Library Categories


More corn, less N

The corn crop was struggling when Darin Skinner drove the high-clearance applicator down the rows at his family’s Hardscrabble Farms last July. Late planting following a wet spring delayed operations on their farm and most others in Ohio. “I really thought we could be looking at a 100-bushel yield,” he says. But things went better than he expected. “We ended up having a pretty decent year.”

The rows where 28% nitrogen was applied using variable-rate technology with on-
the-go infrared sensors that determine optimal rate produced more corn and, in most cases, did it with less N.

The Skinners first learned about the crop-sensor technology through their precision ag consultant, Tim Norris, CEO of Ag Info Tech. Norris tried the process on about 800 acres using a GreenSeeker sensor from Trimble the year before. He admits the sensor actually did a better job of providing for the crop than he expected.

“I tried to outguess it by feeding the better crops more N and the less healthy ones less N. The opposite was true. In 11 tests, my prediction for which would yield better was right zero times. The sensor proved me wrong in every case.”

The key is to hit the short window of opportunity for application. Prime application timing is between V-6 and V-9, he says. “First you have to have a high-clearance applicator. It’s the only way to get into corn that tall,” he notes.

Second, farmers must have the time and dedication to make applications in the summer when the time is right, he says. Third, he recommends farmers test the process on a few acres before going full bore. “Ask another farmer who has tried it about their experience to get a feel for how it might fit,” Norris says.

Some folks you might ask are the Skinners. They plan to use the technology on all of their corn acres this year. “It paid off pretty well last year,” says Skinner.

How well?

For example, the farm featured in the map and data box above shows that the OptRx crop sensor system applied nitrogen at a varying rate that averaged just under 26 gallons per acre. The test area was fertilized at a straight rate of about 35.5 gallons per acre. The average yield on the variable-applied-N ground was 213 bushels per acre. The straight-rate ground averaged 203 bushels. The variable application saved the Skinners 8.52 gallons of 28% N. At a cost of $340 per ton, that’s a savings of $15.42. Add on the improved yield of 10.32 bushels per acre, and the ground where the sensors were used generated $61.92 more per acre. The total return for the system was $77.34.

Tests on other fields offered even better returns. In cases where the variable-rate technology called for more N than the straight-rate applications, the yields were strong enough to overcome the higher application costs with far better yields.

THREE BEAMS: The OptRx crop sensor emits three bands of light. The more photosynthesis taking place, the more light is absorbed and not reflected, indicating a healthy plant. Less photosynthesis reflects more light, triggering more N.

CANOPY KEY: Timing of application is critical. Drop tubes dribbled the 28% N between the Skinners’ 20-inch rows at V-6 to V-8, when the plant is actively taking up N and after a crop canopy is formed to help prevent volatility losses.

This article published in the February, 2012 edition of OHIO FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.