosphorus in the Minnesota River comes from field applied manure. The University of Minnesota's John Moncrief has conducted extensive experiments on manure runoff.
"Manure can be a problem but it doesn't have to be a problem if it's managed properly," says Moncrief. "You got to do your homework and you got to do things right and it's a good environmentally sound system."
He says farmers must pay close attention to their soil types, hillsides and other factors.
"A big issue is how much you apply," says Moncrief.
He says overapplication increases the chances manure runoff will enter water supplies. Moncrief says the threat varies across the state. He says the sandy soils of central Minnesota drain quickly. That means there's a greater chance of runoff carrying nutrients into ground water.
The southeast is also at risk. Parts of that area have a cracked limestone bedrock under the soil. Moncrief says groundwater can quickly flow through the cracks into subsurface aquifers. The Minnesota Pollution Control Agency enforces state manure laws.
The MPCA's Dave Wall says those regulations were strengthened six years ago. Since then he says the MPCA's main emphasis has been educating farmers about manure laws. He says enforcement will become tougher in the years ahead.
"We're in a period right now of transitioning into more and more inspections, of land application both of the records and the actual practices," says Wall. "But in the past few years there's been relatively few fines assessed related to land application of manure."
Another area of concern with animal manure is antibiotics. Many farmers use antibiotics in their livestock to boost weight gain. When their manure is applied to land some of the drugs travel along.
The University of Minnesota's Satish Gupta has studied the issue. He says there's concern microbes living in the soil will become resistant to the antibiotics, creating a type of super bug. Gupta says his preliminary work shows micro-organisms in the manure do build resistance. However, once the manure is applied, he says there's no evidence the resistance is being transferred to soil microbes. Gupta has also studied whether antibiotics are finding their way into crops, like corn.
"At this stage we're finding that plants do have ability to pickup antibiotics from the manure applied soil. However the amounts that are picked up by the plants is relatively small," says Gupta.
Gupta says the uptake doesn't appear to threaten humans, but he and a team of researchers will conduct more studies on the issue.
For hog producer Randy Spronk, the benefits of using manure far outweigh any problems caused by the fertilizer. He's concerned about environmental issues. He keeps detailed records of how much manure goes on his land and where. He believes most farmers use manure responsibly. He says their reward is economic.
"When there is this much value to it guys are going to use it correctly," says Spronk. "They're not going to waste it."
Spronk believes that value means big things for Minnesota and neighboring states. In recent years much of the nation's hog production has moved from the Midwest to other parts of the country.
Spronk says corn, hogs and manure form a circle of growth, each supports the other. He says with manure rising in value, it may be the catalyst for a new model of livestock production. One which will bring more hogs back to the Midwest.