Doug Pohlman didn't realize that he was blazing a trail when he started sidedressing soybeans with manure in 1991.
The southwestern Minnesota corn, soybean and pork producer had run out of corn land on which to apply liquid manure from the pits beneath his hog buildings.
He fall-applied manure on every acre intended for corn that he could get over. He'd start again in the spring doing the same thing, but would have to stop to plant corn. Then he'd follow the corn planter with as much manure as he could get on.
"But when the corn began coming through, we felt we had to stop injecting manure," says Pohlman. "The knives tend to throw a little soil and cover up the small corn plants. It also seemed to burn the corn."
The pits would continue to fill up, though, and if Pohlman did not get rid of some manure in late May or early June, they'd run over by the time soybeans came off in the fall.
That's when he decided to start sidedressing into soybeans.
Pohlman is a ridge-tiller with 30" row spacings. He extended the axles on his 3,000-gallon manure tanker to 120" so the tires would run in the valleys behind his tractor wheels.
When soybeans are about a foot tall, Pohlman starts injecting manure between the rows. So far, he hasn't seen any major detrimental effects.
"We have found that you can burn them, though," he says. "We splattered manure on some beans one year, and it burned the leaves off. I figured they were gone, but they came back. New leaves emerged and you couldn't see the damage in two weeks. Yield was not affected."
Pohlman recognizes that corn can better utilize the nutrients in swine manure.
"But soybeans do make use of some of that phosphate and potash, even if they don't need all the nitrogen."
Last year, he put about 3,000 gallons of liquid manure per acre on about 100 acres of soybeans.
"That's 125 to 175 pounds of nitrogen, 75 to 100 pounds of phosphate and 70 to 80 pounds of potash, depending on which building the manure comes from," he says.
Pohlman routinely tests soil in five-acre grids and also does a manure analysis prior to application. So he has a good idea of the amount of nutrients being applied. He also has a yield monitor on his combine, so he can pinpoint the manure's impact on yield.
Although manure's effect on soybeans has generally been positive, it apparently caused a 2-bu/acre yield hit on one field last year.
"I'll have to do a little more analysis on this," he states. "It's not usual that we get a yield loss where we've applied manure."
Pohlman may be the only soybean grower who sidedresses manure. But Paul Kassel, Iowa State University area extension agronomist in Spencer, has evaluated the effects of applying hog manure just prior to soybean planting. Working with him were the Clay County corn and soybean grower associations.
"We had three sets of plots," Kassel reports. "One, a control, had no manure. Then we applied manure at either 5,000 or 10,000 gallons per acre. Manure was broadcast and worked into the soil two or three days ahead of planting.
"In this case, we saw about a 1.5-bushel increase from the 5,000-bushel rate, and another 1.5-bushel increase from the higher rate," he says.
Kassel is concerned, though, that it doesn't make the best use of the available nitrogen. The manure used in the trial tested 45 lbs N, 15 lbs P and 25 lbs K per 1,000 gallons.
"This practice makes a lot of sense to some growers because it will allow them to empty manure pits from their livestock operations during and after corn planting," says Kassel.
"Soybeans aren't as planting-date sensitive as corn and apparently aren't hurt and may be helped by manure," he adds. "At the same time, they are better able to stand the compaction that may be caused by manure application equipment."
Pohlman plans to continue injecting manure into standing soybeans. The most obvious benefit for a pork producer, of course, is that it stretches the manure application window and empties pits.
Another advantage is odor control.
"When you inject manure into open ground, there's still some odor. But we've found that, when we inject into standing beans, there's no odor problem," he says.
"Manure is a heck of a good fertilizer when used right, too," Pohlman stresses. "I grow crops on two different farms with the same soils. One is too far away from the hog buildings to make manure application economical. In the past few years, though, I've noticed that yields are higher on the farm that gets manure."