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.

Higher yields?

Growers should not expect higher yields from banding fertilizer, Extension experts note.A four-year study at Arlington, WI, found no yield advantage for deep banding, compared with broadcast fertilizer or a planter-placed band, says Richard Wolkowski, a University of Wisconsin Extension soil scientist. The same is true in Illinois, Fernandez says. “Deep banding is sometimes suggested because it makes the nutrient more available, but we have not seen evidence of that.” In Illinois, data doesn’t support lower application rates with banding, either, he adds.

However, “the tillage effect of deep placement might provide some benefit,” Wolkowski says, “since it will remove some compaction and surface residue in the row. This should allow for better planting conditions.”

Wolkowski and Fernandez also remind growers that the likelihood of any plant response to applied P or K depends on your soil test levels and the weather. In high-testing soils, the probability of a yield response to added nutrients is quite low. “Cooler seasons tend to show a greater response potential, whereas seasons like 2010, where heat units were not an issue, are less likely to respond,” Wolkowski says.

Since they started banding about six years ago, the Jahns have cut their P and K use in half. They inject a base rate of 40 lbs./acre of 11-52-0 and 60 lbs./acre of 0-0-60, then vary the rate on the go, according to soil tests, applying as much as 150 lbs./acre of each material in certain areas. They also spread hog manure every fourth or fifth year. In most fields, their soil tests are in the high range for both P and K.

Their goal is to feed the current crop, Rick says, although, “if we were on weaker soils, I don’t know if I’d be comfortable with a half rate.” The Jahns soil test every two years on 2.5-acre grids from the same georeferenced points each time. “So we should see in a timely fashion if we’re losing fertility,” Rick says. His thinking: “Why spend money on fertilizer if you don’t have to?”

Before they bought their own equipment, the Jahns had hired a neighbor with a strip-till rig to band nutrients in the fall. They bought their own air cart and RTK system in 2008 and expect to recoup their $100,000 investment in about four years – just from fertilizer savings, Rick says. In 2008, when fertilizer prices shot up, “we paid for about a third of the system in one year by going to a half rate.”

In 2010, the Jahns put their system to an extreme test when they planted a 30-acre field of corn-after-corn with no tillage beyond the fertilizer knives. Though he doesn’t plan to repeat the experiment, Rick says the field produced an excellent crop, yielding 190 bu./acre.

That was no accident, Lagerstedt says. “Planting over the fertilizer band got the crop off to a good start.”

How to soil sample when you band immobile nutrients?

One disadvantageof deep banding phosphorus (P) and potassium (K) is that it makes it harder to accurately measure field fertility. Do you collect soil samples within the band? Outside the band?

“That’s an unanswered question,” says George Rehm, a retired University of Minnesota Extension soil scientist.

Soil test levels of P and K tend to increase in the band, even with maintenance rates, and decrease everywhere else in the field, says Fabian Fernandez, University of Illinois Extension soil scientist. “If you always sample in the band, you may under-apply fertilizer. Sampling between rows would result in lower test levels than the actual fertility of the field and would lead to over-fertilization.”

Lynn Lagerstedt, a crop consultant from Adams, MN, works with several growers who deep band immobile nutrients. As a practical matter, he doesn’t usually see a big difference between cores taken from within the corn row or half way between the rows, indicating “the fertilizer injected under the row has all been used by the plants. That tells me I don’t have to worry about sampling right over the band.”

The best advice currently is to collect soil samples about 6 in. beside the band and 6-8 in. deep, Rehm says. It’s also a good idea to increase the number of cores per sample in banded fields, says Richard Wolkowski, a University of Wisconsin Extension soil scientist. Collect “at least 10 and perhaps 15-20. Mix well in a bucket, since you will end up saving just a portion of what is collected.”

Rehm notes that “It takes a long time for soil test levels to decline, even if you don’t add any fertilizer.” And corn residue is a good source of recycled K, Wolkowski adds.

Beyond that, Rehm says, the purpose of soil sampling is evolving with the adoption of precision-agriculture methods, such as georeferenced soil sampling. “In the past, soil sampling has been used as a predictive tool. With a move to banded application, I see soil sampling used more and more as a monitoring tool.” 

February 2011