A few years back, Lynn Lagerstedt had a mystery on his hands.

The veteran crop consultant was seeing potassium (K) deficiency symptoms in southeastern Minnesota cornfields – even where sufficient potash had been applied. What was going on?

There were some clues: On headlands, which got an extra tillage pass, K deficiencies were less evident. Growers who applied a 2x2 band of starter fertilizer with the planter had fewer symptoms. Dry products seemed to perform better than liquid.

“We realized this had to be related to fertilizer placement,” says Lagerstedt, president of Farm-Tech, Adams, MN. “We weren’t getting the fertilizer where it was needed.”

Over the years, he’d seen similar placement problems among ridge-tillers, whose corn yields suffered until they injected phosphate (P) and K into the ridge. With the trend toward less tillage these days, it’s no surprise that P and K placement “is an issue for more growers,” he says.

In reduced tillage systems, Lagerstedt recommends deep-banding P and K in the fall or spring, especially for growers who have real-time kinematics (RTK) navigation systems. The two technologies are a perfect fit, says Lagerstedt, who also sells precision-ag services and Bourgault fertilizer rigs. The former vo-ag teacher has persuaded quite a few southern Minnesota farmers to jump on the “bandwagon.” They’ve been able to cut P and K rates 30-50% without sacrificing yields – saving significant dollars, he says. “Injecting fertilizer in a band, combined with variable-rate application, and using RTK to plant over the injected band – I think that is the future.”

Rick Jahn and his father Dick grow corn, soybeans, canning peas and hogs on 1,700 acres of rolling karst terrain near Spring Valley, MN, on the edge of the Driftless Area. About two-thirds of their crop operation is continuous corn.

Because of their environmentally sensitive silt-loam soils, the Jahns apply nitrogen (N) in the spring and do very little tillage, despite typically cool, wet springs and heavy residue. Placing P and K in a subsurface band before planting is a key part of their successful corn-management strategy.

The Jahns go over their corn ground in the spring with a DMI anhydrous ammonia toolbar and Bourgault air-delivery cart, injecting N and dry P and K in one pass. “That’s working well for us,” Rick says. They follow the fertilizer application with light vertical tillage “to fluff up the soil a bit for better planting.” Then they plant right over the band of immobile nutrients, which is about 6 in. deep and 2 in. wide. They also band a small amount of starter fertilizer with the planter.

Deep banding P and K has several benefits. “One advantage we’ve seen with deep placement of P is being able, over time, to lower P test levels in the surface-soil layer without reducing overall fertility of the field,” says Fabian Fernandez, a University of Illinois soil scientist. “This reduction can help minimize potential P runoff from fields.”

Banding diminishes contact between the soil and fertilizer, says George Rehm, a retired University of Minnesota Extension soil scientist. That reduces fixation or “tie up” of P and K – a problem in calcareous soils and soils with certain clay minerals – allowing more efficient use by crops.

Repeated banding of immobile nutrients also “develops a zone of high fertility,” Rehm says. “This justifies the use of lower rates with no sacrifice in yield.” University of Minnesota research from 1998 to 2003 showed that when P and K were placed in a band on medium- and high-testing soils, rates could be cut by one-third to one-half, compared to broadcast rates.