Side-dressing most of your nitrogen is a good deal for your crop, the environment and your bottom line, according to Amboy, MN, farmer David Burk. He should know. He's been side-dressing anhydrous on his corn crops since 1986.

“We put down 6½ gal. of 10-34-0 mixed with 24 oz. of micronutrients at planting, below the seed,” says Burk, who farms with his father William. “As soon as we can row the corn, we'll start to side-dress with 90 units of nitrogen per acre. Ideally the nitrogen goes on between the V3 and V6 stages.

“From an environmental standpoint, this is the way it should be done,” he says. “If you apply anhydrous in the fall, you need to use N-Serve, and there's still the risk of it leaching in the spring. Spring-applied NH3 is awesome, if you can get it on and not screw up the ground. With side-dressing, I'm doing the best management practice available to me with a lower application rate. And it costs me less than 0.2 gal./acre of diesel fuel.”

Tissue tests when Burk's crop reaches the early dent stage indicate Burk's fertility program provides adequate nitrogen for the crop even at 65 units of nitrogen. “We might be able to get by with 65 units of nitrogen per acre, but we're staying with 90 units for now,” he says. “We had a really dry year in 2008 and were disappointed with a 181-bu./acre average. With more typical rainfall, our field corn yields range from 203 to 226 bu./acre. With sweet corn, we'll average almost 7 tons/acre where sweet corn follows field corn.”

With 2,000 acres of corn to side-dress, Burk needs to cover a lot of acres quickly. “If the corn reaches 18 in. before we side-dress, we start to see some signs of nitrogen deficiency,” he says.

So he designed a 90-ft. toolbar, and Bob Groneweg of Rock Valley, IA, built it. “Once we start, we run as long as the conditions allow us,” Burk says. “Last year we side-dressed 1,046 acres in 24 hours, with just a two-hour break. At 6 mph we empty a tank in 50 minutes on 57 acres.

“We switch tanks in the field,” he continues. “We've worked out a system so we can swap tanks in less than 4 minutes and still minimize crop damage to the small corn plants.”

Not impossible

Burk loves when somebody tells him his ideas won't work, like the manufacturers who said it was impossible to build a 90-ft. toolbar without lift assist wheels. Using geometry and a collection of old cultivators, Burk designed a toolbar that is strong enough to side-dress anhydrous at 6 mph and is able to fold together for road travel.

“It's geometry and physics to give the bar strength by design rather than mass,” Burk says. “I wanted a 90-ft. side-dress bar without lift assist wheels because the tanks always get tangled up with the lift assist wheels.”

Burk modified a 2-pt. hitch from another International 183 cultivator and linked it to the 3-pt. hitch on his 4-wd tractor. “Unlike my 90-ft. planter, you don't even know it's back there when you're driving down the road,” he says.

The center section of Burk's seven-section toolbar uses the rigid toolbar from a 12-row planter with a toolbar from an International 183 cultivator welded just 2 in. behind it. A third toolbar completes the center frame. “I reinforced the center section with trusses similar to bridge designs from the 1940s,” he says.

The three tubes of the center section have hydraulic cylinders mounted internally to lift the rest of the frame into travel position. “Mounting the cylinders inside the frame provides more push to lift the frame and more structural strength,” Burk says. “I'll probably mount cylinders on top of the frame also to carry more weight and make the hinge neutral.”

Single, internally mounted hydraulic cylinders fold the outside wings of the toolbar back against the secondary wings, which fold forward against the primary wing section. That section lifts up and over the mainframe for a road width of 25 ft. 9 in.

Four gauge wheels mounted on the outside of the mainframe section and the end of the secondary wing help carry the toolbar's weight through the field. The outside wings can be set to float, and down-pressure springs keep them in contact with the field. A shear pin allows the outside wings to break away.

“I first built a 60-ft. bar with the same design and abused it to find out the weak points in the design,” Burk says. “Once we figured out what we needed to change, we built the 90-ft. bar.”

Skip-row application

Burk originally mounted 36 modified International 153 cultivator row units, 30-in. centers, on the toolbar. “When diesel got high priced, we took off half the units to save fuel,” he says. “Tissue tests showed that all the plants were getting adequate nitrogen with the skip-row application.”

Row units behind the tractor's triple tires use B33 Mole knives, which are more aggressive than the Wiese anhydrous knives mounted on the rest of the row units. Burk runs the knives 6 to 8 in. deep and uses Sukup 24-in. rolling shields to cover the slot.

He uses four orbital manifolds to distribute anhydrous.

Burk says, “It's a very cheap system for fertilizer that's very good to the plants and the environment.”